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,internet ,archive4 ,see                
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ineexpla#jjlardrich   ,transcriber's    
note3        ,text enclosed by          
underscores is in italics 7italics74    
,the notation n means that n is         
superscript4 ,the notation       n means

 that n is subscript4        ,text that 
was in small capitals has been converted
 to all       capitals4        ,the     
original page numbers are embedded in   
square brackets1       e4g4 ,pg#ace4    
,more detailed notes are provided in the
 ,transcriber's endnote4                
,illustration3 ,,watt4  ,engraved by ,h4
 ,adlard1 from a ,drawing by ,h4        
,corbould1 taken with the permission of 
,james ,watt1 ,esq4  ,,from ,,the       
,,statue ,,by ,,chantrey4  ,london3     
,taylor  ,walton1 ,upper ,gower ,street4
   ,,the ,,steam ,,engine ,,explained   
,,and ,,illustrated2  ,with an ,account 
of ,its ,invention and ,progressive     
,improvement1 and ,its ,application to  
,navigation and ,railways2  ,including  
also a ,memoir of ,watt4  by            
,,dionysius ,,lardner1 ,d4,c4,l4        
,f4,r4,s4 c4 c4  ,,seventh ,,edition1   
,illustrated by ,engravings on ,wood4   
,london3 ,printed for ,taylor and       
,walton1 #bh4 ,upper ,gower ,street4    
,,mdcccxl4  ,london3 ,printed by ,a4    

,spottiswoode1 ,new-,street-,square4    
,,to   ,,the ,,right ,,honourable       
,,henry ,,lord ,,brougham ,,and ,,vaux1 
,,fellow ,,of ,,the ,,royal ,,society1  
,,and   ,,member ,,of ,,the ,,national  
,,institute ,,of ,,france1   ,,as ,a    
,,mark ,,of ,,public ,,respect   ,,and  
,a ,,testimony ,,of ,,private ,,regard1 
,,this ,,work   ,,inscribed1 ,,by ,,his 
,,attached ,,friend1   ,,the ,,author4  
,,advertisement4   ,the ,drawings for   
several of the ,cuts in this ,volume    
have been taken1 by the permission of   
,mr4 ,weale1 from the admirable ,plates 
annexed to the last edition of ,tredgold
 on the ,steam ,engine and on ,steam    
,navigation4 ,this acknowledgment is    
especially due for the ,illustrations   
which abound in this ,volume4  ,london1 
,june1 #ahdj4     ,illustration3        
,,london ,,entrance ,,to ,,the          
,,birmingham ,,rail-,,road4             
,,contents4    ,,chapter ,i4            
,,preliminary ,,matter4                 
,page   ,the ,steam ,engine1 a ,subject 

of popular ,interest      #d   ,effects 
of ,steam                               
#e   ,great ,power of ,steam            
#g   ,object of this ,work              
#i   ,disputes respecting the ,invention
                   #aa   ,hero of       
,alexandria's ,machine                  
#ac   ,blasco ,de ,garay's ,proposition 
to propel ,vessels    by a ,machine     
#af   ,solomon ,de ,caus                
#ag   ,giovanni ,branca proposes to work
 ,mills by ,steam     #bb   ,marquis of 
,worcester                              
#bc   ,mechanical ,properties of ,fluids
                     #be   ,elastic and 
,inelastic ,fluids                      
#be   ,elasticity of ,gases             
#bh   ,effects of ,heat                 
#bi   ,application of these ,principles 
to the ,engines    of ,hero1 ,de ,caus1 
and ,lord ,worcester              #cj   
,sir ,samuel ,morland                   
#cd   ,denis ,papin                     
#cf   ,atmospheric ,pressure            
#ch   ,weight of ,air                   

#ci   ,pressure of ,air                 
#da   ,barometer                        
#da   ,elastic ,force of ,air and ,gases
                      #db   ,force      
obtained by a ,vacuum                   
#dc   ,common ,pump                     
#dc   ,rarefaction by ,heat             
#dd   ,process of filling ,thermometers 
#dd   ,papin's ,method of producing a   
,vacuum                #dd   ,his       
,discovery of the ,condensation of      
,steam          #de   ,thomas ,savery   
#dg    ,,chap4 ,,ii4   ,,engines ,,of   
,,savery ,,and ,,newcomen4   ,savery's  
,engine                                 
#di   ,boilers and their ,appendages    
#ej   ,working ,apparatus described     
#ea   ,mode of ,operation               
#eb   ,defects of ,savery's ,engine     
#eh   ,newcomen's ,engine described by  
,papin                #fb   ,newcomen   
and ,cawley obtain a ,patent for        
,atmospheric ,engine                    
#fe   ,accidental ,discovery of         
,condensation by ,injection   #fi       

,potter's ,discovery of the ,method of  
working    the ,valves                  
#ga   ,his ,contrivance improved by the 
,substitution    of a ,plug ,frame      
#gb   ,advantages of the ,atmospheric   
,engine over that    of ,savery         
#gb   ,the ,power of ,savery's ,engine  
restricted             #gc   ,it        
contained no new ,principle             
#gc   ,its practical ,superiority       
#gc    ,,chap4 ,,iii4   ,,early ,,career
 ,,and ,,discoveries ,,of ,,james       
,,watt4   ,atmospheric ,engine improved 
by ,beighton             #ge            
,smeaton's ,improvements in the         
,atmospheric ,engine    #gf   ,brindley 
obtains a ,patent for ,improvement in   
#gf   ,invents the ,self-regulating     
,feeder                  #gf   ,infancy 
of ,james ,watt                         
#gg   ,his ,descent and ,parentage      
#gg   ,anecdotes of his ,boyhood        
#gh   ,his early ,acquirements          
#gi   ,goes to ,london                  
#hj   ,returns to ,glasgow              

#hj   ,appointed ,instrument-maker to   
the ,university        #ha   ,opens a   
,shop in ,glasgow                       
#ha   ,his ,friends and ,patrons        
#ha   ,professor ,robison's ,remarks on 
,watt's personal    ,character          
#hb   ,his industrious and studious     
,habits                 #hb   ,his      
,attention first directed to ,steam     
#hc   ,experiments on ,high-pressure    
,engine                 #hc   ,repairs  
an ,atmospheric ,model                  
#hd   ,experimental ,inquiry consequent 
on this             #hd   ,its ,results 
#hd   ,observes great ,defects in the   
,atmospheric ,engine    #he   ,his first
 ,attempt to improve it                 
#he   ,his early ,experiments on ,steam 
#hg   ,discovery by ,experiment of the  
,expansion which    ,water undergoes in 
,evaporation                    #ij     
,discovers the latent ,heat of ,steam   
#ia   ,informed by ,dr4 ,black of the   
,theory of latent ,heat  #ic   ,his     
,improvement not due to ,black          

#ic    ,,chap4 ,,iv4   ,,exposition ,,of
 ,,physical ,,principles4               
,construction of ,thermometer           
#ih   ,method of graduating it          
#ii   ,freezing and boiling ,points     
#ii   ,latent ,heat of ,water           
#aja   ,quantity of ,heat necessary to  
convert ,ice into    ,water1 first      
noticed by ,dr4 ,black                  
#aja   ,examination of the analogous    
,effects produced    by the continued   
,application of ,heat to ,water    in   
the liquid ,state                       
#ajb   ,process of ,boiling             
#ajd   ,reconversion of ,steam into     
,water                   #ajd           
,conversion of ,water into ,steam       
#aje   ,latent ,heat of ,steam          
#ajg   ,boiling ,point varies           
#ajh   ,different in different ,places  
#aji   ,inquiry whether a ,diminution of
 ,pressure will    produce a            
corresponding ,effect on the boiling    
,point                                  
#aab   ,table showing the ,temperature  

at which ,water    will boil under      
different ,pressures of the             
,atmosphere                             
#aac   ,mechanical ,force of ,steam     
#aae   ,facts to be observed in         
#aag    ,,chap4 ,v4   ,,further         
,,discoveries ,,of ,,watt4   ,watt finds
 that ,condensation in the ,cylinder    
is incompatible with a due ,economy of  
,fuel       #aai   ,conceives the       
,notion of condensing out of the        
,cylinder                               
#abj   ,discovers separate ,condensation
                    #aba   ,invents the 
,air ,pump                              
#abc   ,substitutes ,steam ,pressure for
 ,atmospheric    ,pressure              
#abc   ,invents the ,steam ,case1 or    
,jacket                  #abd   ,his    
first ,experiments to realise these     
,inventions                             
#abe   ,his experimental ,apparatus     
#abe   ,his experimental ,models fitted 
up at ,delft    ,house1 in ,glasgow     
#abh   ,difficulties of bringing the    

improved ,engines    into ,use          
#abi   ,watt first employed by ,roebuck 
as a ,civil    ,engineer                
#acj   ,his ,partnership with ,roebuck  
#acj   ,his first ,patent               
#acj   ,experimental ,engine at ,kinneal
                     #aca   ,abstract of
 the ,act of ,parliament for the        
,extension of his ,patent               
#acb   ,description of his single-acting
 ,steam ,engine      #acc    ,,chap4    
,,vi4   ,,watt',s ,,engines4            
,correspondence of ,watt with ,smeaton  
#ade   ,failure of ,condensation by     
,surface                 #adf           
,improvements in ,construction of       
,piston             #adg   ,method of   
,packing                                
#adh   ,improvements in boring the      
,cylinder                #adi           
,disadvantages of the new compared with 
the old    ,engines                     
#aej   ,greatly increased ,economy of   
,fuel                  #aej   ,economy  
of the ,engine                          

#aea   ,expedients to force the new     
,engines into ,use       #aea           
,correspondence of ,boulton             
#aec   ,correspondence with ,smeaton    
#aee   ,efficiency of ,fuel in the new  
,engines              #aef   ,discovery 
of the expansive ,action of ,steam      
#aeg   ,watt states it in a ,letter to  
,dr4 ,small            #aeg   ,its      
,principle explained                    
#aeh   ,mechanical ,effects resulting   
from it               #afb   ,computed  
,effect of cutting off ,steam at        
different ,portions of the ,stroke      
#afc   ,produces a variable ,power      
#afc   ,expedients for equalising the   
,power                #afd   ,expansive 
,principle in ,watt's ,engines limited  
#afe   ,its more extensive ,application 
in the ,cornish  ,engines               
#afe    ,,chap4 ,,vii4                  
,,double-,,acting ,,engine4   ,common   
,steam                                  
#afh   ,superheated ,steam              
#agj   ,laws of ,dalton and ,gay ,lussac

                      #aga   ,law of    
,mariotte                               
#aga   ,relation between ,temperature   
and ,pressure of    common ,steam       
#aga   ,effects of the ,expansion of    
common ,steam           #agc            
,mechanical ,effects of ,steam          
#agc   ,method of equalising the        
expansive ,force           #agd         
,hornblower's ,engine                   
#age   ,woolf's ,engine                 
#agf   ,watt's ,attempts to extend the  
,steam ,engine to    ,manufactures      
#agh   ,papin's projected ,applications 
of the ,steam    ,engine                
#agh   ,savery's ,application of the    
,engine to move    ,machinery           
#ahj   ,jonathan ,hull's ,application to
 ,water ,wheels        #ahj   ,champion 
of ,bristol applies the ,atmospheric    
,engine to raise ,water                 
#aha   ,stewart's ,application of the   
,engine to    ,mill-work                
#ahb   ,wasbrough's ,application of the 
,fly-wheel and    ,crank                

#ahc   ,reasons why ,watt's             
single-acting ,steam ,engine    was not 
adapted to produce continuous uniform   
,motion of ,rotation                    
#ahd   ,watt's ,second ,patent          
#ahf   ,sun-and-,planet ,wheels         
#ahg   ,valves of double-acting ,engine 
#ahi    ,,chap4 ,,viii4                 
,,double-,,acting ,,engine4   ,methods  
of connecting the ,piston-rod and ,beam 
in the double-acting ,engine            
#aic   ,rack and ,sector                
#aid   ,parallel ,motion                
#aie   ,connection of ,piston-rod and   
,beam                  #aie             
,connecting ,rod and ,crank             
#bjc   ,fly-wheel                       
#bje   ,throttle-valve                  
#bjg   ,governor                        
#bji   ,construction and ,operation of  
the    double-acting ,engine            
#baf   ,eccentric                       
#bbe   ,cocks and ,valves               
#bbg   ,single-clack ,valves            
#bbg   ,double-clack ,valves            

#bbh   ,conical ,valves                 
#bbh   ,slide ,valves                   
#bbi   ,murray's ,slides                
#bbi   ,d ,valves                       
#bcj   ,seaward's ,slides               
#bce   ,single ,cock                    
#bch   ,two-way ,cock                   
#bci   ,four-way ,cock                  
#bci   ,pistons                         
#bdb   ,common hemp-packed ,piston      
#bdb   ,woolf's ,piston                 
#bdc   ,metallic ,pistons               
#bdd   ,cartwright's ,engine            
#bde   ,cartwright's ,piston            
#bdg   ,barton's ,piston                
#bdh    ,,chap4 ,,ix4   ,,boilers ,,and 
,,furnaces4   ,analysis of ,coal        
#beb   ,process of ,combustion          
#bec   ,heat evolved in it              
#bed   ,form and ,structure of ,boiler  
#bee   ,waggon ,boiler                  
#bee   ,furnace                         
#bef   ,method of feeding it            
#beg   ,combustion of ,gas in ,flues    
#bfj   ,williams's ,patent for ,method  

of consuming    unburned ,gases         
#bfj   ,construction of ,grate and      
,ash-pit                  #bfa          
,magnitude of heating ,surface of       
,boiler             #bfb   ,steam-space 
and ,water-space in ,boiler             
#bfc   ,position of ,flues              
#bfd   ,method of feeding ,boiler       
#bfe   ,method of indicating the ,level 
of ,water in    ,boiler                 
#bff   ,level ,gauges                   
#bff   ,self-regulating ,feeders        
#bfg   ,steam ,gauge                    
#bgj   ,barometer ,gauge                
#bgb   ,watt's ,invention of the        
,indicator                  #bgd        
,counter                                
#bgh   ,safety-valve                    
#bgi   ,fusible ,plugs                  
#bhj   ,self-regulating ,damper         
#bha   ,brunton's ,self-regulating      
,furnace                  #bhc   ,gross 
and useful ,effect of an ,engine        
#bhe   ,power and ,duty of ,engines     
#bhg   ,horse-power of ,steam ,engines  

#bhi   ,evaporation proportional to     
,horse-power            #bij   ,sources 
of ,loss of ,power                      
#bib   ,absence of good practical ,rules
 for ,power          #bib   ,common     
,rules followed by ,engine-makers       
#bib   ,duty distinguished from ,power  
#bid   ,duty of ,boilers                
#bid   ,proportion of ,stroke to        
,diameter of ,cylinder       #bie       
,duty of ,engines                       
#bif   ,cornish ,system of ,inspection  
#big   ,table showing the ,improvement  
of ,cornish ,engines   #bih             
,beneficial ,effects of ,cornish        
,inspection           #bii   ,successive
 ,improvements on which the increased   
,duty of ,engines depends1 traced by    
,john ,taylor    in his ,records of     
,mining                       #bii      
,,chap4 ,x4   ,,life ,,of ,,watt4       
,watt's ,friends and ,associates at     
,birmingham        #cjb   ,his          
,invention of the ,copying ,press       
#cjb   ,heating ,apartments and         

,buildings by ,steam          #cjc      
,watt's ,machine for drying ,linen      
#cjc   ,his ,share in the ,discovery of 
the ,composition    of ,water           
#cjc   ,the ,merit of this ,discovery   
shared between    ,cavendish1           
,lavoisier1 and ,watt                   
#cje   ,anecdote of ,watt's ,activity of
 ,mind #cji   ,his ,introduction of the 
,use of ,chlorine in    ,bleaching      
#caj   ,one of the ,founders of the     
,pneumatic    ,institution at ,clifton  
#caj   ,his first ,marriage             
#caa   ,death of his first ,wife        
#caa   ,his second ,marriage            
#caa   ,death of his younger ,son       
#caa   ,extracts from his ,letters      
#cab   ,character of ,watt by ,lord     
,brougham                 #cac          
,extract from ,sir ,walter ,scott's     
,monastery on    the ,character of ,watt
                            #cad        
,sketch of the ,life of ,watt from the  
,scotsman    by ,lord ,jeffrey          
#cae   ,occupation of his old ,age      

#cah   ,his ,invention of ,machine for  
copying ,sculpture     #cah   ,his last 
,days                                   
#cah   ,monuments to his ,memory        
#cai   ,inscription by ,lord ,brougham  
on the ,pedestal    of the ,monument in 
,westminster ,abbey             #cbj    
,,chap4 ,,xi4   ,,locomotive ,,engines  
,,on ,,railways4                        
,page  ,high-pressure ,engines          
#cbb   ,one of the earliest ,forms of   
the ,steam ,engine      #cbb            
,description of ,leupold's ,engine      
#cbc   ,non-condensing ,engine of       
,messrs4 ,trevethick    and ,vivian     
#cbd   ,construction of a ,machine for  
moving ,carriages    on ,railroads      
#cbh   ,effects of ,railway ,transport  
#cbi   ,moral and political             
,consequences of                #ccd    
,history of the ,locomotive ,engine     
#ccg   ,construction of ,locomotive     
,engine by ,blinkensop    #ccg          
,messrs4 ,chapman's ,contrivance        
#ccg   ,walking ,engine                 

#ccg   ,mr4 ,stephenson's ,engines at   
,killingworth           #cci            
,liverpool and ,manchester ,railway     
#cdb   ,the ,directors offer a ,prize   
for the best    ,locomotive ,engine     
#cdd   ,experimental ,trial             
#cdd   ,the ,rocket1 ,sanspareil1 and   
,novelty          #cdd   ,admirable     
,arrangement in the ,rocket             
#cde   ,description of the ,sanspareil  
#cdg   ,description of the ,novelty     
#cdi   ,the ,superiority of the ,rocket 
#cej   ,method of subdividing the ,flue 
into ,tubes          #cec   ,progressive
 ,improvement of ,locomotive ,engines   
#ced   ,dr4 ,lardner's ,experiments in  
#ahcb                  #ceg   ,adoption 
of ,brass ,tubes                        
#cfj   ,great ,expense of ,locomotive   
,power                  #cfa   ,mr4     
,booth's ,report                        
#cfb   ,detailed ,description of the    
most improved    ,locomotive ,engines   
#cfe   ,substitution of ,brass for      
,copper ,tubes    ascribed to ,mr4      

,dixon                            #cgj  
,power of ,locomotive ,engines          
#cgi   ,position of the ,eccentrics     
#cgi   ,pressure of ,steam in the       
,boiler                    #dja   ,dr4  
,lardner's ,experiments in #ahch        
#djf   ,resistance to ,railway ,trains  
#djg   ,dr4 ,lardner's ,experiments on  
the ,great ,western    ,railway         
#djh   ,experiments on ,resistance      
#dji   ,restrictions on ,gradients      
#daj   ,compensating ,effect of         
,gradients                   #dab       
,experiment with the ,hecla             
#dab   ,disposition of ,gradients should
 be uniform         #dae   ,methods of  
surmounting steep ,inclinations         
#dae    ,,chap4 ,,xii4   ,,locomotive   
,,engines ,,on ,,turnpike ,,roads4      
,railways and ,stone ,roads compared    
#dbj   ,gurney's ,steam ,carriage       
#dbc   ,the ,boiler of ,gurney's ,engine
                      #dbc   ,his       
,method of cleansing ,boilers           
#dbh   ,convenience and ,safety of      

,steam ,carriages          #dcb   ,two  
,methods of applying ,locomotive        
,engines    upon common ,roads          
#dcd   ,horse ,carriages compared with  
,steam                #dce   ,extract   
from ,mr4 ,farey's ,evidence before the 
,house of ,commons                      
#dce   ,hancock's ,steam ,carriage      
#dcf   ,how it differs from that of ,mr4
 ,gurney             #dcg   ,ogle's     
,locomotive ,carriage                   
#dch   ,dr4 ,church's ,steam ,engine    
#dci    ,,chap4 ,,xiii4   ,,steam       
,,navigation4   ,form and ,arrangement  
of ,marine ,engines             #dda    
,arrangement of the ,engine-room        
#ddf   ,marine ,boilers                 
#ddh   ,effects of ,sea ,water in       
,boilers                    #dej        
,remedies for them                      
#dea   ,blow-off ,cocks                 
#deb   ,indicators of ,saltness         
#dec   ,seaward's ,indicator            
#ded   ,his ,method of blowing out      
#ded   ,field's ,brine ,pumps           

#def   ,tubular ,condensers applied by  
,mr4 ,watt             #deg   ,hall's   
,condensers                             
#deh   ,substitution of ,copper for     
,iron ,boilers            #dfj          
,process of ,stoking                    
#dfb   ,watt's ,expedient of attaching  
,felt to the    ,boiler ,surface        
#dfc   ,means of economising ,fuel      
#dfc   ,number and ,arrangement of      
,furnaces and ,flues       #dfc         
,howard's ,marine ,engine               
#dfd   ,application of the expansive    
,principle in    ,marine ,engines       
#dff   ,recent ,improvements of ,messrs4
 ,maudslay and    ,field                
#dfg   ,humphrey's ,marine ,engine      
#dgj   ,common ,paddle-wheel            
#dgb   ,feathering ,paddles             
#dgd   ,galloway's ,patent for a        
,paddle-wheel with    movable ,paddles  
#dgf   ,split ,paddle                   
#dgh   ,proportion of ,power to ,tonnage
                     #dhj   ,improved   
,efficiency of ,marine ,engines         

#dhb   ,iron ,steam ,vessels            
#dhc   ,steam ,navigation to ,india     
#dhd    ,,chap4 ,,xiv4   ,,american     
,,steam ,,navigation4   ,steam          
,navigation first established in        
,america      #dhg   ,circumstances     
which led to it                         
#dhh   ,attempts of ,fitch and ,rumsey  
to apply the    single-acting ,engine to
 the ,propulsion of    ,vessels         
#dhi   ,stevens of ,hoboken commences   
,experiments in    ,steam ,navigation   
#dhi   ,experiments of ,livingstone and 
,fulton              #dhi   ,fulton's   
first ,boat                             
#dij   ,the ,hudson navigated by ,steam 
#dia   ,extension and ,improvement of   
,river ,navigation      #dib   ,american
 ,steamers                              
#did   ,difference between them and     
,european ,steamers      #did           
,steamers on the ,hudson                
#did   ,american ,paddle-wheels         
#die   ,sea-going ,american ,steamers   
#dif   ,speed attained by ,american     

,steamers                #dig   ,lake   
,steamers                               
#dii   ,the ,mississippi and its        
,tributaries                #dii        
,steam-boats navigating it              
#ejj   ,their ,structure and ,machinery 
#ejj   ,new ,orleans ,harbour           
#ejc   ,steam ,tugs                     
#ejc    ,,appendix4   ,on the ,relation 
between the ,temperature1 ,pressure1 and
    ,density of ,common ,steam4         
,empirical ,formula of ,biot1 showing   
the    ,relation between the ,pressure  
and ,temperature    #eje   ,empirical   
formula of ,southern                    
#ejf                       ,tredgold    
#ejf                       ,mellet      
#ejf                       ,de ,pambour 
#ejf                       ,,mm4 ,dulong
 and ,arago          #ejf   ,law of the 
,expansion of elastic ,fluids1          
discovered by ,dalton and ,gay ,lussac  
#ejf   ,formula for the ,relation       
between the ,volumes    and             
,temperatures                           

#ejg   ,law of ,mariotte                
#ejg   ,table of ,pressures1            
,temperatures1 ,volumes1 and            
,mechanical ,effects of ,steam          
#eji   ,empirical ,formul for the       
,relation between the    ,volume of     
,water and that of the ,steam produced  
by its ,evaporation under given         
,pressures         #eaa   ,formula of   
,navier                                 
#eaa   ,modified by ,de ,pambour        
#eaa     ,on the ,expansive ,action of  
,steam4   ,mechanical ,effect produced  
during a given    ,extent of ,expansion 
#eaa   ,mechanical ,effect produced     
during ,evaporation    and subsequent   
,expansion                         #eab 
,application to double-acting ,engines  
#eac   ,formula for ,pressure of ,steam 
in ,cylinders         #ead   ,formula   
for total ,mechanical ,effect per       
,minute    of ,steam when cut off at any
 proposed ,part of    the ,stroke       
#ead   ,formul exhibiting the ,relation 
between the    ,resistance of the ,load1

 the ,resistances of the    ,engine1 the
 ,evaporation1 the ,speed of the        
,piston1 and the ,magnitude of the      
,cylinder        #eae   ,formul showing 
the ,relation between the ,power    of  
the ,engine1 the ,evaporation1 and the  
useful    ,load                         
#eaf   ,formul for the useful ,effect   
and the ,duty     #eag   ,estimates of  
the several ,sources of    ,resistances 
#eah   ,tables to facilitate the        
,computation of the    ,effects of      
,expansive ,engines                     
#eai   ,table of the ,areas of ,pistons 
#ebj   ,,examples of the ,application of
 these ,formul       #eba    ,,index4   
#ebc     ,illustration3 ,,viaduct1      
,,near ,,watford1 ,,birmingham          
,,rail-,,road4  ,pg#jja     ,,the       
,,steam ,,engine4     ,pg#jjc           
,illustration3 ,,hero ,,of ,,alexandria4
  ,,chapter ,i4      ,,the ,,steam      
,,engine1 ,a ,,subject ,,of ,,popular   
,,interest4 -- ,,the ,,object     ,,of  
,,this ,,work4 -- ,,disputes            

,,respecting ,,the ,,invention4 --      
,,hero4 -- ,,de     ,,garay4 -- ,,de    
,,caus4 -- ,,branca4 -- ,,marquis ,,of  
,,worcester4 -- ,,physical              
,,principles4 -- ,,elastic ,,and        
,,inelastic ,,fluids4 -- ,,their        
,,properties4 -- ,,application ,,of     
,,these ,,principles ,,to ,,the         
,,engines     ,,of ,,hero1 ,,de ,,caus1 
,,and ,,lord ,,worcester4 -- ,,sir      
,,samuel ,,morland4 --     ,,papin4 --  
,,atmospheric ,,pressure4 -- ,,the      
,,weight ,,of ,,air4 -- ,,less ,,at     
,,greater ,,heights4 -- ,,barometer4 -- 
,,pressure ,,of ,,air4 -- ,,elastic     
,,force ,,of ,,air ,,and ,,gases4 --    
,,force ,,produced ,,by ,a ,,vacuum4 -- 
,,common     ,,pump4 -- ,,rarefaction   
,,by ,,heat4 -- ,,papin',s ,,methods    
,,of ,,producing ,a     ,,vacuum4 --    
,,his ,,discovery ,,of ,,the            
,,condensation ,,of ,,steam4 --         
,,savery4   7#a47 ,that the history of  
the invention of a piece of mechanism1  
and the description of its structure1   

operation1 and ,pg#jjd uses1 should be  
capable of being rendered the subject   
matter of a volume1 destined not alone  
for the instruction of engineers or     
machinists1 but for the information and 
amusement of the public in general1 is a
 statement which at no very remote      
period would have been deemed           
extravagant and incredible4  ,advanced  
as we are in the art of rendering       
knowledge popular1 and cultivated as the
 public taste is in the appreciation of 
the expedients by which science         
ministers to the uses of life1 there is 
still perhaps but one machine of which  
such a proposition can be truly         
predicated3 it is needless to say that  
that machine is the ,,steam ,,engine4   
,there are many circumstances attending 
this extraordinary piece of mechanism   
which impart to it an interest so       
universally felt4 ,whether we regard the
 details of its structure and operation1
 the physical principles which it calls 
into play1 and the beautiful            

contrivances by which these physical    
principles are rendered available2--or1 
passing over these means1 we direct our 
attention to the ends which they attain1
 we are equally filled with astonishment
 and admiration4 ,the history of the    
steam engine offers to our notice a     
series of contrivances which1 for       
exquisite and refined ingenuity1 stand  
without any parallel in the annals of   
mechanical science4 ,these admirable    
inventions1 unlike other results of     
scientific inquiry1 have also this      
peculiarity1 that1 to understand their  
excellence and to perceive their beauty1
 no previous or subsidiary knowledge is 
necessary1 save what may be imparted    
with facility and clearness in the      
progress of the explanation and         
development of the machine itself4 ,a   
simple and clear exposition1 divested of
 needless technicalities and aided by   
well-selected diagrams1 is all that is  
necessary to render the construction and
 operation of the steam engine1 in all  

its forms1 intelligible to persons of   
plain understanding and moderate        
information4  ,but if the contrivances  
by which this vast power is brought to  
bear on the arts and manufactures1 be   
rendered attractive by their great      
mechanical beauty1 how much more        
imposing will the subject become when   
the effects which the steam engine has  
produced upon the well-being of the     
human race are considered4 ,it has      
penetrated the crust of the earth1 and  
drawn from beneath it boundless         
treasures ,pg#jje of mineral wealth1    
which1 without its aid1 would have been 
rendered inaccessible2 it has drawn up1 
in measureless quantity1 the fuel on    
which its own life and activity depend2 
it has relieved men from their most     
slavish toils1 and reduced labour in a  
great degree to light and easy          
superintendence4 ,to enumerate its      
present effects1 would be to count      
almost every comfort and every luxury of
 life4 ,it has increased the sum of     

human happiness1 not only by calling new
 pleasures into existence1 but by so    
cheapening former enjoyments as to      
render them attainable by those who     
before could never have hoped to share  
them3 the surface of the land1 and the  
face of the waters1 are traversed with  
equal facility by its power2 and by thus
 stimulating and facilitating the       
intercourse of nation with nation1 and  
the commerce of people with people1 it  
has knit together remote countries by   
bonds of amity not likely to be broken4 
,streams of knowledge and information   
are kept flowing between distant centres
 of population1 those more advanced     
diffusing civilisation and improvement  
among those that are more backward4 ,the
 press itself1 to which mankind owes in 
so large a degree the rapidity of their 
improvement in modern times1 has had its
 power and influence increased in a     
manifold ratio by its union with the    
steam engine4 ,it is thus that          
literature is cheapened1 and1 by being  

cheapened1 diffused2 it is thus that    
,reason has taken the place of ,force1  
and the pen has superseded the sword2 it
 is thus that war has almost ceased upon
 the earth1 and that the differences    
which inevitably arise between people   
and people are for the most part        
adjusted by peaceful negotiation4  ,deep
 as the interest must be with which the 
steam engine will be regarded in every  
civilised country1 it presents peculiar 
claims upon the attention of the people 
of ,great ,britain4 ,its invention and  
progressive improvement are the work of 
our own time and our own country2 it has
 been produced and matured almost within
 the last century1 and is the exclusive 
offspring of ,british genius1 fostered  
and sustained by ,british enterprise and
 ,british capital4  ,the steam engine is
 a mechanical contrivance1 by which     
coal1 wood1 or other fuel is rendered   
capable of executing any ,pg#jjf kind of
 labour4 ,,coals are by it made to spin1
 weave1 dye1 print and dress silks1     

cottons1 woollens1 and other cloths2 to 
make paper1 and print books upon it when
 made2 to convert corn into flour2 to   
express oil from the olive1 and wine    
from the grape2 to draw up metal from   
the bowels of the earth2 to pound and   
smelt it1 to melt and mould it2 to forge
 it2 to roll it1 and to fashion it into 
every desirable form2 to transport these
 manifold products of its own labour to 
the doors of those for whose convenience
 they are produced2 to carry persons and
 goods over the waters of rivers1 lakes1
 seas1 and oceans1 in opposition alike  
to the natural difficulties of wind and 
water2 to carry the wind-bound ship out 
of port2 to place her on the open deep  
ready to commence her voyage2 to throw  
its arms around the ship of war1 and    
place her side by side with the enemy2  
to transport over the surface of the    
deep persons and information1 from town 
to town1 and from country to country1   
with a speed as much exceeding that of  
the ordinary wind1 as the ordinary wind 

exceeds that of a common pedestrian4    
,such are the virtues1 such the powers1 
which the steam engine has conferred    
upon ,,coals4 ,the means of calling     
these powers into activity are supplied 
by a substance which nature has happily 
provided in unbounded quantity in every 
part of the earth2 and though it has no 
price1 it has inestimable value3 this   
substance is ,,water4  ,a pint of water 
may be evaporated by two ounces of      
coals4 ,in its evaporation it swells    
into two hundred and sixteen gallons of 
steam1 with a mechanical force          
sufficient to raise a weight of         
thirty-seven tons a foot high4 ,the     
steam thus produced has a pressure equal
 to that of common atmospheric air2 and 
by allowing it to expand1 by virtue of  
its elasticity1 a further mechanical    
force may be obtained1 at least equal in
 amount to the former4 ,a pint of water1
 therefore1 and two ounces of common    
coal1 are thus rendered capable of doing
 as much work as is equivalent to       

seventy-four tons raised a foot high4   
,the circumstances under which the steam
 engine is worked on a railway are not  
favourable to the economy of fuel4      
,nevertheless a pound of coke burned in 
a locomotive engine ,pg#jjg will        
evaporate about five pints of water4 ,in
 their evaporation they will exert a    
mechanical force sufficient to draw two 
tons weight on the railway a distance of
 one mile in two minutes4 ,four horses  
working in a stage-coach on a common    
road are necessary to draw the same     
weight the same distance in six minutes4
  ,a train of coaches weighing about    
eighty tons1 and transporting two       
hundred and forty passengers with their 
luggage1 has been taken from ,liverpool 
to ,birmingham1 and back from           
,birmingham to ,liverpool1 the trip each
 way taking about four hours and a      
quarter1 stoppages included4 ,the       
distance between these places by the    
railway is ninety-five miles4 ,this     
double journey of one hundred and ninety

 miles is effected by the mechanical    
force produced in the combustion of four
 tons of coke1 the value of which is    
about five pounds4 ,to carry the same   
number of passengers daily between the  
same places by stage-coaches on a common
 road1 would require twenty coaches and 
an establishment of three thousand eight
 hundred horses1 with which the journey 
in each direction would be performed in 
about twelve hours1 stoppages included4 
,the circumference of the earth measures
 twenty-five thousand miles2 and if it  
were begirt with an iron railway1 such a
 train as above described1 carrying two 
hundred and forty passengers1 would be  
drawn round it by the combustion of     
about thirty tons of coke1 and the      
circuit would be accomplished in five   
weeks4  ,in the drainage of the ,cornish
 mines the economy of fuel is much      
attended to1 and coals are there made to
 do more work than elsewhere4 ,a bushel 
of coals usually raises forty thousand  
tons of water a foot high2 but it has on

 some occasions raised sixty thousand   
tons the same height4 ,let us take its  
labour at fifty thousand tons raised one
 foot high4 ,a horse worked in a fast   
stage-coach pulls against an average    
resistance of about a quarter of a      
hundred weight4 ,against this he is able
 to work at the usual speed through     
about eight miles daily3 his work is    
therefore equivalent to one thousand    
tons raised one foot4 ,a bushel of coals
 consequently1 as used in ,cornwall1    
performs as much labour as a day's work 
of one hundred such horses4 ,pg#jjh     
,the great pyramid of ,egypt stands upon
 a base measuring seven hundred feet    
each way1 and is five hundred feet high1
 its weight being twelve thousand seven 
hundred and sixty millions of pounds4   
,herodotus states1 that in constructing 
it one hundred thousand men were        
constantly employed for twenty years4   
,the materials of this pyramid would be 
raised from the ground to their present 
position by the combustion of about four

 hundred and eighty tons of coals4  ,the
 ,menai ,bridge consists of about two   
thousand tons of iron1 and its height   
above the level of the water is one     
hundred and twenty feet4 ,its mass might
 be lifted from the level of the water  
to its present position by the          
combustion of four bushels of coal4     
,the enormous consumption of coals      
produced by the application of the steam
 engine in the arts and manufactures1 as
 well as to railways and navigation1 has
 of late years excited the fears of many
 as to the possibility of the exhaustion
 of our coal-mines4 ,such apprehensions 
are1 however1 altogether groundless4 ,if
 the present consumption of coal be     
estimated at sixteen millions of tons   
annually1 it is demonstrable that the   
coal-fields of this country would not be
 exhausted for many centuries4  ,but in 
speculations like these1 the probable1  
if not certain progress of improvement  
and discovery ought not be overlooked2  
and we may safely pronounce that1 long  

before such a period of time shall have 
rolled away1 other and more powerful    
mechanical agents will supersede the use
 of coal4 ,philosophy already directs   
her finger at sources of inexhaustible  
power in the phenomena of electricity   
and magnetism4 ,the alternate           
decomposition and recomposition of      
water1 by magnetism and electricity1 has
 too close an analogy to the alternate  
processes of vaporisation and           
condensation1 not to occur at once to   
every mind3 the development of the gases
 from solid matter by the operation of  
the chemical affinities1 and their      
subsequent condensation into the liquid 
form1 has already been essayed as a     
source of power4 ,in a word1 the general
 state of physical science at the       
present moment1 the vigour1 activity1   
and sagacity with which researches in it
 are prosecuted in every civilised      
,pg#jji country1 the increasing         
consideration in which scientific men   
are held1 and the personal honours and  

rewards which begin to be conferred upon
 them1 all justify the expectation that 
we are on the eve of mechanical         
discoveries still greater than any which
 have yet appeared2 and that the steam  
engine itself1 with the gigantic powers 
conferred upon it by the immortal ,watt1
 will dwindle into insignificance in    
comparison with the energies of nature  
which are still to be revealed2 and that
 the day will come when that machine1   
which is now extending the blessings of 
civilisation to the most remote skirts  
of the globe1 will cease to have        
existence except in the page of history4
   7#b47 ,the object of the present     
volume will be to deliver1 in an easy   
and familiar style1 an historical view  
of the invention of the steam engine1   
and an exposition of its structure and  
operation in the various forms in which 
it is now used1 and of its most         
important applications in the arts of   
life1 especially in transport by land   
and water4 ,it is hoped that the details

 of these subjects may be rendered      
easily intelligible to all persons of   
ordinary information1 whether urged by  
that natural and laudable spirit of     
inquiry awakened by contemplating       
effects on the material and social      
condition of our species1 so rapid and  
so memorable as those which have        
followed the invention of the steam     
engine1 and by the pleasure which       
results from the perception of the      
numerous instances of successful        
contrivances and beautiful applications 
of science to art which it unfolds1--or 
impelled by the exigencies of trade or  
profession to acquire an acquaintance   
with a machine on which1 more than any  
other1 the prosperity of our commercial 
and manufacturing interests depends4 ,it
 will be our aim to afford to the former
 class all the information which they   
can require2 and1 if this work be not as
 comprehensive in its scope1 and as     
minute in its details1 as some of the   
latter may wish1 it will at least serve 

as an easy and convenient introduction  
to other works more voluminous1 costly1 
and detailed1 but less elementary in    
their matter1 and less familiar in their
 style4  ,in explaining the different   
forms of steam engine which have been   
proposed in the course of the           
progressive improvement ,pg#jaj of that 
machine from its early rude and         
imperfect state to its present          
comparatively perfect form1 it will be  
necessary to advert to various physical 
phenomena and mechanical principles1    
which1 however obvious to those who are 
conversant with matters of science1 must
 necessarily be at least imperfectly    
known by the great majority of our      
readers4 ,to refer for information on   
such topics to other works on ,mechanics
 and general ,physics1 would be with    
most readers ineffectual1 and with all  
unsatisfactory4 ,in former editions of  
the present work1 we consigned these    
necessary general principles of physics 
and mechanics to a preliminary chapter2 

but it appears1 on the whole1 more      
convenient not to remove the exposition 
of the principle from the place where   
its application is required4 ,we shall  
therefore pause as we proceed1 where    
these difficulties occur1 to give such  
explanation and illustration as may seem
 best suited to render them intelligible
 and interesting to the unscientific    
reader4  ,the history of the arts and   
manufactures affords no example of any  
invention the credit for which has been 
claimed by so many different nations and
 individuals as that of the steam       
engine4 ,the advocates of the           
competitors for this honour have urged  
their pretensions1 and pressed their    
claims1 with a zeal which has           
occasionally outstripped the bounds of  
discretion1 and the contest has not     
unfrequently been tinged with           
prejudices1 national and personal1 and  
characterised by a degree of asperity   
altogether unworthy of so noble a cause1
 and beneath the dignity of science4    

,when a question is clearly proposed1 it
 is already half resolved4 ,let us see  
whether a careful attention to this     
maxim will aid us in the investigation  
of the origin of the steam engine4 ,the 
source of the power of that machine is  
found in the following natural          
phenomena4  ,first4 ,when fire is       
applied to water1 the liquid swells into
 vapour1 and in undergoing this change  
exerts1 as has been already stated1 a   
considerable amount of mechanical force4
 ,this force may1 by proper means1 be   
rendered applicable to any purpose for  
which labour or power is needful4       
,second4 ,the vapour so produced is     
endowed with the property of elasticity1
 in virtue of which it is capable of    
,pg#jaa swelling or expanding into      
increased dimensions1 exerting1 as it   
expands1 a force1 the energy of which is
 gradually diminished as the dimensions 
of the vapour are increased4 ,this      
mechanical force is likewise capable of 
being applied to any useful purpose for 

which labour or power is necessary4     
,third4 ,this vapour is capable1 by     
proper means1 of being reconverted into 
water2 and when so reconverted1 it      
shrinks into its original dimensions1   
deserting the large space which it      
occupied as vapour1 and leaving that    
space a vacuum4 ,it is known in physics1
 that when a vacuum is produced1        
surrounding bodies have a tendency to   
rush into it with a definite amount of  
force4 ,consequently any agent which    
produces a vacuum1 becomes a source of a
 considerable amount of mechanical      
power4 ,by its reconversion into water1 
therefore1 steam again becomes a        
mechanical agent4  ,such are the natural
 phenomena in which are found the       
original sources of all steam power4 ,in
 some forms of steam engine one of these
 is used1 and in some another1 and in   
some the application of all of them is  
combined2 but in no existing form of    
steam engine whatever is there any other
 source of mechanical power4  ,neither  

these nor any other natural forces can  
be applied immediately to any useful    
purpose4 ,the interposition of mechanism
 is indispensable2 on the invention and 
contrivance of that mechanism depends   
altogether the useful application of    
these natural forces4  ,the world owes  
the steam engine then partly to         
discovery1 and partly to invention4  ,he
 that discovered the fact1 that         
mechanical force was produced in the    
conversion of water into steam1 must be 
justly held to be a sharer in the merit 
of the steam engine1 even though he     
should never have practically applied   
his discovery4 ,the like may be said of 
him who first discovered the source of  
the mechanical power arising from the   
expansion of steam4  ,the discoverer of 
the fact1 that steam being reconverted  
into water greatly contracted its       
dimensions1 and thereby produced a      
vacuum1 is likewise entitled to a share 
of the credit4 ,pg#jab  ,the mechanism  
by which these natural forces have been 

rendered so universally available as a  
moving power1 is very various and       
complicated1 and cannot be traced to one
 inventor4 ,if a watchmaker1 says ,m4   
,arago1 well instructed in the history  
of his art1 were required to give a     
categorical answer to the question1 ,who
 has invented watches8 he would remain  
mute2 but the question would be divested
 of much of its difficulty if he were   
required separately to declare who      
discovered the use of the main spring1  
the different forms of escapement1 or   
the balance wheel4 ,so it is with the   
steam engine4 ,it is a combination of a 
great variety of contrivances1 distinct 
from each other1 which are the          
production of several inventors4 ,if1   
however1 one name more than the rest be 
entitled to special notice2 if he is    
entitled to the chief credit of the     
invention who by the powers of his      
mechanical genius has imparted to the   
steam engine that form1 and conferred   
upon it those qualities1 on which mainly

 depends its present extensive utility1 
and by which it has become an agent of  
transcendant power1 spreading its       
beneficial effects throughout every part
 of the civilised globe1 then the       
universal voice will1 as it were by     
acclamation1 award the honour to one    
individual1 whose pre-eminent genius    
places him far above all other          
competitors1 and from the application of
 whose mental energies to this machine  
may be dated those grand effects which  
render it a topic of interest to all for
 whom the progress of civilisation has  
any attractions4 ,before the era        
rendered memorable by the discoveries of
 ,,james ,,watt1 the steam engine1 which
 has since become an object of such     
universal interest1 was a machine of    
extremely limited power1 inferior in    
importance and usefulness to most other 
mechanical agents used as prime movers2 
but1 from that epoch1 it is scarcely    
necessary here to state1 that it became 
a subject not of ,british interest only1

 but one having an important connection 
with the progress of the human race4    
,,hero ,,of ,,alexandria1 #abj ,b4 ,c4  
,illustration3 ,fig4 #a4   7#c47 ,the   
discovery of the fact1 that a mechanical
 force is produced when water is        
evaporated by the application of heat1  
,pg#jac must be considered as the first 
capital step in the invention of the    
steam engine4 ,it is recorded in a work 
entitled ,spiritalia seu ,pneumatica1   
that ,hero of ,alexandria contrived a   
machine1 #abj years before the          
,christian era1 which was moved by the  
mechanical force of the vapour of water4
 ,the principle of this machine admits  
of easy explanation3 ,when a fluid      
issues from any vessel in which it is   
confined1 that vessel suffers a force   
equal to that with which the fluid      
escapes from it1 and in the opposite    
direction4 ,if water issues from an     
orifice1 a pressure is produced behind  
the orifice corresponding to the force  
with which the water escapes4 ,if a man 

discharge a gun1 the gases produced by  
the explosion of the powder issue with a
 certain force from the muzzle1 and his 
shoulder is driven backwards by the     
recoil with a corresponding force4 ,if  
the muzzle1 instead of being presented  
forwards1 were turned at right angles to
 the length of the gun1 then1 as the    
gases of explosion would escape         
sideways1 the recoil would likewise take
 place sideways1 and the shooter1       
instead of being driven backward1 would 
be made to spin round as a dancer       
pirouettes4 ,this was the principle of  
,hero's steam engine4 ,a small globe or 
ball was placed on pivots at ,a and ,b  
7fig4 #a471 on which it was capable of  
revolving3 steam was supplied through   
one of these pivots from one of the     
tubes ,d ,c ,e ,f1 which communicated   
with the boiler4 ,this steam filled the 
globe ,a ,i ,b ,k1 and also the arms ,i 
,h and ,k ,g4 ,a lateral orifice1       
represented at ,g1 near the end of these
 arms1 allowed the steam to escape in a 

jet1 and the reaction1 producing a      
recoil1 had a tendency to drive the arm 
round4 ,a small orifice at ,h1 on the   
other side of the tube1 produced a like 
effect4 ,in the same manner1 any        
convenient number of arms might be      
provided1 surrounding the globe and     
communicating with its interior like the
 spokes of a wheel4 ,thus these arms1   
having lateral orifices for the escape  
of the steam1 all placed so that the    
recoil may ,pg#jad tend to turn the     
globe in the same direction1 a rotatory 
motion might be communicated to any     
machinery which it was desired to move4 
,after having been allowed to slumber   
for nearly two thousand years1 this     
machine has recently been revived1 and  
engines constructed similar to it are   
now working in these countries4 ,in the 
proper place we shall describe ,avery's 
,rotatory ,engine1 which it will be seen
 is1 not only in its principle1 but     
almost in its details1 the machine of   
,,hero ,,of ,,alexandria4  ,although the

 elastic force of steam was not reduced 
to numerical measure by the ancients1   
nor brought under control1 nor applied  
to any useful purpose1 yet it appears to
 have been recognised in vague and      
general terms4 ,aristotle1 ,seneca1 and 
other ancient writers1 accounted for    
earthquakes by the sudden conversion of 
water into steam within the earth4 ,this
 change1 according to them1 was effected
 by subterranean heat4 ,such tremendous 
effects being ascribed to steam1 it can 
scarcely be doubted that the ,greeks and
 ,romans were acquainted with the fact1 
that water in passing into vapour       
exercises considerable mechanical power4
 ,they were aware that the earthquakes1 
which they ascribed to this cause1      
exerted forces sufficiently powerful to 
extend the natural limits of the ocean2 
to overturn from their foundations the  
most massive monuments of human labour2 
to raise islands in the midst of seas2  
and to heave up the surface of the land 
of level continents so as to form lofty 

mountains4  ,such notions1 however1     
resulted not as consequences of any     
exact or scientific principles1 but from
 vague analogies derived from effects   
which could not fail to have been       
manifested in the arts1 such as those   
which commonly occurred in the process  
of casting in metal the splendid statues
 which adorned the temples1 gardens1 and
 public places of ,rome and ,athens4    
,the artisan was liable to the same     
accidents to which modern founders are  
exposed1 produced by the casual presence
 of a little water in the mould into    
which the molten metal is poured4 ,under
 such circumstances1 the sudden         
formation of steam of an extreme        
pressure produces1 as is well known1    
explosions attended with destructive    
effects4 ,the ,grecian ,pg#jae and      
,roman artisans were subject to such    
accidents2 and the philosopher1         
generalising such a fact1 would arrive  
at a solution of the grander class of   
phenomena of earthquakes and volcanoes4 

,before natural phenomena are rendered  
subservient to purposes of utility1 they
 are often made to minister to the      
objects of superstition4 ,the power of  
steam is not an exception to this rule4 
,it is recorded in the ,chronicles1 that
 upon the banks of the ,weser the       
ancient ,teutonic gods sometimes marked 
their displeasure by a sort of          
thunderbolt1 which was immediately      
succeeded by a cloud that filled the    
temple4 ,an image of the god ,busterich1
 which was found in some excavations1   
clearly explains the manner in which    
this prodigy was accomplished by the    
priests4 ,the head of the metal god was 
hollow1 and contained within it a pot of
 water3 the mouth1 and another hole1    
above the forehead1 were stopped by     
wooden plugs2 a small stove1 adroitly   
placed in a cavity of the head under the
 pot1 contained charcoal1 which1 being  
lighted1 gradually heated the liquid    
contained in the head4 ,the vapour      
produced from the water1 having acquired

 sufficient pressure1 forced out the    
wooden plugs with a loud report1 and    
they were immediately followed by two   
jets of steam1 which formed a dense     
cloud round the god1 and concealed him  
from his astonished worshippers4#a      
,among other amusing anecdotes showing  
the knowledge which the ancients had of 
the mechanical force of steam1 it is    
related that ,anthemius1 the architect  
of ,saint ,sophia1 occupied a house next
 door to that of ,zeno1 between whom and
 ,anthemius there existed a feud4 ,to   
annoy his neighbour1 ,anthemius placed  
on the ground floor of his own house    
several close digesters1 or boilers1    
containing water4 ,a flexible tube      
proceeded from the top of each of these1
 which was conducted through a hole made
 in the wall between the houses1 and    
which communicated with the space under 
the floors of the rooms in the house of 
,zeno4 ,when ,anthemius desired to annoy
 his neighbour1 he lighted fires under  
his boilers1 and the steam produced by  

them rushed in such quantity and with   
,pg#jaf such force under ,zeno's floors1
 that they were made to heave with all  
the usual symptoms of an earthquake4#b  
,,blasco ,,de ,,garay1 ,a4 ,d4 #aedc4   
7#d47 ,in the year #ahbf1 ,m4 de        
,navarrete published1 in ,zach's        
,astronomical ,correspondence1 a        
communication from ,thomas ,gonzales1   
,director of the royal archives of      
,simancas1 giving an account of an      
experiment reported to have been made in
 the year #aedc1 in which a vessel was  
propelled by a machine having the       
appearance of a steam engine4  ,blasco  
de ,garay1 a sea captain1 proposed in   
that year to the ,emperor ,charles ,v4  
to propel vessels by a machine which he 
had invented1 even in time of calm1     
without oars or sails4 ,notwithstanding 
the apparent improbability attending    
this project1 the ,emperor ordered the  
experiment to be made in the port of    
,barcelona1 and the #agth of ,june1     
#aedc1 was the day appointed for its    

trial4 ,the commissioners appointed by  
,charles ,v4 to attend and witness the  
experiment were ,don ,henry of ,toledo1 
,don ,pedro of ,cardona1 the treasurer  
,ravago1 the vice chancellor and        
intendant of ,catalonia1 and others4    
,the vessel on which the experiment was 
made was the ,trinity1 #bjj tons        
burthen1 which had just discharged a    
cargo of corn at ,barcelona4 ,garay     
concealed the nature of his machinery1  
even from the commissioners4 ,all that  
could be discovered during the trial    
was1 that it consisted of a large boiler
 containing water1 and that wheels were 
attached to each side of the vessel1 by 
the revolution of which it was          
propelled4 ,the commissioners having    
witnessed the experiment1 made a report 
to the king1 approving generally of the 
invention1 particularly on account of   
the ease and promptitude with which the 
vessel could be put about by it4  ,the  
treasurer ,ravago1 who was himself      
hostile to the project1 reported that   

the machine was capable of propelling a 
vessel at the rate of two leagues in    
three hours2 but the other commissioners
 stated that it made a league an hour at
 the least1 and that it put the vessel  
about as speedily as would be           
accomplished with a galley worked       
according to the common ,pg#jag method4 
,ravago reported that the machinery was 
too complicated and expensive1 and that 
it was subject to the danger of the     
boiler bursting4  ,after the experiment 
was made1 ,garay took away all the      
machinery1 leaving nothing but the      
framing of wood in the arsenals of      
,barcelona4  ,notwithstanding the       
opposition of ,ravago1 the invention was
 approved1 and the inventor was promoted
 and received a pecuniary reward1       
besides having all his expenses paid4   
,from the circumstance of the nature of 
the machinery having been concealed1 it 
is impossible to say in what this       
machine consisted2 but as a boiler was  
used1 it is probable1 though not        

certain1 that steam was the agent4      
,there have been various machines       
proposed1 of which a furnace and boiler 
form a part1 and in which the agency of 
steam is not used4 ,the machine of      
,amontons furnishes an example of this4 
,it is most probable that the           
contrivance of ,garay was identical with
 that of ,hero4 ,the low state of the   
arts in ,spain in the sixteenth century 
would be incompatible with the          
construction of any machine requiring   
great precision of execution4 ,but the  
simplicity of ,hero's contrivance would 
have rendered its construction and      
operation quite practicable4 ,as to the 
claims to the invention of the steam    
engine advanced by the advocates of ,de 
,garay1 founded on the above document1 a
 refutation is supplied by the          
admission1 that though he was rewarded  
and promoted by the government of the   
day1 in consequence of the experiment1  
and although the great usefulness of the
 contrivance in towing ships out of     

port1 c41 was admitted1 yet it does not 
appear that a second experiment was ever
 tried1 much less that the machine was  
ever brought into practical use4        
,,solomon ,,de ,,caus1 #afae4   7#e47   
,solomon ,de ,caus was engineer and     
architect to ,louis ,,xiii41 king of    
,france1 before the year #afab4 ,in that
 year he entered the service of the     
,elector ,palatine1 who married the     
daughter of ,king ,james ,i41 with whom 
he came to ,england4 ,he was there      
employed by the ,prince of ,wales in    
ornamenting the gardens of his house at 
,richmond4 ,pg#jah ,during his sojourn  
in ,england he composed and published at
 ,london1 in the same year1 a ,treatise 
on ,perspective4 ,this person was the   
author of a work entitled1 ,les ,raisons
 des ,forces ,mouvantes1 avec diverses  
,machines tant utiles que plaisantes1   
which was apparently composed at        
,heidelburg1 but published at           
,franckfort1 in #afae4 ,the same work   
was subsequently republished in ,paris  

in #afbc4  ,the treatise commences with 
definitions of what were then considered
 the four elements3 earth1 air1 fire1   
and water4 ,air is defined to be a cold1
 dry1 and light element1 capable of     
compression1 by which it may be rendered
 very violent4 ,he says1 ,the violence  
will be great when water exhales in air 
by means of fire1 and that the said air 
is enclosed3 as1 for example1 take a    
ball of copper of one or two feet       
diameter1 and one inch thick1 which     
being filled with water by a small hole1
 which shall be strongly stopped with a 
peg1 so that neither air nor water can  
escape1 it is certain that if we put the
 said ball upon a great fire1 so that it
 will become very hot1 that it will     
cause a compression so violent1 that the
 ball will burst in pieces1 with a noise
 like a petard4  ,the effect which is   
here described is due to the combined   
pressure of the heated air contained in 
the ball and the high pressure steam    
raised from the water1 but much more to 

the latter than to the former4 ,it is   
evident1 however1 from the language of  
,de ,caus1 that he ascribes the force   
entirely to the air1 and seems to       
consider that the force of the air      
proceeded from the water which exhaled  
in it4  ,the first theorem is1 that the 
parts of the elements mix together for a
 time1 and then each returns to its     
place 7the elements here referred to    
being apparently air and water74 ,upon  
this subject the following is an        
example3 ,take a round vessel of copper1
 soldered close on every side1 and with 
a tube1 whereof one end approaches      
nearly to the bottom of the vessel1 and 
the other end1 which projects on the    
outside of the vessel1 has a stop-cock2 
there is also a hole in the top of the  
vessel1 with a plug to stop it4 ,if this
 vessel will contain three pots of      
water1 then pour in one pot of water1   
and place the vessel on the fire about  
three or four minutes1 leaving the hole 
open2 then take the vessel off the      

,pg#jai fire1 and a little after pour   
out the water at the hole1 and it will  
be found that a part of the said water  
has been evaporated by the heat of the  
fire4 ,then pour in one pot of water as 
before1 and stop up the hole and the    
cock1 and put the vessel on the fire for
 the same time as before2 then take it  
off1 and let it cool of itself1 without 
opening the plug1 and after it is quite 
cold pour out the water1 and it will be 
found exactly the same quantity as was  
put in4 ,thus we see that the water     
which was evaporated 7the first time    
that the vessel was put on the fire7 is 
returned into water the second time when
 that vapour has been shut up in the    
vessel1 and cooled of itself4  ,in the  
description of these experiments1 the   
processes of evaporation and            
condensation are obscurely indicated2   
but there is no intimation that the     
author possessed any knowledge of the   
elastic force of steam4 ,his theorem is1
 that the parts of the element water mix

 for a time with the parts of the       
element air2 that fire causes this      
mixture1 and that on removing the fire1 
and dissipating the heat1 then the parts
 of the water mixed with air return to  
their proper place1 forming again part  
of the water4 ,there is no indication of
 a change of property of the water in   
passing into vapour4 ,it is difficult to
 conceive1 if ,de ,caus had been aware  
that the vapour of water possessed the  
same violent force which he distinctly  
and in terms ascribes to air1 or if he  
had been aware that in effect the vapour
 of the water produced by the fire was a
 fluid1 possessing exactly the same     
mechanical qualities1 and producing the 
same mechanical effects as air1 that he 
would not have expressed himself clearly
 on the subject4  ,he proceeds to give  
another demonstration that heat will    
cause the particles of water to mix with
 those of air4  ,after having put the   
measure of water into the vessel1 and   
shut the vent-hole1 and opened the cock1

 put the vessel on the fire1 and put the
 pot under the cock2 then the water of  
the vessel1 raising itself by the heat  
of the fire1 will run out through the   
cock2 but about one sixth or one eighth 
part of the water will not run out1     
because the violence of the vapour which
 causes the water to rise proceeds from 
the ,pg#jbj said water2 which vapour    
goes out through the cock after the     
water with great violence4 ,there is    
also another example in quicksilver1 or 
mercury1 which is a fluid mineral1 but  
being heated by fire1 exhales in vapour1
 and mixes with the air for a time2 but 
after the said vapour is cooled1 it     
returns to its first nature of          
quicksilver4 ,the vapour of water is    
much lighter1 and therefore it rises    
higher1 c4 c4  ,in this second          
demonstration there appears to be some  
obscure indication of the force of steam
 in the words because of the violence of
 the vapour which causes the water to   
rise1 c4  ,the fifth theorem is the     

following3--  ,water will mount by the  
help of fire higher than its level1     
which is explained and proved in the    
following terms3--  ,illustration3 ,fig4
 #b4  ,the third method of raising water
 is by the aid of fire4 ,on this        
principle may be constructed various    
machines3 ,i shall here describe one4   
,let a ball of copper marked ,a2 well   
soldered in every part1 to which is     
attached a tube and stop-cock marked ,d1
 by which water may be introduced2 and  
also another tube marked ,b ,c1 which   
will be soldered into the top of the    
ball1 and the lower end ,c of which     
shall descend nearly to the bottom of   
the ball without touching it4 ,let the  
said ball be filled with water through  
the tube ,d1 then shutting the stop-cock
 ,d1 and opening the stop-cock in the   
vertical tube ,b ,c1 let the ball be    
placed upon a fire the heat acting upon 
the said ball will cause the water to   
rise in the tube ,b ,c4  ,in the        
apparatus as here described1 the space  

enclosed in the boiler above the surface
 of the water is filled with air4 ,by   
the action of the fire1 two effects are 
produced3 first1 the air enclosed above 
the water1 being heated1 acquires       
increased elasticity1 and presses with a
 corresponding force on the surface of  
the water4 ,by this means a column of   
water will be driven up the tube ,a ,b  
at such a height as will balance the    
elasticity of the heated air confined in
 the boiler2 but besides ,pg#jba this   
the water contained in the boiler being 
heated1 will produce steam1 which being 
mixed with air contained in the boiler1 
will likewise press with its proper     
elasticity on the surface of the water1 
and will combine with the air in raising
 a column of water in the tube ,a ,b4   
,in the above description of the        
machine1 the force which raises the     
water in the tube ,a ,b is ascribed to  
the fire1 no mention being made of the  
water1 or of the vapour or steam        
produced from it having any agency in   

raising the water in the tube ,a ,b4    
,antecedently to the date of this       
invention1 the effect of heat in        
increasing the elastic force of air was 
known1 and so far as the above          
description goes1 the whole operation   
might be ascribed to the air by a person
 having no knowledge whatever of the    
elasticity of steam4 ,m4 ,arago1        
however1 who1 on the grounds of this    
passage in the work of ,de ,caus1 claims
 for him a share of the honour of the   
invention of the steam engine1 contends 
that the agency of steam in this        
apparatus was perfectly known to ,de    
,caus1 although no mention is made of   
steam in the above description1 because 
in the second demonstration above quoted
 he uses the words1 the violence of the 
vapour which causes the water to rise   
proceeds from the said water2 which     
vapour goes out from the cock after the 
water with great violence4 ,by these    
words ,m4 ,arago considers that ,de     
,caus expresses the quality of          

elasticity proper to the vapour1 and    
that the context justifies the          
inference1 that to this elasticity he   
ascribed the elevation of the water in  
the tube ,c ,b4  ,there appears to be   
some uncertainty attending the          
birthplace of ,de ,caus4 ,in the        
,biographie ,universelle he is said to  
have been born and to have died in      
,normandy4 ,m4 ,arago assigns ,dieppe1  
or its neighbourhood1 as his birthplace4
  ,there was another engineer and       
architect1 ,isaac ,de ,caus1 a native of
 ,dieppe1 who published a work in folio1
 entitled ,nouvelle ,invention de ,lever
 l',eau plus haut que sa ,source1 avec  
quelque ,machines mouvantes1 par le     
,moyen de l',eau1 et un ,discours de la 
,conduite d',icelle4 ,this volume is    
without a date1 but from the nature of  
its contents it would appear to have    
been published before the work of       
,solomon ,de ,caus already cited4 ,the  
drawings and machines described in both 
,pg#jbb are exactly the same2 but the   

definitions and theorems quoted above on
 raising water by fire are not given in 
the work of ,isaac4 ,it seems1          
therefore1 that ,solomon ,de ,caus      
re-published1 with additions1 the work  
of ,isaac ,de ,caus4 ,from the same     
birthplace being assigned to both these 
authors1 as well as from the similarity 
of their pursuits1 it is likely they    
were members of the same family1 and    
from their christian names they were    
probably ,jews4  ,the work cited above1 
was dedicated to ,louis ,,xiii41 and in 
the dedication ,solomon ,de ,caus calls 
himself the subject of that monarch2 and
 in the privilege prefixed to the work  
he is designated1 ,our well-beloved     
,solomon ,de ,caus1 master engineer1    
being at present in the service of our  
dear and well-beloved cousin1 the       
,prince ,elector ,palatine1 has made    
known to us1 c4--we1 desiring to gratify
 the said ,de ,caus1 he being our       
subject1 c4  ,it is therefore certain1  
whatever may have been the birthplace of

 ,de ,caus1 that he was at least a      
subject of ,france4 ,the circumstance of
 his work being written in ,french1     
though published beyond the ,rhine1 is  
also an argument in favour of his being 
a native of that country4   ,,giovanni  
,,branca1 #afbi4   7#f47 ,giovanni      
,branca of ,loretto in ,italy1 an       
engineer and architect1 proposed to work
 mills of different kinds by steam      
issuing from a large olopile1 and       
blowing against the vanes of a wheel4   
,branca was the author of many ingenious
 mechanical inventions1 a collection of 
which he dedicated to ,m4 ,cenci1 the   
governor of ,loretto4 ,these were       
published in a work printed at ,rome in 
#afbi4 ,it is a thin quarto1 entitled   
,le ,machine volume nuovo1 et di molto  
artificio da fare effetti maravigliosi  
tanto ,spiritali quanto di ,animale     
,operatione1 arichito di bellissime     
figure4 ,del ,sig4 ,giovanni ,branca1   
,cittadino ,romano4 ,in ,roma1 #afbi4   
,the work contains sixty-three          

engravings1 accompanied by descriptions 
in ,italian and ,latin4 ,branca's steam 
engine1 represented in the twenty-fifth 
plate1 consists of a wheel furnished    
with flat vanes upon its rim1 like the  
boards of a paddle wheel4 ,the steam is 
produced in a close vessel1 and made to 
issue with violence from the extremity  
,pg#jbc of a pipe directed against the  
vanes1 and causes the wheel to revolve4 
,this motion being imparted by the usual
 mechanical contrivances1 any machinery 
may be impelled by it4 ,different useful
 applications of this power are         
contained in the work1 viz4 pestles and 
mortars for pounding materials to make  
gunpowder1 and rolling stones for       
grinding the same2 machines for raising 
water by buckets1 for sawing timbers1   
for driving piles1 c4 c4  ,this method  
of applying the force of steam has no   
analogy to any application of steam in  
modern engines4   ,,edward ,,somerset1  
,,marquis ,,of ,,worcester1 #affc4      
7#g47 ,of all the names which figure in 

the early annals of steam1 by far the   
most remarkable is that of the ,marquis 
of ,worcester1 who has left a           
description of a machine in a work1     
entitled ,the ,scantling of ,one        
,hundred ,inventions1 which has been    
generally in this country considered as 
giving him a right to the honour of     
having been the inventor of the steam   
engine4  ,lord ,worcester having been   
engaged on the side of the ,royalists in
 the civil wars of the revolution1 lost 
his fortune1 and went to ,ireland1 where
 he was imprisoned4 ,he escaped from    
thence1 and reached ,france2 from that  
country he ventured to ,london1 as a    
secret agent of ,charles ,,ii41 but was 
detected1 and imprisoned in the ,tower1 
where he remained until the restoration1
 when he was set at liberty4 ,tradition 
has connected the invention of the steam
 engine with the following              
anecdote3--,one day1 during his         
imprisonment1 ,lord ,worcester observed 
the lid of the pot in which his dinner  

was being cooked1 suddenly forced       
upwards by the vapour of the water which
 was boiling in it4 ,reflecting on this1
 it occurred to him that the same force 
which raised the cover of the pot might 
be rendered1 when properly applied1 a   
useful and convenient moving power4     
,after he recovered his liberty1 he     
accordingly proceeded to carry into     
effect this conception4 ,the contrivance
 to which he was ultimately led is      
described in the following terms in the 
sixty-eighth invention1 in the work     
above named3--  ,i have invented an     
admirable and forcible way to drive     
,pg#jbd up water by fire2 not by drawing
 or sucking it upwards1 for that must   
be1 as the philosopher terms it1 infra  
sphrum activitatis1 which is but at such
 a distance4 ,but this way hath no      
bounder if the vessels be strong enough4
 ,for ,i have taken a piece of whole    
cannon whereof the end was burst1 and   
filled it three quarters full of water1 
stopping and screwing up the broken end1

 as also the touch-hole1 and making a   
constant fire under it2 within          
twenty-four hours1 it burst and made a  
great crack4 ,so that1 having a way to  
make my vessels so that they are        
strengthened by the force within them1  
and the one to fill after the other1 ,i 
have seen the water run like a constant 
fountain stream forty feet high4 ,one   
vessel of water rarefied by fire driveth
 up forty of cold water1 and a man that 
tends the work has but to turn two      
cocks2 that one vessel of water being   
consumed1 another begins to force and   
refill with cold water1 and so          
successively2 the fire being tended and 
kept constant1 which the self-same      
person may likewise abundantly perform  
in the interim between the necessity of 
turning the said cocks4  ,since the date
 of the publication of the ,century of  
,inventions was the year #affc1 the     
experiments here mentioned must have    
been made before that year4 ,the        
description of the machine here given1  

as well as others in the same work1 was 
intended by the author1 not to convey a 
knowledge of the nature of the mechanism
 which he used1 but only to express the 
effects produced1 and to indicate the   
physical principle on which they        
depended4 ,it should also be observed1  
that an air of mystery was thrown by    
,worcester over the accounts of all the 
machines which he described2 and        
therefore any obscurity in the above    
description ought not to be regarded as 
an evidence against his claim to the    
discovery of the mechanical agency of   
steam1 so far as that agency is         
indicated by the effects said by him to 
be produced4 ,the above account is1     
however1 sufficiently distinct and      
explicit to enable any one possessing a 
knowledge of the mechanical qualities of
 steam to perceive the general nature of
 the machine described4 ,to render this 
machine1 and that of ,de ,caus1         
previously described1 intelligible to   
those who are not familiar with physical

 science1 we must here explain some     
general principles on which their agency
 depends4 ,pg#jbe   7#h47 ,fluid bodies 
are of two kinds1 inelastic fluids1 or  
liquids1 and elastic fluids1 or gases4  
,of the former of these classes1 water  
is the most familiar example1 and of the
 latter1 air4  ,these two species of    
fluids are each distinguished by        
peculiar mechanical properties4         
,illustration3 ,fig4 #c4   7#i47 ,the   
constituent particles of a liquid are   
distinguished from those of solids by   
having little or no coherence2 so that  
unless the mass be confined by the sides
 of the vessel which contains it1 the   
particles will fall asunder by their    
gravity4 ,a mass of liquid1 therefore1  
unlike a solid1 can never retain any    
particular form1 but will accommodate   
itself to the form of the vessel in     
which it is placed4 ,it will press      
against the bottom of the vessel which  
contains it with the whole force of its 
weight1 and it will press against the   

sides with a force proportional to the  
depth of the particles in contact with  
the sides measured from the surface of  
the liquid above4 ,this lateral pressure
 also distinguishes liquids from solids4
 ,let us take for illustration the case 
of a square or a cubical vessel1 ,a ,b  
,c ,d1 fig4 #c4 ,if a solid body1 such  
as a piece of lead1 be cut to the shape 
of this vessel1 so as to fit in it      
without pressing with any force against 
its sides1 the mechanical effect which  
would be produced by it when placed in  
the vessel1 would be merely a pressure  
upon the bottom1 ,b ,c1 the amount of   
which would be equal to the weight of   
the metallic mass4 ,no pressure would be
 exerted against the sides2 for the     
coherence of the particles of the solid 
maintaining them in their position1 the 
removal of the sides would not subject  
the solid body contained in the vessel  
to any change4  ,now let us suppose this
 solid mass of lead to be rendered      
liquid by being melted4 ,the constituent

 particles will then be deprived of that
 cohesion by which they were held       
together2 they will accordingly have a  
tendency to separate1 and fall asunder  
by their gravity1 and will only be      
prevented from actually doing so by the 
support afforded to them by the sides1  
,pg#jbf ,a ,b1 ,d ,c1 of the vessel4    
,they will therefore produce a pressure 
against the sides1 which was not        
produced by the lead in its solid state4
 ,this pressure will vary at different  
depths3 thus a part of the side of the  
vessel at ,p will receive a pressure    
proportional to the depth of the point  
,p below the surface of the lead4 ,if1  
for example1 we take a square inch of   
the inner surface of the side of the    
vessel at ,p1 it will sustain an outward
 pressure equal to the weight of a      
column of lead having a square inch for 
its base1 and a height equal to ,p ,a4  
,and1 in like manner1 every square inch 
of the sides of the vessel will sustain 
an outward pressure equal to the weight 

of a column of lead having a square inch
 for its base1 and a height equal to the
 depth of the point below the surface of
 the lead4   7#aj47 ,we have here       
proceeded upon the supposition that no  
force acts on the upper surface ,a ,d of
 the lead4 ,if any force presses ,a ,d  
downwards1 that force would be          
transferred to the bottom by the lead1  
and would produce a pressure on the     
bottom ,b ,c equal to its own amount in 
addition to the weight of the lead2 and 
if the lead were solid1 this would be   
the only additional mechanical effect   
which such a force acting on the surface
 ,a ,d of the lead would produce4 ,but  
if1 on the other hand1 the lead were    
liquified1 then the force now adverted  
to1 acting on the surface ,a ,d1 would  
not only produce a pressure on the      
bottom ,b ,c1 equal to its own amount in
 addition to the weight of the lead1 but
 it would also produce a pressure       
against every part of the sides of the  
vessel1 equal to that which it would    

produce upon an equal magnitude of the  
surface ,a ,d4  ,thus if we suppose any 
mechanical cause producing a pressure on
 the surface ,a ,d amounting to ten     
pounds on each square inch1 the effect  
which would be produced1 if the lead    
were solid1 would be an additional      
pressure on the base ,b ,c amounting to 
ten pounds per square inch4 ,but if the 
lead were liquid1 besides this pressure 
on each square inch of the base ,b ,c1  
there would likewise be a pressure of   
ten pounds on every square inch of the  
sides of the vessel4  ,all that has been
 here stated with respect to a square or
 a cubical vessel will be equally       
applicable to a vessel of any other     
form4 ,pg#jbg   7#aa47 ,the second class
 of fluids are distinguished from       
liquids by the particles not merely     
being destitute of cohesion1 but having 
a tendency directly the reverse1 to     
repel each other1 and fly asunder with  
more or less force4 ,thus if a vessel1  
such as that represented in fig4 #c41   

were filled with a fluid of this kind1  
being open at the top1 and not being    
restrained by any pressure incumbent    
upon it1 the particles of the fluid     
would not rest in the vessel by their   
gravity1 as those of the liquid would   
do2 but they would1 by their mutual     
repulsion1 fly asunder1 and rise out of 
the vessel1 as smoke is seen to rise    
from a chimney1 or steam from the spout 
of a kettle4 ,let us suppose1 then1 that
 the vessel in which an elastic fluid is
 contained is closed on every side by   
solid surfaces4 ,in fact1 let us imagine
 that the square or cubical vessel      
represented in fig4 #c4 is closed by a  
square lid at the top ,a ,d1 having     
contained in it an elastic fluid1 such  
as atmospheric air4  ,if such a cover1  
or lid1 had been placed upon a liquid1  
the cover would sustain no pressure from
 the fluid1 nor would any mechanical    
effect be produced1 save those already  
described in the case of the open       
vessel2 but when the fluid contained in 

the vessel is elastic1 as is the case   
with air1 then the elasticity 7by which 
name is expressed the tendency of the   
particles of the fluid to fly asunder7  
will produce peculiar mechanical        
effects1 which have no existence        
whatever in the case of a liquid4  ,it  
is true that1 supposing the fluid to be 
air or any other gas or vapour1 a       
pressure will be produced upon the      
bottom ,b ,c of the vessel equivalent to
 the weight of such fluid1 and lateral  
pressures will be produced on the       
different points of the sides by the    
weight of that part of the fluid which  
is above these points2 but gases and    
vapours are bodies of such extreme      
levity1 that these effects due to their 
weight are neglected in practice4       
,putting1 then1 the weight of the air   
contained in the vessel out of the      
question1 let us consider the effect of 
its elasticity4 ,if the vessel1 as      
already described1 be supposed to       
contain atmospheric air in its ordinary 

state1 the tendency of the constituent  
particles to fly asunder will be such as
 to produce on every square inch of the 
inner surface of the vessel ,pg#jbh a   
pressure amounting to fifteen pounds2   
this pressure being1 as already stated1 
quite independent of the weight of the  
air4 ,in fact1 this pressure would      
continue to exist if the air contained  
in the vessel actually ceased to have   
weight by being removed from the        
neighbourhood of the earth1 which is the
 cause of its gravity4   7#ab47         
,different gases are endowed with       
different degrees of elasticity1 and the
 same gas may have its elasticity       
increased or diminished1 either by      
varying the space within which it is    
confined1 or by altering the temperature
 to which it is exposed4  ,if the space 
within which an elastic fluid is        
enclosed be enlarged1 its elasticity is 
found to diminish in the same           
proportion4 ,thus if the air contained  
in the vessel ,a ,b ,c ,d 7fig4 #c47 be 

allowed to pass into a vessel of twice  
the magnitude1 the elasticity of the    
particles will cause them to repel each 
other1 so that the same quantity of air 
shall diffuse itself throughout the     
larger vessel1 assuming double its      
former bulk4 ,under such circumstances1 
the pressure which it would exert upon  
the sides of the larger vessel would be 
only half that which it had exerted on  
the sides of the smaller vessel4 ,if1 on
 the other hand1 it were forced into a  
vessel of half the magnitude of ,a ,b ,c
 ,d1 as it might be1 then its elasticity
 would be double1 and it would press on 
the inner surface of that vessel with   
twice the force with which it pressed on
 that of the vessel ,a ,b ,c ,d4  ,this 
power of swelling and contracting its   
dimensions according to the dimensions  
of the vessel in which it is confined1  
or to the force compressing it1 is a    
quality which results immediately from  
elasticity1 and is consequently one     
which is peculiar to the gases or       

elastic fluids1 and does not at all     
appertain to liquids4 ,if the liquid    
contained in the vessel ,a ,b ,c ,d were
 transferred to a vessel of twice the   
magnitude1 it would only occupy half the
 capacity of that vessel1 and it could  
not by any means be transferred1 as we  
have supposed the air or gas to be1 to a
 vessel of half the dimensions1 since it
 is inelastic and incompressible4       
7#ac47 ,the elasticity of gases is      
likewise varied by varying the          
temperature to which they are exposed2  
thus1 in general1 ,pg#jbi if air or any 
other gas be augmented in temperature1  
it will likewise be increased in        
elasticity2 and if1 on the other hand1  
it be diminished in temperature1 it will
 be likewise diminished in its elastic  
force4 ,the more heated1 therefore1 any 
air or gas confined in a vessel becomes1
 the greater will be the force with     
which it will press on the inner surface
 of that vessel1 and tend to burst it4  
7#ad47 ,the same body may1 by the agency

 of heat1 be made to pass successively  
through the different states of solid1  
liquid1 and gas1 or vapour4 ,the most   
familiar and obvious example of these   
successive transitions is presented by  
water4 ,exposed to a certain            
temperature1 water can only exist as a  
solid2 as the temperature is increased1 
the ice1 or solid water1 is liquefied2  
and by the continued application of     
heat1 this water again undergoes a      
change1 and assumes the form1 and       
acquires the mechanical qualities1 of   
air or gas3 in such a state it is called
 ,,steam4  ,this is a common property of
 all liquids4 ,if they be exposed for a 
sufficient length of time to a          
sufficient degree of heat1 they will    
always be converted into elastic fluids4
 ,these are usually distinguished from  
air and other permanent gases1 which    
never are known to exist in the liquid  
form1 by the term vapour1 by which1     
therefore1 must be understood an elastic
 fluid which at common temperatures     

exists in the liquid or solid state2 by 
steam is expressed the vapour of water2 
and by gases1 those elastic fluids which
 like air are never known--at least1    
under ordinary circumstances--to exist  
in any other but the elastic form4      
7#ae47 ,when a liquid is caused1 by the 
application of heat1 to take the form of
 an elastic fluid1 or is evaporated1    
besides acquiring the property of       
elasticity1 it always undergoes a       
considerable change of bulk4 ,the amount
 of this change is different with       
different liquids1 and even with the    
same liquid it varies with the          
circumstances under which the change is 
produced4   7#af47 ,when water is       
evaporated under ordinary               
circumstances1--that is1 when exposed to
 no other external pressure than that of
 the atmosphere1--it increases its      
volume about seventeen-hundred-fold4    
,thus a cubic inch of liquid ,pg#jcj    
water would form about seventeen hundred
 cubic inches of common steam4 ,if1     

however1 the water be confined by a     
greater pressure than that produced by  
the common atmosphere1 then the increase
 of volume which takes place in its     
evaporation would be less in proportion4
  ,these important physical             
circumstances are now only indicated in 
a general way4 ,as we proceed with our  
account of the invention and improvement
 of the steam engine1 they will be      
developed more fully and accurately4    
7#ag47 ,after duly considering what has 
been just explained1 no difficulty will 
be found in comprehending the principles
 on which the first rude attempts at the
 mechanical application of steam already
 stated depend4 ,in the apparatus       
ascribed to ,hero of ,alexandria1 the   
elasticity of the vapour contained in   
the arms of the revolving ball causes   
that vapour to issue from the lateral   
orifices in the arms1 such as that of   
,g1 fig4 #a4 ,as these orifices1        
however1 are exposed to the common      
atmosphere pressing inwards with a      

force1 the mean amount of which has been
 stated to be about fifteen pounds per  
square inch1 it follows that the steam  
cannot escape from these orifices until 
its pressure or elasticity exceeds this 
amount1 and that when it does1 the force
 with which it will so escape will be   
the excess of its elasticity above that 
of the atmosphere2 and it is the        
reaction produced by this difference of 
pressure1 causing the arms to recoil1   
which will give motion to the machine4  
,in the case of the apparatus of ,de    
,caus 7#e471 the heat of the fire acting
 on the vessel ,d ,c 7fig4 #b47 will    
raise the temperature of the water      
contained in it1 and also of the air    
confined within it above the surface of 
that water4 ,this air1 as it is         
increased in temperature1 will also     
increase in elasticity2 it will         
therefore press on the surface of the   
water with increased force1 and will    
gradually force the water upwards in the
 tube2 and this effect would continue   

until all the water in the vessel would 
be forced up the tube4  ,but at the same
 time that the heat acting on the vessel
 increases the temperature of the air   
above the water1 it also produces a     
partial evaporation of the water1 so    
that more or less steam is mixed with   
the air in the vessel above the surface 
,pg#jca of the water2 and this steam    
possessing elasticity1 unites with the  
air in pressing on the surface of the   
water1 and in raising it in the tube4   
,illustration3 ,figs4 #d1 #e1 and #f4   
,let us now revert to the brief account 
of the engine of the ,marquis of        
,worcester1 described in ,the ,century  
of ,inventions4 ,we collect from that   
description that the vessel in which the
 water was evaporated was separate from 
those which contained the water to be   
elevated2 also that there were two      
vessels of the like description1 the    
contents of which were alternately      
elevated by the pressure of the water   
rarefied by the fire2 in other words by 

steam2 and that the water was raised in 
an uninterrupted stream1 by the         
management of two cocks communicating   
with these vessels and with the boiler4 
,the following is such an apparatus as  
would answer this description4 ,let ,e  
7fig4 #d47 be the vessel containing the 
water to be evaporated1 placed over a   
proper furnace ,a2 let ,s be a pipe to  
allow the steam produced from the       
boiling water in ,e to pass into the    
vessels where its mechanical action is  
required4 ,let ,r represent a cock or   
regulator1 having in it a curved        
passage1 leading from ,s to the tube ,t1
 when the lever or handle ,l is in the  
position represented by the cut2 but    
leading to the tube ,t1 when the lever  
,l is turned one quarter of a revolution
 to the right1 as represented in fig4   
#e4 ,by the shifting of this lever1     
therefore1 the steam pipe ,s may be made
 to communicate alternately with the    
tubes ,t and ,t4 ,the tubes ,t and ,t   
are carried respectively to two vessels 

,v and ,v1 which are filled with the    
water required to be raised4 ,in these  
,pg#jcb vessels tubes enter at ,c and   
,c1 descending nearly to the bottom3    
these tubes have valves at ,b and ,b1   
opening upwards1 by which water will be 
allowed to pass into the vertical tube  
,f1 but which will not allow it to      
return downwards1 the valves ,b and ,b  
being then closed by the weight of the  
water above them4  ,let ,g ,g be a pipe 
entering the sides of the vessels ,v and
 ,v1 for the purpose of filling them    
with the water to be raised3 let ,k be a
 cock having a curved passage similar to
 the cock ,r1 and leading to a tube by  
which water is supplied from the        
reservoir or other source from which the
 water to be raised is drawn4 ,when the 
cock ,k is placed as represented in fig4
 #d41 the water from the reservoir will 
flow through the curved passage in the  
cock ,k into the tube ,g1 and thence    
into the vessel ,v2 but when this cock  
is turned one quarter round1 by shifting

 the lever to the left1 it will take the
 position represented in fig4 #f41 and  
the water will flow through the curved  
passage into the tube ,g1 and thence    
into the vessel ,v4 ,let us now suppose 
the vessel ,v already filled with water 
to be elevated1 and the vessel ,v to    
have discharged its contents4 ,the cock 
,r is turned1 so as to allow the steam  
generated in the boiler ,e to pass into 
the tube ,t1 and thence into the upper  
part of the vessel ,v1 while the cock ,k
 is turned so as to allow the water from
 the reservoir to pass into the tube ,g1
 and thence into the vessel ,v4 ,the    
steam collecting in the upper part of   
the vessel ,v presses with its elastic  
force on the surface of the water       
therein1 and forces the water upwards in
 the tube ,c2 it passes through the     
valve ,b1 which it opens by the upward  
pressure received from the action of the
 steam1 and thence into the tube ,f1 its
 descent into the tube ,c being         
prevented by the valve ,v1 which can    

only be opened upwards4 ,as the steam is
 gradually supplied from the boiler ,e1 
the water in the vessel ,v is forced up 
the tube ,c1 through the valve ,b1 and  
into the tube ,f1 until all the contents
 of the vessel ,v above the lower end of
 the tube ,c have been raised4 ,in the  
meanwhile1 the vessel ,v has been filled
 with water1 through the cock ,k3 when  
this has been accomplished1 the man who 
attends the machine shifts the cocks ,r 
and ,k1 so as to give them the position 
represented in fig4 #e4 and fig4 #f4    
,pg#jcc ,in this position1 the steam    
from the boiler1 being excluded from the
 tube ,t1 will be conducted to the tube 
,t1 and thence to the vessel ,v1 while  
the water from the reservoir will be    
excluded from the tube ,g1 and conducted
 through the tube ,g to the vessel ,v4  
,the vessel ,v will thus be replenished 
and1 by a process similar to that       
already described1 the contents of the  
vessel ,v will be forced up the tube ,c1
 through the valve ,b1 and into the tube

 ,f2 its descent into the tube ,c being 
prevented by the valve ,b1 which will   
then be closed4 ,after the contents of  
the vessel ,v have thus been raised1 and
 the vessel ,v replenished1 the two     
cocks ,r and ,k are once more shifted1  
and the contents of ,v raised while ,v  
is replenished1 and so on4              
,illustration3 ,fig4 #d1 #e1 and #f4    
,if1 having comprehended the apparatus  
here described1 the reader refers to the
 description of the ,marquis of         
,worcester's machine1 he will find that 
all the conditions therein laid down are
 fulfilled by it4 ,one vessel 7,e7 of   
water rarefied by fire may by such means
 drive up forty 7or more7 of cold water2
 and the man that tends the work has but
 to turn two cocks1 that one vessel 7,v7
 of water being consumed1 another 7,v7  
begins to force and refill with cold    
water1 and so on successively1 the fire 
being tended and kept constant2 which   
the self-same person may likewise       
abundantly perform1 in the interim      

between the necessity of turning the    
said cocks4  ,on comparing this with the
 contrivance previously suggested by ,de
 ,caus1 it will be observed1 that even  
if ,de ,caus ,pg#jcd knew the physical  
agent by which the water was driven     
upwards in the apparatus described by   
him1 still it was only a method of      
causing a vessel of boiling water to    
empty itself2 and before a repetition of
 the process could be made1 the vessel  
should be refilled1 and again boiled4   
,in the contrivance of ,lord ,worcester1
 on the other hand1 the agency of the   
steam was employed in the same manner as
 it is in the steam engines of the      
present day1 being generated in one     
vessel1 and used for mechanical purposes
 in another4 ,nor must this distinction 
be regarded as trifling or              
insignificant1 because on it depends the
 whole practicability of using steam as 
a mechanical agent4 ,had its action been
 confined to the vessel in which it was 
produced1 it never could have been      

employed for any useful purpose4        
,although many of the projects contained
 in ,lord ,worcester's work were in the 
highest degree extravagant and absurd1  
yet the engine above described is far   
from being the only practicable and     
useful invention proposed in it4 ,on the
 contrary1 many of his inventions have  
been reproduced1 and some brought into  
general use since his time4 ,among these
 may be mentioned1 stenography1         
telegraphs1 floating baths1 speaking    
statues1 carriages from which horses can
 be disengaged if unruly1 combination   
locks1 secret escutcheons for locks1    
candle moulds1 the rasping mill1 the    
gravel engine1 c4   ,,sir ,,samuel      
,,morland1 #afhc4   7#ah47 ,sir ,samuel 
,morland was the son of a baronet of the
 same name1 who had received his title  
at the restoration for some services to 
the royalist party1 performed by him    
during the wars of the ,commonwealth4   
,he appears to have devoted much        
attention to mechanics1 in which he     

attained some celebrity4 ,he was the    
reputed inventor of several ingenious   
contrivances1 such as the drum capstan  
for ships1 the plunger pump1 c4 ,he also
 investigated various questions in      
acoustics1 and among others1 the        
determination of the best form for the  
speaking-trumpet4  ,in #afhj1 ,sir      
,samuel ,morland was appointed ,master  
,pg#jce of the ,works to ,charles ,,ii41
 and in the following year was sent to  
,france1 to execute some waterworks for 
,louis ,,xiv4 ,in #afhc1 while in       
,france1 he wrote in the ,french        
language1 a work entitled ,elevation des
 ,eaux par toute sorte de ,machines1    
reduite  la ,mesure1 au ,poids et  la   
,balance4 ,presente  sa ,majest trs     
,chrestienne1 par le ,chevalier         
,morland1 ,gentilhomme ,ordinaire de la 
,chambre ,prive1 et ,maistre des        
,mchaniques du ,roi de la ,grande       
,brtagne1 #afhc4 ,this book is preserved
 in manuscript in the ,harleian         
,collection in the ,british ,museum4 ,it

 is written on vellum1 and consists of  
only thirty-eight pages4 ,it contains   
tables of measures and weights1 theorems
 for the calculation of the volumes of  
cylinders1 the weights of columns of    
water1 the thickness of lead for pipes1 
and is concluded by a chapter on steam1 
consisting of four pages1 of which the  
following is a translation3--  ,the     
principles of the new force of fire     
invented by ,chevalier ,morland in      
#afhb1 and presented to ,his ,most      
,christian ,majesty in #afhc3--  ',water
 being converted into vapour by the     
force of fire1 these vapours shortly    
require a greater space 7about #bjjj    
times7 than the water before occupied1  
and sooner than be constantly confined  
would split a piece of cannon4 ,but     
being duly regulated according to the   
rules of statics1 and by science reduced
 to measure1 weight1 and balance1 then  
they bear their load peaceably 7like    
good horses71 and thus become of great  
use to mankind1 particularly for raising

 water1 according to the following      
table1 which shows the number of pounds 
that may be raised #ahjj times per hour 
to a height of six inches by cylinders  
half filled with water1 as well as the  
different diameters and depths of the   
said cylinders4'  ,there is nothing in  
the description here given which can    
indicate the form of the machine by     
which ,morland proposed to render the   
force of steam a useful mover4 ,it is1  
however1 remarkable1 that at this early 
period1 before experiments had been made
 on the expansion which water undergoes 
in evaporation1 he should have given so 
near an approximation to ,pg#jcf the    
actual amount of that expansion4 ,it is 
scarcely supposable that such an        
estimate could be obtained by him       
otherwise than by experiment4  ,the work
 containing the above description was   
not printed2 but a work bearing nearly  
the same title1 containing1 however1 no 
mention of the force of steam1 was      
published by him in ,paris in the year  

#afhe4 ,in this he describes various    
experiments made by him at ,st4         
,germains on the weight of the water of 
the ,seine1 and gives weights of the    
columns of water1 the contents of       
cylinders1 c4  ,soon after the          
publication of this work1 ,morland      
returned to ,england1 and resided near  
the court till his death4 ,the          
celebrated ,john ,evelyn mentioned      
having paid a visit to him at his house 
at ,hammersmith1 in #afie1 when he had  
become aged and blind1 but was still    
remarkable for his mechanical ingenuity4
 ,on the #beth of ,october1 says        
,evelyn1 the ,archbishop and myself went
 to ,hammersmith to visit ,sir ,samuel  
,morland1 who was entirely blind2 a very
 mortifying sight4 ,he showed us his    
invention of writing 7short-hand71 which
 was very ingenious2 also his wooden    
kalendar1 which instructed him all by   
feeling2 and other pretty and useful    
inventions of mills1 pumps1 c42 and the 
pump he had erected1 that serves water  

to his garden and to passengers1 with an
 inscription1 and brings from a filthy  
part of the ,thames near it a most      
perfect and pure water4#c  ,he died at  
,hammersmith1 in ,january #afif2 and    
before his death1 as a penance for his  
past life1 was guilty of the            
eccentricity of burying in the ground   
six feet deep a great collection of     
music which he possessed4#d   ,,denis   
,,papin1 #afhh4   7#ai47 ,denis ,papin1 
a native of ,blois in ,france1 and      
professor of mathematics at ,marbourg1  
is the name which stands next recorded  
in the progressive invention of the     
steam engine4 ,to this philosopher is   
due the discovery of one of the         
qualities of steam1 to the proper       
management of which is owing much of the
 efficacy of the modern steam engine4   
,pg#jcg  ,papin was born at ,blois in   
,france4 ,he devoted his youth to the   
study of medicine1 in which he took a   
degree at ,paris4 ,the revocation of the
 ,edict of ,nantes having driven him    

into exile1 he went to ,england1 where  
the celebrated ,boyle associated him in 
several of his experiments with the     
air-pump1 and caused him to be elected a
 fellow of the ,royal ,society in #afha4
 ,having been invited to ,germany by the
 ,landgrave of ,hesse1 he discharged    
during several years the duties of      
professor of mathematics at the         
university of ,marbourg1 where he died  
in #agaj4 ,notwithstanding his          
discoveries respecting the agency of    
steam1 he never received any mark of    
distinction in his own country4 ,the    
truth is1 the importance and value of   
these investigations were not apparent  
until long afterwards4  ,this           
philosopher conceived the idea of       
producing a moving power by means of a  
piston working in a cylinder1 in the    
manner which we shall now briefly       
explain4  ,illustration3 ,fig4 #g4  ,let
 ,a ,b 7fig4 #g47 be a cylinder open at 
the top1 and let a piston ,p be fitted  
into it1 so as to move in it air tight4 

,at the bottom of the cylinder suppose  
an opening provided1 which can be closed
 at pleasure1 by a stop-cock1 or        
otherwise1 so that the communication may
 be opened and closed at will between   
the interior of the cylinder and the    
external air4 ,this stop-cock being     
opened1 let the piston be drawn upwards 
till it reach the top of the cylinder4  
,let the stop-cock at the bottom be then
 removed1 and imagine that some means   
can be supplied by which the air within 
the cylinder can be suddenly            
annihilated4 ,the piston1 now at the    
top1 will have above it the pressure of 
the atmosphere2 and having no air below1
 it will be resisted in its descent by  
no force save that arising from its     
friction with the cylinder4 ,if1 then1  
the force of the air above the piston be
 greater than the resistance arising    
from this friction1 the piston will     
descend with the excess of this force1  
and will continue so to descend until it
 reach the bottom of the cylinder4      

,having attained that position1 let us  
,pg#jch suppose the stop-cock in the    
bottom opened1 so as to allow the       
external air to pass freely below the   
piston4 ,the piston may now be drawn to 
the top of the cylinder again1 offering 
no resistance save that of its weight1  
and its friction with the cylinder4     
,having reached the top of the cylinder 
once more1 let the stop-cock be closed1 
and the air included within the cylinder
 once more annihilated4 ,a second       
descent of the piston will take place1  
with the same force as before1 and in   
like manner the process may be continued
 indefinitely4  ,now1 if it should      
appear that means could be provided     
suddenly and repeatedly to annihilate   
the air within the cylinder1 and that   
the pressure of the atmosphere above the
 piston should exert a force compared   
with which the weight of the piston and 
its friction are trifling1 it is evident
 that a moving power would be obtained  
which would be capable1 by proper       

mechanism1 of being applied to any      
useful purpose1 but which would more    
especially be applicable to the working 
of pumps1 the motion of which           
corresponds with that which has been    
just ascribed to the piston in the      
cylinder4 ,such were the first ideas of 
,papin4 ,but in order to enable those   
who are not conversant with physical    
science fully to appreciate their       
importance1 it will be necessary here to
 explain some of the mechanical         
properties of atmospheric air4   7#bj47 
,the atmosphere is the thin1            
transparent1 colourless1 and therefore  
invisible1 fluid in which we live and   
move1 which by respiration sustains     
animal life1 and is otherwise connected 
with various important functions of     
organised matter4 ,this fluid is so     
light and attenuated1 that it might at  
first be doubted whether it be really a 
body at all2 and1 indeed1 the name      
expressing incorporeal beings1 spirit1  
is a word in its origin signifying      

air4#e ,the air1 however1 is light only 
as compared with other material         
substances1 which exist in a more       
condensed state3 it possesses the       
quality of weight as absolutely as the  
most solid and massive bodies in nature1
 and to render this quality manifest1 it
 is only necessary to submit a          
sufficient quantity of air to any of the
 usual tests of gravitation4 ,pg#jci  ,a
 direct demonstration of this may be    
given by the following experiment3--,on 
the mouth of a flask let a stop-cock be 
fastened so as to be air-tight4 ,the    
interior of the flask may then be put   
into free communication with the        
external air1 or that communication may 
be cut off at pleasure1 by opening or   
closing the stop-cock4 ,if a syringe be 
applied to the mouth of the flask1 the  
stop-cock being open a part of the air  
contained in it may be drawn out4 ,after
 this1 the stop-cock being closed1 and  
the syringe detached1 let the flask be  
placed in the dish of a good balance1   

and accurately counterpoised by weights 
in the other dish4 ,this counterpoise   
will then represent the weight of the   
flask1 and of the air which has remained
 in it4 ,if the stop-cock be now opened1
 air will immediately rush in1 and      
replace that which the syringe had      
withdrawn from the flask2 and           
immediately the dish of the balance     
containing the flask will sink by the   
effect of the weight of the air thus    
admitted into the flask4  ,if the weight
 of quantity of air so small as to be   
capable of being withdrawn by a syringe 
from an ordinary flask be thus of       
sensible amount1 it may be easily       
imagined that the vast mass of          
atmosphere extending from the surface of
 the earth upwards1 to a height not     
ascertained with precision1 but         
certainly not being less than thirty    
miles1 must be very considerable4 ,such 
a force1 pressing as it must constantly 
do1 upon the surfaces of all bodies1    
whether solid or fluid1 and resisting   

and modifying their movements1 would    
play an important part in all mechanical
 phenomena2 and it is1 therefore1 not   
sufficient merely to have recognised its
 existence1 but it is most needful to   
measure its amount with that degree of  
certainty and precision1 which will     
enable us to estimate its effects on    
those phenomena which we shall have to  
investigate4   7#ba47 ,the amount of the
 pressure of the atmosphere on each     
square inch of horizontal surface on    
which it rests1 is obviously the weight 
of the column of air extending from that
 square inch of surface upwards to the  
top of the atmosphere4 ,this force is   
measured by the following means3--      
,illustration3 ,fig4 #h4  ,illustration3
 ,fig4 #i4  ,take a glass tube1 ,a ,b   
7fig4 #h471 above #cb inches long1 open 
at one end ,a1 and closed at the other  
end ,b1 and let it ,pg#jdj be filled    
with mercury 7quicksilver74 ,let a glass
 vessel or cistern ,c1 containing a     
quantity of mercury1 be also provided4  

,applying the finger at ,a1 so as to    
prevent the mercury in the tube from    
falling out1 let the tube be inverted1  
and the end1 stopped by the finger1     
plunged into the mercury in ,c4 ,when   
the end of the tube is below the surface
 of the mercury in ,c 7fig4 #i471 let   
the finger be removed4 ,it will be found
 that the mercury in the tube will not1 
as might be expected1 fall to the level 
of the mercury in the cistern ,c1 which 
it would do were the end ,b open1 so as 
to admit the air into the upper part of 
the tube4 ,on the other hand1 the level 
,d of the mercury in the tube will be   
nearly #cj inches above the level ,c of 
the mercury in the cistern4  ,the cause 
of this effect is1 that the weight of   
the atmosphere rests on the surface ,c  
of the mercury in the cistern1 and tends
 thereby to press it up1 or rather to   
resist its fall in the tube2 and as the 
fall is not assisted by the weight of   
the atmosphere on the surface ,d 7since 
,b is closed71 it follows1 that as much 

mercury remains suspended in the tube   
above the level ,c1 as the weight of the
 atmosphere is able to support4  ,if the
 section of the tube were equal to the  
magnitude of a square inch1 the weight  
of the column of mercury in the tube    
above the level ,c would be exactly     
equal to the weight of the atmosphere on
 each square inch of the surface ,c4    
7#bb47 ,if such an apparatus be observed
 from time to time1 it will be found    
that the column of mercury sustained in 
the tube will be subject to variation   
between certain limits1 never falling   
below twenty-eight inches1 and never    
rising above thirty-one inches4 ,this   
variation of the mercurial column is    
produced by a corresponding variation in
 the weight of the atmosphere4  ,if the 
apparatus be transported to any height  
above its ordinary position1 it will    
have a less quantity of atmosphere above
 it1 and therefore the surface of the   
mercury in the cistern will be pressed  
by a less weight1 and consequently the  

,pg#jda column of mercury will fall     
proportionally4 ,in virtue of this      
effect1 such an instrument has been     
rendered a means of measuring heights1  
such as the heights of mountains1 the   
ascents of balloons1 c4 c4   7#bc47 ,if 
a proper scale be attached to the tube  
containing the mercurial column1 showing
 the absolute height of the column      
sustained at any time1 and indicating   
its changes of height1 the instrument   
becomes a ,,barometer4  ,two cubic      
inches of mercury weigh very nearly one 
pound avoirdupois4#f ,hence1 when the   
barometric column measures thirty       
inches1 the weight of the atmosphere    
resting on each square inch of surface  
is about fifteen pounds4   7#bd47 ,it is
 an established property of fluids1 that
 they press equally in all directions2  
and air1 like every other fluid1        
participates in this quality4 ,hence1 it
 follows1 that when the downward        
pressure or weight of the atmosphere is 
fifteen pounds on the square inch1 the  

lateral1 upward1 and oblique pressures  
are of the same amount4 ,but1           
independently of the general principle1 
it may be satisfactory to give          
experimental proof of this4             
,illustration3 ,fig4 #aj4  ,let four    
glass tubes1 ,a1 ,b1 ,c1 ,d 7fig4 #aj471
 be constructed of sufficient length1   
closed at one end1 ,a1 ,b1 ,c1 ,d1 and  
open at the other4 ,let the open ends of
 three of them be bent1 as represented  
in the tubes ,b1 ,c1 ,d4 ,being         
previously filled with mercury1 let them
 all be gently inverted1 so as to have  
their closed ends up1 as here           
represented4 ,it will be found that the 
mercury will be sustained in all1 and   
that the difference of the levels in all
 will be the same4#g ,thus1 the mercury 
is sustained in ,a by the upward        
pressure of the atmosphere2 in ,b1 by   
its horizontal or lateral pressure2 in  
,c1 by its downward pressure2 ,pg#jdb   
and in ,d1 by its oblique pressure3 and1
 as the difference of the levels is the 

same in all1 these pressures are exactly
 equal4   7#be47 ,the same arrangement  
by which the pressure of the atmosphere 
is measured by a mercurial column of    
equivalent weight1 also supplies the    
means of measuring the pressure or      
elasticity of atmospheric air1 or any   
other gas or vapour1 whether in a more  
or less compressed or rarefied state2   
and as instruments constructed on this  
principle are of considerable use in    
steam engines1 we shall take this       
occasion to explain their principle and 
application4  ,in the experiments       
described in 7#ba71 the space ,d ,b in  
the top of the barometer-tube1 from     
which the mercury descended1 is a       
vacuum4 ,if1 however1 it were occupied  
by a quantity of air in a rarefied      
state1 or any other gas or vapour1 such 
gas or vapour would press on the surface
 of the mercury at ,d1 with a force     
determined by its elasticity4 ,in that  
case1 the atmospheric pressure acting on
 the surface of the mercury ,c in the   

cistern1 would be balanced by the       
combined forces of the weight of the    
mercurial column sustained in the tube1 
and the elasticity of the gas or vapour 
in the upper part of it4 ,now if we know
 the actual amount of the atmospheric   
pressure1--that is to say1 the height of
 the column of mercury which it would be
 capable of sustaining1--we should then 
be able to determine the pressure of the
 rarefied air in the space ,c ,d4  ,for 
example1 let us suppose that the        
barometric column1 when ,b ,d 7fig4 #i47
 is a vacuum1 measures thirty inches3   
the atmospheric pressure1 therefore1    
would be equal to the weight of a column
 of mercury of that height4 ,let us     
suppose that the elasticity of the gas  
or vapour occupying the upper part of   
the tube ,d ,b causes the column to fall
 to the height of twenty-six inches3 it 
is evident1 then1 that the pressure of  
the air in the top of the tube would be 
equal to the weight of a column of      
mercury of four inches4 ,in fine1 to    

determine the pressure of the rarefied  
gas or vapour in the top of the tube1 it
 is only necessary to observe the       
difference between the height of the    
column of mercury actually sustained in 
the tube1 and the column sustained at   
the same time and ,pg#jdc place in a    
common barometer3 the difference of the 
two will be the column of mercury whose 
weight will represent the pressure of   
the vapour or gas in the top of the     
tube4   7#bf47 ,whenever the air        
contained in any vessel or other        
enclosed space has by any means had its 
pressure reduced so as to be rendered   
less than that of the external air1 the 
external air will have a tendency to    
rush into such vessel or enclosed space 
with a force proportionate to the excess
 of the pressure of such external air   
over that of the air within2 and if any 
communication be opened between the     
interior of such vessel or enclosed     
space1 and the external air1 the latter 
will rush in until an equilibrium be    

established between the pressures within
 and without4 ,it is evident that the   
force thus obtained by diminishing the  
pressure of air within a vessel may be  
applied to any mechanical purpose4  ,it 
is by such means that water is raised in
 an ordinary pump4 ,a portion of the air
 contained between the piston of the    
pump and the surface of the water below1
 is withdrawn by the action of the      
piston1 and the pressure of the air     
remaining under the piston is thereby   
diminished4 ,the superior pressure of   
the atmosphere upon the external surface
 of the water in the well then forces up
 a column of water in the pump-barrel1  
and this is continued as the air is more
 and more rarefied by the action of the 
piston4 ,by whatever means1 therefore1  
the air can be wholly or partially      
withdrawn from any space1 a mechanical  
power will be thereby developed1        
proportional in its amount and efficacy 
to the quantity of air so withdrawn4    
,if1 however1 such air be withdrawn by  

any mechanical process1 such as by a    
syringe1 by a common pump1 or by an     
air-pump1 the quantity of force expended
 in withdrawing it is always equivalent 
to the amount of mechanical power       
obtained by the vacuum or partial vacuum
 so produced4 ,indeed the power expended
 is greater than the power so obtained1 
inasmuch as the friction1 leakage1 c4 of
 the exhausting apparatus must be       
allowed for4   7#bg47 ,there are1       
however1 various other means by which   
air may be partially expelled from a    
vessel besides the direct application of
 mechanical force4 ,thus if heat be     
applied to ,pg#jdd the vessel1 the air1 
as has been already explained1 will     
acquire increased elasticity1 and will  
rush from the vessel with a force       
proportionate to the excess of its      
elasticity above that of the external   
air1 and this process may be continued  
by increasing the heat to which the     
vessel is exposed1 until a very         
considerable portion of the air has been

 expelled4 ,if the orifice by which the 
air has escaped be then closed1 and the 
vessel be allowed to cool1 the air      
within1 by having its temperature       
reduced to that of the external air1    
will lose all the elasticity which it   
had gained from the heat1 and will be in
 the same condition as if an equivalent 
quantity of air had been withdrawn by   
any mechanical agent4 ,the external air1
 therefore1 will have a tendency to rush
 in with a force corresponding to the   
difference of pressures4  ,the process  
of filling thermometers with mercury    
shows one use of producing a high degree
 of rarefaction by heat4 ,to construct  
the instrument it is necessary to fill  
the bulb and a part of the tube with    
mercury2 but the bore of the tube is so 
small that the mercury cannot be        
introduced by any ordinary means4 ,it is
 therefore held over flame until heated 
to a high temperature4 ,the air within  
it gradually increasing in pressure as  
its temperature is raised1 is forced    

through the small bore of the tube1     
until the pressure of the air within    
becomes no more than equal to the       
pressure of the external atmosphere2    
this air being so rarefied that quantity
 in the bulb bears a very small         
proportion to its contents at common    
temperatures4 ,the mouth of the tube is 
then plunged into mercury1 and as the   
bulb cools1 the air within it loses its 
elasticity1 and the superior pressure   
upon the external surface forces the    
mercury into the tube4 ,this continues  
until the air remaining within the bulb 
has been so contracted1 that its        
pressure combined with the weight of the
 mercury1 shall balance the atmospheric 
pressure4 ,the tube is then reversed1   
and the air which remained rises in a   
bubble to the surface1 and escapes4     
7#bh47 ,let us now return to the        
proceedings of ,papin4 ,how great a     
power would result from such a machine  
as he conceived1 will be apparent1 if it
 be considered that the unresisted      

atmosphere exercises a pressure of about
 fifteen pounds on ,pg#jde each square  
inch of surface exposed to it1 and that 
if the piston in the cylinder imagined  
by ,papin1 had a diameter of only one   
foot1 its superficial magnitude would be
 about #aad square inches4 ,the pressure
 of the atmosphere upon it1 therefore1  
would be #aad times fifteen pounds1 or  
#agaj pounds4 ,papin first proposed to  
produce the vacuum under the piston by  
means of common air pumps1 worked by a  
water-wheel2 and by such means he       
conceived that the power of a river1    
stream1 or waterfall might be conveyed  
by pipes to a distance4 ,while he was in
 ,england1 in #afhg1 he laid his        
contrivance before the ,royal ,society  
of ,london1 but was met by objections   
and difficulties1 the nature of which he
 does not explain4  ,it is1 however1    
apparent1 from what has been already    
explained1 that such a method of        
proceeding would amount to a mere       
transfer of power1 and would not1       

properly speaking1 be itself a moving   
force3 the moving power would1 in       
reality1 be the force of the water by   
which the water-wheel would be driven2  
and the air-pumps1 tubes1 together with 
the piston and cylinder1 would be merely
 means of conveying the power of the    
water-wheel to the objects to be moved1 
or the machinery to be driven4 ,papin   
states1 that1 long before this1 he had  
attempted to expel the air from his     
cylinder by means of gunpowder2 but1    
notwithstanding all the precautions     
which he could take1 there always       
remained a considerable quantity2 so    
much1 indeed1 as to deprive the vacuum  
of more than half its proper force4 ,at 
length he adopted an expedient for the  
production of a vacuum which forms a    
most important step in the progressive  
invention of the steam engine1 and which
 gives to ,papin's name a high place in 
the history of that machine4 ,this      
method is explained in the following    
paragraph of a work published by ,papin 

in #afie1 at ,cassel1 entitled ,recueil 
de diverses ,pices touchant quelques    
nouvelles ,machines1 p4 #ec4  ,i have   
endeavoured1 says he1 to attain this end
 7viz4 the production of a vacuum in the
 cylinder7 in another way4 ,as water has
 the property of elasticity1 when       
converted into steam by heat1 and       
afterwards of being so completely       
recondensed by cold1 that there does not
 remain the least ,pg#jdf appearance of 
this elasticity1 ,i have thought that it
 would not be difficult to work machines
 in which1 by means of a moderate heat  
and at a small cost1 water might produce
 that perfect vacuum which has vainly   
been sought by means of gunpowder4      
,this remarkable passage is given in the
 work just cited1 as an extract from the
 ,leipsic ,acts1 of ,august1 #afij4     
,let us pause here to explain more fully
 this important discovery4   7#bi47 ,we 
have explained that1 in its conversion  
into vapour1 by the application of heat1
 water1 besides acquiring the property  

of elasticity1 undergoes a vast         
enlargement of bulk1 filling1 under     
ordinary circumstances1 about #agjj     
times more space than it occupied in the
 liquid form4 ,this fact was known      
generally1 though not with numerical    
accuracy1 by ,papin1 having been the    
foundation of the machines previously   
invented and published by ,de ,caus and 
,lord ,worcester2 the happy idea of     
reversing the process occurred to him4  
,if water in its conversion into steam  
swelled into many hundred times its     
original bulk1 it would necessarily     
follow1 that steam1 being reconverted   
into water1 would shrink into its       
primitive dimensions4 ,papin therefore  
saw1 that if he could by any means expel
 the air from his cylinder under the    
piston1 and replace it by the pure      
vapour of water1 he could cause that    
vapour to be reconverted into a         
comparatively minute quantity of water  
by depriving it of the heat which       
sustained it in the state of steam1 and 

that by accomplishing this1 the space in
 the cylinder under the piston would    
become a vacuum2 that by such means1 the
 pressure of the atmosphere above the   
piston would take full effect1 and would
 urge the piston down2 that by          
introducing more steam under the piston1
 it might be again raised by the elastic
 force of the steam1 the destruction of 
which by cold water would again produce 
the descent of the piston with the same 
mechanical force2 and that in this way  
the alternate ascent and descent of the 
piston might be continued indefinitely4 
,in accordance with these ideas1 ,papin 
constructed a model consisting of a     
small cylinder1 in which was placed a   
solid piston2 ,pg#jdg and in the bottom 
of the cylinder under the piston was    
contained in a small quantity of water4 
,the piston being in immediate contact  
with this water1 so as to exclude the   
atmospheric air1 on applying fire to the
 bottom of the cylinder1 steam was      
produced1 the elastic force of which    

raised the piston to the top of the     
cylinder2 the fire being then removed1  
and the cylinder being cooled by the    
surrounding air1 the steam was condensed
 and reconverted into water1 leaving a  
vacuum in the cylinder into which the   
piston was pressed by the force of the  
atmosphere4 ,the fire being applied and 
subsequently removed1 another ascent and
 descent were accomplished2 and in the  
same manner the alternate motion of the 
piston might be continued4 ,papin       
described no other form of machine by   
which this property could be rendered   
available in practice2 but he states    
generally1 that the same end may be     
attained by various forms of machines   
easy to be imagined4#h   ,,thomas       
,,savery1 #afih4   7#cj47 ,the discovery
 of the method of making a vacuum by the
 condensation of steam was reproduced1  
before #afih1 by ,captain ,thomas       
,savery1 to whom a patent was granted in
 that year for a steam engine to be     
applied to the raising of water1 c4     

,savery proposed to combine the machine 
described by the ,marquis of ,worcester 
with an apparatus for raising water by  
suction into a vacuum produced by the   
condensation of steam4  ,savery appears 
to have been ignorant of the publication
 of ,papin1 and stated that his         
discovery of the condensing principle   
arose from the following circumstance3--
  ,having drunk a flask of ,florence at 
a tavern1 and flung the empty flask on  
the fire1 he called for a basin of water
 to wash his hands4 ,a small quantity   
which remained in the flask began to    
boil1 and steam issued from its mouth4  
,it occurred to him to try what effect  
would be produced by inverting the flask
 and plunging its mouth in the cold     
water4 ,putting on a thick glove to     
defend his hand from the heat1 he seized
 the ,pg#jdh flask1 and the moment he   
plunged its mouth in the water the      
liquid immediately rushed up into the   
flask and filled it4  ,savery stated    
that this circumstance immediately      

suggested to him the possibility of     
giving effect to the atmospheric        
pressure by creating a vacuum in this   
manner4 ,he thought that if1 instead of 
exhausting the barrel of a pump by the  
usual laborious method of a piston and  
sucker1 it was exhausted by first       
filling it with steam1 and then         
condensing the same steam1 the          
atmospheric pressure would force the    
water from the well into the            
pump-barrel1 and into any vessel        
connected with it1 provided that vessel 
were not more than about thirty-four    
feet above the elevation of the water in
 the well4 ,he perceived also1 that1    
having lifted the water to this height1 
he might use the elastic force of steam 
in the manner described by the ,marquis 
of ,worcester to raise the same water to
 a still greater elevation1 and that the
 same steam which accomplished this     
mechanical effect would serve1 by its   
subsequent condensation1 to reproduce   
the vacuum1 and draw up more water4 ,it 

was on this principle that ,savery      
constructed the first engine in which   
steam was ever brought into practical   
operation4  ,illustration3 ,,branca',s  
,,engine4    ,,footnotes3    #a ,arago1 
,eloge historique de ,james ,watt2 p4   
#bb4    #b ,ibid41 p4 #ba4 note4    #c  
,farey1 ,treatise on the ,steam ,engine1
 p4 #ic4    #d ,arago1 sur les ,machines
  ,vapeur1 ,annuaire1 #ahbi1 p4 #afe    
#e ,,spiritus1 breath or air4    #f     
,exactly #aefh oz4  #jih lb4    #g ,this
 experiment with the tube ,a requires to
 be very   carefully executed1 and the  
tube should be one of small bore4    #h 
,recueil de diverses ,pices touchant    
quelques nouvelles   ,machines1 p4 #ch4 
,pg#jdi     ,illustration3 ,,savery',s  
,,engine4  ,,chap4 ,,ii4  ,,engines ,,of
 ,,savery ,,and ,,newcomen4             
,,savery',s ,,engine4 -- ,,boilers ,,and
 ,,their ,,appendages4 -- ,,working     
,,apparatus4 -- ,,mode ,,of ,,operation4
 -- ,,defects ,,of ,,the ,,engine4 --   
,,newcomen ,,and ,,cawley4 --           

,,atmospheric ,,engine4 -- ,,accidental 
,,discovery ,,of ,,condensation ,,by    
,,injection4 -- ,,humphrey ,,potter     
,,makes ,,the ,,engine ,,work ,,itself4 
-- ,,advantages ,,of ,,the ,,atmospheric
     ,,engine ,,over ,,that ,,of        
,,savery4 -- ,,it ,,contained ,,no ,,new
 ,,principle4 --     ,,its ,,practical  
,,superiority4   7#ca47 ,the steam      
engine contrived by ,savery1 like every 
other which has since been constructed1 
consists of two parts1 essentially      
distinct4 ,the first is that which is   
employed to ,pg#jej generate the steam1 
which is called the boiler2 and the     
second1 that in which the steam is      
applied as a moving power4              
,illustration3 ,fig4 #aa4  ,the former  
apparatus in ,savery's engine consists  
of two strong boilers1 sections of which
 are represented at ,d and ,e in fig4   
#aa42 ,d the greater boiler1 and ,e the 
less4 ,the tubes ,t and ,t communicate  
with the working apparatus1 which we    
shall presently describe4 ,a thin plate 

of metal ,r1 is applied closely to the  
top of the great boiler ,d1 turning on a
 centre ,c1 so that by moving a lever   
applied to the axis ,c on the outside of
 the top1 the sliding plate ,r can be   
brought from the mouth of the one tube  
to the mouth of the other alternately4  
,this sliding valve is called the       
regulator1 since it is by it that the   
communications between the boiler and   
two steam vessels 7hereafter described7 
are alternately opened and closed1 the  
lever which effects this being moved at 
intervals by the hand of the attendant4 
,two gauge cocks are represented at ,g1 
,g1 the use of which is to determine the
 depth of water in the boiler4 ,one1 ,g1
 has its lower aperture a little above  
the proper depth2 and the other1 ,g1 a  
little below it4 ,cocks are attached to 
the upper ends ,g1 ,g1 which can be     
opened or closed at pleasure4 ,the steam
 collected in the top of the boiler     
pressing on the surface of the water1   
forces it up in the tubes ,g1 ,g1 if    

their lower ends be immersed4 ,upon     
opening the cocks ,g1 ,g1 if water be   
forced from both1 there is too much     
water in the boiler1 since the mouth of 
,g is below its level4 ,if steam issue  
from both1 there is too little water in 
the boiler1 since the mouth of ,g is    
above its level4 ,but if steam issue    
from ,g1 and water from ,g1 the water in
 the boiler is at its proper level4     
,this ingenious contrivance for         
determining the level of the water in   
the boiler is the invention of ,savery1 
and is used in many instances at the    
present day4  ,the mouth of the pipe ,g 
should be at a level of a little less   
,pg#jea than one third of the whole     
depth1 and the mouth of ,g at a level   
little lower than one third2 for it is  
requisite that about two thirds of the  
boiler should be kept filled with water4
 ,the tube ,i forms a communication     
between the greater boiler ,d and the   
lesser or feeding boiler ,e1 descending 
nearly to the bottom of it4 ,this       

communication can be opened and closed  
at pleasure by the cock ,k4 ,a gauge    
pipe is inserted similar to ,g1 ,g1 but 
extending nearly to the bottom4 ,from   
this boiler a tube ,f extends1 which is 
continued to a cistern ,c 7fig4 #ab471  
and a cock is placed at ,m1 which1 when 
opened1 allows the water from the       
cistern to flow into the feeding boiler 
,e1 and which is closed when that boiler
 is filled4 ,the manner in which this   
cistern is supplied will be described   
hereafter4  ,let us now suppose that the
 principal boiler is filled to the level
 between the gauge pipes1 and that the  
subsidiary boiler is nearly full of     
water1 the cock ,k and the gauge cocks  
,g ,g being all closed4 ,the fire being 
lighted beneath ,d1 and the water       
boiled1 steam is produced1 and is       
transmitted through one or other of the 
tubes ,t1 ,t1 to the working apparatus4 
,when evaporation has reduced the water 
in ,d below the level of ,g1 it will be 
necessary to replenish the boiler ,d4   

,this is effected thus3--,a fire being  
lighted beneath the feeding boiler ,e1  
steam is produced in it above the       
surface of the water1 which1 having no  
escape1 presses on the surface so as to 
force it up in the pipe ,i4 ,the cock ,k
 being then opened1 the boiling water is
 forced into the principal boiler ,d1   
into which it is allowed to flow until  
water issues from the gauge cock ,g4    
,when this takes place1 the cock ,k is  
closed1 and the fire removed from ,e    
until the great boiler again wants      
replenishing4 ,when the feeding boiler  
,e has been exhausted1 it is replenished
 from the cistern ,c 7fig4 #ab471       
through the pipe ,f1 by opening the cock
 ,m4   7#cb47 ,we shall now describe the
 working apparatus in which the steam is
 used as a moving power4  ,let ,v ,v    
7fig4 #ab47 be two steam vessels        
communicating by the tubes ,t ,t 7marked
 by the same letters in fig4 #aa47 with 
the greater boiler ,d4  ,illustration3  
,fig4 #ab4  ,let ,s be a pipe1 called   

the suction pipe1 descending into       
,pg#jeb the well or reservoir from which
 the water is to be raised1 and         
communicating with each of the steam    
vessels through tubes ,d ,d1 by valves  
,a ,a1 which open upwards4 ,let ,f be a 
pipe continued from the level of the    
engine to whatever higher level it is   
intended to elevate the water4 ,the     
steam vessels ,v ,v communicate with the
 force-pipe ,f by valves ,b ,b1 which   
open upwards1 through the tubes ,e ,e4  
,over the steam vessels and on the      
force-pipe is placed a small cistern ,c1
 already mentioned1 which is kept filled
 with cold water from the force-pipe1   
and from the bottom of which proceeds a 
pipe terminated with a cock ,g4 ,this is
 called the condensing pipe1 and can be 
brought alternately over each steam     
vessel4 ,from this cistern another pipe 
communicates with the feeding boiler    
7fig4 #aa471 by the cock ,m4#i  ,the    
communication of the pipes ,t ,t with   
the boiler can be opened and closed     

alternately1 by the regulator ,r 7fig4  
#aa471 already described4  ,now suppose 
the steam vessels and tubes to be all   
filled with common atmospheric air1 and 
that the regulator be placed so that the
 communication between the tube ,t and  
the boiler be opened1 the communication 
between the other tube ,t and the boiler
 being closed1 steam will flow into ,v  
through ,t4 ,at first1 while the vessel 
,v is cold1 the steam will be condensed1
 and will fall in drops of water on the 
bottom and sides of the vessel4 ,the    
continued supply of steam from the      
boiler will at length impart such a     
degree of heat to the vessel ,v1 that it
 will cease to condense it4 ,mixed with 
the heated air ,pg#jec contained in the 
vessel ,v1 it will have an elastic force
 greater than the atmospheric pressure1 
and will therefore force open the valve 
,b1 through which a mixture of air and  
steam will be driven until all the air  
in the vessel ,v will have passed out1  
and it will contain nothing but the pure

 vapour of water4  ,when this has taken 
place1 suppose the regulator be moved so
 as to close the communication between  
the tube ,t and the boiler1 and to stop 
the further supply of steam to the      
vessel ,v2 and at the same time let the 
condensing pipe ,g be brought over the  
vessel ,v1 and the cock opened so as to 
let a stream of cold water flow upon it4
 ,this will cool the vessel ,v1 and the 
steam with which it is filled will be   
condensed and fall in a few drops of    
water1 leaving the interior of the      
vessel a vacuum4 ,the valve ,b will be  
kept closed by the atmospheric pressure4
 ,but the elastic force of the air      
between the valve ,a and the surface of 
the water in the well1 or reservoir1    
will open ,a1 so that a part of this air
 will rush in1 and occupy the vessel ,v4
 ,the air in the suction pipe ,s1 being 
thus allowed an increased space1 will be
 proportionally diminished in its       
elastic force1 and its pressure will no 
longer balance that of the atmosphere   

acting on the external surface of the   
water in the reservoir4 ,this pressure  
will1 therefore1 force water up in the  
tube ,s until its weight1 together with 
the elastic force of the air above it1  
balances the atmospheric pressure4 ,when
 this has taken place1 the water will   
cease to ascend4  ,let us now suppose   
that1 by shifting the regulator1 the    
communication is opened between ,t and  
the boiler1 so that steam flows again   
into ,v4 ,the condensing cock ,g being  
removed1 the vessel will be again heated
 as before1 the air expelled1 and its   
place filled by the steam4 ,the         
condensing pipe being again allowed to  
play upon the vessel ,v1 and the further
 supply of steam being stopped1 a vacuum
 will be produced in ,v1 and the        
atmospheric pressure will force the     
water through the valve ,a into the     
vessel ,v1 which it will nearly fill1 a 
small quantity of air1 however1         
remaining above it4  ,thus far the      
mechanical agency employed in elevating 

the water is the atmospheric pressure2  
and the power of steam is no further    
employed than in the production of a    
vacuum4 ,pg#jed ,but1 in order to       
continue the elevation of the water     
through the force pipe ,f1 above the    
level of the steam vessel1 it will be   
necessary to use the elastic pressure of
 the steam4 ,the vessel ,v is now nearly
 filled by the water which has been     
forced into it by the atmosphere4 ,let  
us suppose that1 the regulator being    
shifted again1 the communication between
 the tube ,t and the boiler is opened1  
the condensing cock removed1 and that   
steam flows into ,v4 ,at first1 coming  
in contact with the cold surface of the 
water and that of the vessel1 it is     
condensed2 but the vessel is soon       
heated1 and the water formed by the     
condensed steam collects in a sheet or  
film upon the surface of the water in   
,v1 so as to form a surface as hot as   
boiling water4#aj ,the steam then being 
no longer condensed1 presses on the     

surface of the water with its elastic   
force2 and when that pressure becomes   
greater than the atmospheric pressure1  
the valve ,b is forced open1 and the    
water issuing through it1 passes through
 ,e into the force-pipe ,f2 and this is 
continued until the steam has forced all
 the water from ,v1 and occupies its    
place4  ,the further admission of steam 
through ,t is once more stopped by      
moving the regulator2 and the condensing
 pipe being again allowed to play on ,v1
 so as to condense the steam which fills
 it1 produces a vacuum4 ,into this      
vacuum1 as before1 the atmospheric      
pressure will force the water1 and fill 
the vessel ,v4 ,the condensing pipe     
being then closed1 and steam admitted   
through ,t1 the water in ,v will be     
forced by its pressure through the valve
 ,b and tube ,e into ,f1 and so the     
process is continued4  ,we have not yet 
noticed the other steam vessel ,v1      
which1 as far as we have described1     
would have remained filled with common  

atmospheric air1 the pressure of which  
on the valve ,a would have prevented the
 water raised in the suction pipe ,s    
from passing through it4 ,however1 this 
is not the case2 for1 during the entire 
process which has been described in ,v1 
similar effects have been produced in   
,v1 which we have only omitted to notice
 to avoid the confusion which the two   
processes might produce4 ,it will be    
remembered1 that after the steam1 in the
 first instance1 having flowed from the 
boiler ,pg#jee through ,t1 has blown the
 air out of ,v through ,b1 the          
communication between ,t and the boiler 
is closed4 ,now the same motion of the  
regulator which closes this1 opens the  
communication between ,t and the boiler2
 for the sliding plate ,r 7fig4 #aa47 is
 moved from the one tube to the other1  
and at the same time1 as we have already
 stated1 the condensing pipe is brought 
to play on ,v4 ,while1 therefore1 a     
vacuum is being formed in ,v by         
condensation1 the steam1 flowing through

 ,t1 blows out the air through ,b1 as   
already described in the other vessel   
,v2 and while the air in ,s is rushing  
up through ,a into ,v1 followed by the  
water raised in ,s by the atmospheric   
pressure1 the vessel ,v is being filled 
with steam1 and the air is completely   
expelled from it4  ,the communication   
between ,t and the boiler is now again  
opened1 and the communication between ,t
 and the boiler closed by moving the    
regulator ,r 7fig4 #aa47 from the tube  
,t to ,t2 at the same time the          
condensing pipe is removed from over ,v1
 and brought to play upon ,v4 ,while the
 steam once more expels the air from ,v 
through ,b1 a vacuum is formed by       
condensation in ,v1 into which the water
 in ,s rushes through the valve ,a4 ,in 
the mean time ,v is again filled with   
steam4 ,the communication between ,t and
 the boiler is now closed1 and that     
between ,t and the boiler is opened1 and
 the condensing pipe removed from ,v1   
and brought to play on ,v4 ,while the   

steam from the boiler forces the water  
in ,v through ,b into the force-pipe ,f1
 a vacuum is being produced in ,v1 into 
which water is raised by the atmospheric
 pressure4  ,thus each of the vessels ,v
 ,v is alternately filled from ,s1 and  
the water thence forced into ,f4 ,the   
same steam which forces the water from  
the vessels into ,f1 having done its    
duty1 is condensed1 and brings up the   
water from ,s1 by giving effect to the  
atmospheric pressure4  ,during this     
process1 two alternate motions or       
adjustments must be constantly made2 the
 communication between ,t and the boiler
 must be opened1 and that between ,t and
 the boiler closed1 which is done by one
 motion of the regulator4 ,the          
condensing pipe at the same time must be
 brought from ,v to play on ,v1 which is
 done by the lever placed upon it4      
,again ,pg#jef the communication between
 ,t and the boiler is to be opened1 and 
that between ,t and the boiler closed2  
this is done by moving back the         

regulator4 ,the condensing pipe is      
brought from ,v to ,v by moving back the
 other lever1 and so on alternately4    
,for the clearness and convenience of   
description1 some slight and otherwise  
unimportant changes have been made in   
the position of the parts4 ,a           
perspective view of this engine is      
represented at the head of this chapter4
 ,the different parts already described 
will easily be recognised4  ,the engine 
of ,savery was very clearly described in
 a small work published in ,london in   
#agjb1 entitled1 ,the ,miner's ,friend1 
or an ,engine to raise ,water by ,fire  
described1 and the ,manner of ,fixing it
 in ,mines2 with an ,account of the     
several ,uses it is applicable unto1 and
 an ,answer to the ,objection made      
against it2 by ,thomas ,savery1         
,gentleman4 ,this volume was dedicated  
to ,william ,,iii4 7to whom the engine  
had been exhibited at ,hampton ,court   
palace71 to the ,royal ,society1 and to 
the mining adventurers of ,england4 ,the

 following are the uses to which ,savery
 proposed the engine should be applied3 
,first1 to raise water for turning all  
sorts of mills2 second1 supplying       
palaces and houses with water1 and      
supplying means of extinguishing fire   
therein by the water so raised2 third1  
the supplying cities and towns with     
water2 fourth1 draining fens or marshes2
 fifth1 for ships2 sixth1 the drainage  
of mines4  ,dr4 ,harris1 in his ,lexicon
 ,technicum1 or ,dictionary of ,arts and
 ,sciences1 mentions a machine of       
,savery's for propelling a vessel in a  
calm1 by paddle-wheels placed at the    
side2 but it does not appear that       
,savery contemplated the application of 
a steam engine to work these wheels4    
,it is only from scattered passages in  
publications of the day that it can be  
ascertained to what extent the engines  
of ,savery were practically applied4 ,in
 his address to the ,royal ,society1 he 
speaks of the difficulties and expense  
which he encountered in instructing     

artisans to make engines according to   
his wish2 but that after much experience
 the workmen had become such masters of 
the thing1 that they bound themselves to
 deliver the engines 'exactly tight and 
fit for ,pg#jeg service1 and such as he 
7,savery7 dare warrant them to every one
 that has occasion for them4'  ,in his  
address to the miners of ,england he    
also says1 that the frequent disorders  
and cumbersomeness of water engines then
 in use encouraged him to invent engines
 to work by this new force2 that though 
they were obliged to encounter the      
oddest and almost insuperable           
difficulties1 yet he spared neither     
time1 pains1 nor money1 till he had     
conquered them4  ,in ,bradley's         
,improvements of ,planting and          
,gardening1 #agah1 the author thus      
speaks of an engine erected by          
,savery3--  ,supposing the situation of 
a house or garden to be a considerable  
height above any pond1 river1 or spring1
 and that it has at present no other    

conveniency of water than what is       
brought continually by men or horses to 
it4 ,in this case1 the wonderful        
invention of the late ,mr4 ,savery1     
,f4,r4,s41 for raising water by fire1   
will not only supply the defect1 by     
flinging up as much water as may be     
desired1 but may be maintained with very
 little trouble and very small expense4 
,it is now about six years since ,mr4   
,savery set up one of them for that     
curious gentleman ,mr4 ,balle1 at       
,cambden ,house1 ,kensington1 near      
,london1 which has succeeded so well    
that there has not been any want of     
water since it has been built2 and1 with
 the improvements since made to it1 ,i  
am apt to believe will be less subject  
to be out of order than any engine      
whatever4  ,it is remarkable that1      
notwithstanding the high pressure steam 
necessary for the operation of ,savery's
 engine1 he does not appear to have     
adopted the obvious expedient of a      
safety valve4 ,the safety valve had been

 previously known1 having been invented 
about the year #afha1 by ,papin1 for his
 digester1 which was a close boiler1    
contrived by him for stewing meat and   
digesting bones1 by submitting them to a
 higher temperature than that of water  
boiling in an open vessel4  ,the safety 
valve which has ever since been used for
 steam boilers of every kind is a valve 
which opens outwards1 and is fitted to  
an aperture in the boiler1 so as to be  
steam tight4 ,it is pressed down by a   
weight1 the amount of which is regulated
 by the maximum pressure to which it is 
intended the steam ,pg#jeh shall be     
limited4 ,thus1 if the magnitude of the 
valve be a square inch1 and the pressure
 of the steam be limited to #aj lbs4 per
 square inch above the pressure of the  
atmosphere1 then the valve would be     
loaded with a weight of #aj lbs42 but as
 it was found necessary to vary from    
time to time the limiting pressure of   
the steam1 or the load of the safety    
valve1 these valves were usually        

constructed so as to be held down by the
 pressure of a lever having a sliding   
weight upon it4 ,by moving the weight on
 the arm of the lever1 the pressure on  
the valve could be increased or         
diminished at the discretion of the     
engineer4 ,this contrivance was first   
applied to ,savery's engines1 by        
,desaguliers1 about the year #agag1     
before which year ,savery died4  ,it is 
justly observed by ,mr4 ,farey1 in his  
treatise on the steam engine1 that1 when
 a comparison is made between           
,captain#aa ,savery's engine and those  
of his predecessors1 the result will be 
in every respect favourable to his      
character as an inventor1 and as a      
practical engineer2 all the details of  
his invention are made out in a masterly
 style1 and accidents and contingencies 
are provided for1 so as to render it a  
real working engine2 whereas ,de ,caus1 
the ,marquis of ,worcester1 ,sir ,samuel
 ,morland1 and ,papin1 though ingenious 
philosophers1 only produced mere        

outlines1 which required great labour   
and skill of subsequent inventors to    
fill up1 and make them sufficiently     
complete to be put in execution4  ,about
 the year #agah further improvements    
were made in the construction of        
,savery's engine1 by ,dr4 ,desaguliers2 
but it is probable that some of these   
were suggested by the proceedings of the
 inventors of the atmospheric engine1   
which shall presently describe4   7#cc47
 ,in order duly to appreciate the value 
of improvements1 it is necessary first  
to perceive the defects which these     
improvements are designed to remove4    
,savery's steam engine1 considering how 
little was known of the value and       
properties of steam1 and how low the    
general standard of mechanical knowledge
 was in his day1 is certainly highly    
,pg#jei creditable to his genius4       
,nevertheless it had very considerable  
defects1 and was finally found to be    
inefficient for the most important      
purposes to which he proposed applying  

it4  ,at the time of this invention1 the
 mines in ,england had greatly increased
 in depth1 and the process of draining  
them had become both expensive and      
difficult2 so much so1 that it was found
 in many instances that their produce   
did not cover the cost of working them4 
,the drainage of these mines was the    
most important purpose to which ,savery 
proposed to apply his steam engine4  ,it
 has been already stated that the       
pressure of the atmosphere amounts to   
about fifteen pounds on every square    
inch4 ,now1 a column of water1 whose    
base is one square inch1 and whose      
height is thirty-four feet1 weighs about
 fifteen pounds4 ,if we suppose that a  
perfect vacuum were produced in the     
steam vessels ,v ,v 7fig4 #ab47 by      
condensation1 the atmospheric pressure  
would fail to force up the water1 if the
 height of the top of these vessels     
above the water to be raised exceeded   
thirty-four feet4 ,it is plain1         
therefore1 that the engine cannot be    

more than thirty-four feet above the    
water which it is intended to elevate4  
,but in fact it cannot be so much2 for  
the vacuum produced in the steam vessels
 ,v ,v is never perfect4 ,water1 when   
not submitted to the pressure of the    
atmosphere1 will vaporise at a very low 
temperature1 as we shall hereafter      
explain2 and it was found that a vapour 
possessing a considerable elasticity    
would1 notwithstanding the condensation1
 remain in the vessels ,v ,v and the    
pipe ,s1 and would oppose the ascent of 
the water4 ,in consequence of this1 the 
engine could never be placed with       
practical advantage at a greater height 
than twenty-six feet above the level of 
the water to be raised4   7#cd47 ,when  
the water is elevated to the engine1 and
 the steam vessels filled1 if steam be  
introduced above the water in ,v1 it    
must first balance the atmospheric      
pressure1 before it can force the water 
through the valve ,b4 ,here1 then1 is a 
mechanical pressure of fifteen pounds   

per square inch expended1 without any   
water being raised by it4 ,if steam of  
twice that elastic force be used1 it    
will elevate a column in ,f of          
thirty-four feet in height2 and if steam
 of triple the force be used1 it will   
raise a column of sixty-eight feet high1
 ,pg#jfj which1 added to twenty-six feet
 raised by the atmosphere1 gives a total
 lift of ninety-four feet4  ,in         
effecting this1 steam of a pressure     
equal to three times that of the        
atmosphere acts on the inner surface of 
the vessels ,v ,v4 ,one third of this   
bursting pressure is balanced by the    
pressure of the atmosphere on the       
external surface of the vessels2 but an 
effective pressure of thirty pounds per 
square inch still remains1 tending to   
burst the vessels4 ,it was found that   
the apparatus could not be constructed  
to bear more than this with safety2 and1
 therefore1 in practice1 the lift of    
such an engine was limited to about     
ninety perpendicular feet4 ,in order to 

raise the water from the bottom of the  
mine by these engines1 therefore1 it was
 necessary to place one at every ninety 
feet of the depth2 so that the water    
raised by one through the first ninety  
feet should be received in a reservoir1 
from which it was to be elevated the    
next ninety feet by another1 and so on4 
,besides this1 it was found that        
sufficient strength could not be given  
to those engines1 if constructed upon a 
large scale4  ,they were1 therefore1    
necessarily very limited in their       
dimensions1 and were incapable of       
raising the water with sufficient speed4
 ,hence arose a necessity for several   
engines at each level1 which greatly    
increased the expense4   7#ce47 ,these1 
however1 were not the only defects of   
,savery's engines4 ,the consumption of  
fuel was enormous1 the proportion of    
heat wasted being much more than what   
was used in either forcing up the water1
 or producing a vacuum4 ,this will be   
very easily understood by attending to  

the process of working the engine       
already described4  ,when the steam is  
first introduced from the boiler into   
the steam vessels ,v ,v1 preparatory to 
the formation of a vacuum1 it is        
necessary that it should heat these     
vessels up to the temperature of the    
steam itself2 for until then the steam  
will be condensed the moment it enters  
the vessel by the cold surface4 ,all    
this heat1 therefore1 spent in raising  
the temperature of the steam vessels is 
wasted4 ,again1 when the water has      
ascended and filled the vessels ,v ,v1  
and steam is introduced to force this   
water through ,b ,b into ,f1 it is      
immediately condensed by the cold       
surface in ,v ,v1 and does not ,pg#jfa  
begin to act until a quantity of hot    
water1 formed by condensed steam1 is    
collected on the surface of the cold    
water which fills these vessels4 ,hence 
another source of the waste of heat     
arises4  ,when the steam begins to act  
upon the surface of the water in ,v ,v1 

and to force it down1 the cold surface  
of the vessels is gradually exposed to  
the steam1 and must be heated while the 
steam continues its action2 and when the
 water has been forced out of the       
vessel1 the vessel itself has been      
heated to the temperature of the steam  
which fills it1 all which heat is       
dissipated by the subsequent process of 
condensation4 ,it must thus be evident  
that the steam used in forcing up the   
the water in ,f1 and in producing a     
vacuum1 bears a very small proportion   
indeed to what is consumed in heating   
the apparatus after condensation4       
7#cf47 ,there is also another           
circumstance which increases the        
consumption of fuel4 ,the water must be 
forced through ,b1 not only against the 
atmospheric pressure1 but also against a
 column of sixty-eight feet of water4   
,steam is therefore required of a       
pressure of forty-five pounds on the    
square inch4 ,consequently the water in 
the boiler must be boiled under this    

pressure4 ,that this should take place1 
it is necessary that the water should be
 raised to a temperature considerably   
above #bab1 even so high as #bge2 and   
thus an increased heat must be given to 
the boiler4 ,independently of the other 
defects1 this intense heat weakened and 
gradually destroyed the apparatus4      
,savery was the first who suggested the 
method of expressing the power of an    
engine with reference to that of horses4
 ,in this comparison1 however1 he       
supposed each horse to work but eight   
hours a day1 while the engine works for 
twenty-four hours4 ,this method of      
expressing the power of steam engines   
will be explained hereafter4   7#cg47   
,the failure of the engines proposed by 
,captain ,savery in the work of         
drainage1 from the causes which have    
been just mentioned1 and the increasing 
necessity for effecting this object1    
arising from the large property in mines
 which became every year unproductive by
 being flooded1 stimulated the ingenuity

 ,pg#jfb of mechanics to contrive some  
means of rendering those powers of steam
 exhibited in ,savery's engine          
available4  ,thomas ,newcomen1 the      
reputed inventor of the atmospheric     
engine1 was an ironmonger1 or1 according
 to some1 a blacksmith1 in the town of  
,dartmouth in ,devonshire4 ,from his    
personal acquaintance and intercourse   
with ,dr4 ,hooke1 the celebrated natural
 philosopher1 it is probable that he was
 a person of some education1 and        
therefore likely to be above the        
position of a blacksmith4 ,being in the 
habit of visiting the tin mines in      
,cornwall1 ,newcomen became acquainted  
with the engine invented by ,savery1 and
 with the causes which led to its       
inefficiency for the purposes of        
drainage4  ,it has been stated that     
,papin1 about the year #afij1 proposed  
the construction of an engine working by
 the atmospheric pressure acting on one 
side of a piston against a vacuum       
produced by the condensation of steam on

 the other side4 ,papin was not         
conscious of the importance of this     
principle2 for1 so far from ever having 
attempted to apply it to practical      
purposes1 he probably never constructed1
 even on a small scale1 any machine     
illustrating it4 ,on the contrary1 he   
abandoned the project the moment he was 
informed of the principle and structure 
of the steam engine of ,savery2 and he  
then proposed an engine for raising     
water1 acting by the expansive force of 
steam similar to ,savery's1 but         
abandoning the method of working by a   
vacuum4  ,this engine is described by   
,papin in a work published in #agjg4    
,illustration3 ,fig4 #ac4  ,a 7fig4     
#ac47 is an oval boiler1 having a       
safety-valve ,b1 which limits the       
pressure of the steam4 ,it is connected 
with a cylinder ,c1 by a curved pipe    
having a stop-cock at ,d4 ,a pipe with a
 stop-cock ,g opens from the top of the 
cylinder into the atmosphere1 and a     
safety-valve ,f is placed upon the      

cylinder4 ,a hollow copper piston ,h    
moves freely in the cylinder1 and floats
 upon the water4 ,o is a funnel with a  
valve ,l in the bottom1 opening         
downwards1 through which the cylinder ,c
 may be filled with water to the level  
of the top of the funnel4 ,a close      
air-vessel communicates with the        
cylinder ,c by the curved tube1 and has 
a valve ,k opening upwards4 ,the        
force-pipe through which the water is   
raised communicates ,pg#jfc with the    
air-vessel ,i4 ,if the cock ,d be shut1 
and the cock ,g opened1 water poured    
into the funnel ,o will rise into the   
cylinder ,c1 the air which fills the    
cylinder escaping through the open pipe 
,g4 ,when the cylinder is thus filled   
with water1 let the cock ,g be closed1  
and the cock ,d opened4 ,the steam from 
the boiler1 after heating the metal of  
the cylinder1 will force the piston     
downwards1 and drive the water through  
the curved tube into the vessel ,i1 from
 which its return is prevented by the   

valve ,k1 which is closed by its weight4
 ,the air which filled the vessel ,i    
will then be compressed1 and by its     
elasticity will drive a column of water 
up the pipe ,n4 ,after the contents of  
the cylinder have been thus discharged  
it may be refilled in the same manner1  
and the process repeated4  ,it will be  
perceived that this project is nothing  
more than a reproduction of the engine  
of the ,marquis of ,worcester4 ,in the  
preface to the work containing this     
description1 ,papin gives an extract    
from a letter addressed by him to       
,leibnitz in #afih1 from which it       
appears that he had abandoned his idea  
of working the piston by the atmospheric
 pressure acting against a vacuum1      
considering it to be a contrivance      
inferior ,pg#jfd to the engine now      
described4 ,we now raise water1 he says1
 by the force of fire1 in a more        
advantageous manner than that which ,i  
had published some years before2 for    
besides the suction1 we now also use the

 pressure which the water exerts upon   
other bodies in dilating itself by heat2
 instead of which ,i before employed the
 suction only1 the effects of which are 
more limited4  ,from documents which    
have been preserved in the ,royal       
,society1 it appears that ,newcomen was 
acquainted with ,papin's writings1 and  
therefore probably first derived from   
them the suggestion which he            
subsequently realised in the atmospheric
 engine4 ,among some papers of ,dr4     
,hooke's have been found notes for the  
use of ,newcomen1 on ,papin's method of 
transmitting the force of a stream or   
fall of water to a distance by pipes4   
,hooke dissuaded ,newcomen from         
attempting any machine on this          
principle1 which1 as first proposed by  
,papin1 was impracticable4 ,he exposed  
the fallacy of ,papin's first project in
 several discourses before the ,royal   
,society1 and considered his improved   
edition of it1 though free from fallacy1
 as impracticable4  ,papin's project for

 producing a vacuum under a piston by   
condensing the steam having been        
published in the ,act ,eruditorum1 in   
,latin1 in #afij1 and in ,french1 at    
,cassel1 in #afie1 and subsequently1 in 
the ,philosophical ,transactions1 in    
,england in #afig1 cannot be supposed to
 be unknown to ,dr4 ,hooke2 and if known
 to him1 would probably have been       
communicated to ,newcomen4 ,dr4 ,hooke  
died in #agjc1 some years before the    
date of ,newcomen's invention4  ,john   
,cawley1 who was the associate of       
,newcomen in his experiments and        
inquiries1 was a plumber and glazier of 
the same town4 ,newcomen and ,cawley    
obtained a patent for the atmospheric   
engine in #agje1 in which ,savery was   
associated1 he having previously        
obtained a patent for the method of     
producing a vacuum by the condensation  
of steam1 which was essential to        
,newcomen's contrivance4 ,it was not1   
however1 until about the year #agaa that
 any engine had been constructed under  

this patent4  ,in the latter end of that
 year1 according to ,desaguliers1 the   
patentees made proposals to drain a     
colliery at ,griff1 in ,pg#jfe          
,warwickshire1 in which work five       
hundred horses were constantly employed4
 ,this proposal not being accepted1 they
 contracted1 in the following ,march1 to
 drain water for ,mr4 ,back of          
,wolverhampton1 where1 after many       
laborious attempts1 they succeeded in   
making their engine work2 but not being 
either philosophers to understand the   
reason1 or mathematicians enough to     
calculate the power and proportions of  
the parts1 they very luckily1 by        
accident1 found what they sought for4   
,illustration3 ,fig4 #ad4  ,newcomen    
resumed the old method of raising the   
water from the mines by ordinary pumps1 
but conceived the idea of working these 
pumps by some moving power less         
expensive than that of horses4 ,the     
means whereby he proposed effecting     
this1 was by connecting the end of the  

pump-rod ,d 7fig4 #ad47 by a chain with 
the arch head ,a of a ,pg#jff           
working-beam ,a ,b1 playing on an axis  
,c4 ,the other arch head ,b of this beam
 was connected by a chain with the rod  
,e of a solid piston ,p1 which moved    
air-tight in a cylinder ,f4 ,if a vacuum
 be created beneath the piston ,p1 the  
atmospheric pressure acting upon it will
 press it down with a force of fifteen  
pounds per square inch2 and the end ,a  
of the beam being thus raised1 the      
pump-rod ,d will be drawn up4 ,if a     
pressure equivalent to the atmosphere be
 then introduced below the piston1 so as
 to neutralise the downward pressure1   
the piston will be in a state of        
indifference as to the rising or        
falling2 and if in this case the rod ,d 
be made heavier than the piston and its 
rod1 so as to overcome the friction1 it 
will descend1 and elevate the piston    
again to the top of the cylinder4 ,the  
vacuum being again produced1 another    
descent of the piston1 and consequent   

elevation of the pump-rod1 will take    
place2 and so the process may be        
continued4  ,such was ,newcomen's first 
conception of the atmospheric engine2   
and the contrivance had much1 even at   
the first view1 to recommend it4 ,the   
power of such a machine would depend    
entirely on the magnitude of the piston2
 and being independent of highly elastic
 steam1 would not expose the materials  
to the destructive heat which was       
necessary for working ,savery's engine4 
,supposing a perfect vacuum to be       
produced under the piston in the        
cylinder1 an effective downward pressure
 would be obtained1 amounting to fifteen
 times as many pounds as there are      
square inches in the section of the     
piston4#ab ,thus1 if the base of the    
piston were #ajj square inches1 a       
pressure equal to #aejj pounds would be 
obtained4   7#ch47 ,in order to         
accomplish this1 two things were        
necessary3 #a4 ,to make a speedy and    
effectual vacuum below the ,pg#jfg      

piston in the descent2 and1 #b4 ,to     
contrive a counterpoise for the         
atmosphere in the ascent4  ,the         
condensation of steam immediately       
presented itself as the most effectual  
means of accomplishing the former2 and  
the elastic force of the same steam     
previous to condensation an obvious     
method of effecting the latter4 ,nothing
 now remained to carry the design into  
execution1 but the contrivance of means 
for the alternate introduction and      
condensation of the steam2 and ,newcomen
 and ,cawley were accordingly granted a 
patent in #agjg1 in which ,savery was   
united1 in consequence of the principle 
of condensation for which he had        
previously received a patent being      
necessary to the projected machine4 ,we 
shall now describe the atmospheric      
engine1 as first constructed by         
,newcomen3--  ,the boiler ,k 7fig4 #ad47
 is placed over a furnace ,i1 the flue  
of which winds round it1 so as to       
communicate heat to every part of the   

bottom of it4 ,in the top1 which is     
hemispherical1 two gauge-cocks ,g ,g are
 placed1 as in ,savery's engine1 and a  
puppet valve ,v1 which opens upward1 and
 is loaded at one pound per square inch2
 so that when the steam produced in the 
boiler exceeds the pressure of the      
atmosphere by more than one pound on the
 square inch1 the valve ,v is lifted1   
and the steam escapes through it1 and   
continues to escape until its pressure  
is sufficiently diminished1 when the    
valve ,v again falls into its seat4     
,this valve performs the office of the  
safety-valve in modern engines4  ,the   
great steam-tube is represented at ,s1  
which conducts steam from the boiler to 
the cylinder2 and a feeding pipe ,t1    
furnished with a cock1 which is opened  
and closed at pleasure1 proceeds from a 
cistern ,l to the boiler4 ,by this pipe 
the boiler may be replenished from the  
cistern1 when the gauge cock ,g         
indicates that the level has fallen     
below it4 ,the cistern ,l is supplied   

with hot water1 by means which we shall 
presently explain4   7#ci47 ,to         
understand the mechanism necessary to   
work the piston1 let us consider how the
 supply and condensation of steam must  
be regulated4 ,when the piston has been 
forced to the bottom of the cylinder by 
the atmospheric pressure acting against 
a vacuum1 in order to balance that      
pressure1 ,pg#jfh and enable it to be   
drawn up by the weight of the pump-rod1 
it is necessary to introduce steam from 
the boiler4 ,this is accomplished by    
opening the cock ,r in the steam pipe   
,s4 ,the steam being thus introduced    
from the boiler1 its pressure balances  
the action of the atmosphere upon the   
piston1 which is immediately drawn to   
the top of the cylinder by the weight of
 the pump-rod ,d4 ,it then becomes      
necessary to condense this steam1 in    
order to produce a vacuum4 ,to          
accomplish this1 the further supply of  
steam must be cut off1 which is done by 
closing the cock ,r4 ,the supply of     

steam from the boiler being thus        
suspended1 the application of cold water
 on the external surface of the cylinder
 becomes necessary to condense the steam
 within it4 ,this was done by enclosing 
the cylinder within another1 leaving a  
space between them4#ac ,into this space 
cold water was allowed to flow from a   
cock ,m placed over it1 supplied by a   
pipe from the cistern ,n4 ,this cistern 
is supplied with water by a pump ,o1    
which is worked by the engine4  ,the    
cold water supplied from ,m1 having     
filled the space between the two        
cylinders1 abstracts the heat from the  
inner one2 and condensing the steam1    
produces a vacuum1 into which the piston
 is forced by the atmospheric pressure4 
,preparatory to the next descent1 the   
water which thus fills the space between
 the cylinders1 and which is warmed by  
the heat abstracted from the steam1 must
 be discharged1 in order to give room   
for a fresh supply of cold water from   
,m4 ,an aperture1 furnished with a cock1

 is accordingly provided in the bottom  
of the cylinder1 through which the water
 is discharged into the cistern ,l2 and 
being warm1 is adapted for the supply of
 the boiler through ,t1 as already      
mentioned4  ,the cock ,r being now again
 opened1 steam is admitted below the    
piston1 which1 as before1 ascends1 and  
the descent is again accomplished by    
closing the cock ,r1 and opening the    
cock ,m1 admitting cold water between   
the cylinders1 and thereby condensing   
the steam below the piston4  ,the       
condensed steam1 thus reduced to water1 
will collect ,pg#jfi in the bottom of   
the cylinder1 and resist the descent of 
the piston4 ,it is therefore necessary  
to provide an exit for it1 which is done
 by a valve opening outwards into a tube
 which leads to the feeding cistern ,l1 
into which the condensed steam is       
driven4  ,that the piston should        
continue to be air-tight1 it was        
necessary to keep a constant supply of  
water over it2 this was done by a cock  

similar to ,m1 which allowed water to   
flow from the pipe ,m on the piston4    
7#dj47 ,soon after the first            
construction of these engines1 an       
accidental circumstance suggested to    
,newcomen a much better method of       
condensation than the application of    
cold water on the external surface of   
the cylinder4 ,an engine was observed to
 work several strokes with unusual      
rapidity1 and without the regular supply
 of the condensing water4 ,upon         
examining the piston1 a hole was found  
in it1 through which the water1 which   
was poured on to keep it air-tight1     
flowed1 and instantly condensed the     
steam under it4  ,on this suggestion    
,newcomen abandoned the external        
cylinder1 and introduced a pipe ,h1     
furnished with a cock ,q1 into the      
bottom of the cylinder1 so that1 on     
turning the cock1 the pressure of the   
water in the pipe ,h1 from the level of 
the water in the cistern ,n1 would force
 the water to rise as a jet into the    

cylinder1 and would instantly condense  
the steam4 ,this method of condensing by
 injection formed a very important      
improvement in the engine1 and is still 
used4   7#da47 ,having taken a general  
view of the parts of the atmospheric    
engine1 let us now consider more        
particularly its operation4  ,when the  
engine is not working1 the weight of the
 pump-rod ,d 7fig4 #ad47 draws down the 
beam ,a1 and draws the piston to the top
 of the cylinder1 where it rests4 ,let  
us suppose all the cocks and valves     
closed1 and the boiler filled to the    
proper depth4 ,the fire being lighted   
beneath it1 the water is boiled until   
the steam acquires sufficient force to  
lift the valve ,v4 ,when this takes     
place1 the engine may be started4 ,for  
this purpose the regulating valve ,r is 
opened4 ,the steam rushes in1 and is    
first condensed by the cold cylinder4   
,after a short time the cylinder        
acquires the temperature of the steam1  
which then ,pg#jgj ceases to be         

condensed1 and mixes with the air which 
filled the cylinder4 ,the steam and     
heated air1 having a greater force than 
the atmospheric pressure1 will open a   
valve placed at the end ,x of a small   
tube in the bottom of the cylinder1 and 
which opens outwards4 ,from this 7which 
is called the blowing valve#ad7 the     
steam and air rush in a constant stream1
 until all the air has been expelled1   
and the cylinder is filled with the pure
 vapour of water4 ,this process is      
called blowing the engine preparatory to
 starting it4  ,when it is about to be  
started1 the engine-man closes the      
regulator ,r1 and thereby suspends the  
supply of steam from the boiler4 ,at the
 same time he opens the condensing valve
 ,h#ae2 and thereby throws up a jet of  
cold water into the cylinder4 ,this     
immediately condenses the steam         
contained in the cylinder1 and produces 
the vacuum4 7,the atmosphere cannot     
enter the blowing valve1 because it     
opens outwards1 so that no air can enter

 to vitiate the vacuum47 ,the           
atmospheric pressure above the piston   
now takes effect1 and forces it down in 
the cylinder4 ,the descent being        
completed1 the engine-man closes the    
condensing valve ,h1 and opens the      
regulator1 ,r4 ,by this means he stops  
the play of the jet within the cylinder1
 and admits the steam from the boiler4  
,the first effect of the steam is to    
expel the condensing water and condensed
 steam which are collected in the bottom
 of the cylinder1 through the tube ,y1  
containing a valve which opens outwards 
7called the eduction valve71 which leads
 to the hot cistern ,l1 into which this 
water is therefore discharged4  ,when   
the steam admitted through ,r ceases to 
be condensed1 it balances the           
atmospheric pressure above the piston1  
and thus permits it to be drawn to the  
top of the cylinder by the weight of the
 rod ,d4 ,this ascent of the piston is  
also assisted by the circumstance of the
 steam being somewhat stronger than the 

atmosphere4  ,when the piston has       
reached the top1 the regulating valve ,r
 is closed1 and the condensing valve ,h 
opened1 and another descent produced1 as
 before1 and so the process is          
continued4 ,pg#jga  ,the manipulation   
necessary in working this engine was1   
therefore1 the alternate opening and    
closing of two valves2 the regulating   
and condensing valves4 ,when the piston 
reached the top of the cylinder1 the    
former was to be closed1 and the latter 
opened2 and1 on reaching the bottom1 the
 former was to be opened1 and the latter
 closed4   7#db47 ,the duty of working  
the engine requiring no great amount of 
labour1 or skill1 was usually entrusted 
to boys1 called1 cock boys4 ,it happened
 that one of the most important         
improvements which has ever been made in
 the working of steam engines was due to
 the ingenuity of one of these boys4 ,it
 is said that a lad1 named ,humphrey    
,potter1 was employed to work the cocks 
of an atmospheric engine1 and being     

tempted to escape from the monotonous   
drudgery to which his duty confined him1
 his ingenuity was sharpened so as to   
prompt him to devise some means by which
 he might indulge his disposition to    
play without exposing himself to the    
consequences of suspending the          
performance of the engine4 ,on observing
 the alternate ascending and descending 
motion of the beam above him1 and       
considering it in reference to the      
labour of his own hands1 in alternately 
raising and lowering the levers which   
governed the cocks1 he perceived a      
relation which served as a clue to a    
simple contrivance1 by which the steam  
engine1 for the first time1 became an   
automaton4 ,when the beam arrived at the
 top of its play1 it was necessary to   
open the steam valve by raising a lever1
 and to close the injection valve by    
raising another4 ,this he saw could be  
accomplished by attaching strings of    
proper length to these levers1 and tying
 them to some part of the beam4 ,these  

levers required to be moved in the      
opposite direction when the beam        
attained the lowest point of its play4  
,this he saw could be accomplished by   
strings1 either connected with the outer
 arm of the beam1 or conducted over rods
 or pulleys4 ,in short1 he contrived    
means of so connecting the levers which 
governed the two cocks by strings with  
the beam1 that the beam opened and      
closed these cocks with the most perfect
 regularity and certainty as it moved   
upwards and downwards4  ,besides        
rendering the machine independent of    
manual ,pg#jgb superintendence1 this    
process conferred upon it much greater  
regularity of performance than any      
manual superintendence could ensure4    
,this contrivance of ,potter was very   
soon improved by the substitution of a  
bar1 called a plug frame1 which was     
suspended from the arm of the beam1 and 
which carried upon it pins1 by which the
 arms of the levers governing the cocks 
were struck as the plug-frame ascended  

and descended1 so as to be opened and   
closed at the proper times4  ,the engine
 thus improved required no other        
attendance except to feed the boiler    
occasionally by the cock ,t1 and to     
attend the furnace4   7#dc47 ,however   
the merit of the discovery of the       
physical principles on which the        
mechanical application of steam depends 
may be awarded1 it must be admitted that
 the engine contrived by ,newcomen and  
his associates1 considered as a         
practical machine1 was immeasurably     
superior to that which preceded it2     
superior1 indeed1 to such a degree1 that
 while the one was incapable of any     
permanently useful application1 the     
other soon became a machine of extensive
 utility in the drainage of mines2 and1 
even at the present time1 the           
atmospheric engine is not unfrequently  
used in preference to the modern steam  
engine1 in districts where fuel is      
abundant and cheap2 the expense of      
constructing and maintaining it being   

considerably less than that of an       
improved steam engine4 ,the low pressure
 of the steam used in working it1       
rendered it perfectly safe4 ,while      
,savery's engine1 to work with effect1  
required that the steam confined in the 
vessels should have a bursting pressure 
amounting to about thirty pounds per    
square inch1 the pressure of steam in   
the boiler and cylinder of the          
atmospheric engine required only a      
pressure about one pound per square     
inch4 ,the high pressure also of the    
steam used in ,savery's engine1 was     
necessarily accompanied1 as we shall    
presently explain1 by a greatly         
increased temperature4 ,the effect of   
this was1 to weaken and gradually       
destroy the vessels1 especially those   
which1 like the steam vessels ,v and ,v 
7fig4 #ab471 were alternately heated and
 cooled4  ,besides these defects1 the   
power of ,savery's engines was ,pg#jgc  
also very restricted1 both as to the    
quantity of water raised and as to the  

height to which it was elevated4 ,on the
 other hand1 the atmospheric engine was 
limited in its power only by the        
dimensions of its piston4 ,another      
considerable advantage which the        
atmospheric engine possessed over that  
of ,savery1 was the facility with which 
it was capable of driving machinery by  
means of the working-beam4 ,the merit1  
however1 of ,newcomen's engine1 regarded
 as an invention1 and apart from merely 
practical considerations1 must be       
ascribed principally to its mechanism   
and combinations4 ,we find in it no new 
principle1 and scarcely even a novel    
application of a principle4 ,the agency 
of the atmospheric pressure acting      
against a vacuum1 or partial vacuum1 had
 been long known3 the method of         
producing a vacuum by the condensation  
of steam had been suggested by ,papin1  
and carried into practical effect by    
,savery4 ,the mechanical power obtained 
from the direct pressure of the elastic 
force of steam1 used in the atmospheric 

engine to balance the atmosphere during 
the ascent of the piston1 was suggested 
by ,de ,caus and ,lord ,worcester4 ,the 
boiler1 gauge pipes1 and the regulator1 
were all borrowed from the engine of    
,savery4 ,the idea of using the         
atmospheric pressure against a vacuum or
 partial vacuum1 to work a piston in a  
cylinder1 had been suggested by ,otto   
,guericke1 an ingenious ,german         
philosopher1 who invented the air-pump2 
and this1 combined with the production  
of a vacuum by the condensation of      
steam1 was subsequently suggested by    
,papin4 ,the use of a working-beam could
 not have been unknown4 ,nevertheless1  
the judicious combination of these      
scattered principles must be            
acknowledged to deserve considerable    
credit4 ,in fact1 the mechanism         
contrived by ,newcomen rendered a       
machine which was before altogether     
inefficient1 highly efficient3 and1 as  
observed by ,tredgold1 such a result1   
considered in a practical sense1 should 

be more highly valued than the          
fortuitous discovery of a physical      
principle4 ,the method of condensing the
 steam by the sudden injection of water1
 and of expelling the air and water from
 the cylinder by the injection of steam1
 are two contrivances not before in use1
 which are quite essential to the       
,pg#jgd effective operation of the      
engine4 ,these processes1 which are     
still necessary to the operation of the 
improved steam engine1 appear to be     
wholly due to the inventors of the      
atmospheric engine4  ,illustration3     
,,atmospheric ,,engine4    ,,footnotes3 
#i ,this pipe is represented as         
proceeding from the force-pipe   above  
the cistern ,c1 in the perspective view 
of ,savery's   engine at the head of    
this chapter4    #aj ,hot water being   
lighter than cold1 floats on the        
surface4    #aa ,captain is a title     
given in ,cornwall to the               
superintendent of the works connected   
with a mine4    #ab ,as the calculation 

of the power of an engine depends on    
the number of square inches in the      
section of the piston1 it   may be      
useful to give a rule for computing the 
number of   square inches in a circle4  
,the following rule will always give    
the dimensions with sufficient          
accuracy3--,multiply the number   of    
inches in the diameter by itself2 divide
 the product by #ad1   and multiply the 
quotient thus obtained by #aa1 and the  
result   will be the number of square   
inches in the circle4 ,thus1 if   there 
be #ab inches in the diameter1 this     
multiplied by itself   gives #add1 which
 divided by #ad gives #aj-d_/dd1 which  
multiplied   by #aa gives #aae1         
neglecting fractions4 ,there are1       
therefore1   #aae square inches in a    
circle whose diameter is #ab inches4    
#ac ,the external cylinder is not       
represented in the diagram4    #ad ,also
 called the snifting valve1 from the    
peculiar noise   made by the air and    
steam escaping from it4    #ae ,also    

called the injection valve4  ,pg#jge    
,illustration3 ,,greenock1 ,,in #ahbd4  
,,chap4 ,,iii4      ,,progress ,,of     
,,the ,,atmospheric ,,engine4 --        
,,smeaton',s ,,improvements4     --     
,,brindley1 ,,engineer ,,of ,,the       
,,bridgewater ,,canal4 -- ,,invents     
,,the     ,,self-,,regulating ,,feeder4 
-- ,,james ,,watt4 -- ,,his ,,descent   
,,and     ,,parentage4 -- ,,anecdotes   
,,of ,,his ,,boyhood4 -- ,,his ,,early  
,,aquirements4     -- ,,goes ,,to       
,,london4 -- ,,returns ,,to ,,glasgow4  
-- ,,is ,,appointed                     
,,instrument-,,maker ,,to ,,the         
,,university4 -- ,,opens ,a ,,shop ,,in 
,,glasgow4     -- ,,his ,,friends ,,and 
,,patrons4 -- ,,adam ,,smith4 -- ,,dr4  
,,black4 -- ,,robert     ,,simson4 --   
,,professor ,,robison4 -- ,,watt',s     
,,personal ,,character4 --              
,,industrious ,,and ,,studious ,,habits4
 -- ,,his ,,attention ,,first           
,,directed ,,to ,,steam4 --             
,,experiments ,,on ,,high-,,pressure    

,,steam4 --     ,,repairs ,,an          
,,atmospheric ,,model4 -- ,,experimental
 ,,inquiry     ,,consequent ,,on ,,this4
 -- ,,its ,,results4 -- ,,discovers     
,,the ,,great     ,,defects ,,of ,,the  
,,atmospheric ,,engine4 -- ,,discovery  
,,by ,,experiment     ,,of ,,the        
,,expansion ,,which ,,water ,,undergoes 
,,in ,,evaporation4 --     ,,discovers  
,,the ,,latent ,,heat ,,of ,,steam4 --  
,,is ,,informed ,,by ,,dr4 ,,black      
,,of ,,the ,,theory ,,of ,,latent       
,,heat4   7#dd47 ,the atmospheric engine
 was brought to a state of considerable 
efficiency and improvement by ,mr4      
,beighton1 in #agah4 ,from that time it 
continued in use without any change in  
its ,pg#jgf principle1 and with little  
improvement in its structure1 for half a
 century4 ,although engines of this kind
 continued to be extensively            
constructed1 they were usually executed 
by ordinary mechanics1 incapable of     
applying to them the just principles of 
practical science2 and1 consequently1   

little attention was paid to their      
proportions4 ,it was not until about the
 year #aggb1 that ,mr4 ,john ,smeaton1  
the celebrated engineer1 applied the    
powers of his mind to the investigation 
of this machine1 as he had previously   
done with such success to wind and water
 mills4 ,although he did not introduce  
any new principle into the atmospheric  
engine1 yet it derived greatly augmented
 power from the proportions which he    
established for engines of different    
magnitudes4  ,in #agei1 ,mr4 ,james     
,brindley1 whose name is so celebrated  
as the engineer of the ,duke of         
,bridgewater's canal1 obtained a patent 
for some improvements in the atmospheric
 engine4 ,he proposed that the boiler   
should be made of wood and stone1 with a
 stove or fire-place of cast iron within
 it1 so that the fire should be         
surrounded on every side by water4 ,the 
chimney was to be an iron pipe or tube1 
conducted through the boiler2 so that   
the heated air1 in passing from the     

fire1 should impart a portion of its    
heat to the water4 ,he also proposed a  
method of feeding the boiler1 which1 by 
self-acting machinery1 would keep the   
water in the boiler at a fixed level1   
independently of any attention on the   
part of the engine-man4 ,this was to be 
accomplished by a buoy or float upon the
 surface of the water in the boiler1    
which should communicate with a valve in
 the feed-pipe1 so that when the level  
of the water in the boiler fell1 the    
float or buoy1 falling with it1 would   
open the valve and supply the feed4 ,it 
is stated1 in the ,biographia           
,britannica1 that ,mr4 ,brindley1 in    
#agef1 undertook to erect an engine at  
,newcastle-under-,lyne2 but he is said  
to have been discouraged by the         
obstacles which were thrown in his way1 
and to have abandoned the steam engine4 
,the interval between the invention of  
the atmospheric engine1 and the         
amelioration it received at the hands of
 ,smeaton1 has been rendered memorable  

by the advent of one who was destined to
 work a mighty change in the condition  
,pg#jgg of the human race by the        
application of his vast genius to the   
adaptation of steam power to the uses of
 life4   7#de47 ,,james ,,watt was born 
at ,greenock1 in ,scotland1 on the      
nineteenth day of ,january1 in the year 
#agcf4af  ,the great-grandfather of     
,watt1 a farmer in ,aberdeenshire1 was  
killed in one of the battles of         
,montrose4 ,the victorious party1 not   
thinking death a sufficient expiation   
for the political opinions in support of
 which he had fought and bled1 punished 
him in the person of his son1 by        
confiscating his little property4       
,thomas ,watt1 the son1 thus deprived of
 support1 was received by distant       
relations1 and1 for a time1 applied     
himself to study1 by which he was       
enabled1 after the restoration of       
tranquillity1 to establish himself at   
,greenock as a teacher of practical     
mathematics and navigation4 ,he resided 

in the burgh or barony of ,crawford's   
,dyke1 and attained a position of       
sufficient respectability to be elected 
to the office of baron-baillie1 or chief
 magistrate1 and died in #agcd1 at the  
advanced age of ninety-two years4       
,thomas ,watt had two sons4 ,the elder1 
,john1 adopted the profession of his    
father1 and was a teacher of mathematics
 and navigation at ,glasgow3 he died in 
#agcg1 at the age of fifty years4 ,the  
second son1 ,james1 the father of the   
celebrated engineer1 was1 during a      
quarter of a century1 treasurer of the  
town council of ,greenock1 and a local  
magistrate4 ,he was remarked for the    
ardent zeal and enlightened spirit with 
which he discharged his public duties4  
,his business was that of a             
ship-chandler1 builder1 and general     
merchant2 but1 unhappily1               
notwithstanding his active industry1 he 
lost1 in the decline of his life1 by    
unsuccessful commercial speculations1 a 
part of the property which he had so    

honourably acquired4 ,he died in #aghb1 
at the age of eighty-four years4        
,,james ,,watt1 to whom the world is so 
largely indebted for the extension and  
improvement of steam power1 had from his
 birth an extremely delicate            
constitution4 ,from his mother1 ,pg#jgh 
whose family name was ,muirhead1 he     
received his first lessons in reading1  
and he learned from his father writing  
and arithmetic4 ,although he was entered
 as a pupil in the grammar school of    
,greenock1 yet such was his delicate    
state of health1 that his attendance    
there was so interrupted by constant    
indisposition that he could derive but  
little benefit from the opportunities of
 instruction which it afforded4 ,for a  
great period of the year he was confined
 to his room1 where he devoted himself  
to study without the aid of instruction4
 ,it was in the retirement of the sick  
chamber that the high intellectual      
faculties of ,watt1 which were destined 
to produce such precious fruits1 began  

to unfold themselves4 ,he was too sickly
 to be subjected to the restraints which
 the business of education usually      
imposes on children4 ,his parents1      
therefore1 found it necessary to leave  
him at liberty to choose his occupations
 and amusements4 ,the following         
anecdotes will show the use he made of  
this freedom4  ,a friend of his father  
found the boy one day stretched upon the
 hearth tracing with chalk various lines
 and angles4 ,why do you permit this    
child1 said he1 to waste his time so2   
why not send him to school8 ,mr4 ,watt  
replied1 ,you judge him hastily2 before 
you condemn us1 ascertain how he is     
employed4 ,on examining the boy1 then   
six years of age1 it was found that he  
was engaged in the solution of a problem
 of ,euclid6  ,having observed the      
tendency of his son's mind1 ,mr4 ,watt  
placed at his disposal a collection of  
tools4 ,these he soon learned to use    
with the greatest skill4 ,he took to    
pieces and put together1 again and      

again1 all the children's toys which he 
could procure2 and he was constantly    
employed in making new ones4            
,subsequently he used his tools in      
constructing a little electrical        
machine1 the sparks proceeding from     
which became a great subject of         
amusement to all the playfellows of the 
poor invalid4  ,though endowed with     
great retentive powers1 ,watt would     
probably never have figured among the   
prodigies of a common school3 he would  
have been slow to commit his lessons to 
memory1 from the repugnance which he    
would feel to repeat like a parrot      
anything which he did not perfectly     
,pg#jgi understand4 ,the natural        
tendency of his mind to meditate on     
whatever came before it1 would give him1
 to superficial observers1 the          
appearance of dullness4 ,happily1       
however1 he had a parent who was        
sufficiently clear-sighted1 and who     
entertained high hopes of the growing   
faculties of his son4 ,more distant and 

less sagacious relations were not so    
sanguine4 ,one day ,mrs4 ,muirhead1 the 
aunt of the boy1 reproaching him for    
what she conceived to be listless       
idleness1 desired him to take a book and
 occupy himself usefully4 ,more than an 
hour has now passed away1 said she1 and 
you have not uttered a single word4 ,do 
you know what you have been doing all   
this time8 ,you have taken off1 and put 
on1 repeatedly1 the lid of the tea-pot2 
you have been holding the saucers and   
the spoons over the steam1 and you have 
been endeavouring to catch the drops of 
water formed on them by the vapour4 ,is 
it not a shame for you to waste your    
time so8  ,mrs4 ,muirhead was little    
aware that this was the first experiment
 in the splendid career of discovery    
which was subsequently to immortalise   
her little nephew4 ,she did not see1 as 
we now can1 in the little boy playing   
with the tea-pot1 the great engineer    
preluding to those discoveries which    
were destined to confer on mankind      

benefits so inestimable4  ,one of the   
social qualities of mind which was      
remarkable throughout his life1 was the 
singular felicity and grace with which  
he related anecdotes4 ,this power was   
manifested even in his earliest         
childhood4 ,the following is an extract 
from a letter written by ,mrs4 ,marion  
,campbell1 his cousin1 and the          
playfellow of his childhood3--  ,he was 
not fourteen when his mother brought him
 to ,glasgow to visit a friend of hers2 
his brother ,john accompanied him4 ,on  
,mrs4 ,watt's return to ,glasgow1 some  
weeks after1 her friend said1 ',you must
 take your son ,james home2 ,i cannot   
stand the degree of excitement he keeps 
me in2 ,i am worn out for want of sleep4
 ,every evening before ten o'clock1 our 
usual hour of retiring to rest1 he      
contrives to engage me in conversation1 
then begins some striking tale1 and1    
whether humorous or pathetic1 the       
interest is so overpowering that the    
family all listen to him with breathless

 attention1 and hour after hour strikes 
unheeded4' ,pg#jhj  ,watt had a younger 
brother1 ,john1 who was subsequently    
lost by shipwreck1 in a voyage from     
,scotland to the ,united ,states4 ,this 
lad1 having determined on following the 
business of his father1 left ,james more
 completely at liberty to choose his own
 occupation4 ,but such a choice was     
difficult for a student who commanded   
equal success in every thing to which he
 directed his attention4  ,the          
excursions which he was in the habit of 
making on the ,scottish mountains       
surrounding ,loch ,lomond1 naturally    
directed his attention to botany and    
mineralogy1 in each of which he attained
 considerable knowledge4 ,his love of   
anecdote and romance was likewise       
gratified by the scenery which he       
enjoyed in these walks2 and the         
traditions and popular songs with which 
they made him acquainted4 ,when from    
ill-health1 as constantly happened1 he  
was confined to the house1 he devoted   

himself to chemistry1 natural           
philosophy1 and even to medicine and    
surgery4 ,in chemistry he acquired some 
experimental skill1 and studied with    
eager zeal the elements of natural      
philosophy by ,s'4 ,gravesande4 ,his own
 unhappy maladies prompted him to read  
works on surgery and medicine2 and to   
such an extent did the activity of his  
mind impel him on these subjects1 that  
he was found one day dissecting1 in his 
room1 the head of a child1 who had died 
of some unknown disease1 with a view to 
ascertain the cause of its death4  ,in  
#agge1 at the age of nineteen1 at the   
recommendation of ,dr4 ,dick1 professor 
of natural philosophy in the university 
of ,glasgow1 he went to ,london1 where  
he employed himself in the house of ,mr4
 ,john ,morgan1 a mathematical          
instrument maker1 in ,finch ,lane1      
,cornhill1 to whom he apprenticed       
himself for three years4 ,he remained1  
however1 only a year1 at the expiration 
of which 7probably owing to his delicate

 state of health7 he was released from  
his apprenticeship1 and returned to     
,glasgow1 with the intention of         
establishing himself in business as an  
optician and mathematical instrument    
maker4 ,in the fulfilment of this       
intention1 however1 he was obstructed by
 the interposition of the ,corporation  
of ,trades in that town1 who regarded   
him as an intruder1 not qualified by the
 necessary apprenticeship to carry on   
business4 ,all means of conciliation    
being ,pg#jha exhausted1 the ,professors
 of the ,university interfered1 and gave
 him the use of three apartments within 
the college1 for carrying on his        
business1 and likewise appointed him    
mathematical instrument maker to the    
,university4 ,soon afterwards the       
opposition of the local trades seems to 
have given way1 and he opened a shop in 
,glasgow for the sale of mathematical   
instruments4  ,after the celebrity at   
which he has arrived1 it will be easily 
believed that every trace of his earlier

 connection with ,glasgow college is    
carefully cherished4 ,there are         
accordingly preserved at that place     
little instruments and pieces of        
apparatus of exquisite workmanship1     
which were executed entirely by the hand
 of ,watt1 at a time when he was not in 
a condition to command the aid of       
workmen under him4  ,at the time of     
obtaining this appointment in the       
,university1 ,watt was in his           
twenty-first year4 ,his natural talents 
and winning manners were speedily the   
means of gaining for him the esteem and 
friendship of all those eminent persons 
connected at the time with that         
university whose regard was most valued4
 ,among these the earliest of his       
friends and patrons were--,,adam        
,,smith1 the author of ,the ,wealth of  
,nations2 ,,black1 afterwards celebrated
 for his chemical discoveries1 and more 
especially for his theory of latent     
heat2 and ,,robert ,,simson1 rendered   
illustrious by his works on ancient     

geometry4 ,in releasing ,watt from the  
persecution of the ,glasgow corporation1
 these distinguished persons first      
imagined that they were conferring a    
benefit merely on an industrious and    
clever artisan1 whose engaging manners  
won their regard2 but a short           
acquaintance with him was sufficient to 
convince them how superior his mind was 
to his position1 and they conceived     
towards him the most lively friendship4 
,his shop became the common rendezvous1 
the afternoon lounge1 of all who were   
most distinguished for literary and     
scientific attainments among the        
professors and students4 ,there they met
 to discuss the topics of the day in    
art1 science1 and literature4 ,among    
these students1 the name which          
afterwards attained the highest         
distinctions1 and among these           
distinctions1 not the least1 the lasting
 personal friendship and esteem of ,watt
 himself1 was ,,robison1 ,pg#jhb the    
author of a well known work on          

,mechanics1 and one of the contributors 
to the ,encyclopdia ,britannica4  ,the  
following extract from an unpublished   
manuscript by ,robison himself will show
 at once the estimation in which ,watt  
was held1 and will illustrate one of the
 most interesting traits of his personal
 character3--  ,i had always1 from my   
earliest youth1 a great relish for the  
natural sciences1 and particularly for  
mathematical and mechanical philosophy1 
when ,i was introduced by ,drs4 ,simson1
 ,dick1 and ,moor1 gentlemen eminent for
 their mathematical abilities1 to ,mr4  
,watt4 ,i saw a workman1 and expected no
 more2 but was surprised to find a      
philosopher as young as myself1 and     
always ready to instruct me4 ,i had the 
vanity to think myself a pretty good    
proficient in my favourite study1 and   
was rather mortified at finding ,mr4    
,watt so much my superior4 4 4 4        
,whenever any puzzle came in the way of 
any of the young students1 we went to   
,mr4 ,watt4 ,he needed only to be       

prompted1 for every thing became to him 
the beginning of a new and serious      
study1 and we knew that he would not    
quit it till he had either discovered   
its insignificancy1 or had made         
something of it4 ,he learnt the ,german 
language in order to peruse ,leupold's  
',theatrum ,machinarum2' so did ,i1 to  
know what he was about4 ,similar reasons
 made us both learn the ,italian        
language4  99  99  99 ,when to his      
superiority of knowledge is added the   
nave simplicity and candour of ,mr4     
,watt's character1 it is no wonder that 
the attachment of his acquaintances was 
strong4 ,i have seen something of the   
world1 and am obliged to say ,i never   
saw such another instance of general and
 cordial attachment to a person whom all
 acknowledged to be their superior4 ,but
 that superiority was concealed under   
the most amiable candour1 and a liberal 
allowance of merit to every man4 ,mr4   
,watt was the first to ascribe to the   
ingenuity of a friend things which were 

nothing but his own surmises1 followed  
out and embodied by another4 ,i am the  
more entitled to say this1 as ,i have   
often experienced it in my own case4    
,watt never permitted the inquiries     
which arose out of these reunions to    
interfere with the discharge of the     
duties of his workshop4 ,there he passed
 the day1 devoting the ,pg#jhc night to 
study4 ,every inquiry appeared to him to
 be attractive in proportion to its     
difficulty1 and to have charms in       
proportion as it was removed from the   
common routine of his business4 ,as an  
example of this may be mentioned the    
fact1 that1 being himself so insensible 
to the charms of music that he could not
 distinguish one note from another1 he  
was actually induced to undertake the   
construction of an organ1 in which he   
was nevertheless completely successful4 
,the instrument he constructed1 as might
 have been expected1 contained many     
improvements in its mechanism2 but what 
is much more remarkable1 its tone and   

its musical qualities commanded the     
admiration of all the professional      
musicians who heard it4 ,in the         
construction of this instrument ,watt   
showed that vigorous spirit of          
investigation which characterised all   
the subsequent labours of his life4 ,he 
made out the scale of temperament by the
 aid of the phenomena of beats1 of which
 he could only obtain a knowledge by a  
profound but obscure work published by  
,dr4 ,robert ,smith of ,cambridge4  ,the
 earliest occasion on which the         
attention of ,watt is said to have been 
called to the agency of steam1 was in   
the year #agei1 when his friend ,robison
 entertained some speculations for      
applying that agent as a means of       
propelling wheel carriages2 and he      
consulted ,watt on the subject4 ,no     
record1 however1 has been preserved of  
any experiments which were tried on this
 occasion2 nor does it appear that the  
inquiry was carried farther than a      
verbal discussion1 such as habitually   

took place on other subjects of science 
between ,watt and his friends4   7#df47 
,in #agfb1 ,watt tried some experiments 
on the force of steam at a high         
pressure1 confined in a close digester2 
and he then constructed a small model to
 show how motion could be obtained from 
that power4 ,the practicability of what 
has since been called the ,high         
,pressure ,engine1 was demonstrated by  
him on this occasion2 but he did not    
pursue the inquiry1 on account of the   
supposed danger of working with such    
compressed steam as was required4  ,it  
is usual to provide1 in the cabinets of 
experimental apparatus for the          
instruction of the students of          
universities1 ,pg#jhd small working     
models of the most useful machines4 ,in 
the collection for the illustration of  
the lectures delivered to the ,natural  
,philosophy class in the ,university of 
,glasgow was a working model of         
,newcomen's atmospheric engine1 applied 
to a pump for raising water2 which1     

however1 had never been found to work   
satisfactorily4 ,the ,professor of      
,experimental ,philosophy of that day1  
,dr4 ,john ,anderson 7the founder of the
 celebrated ,andersonian ,institution71 
sent this model in #agfc to ,watt's     
workshop1 to be repaired4 ,its defects  
soon disappeared1 and it was made to    
work to the satisfaction of the         
professor and students4  ,this simple   
discharge of his duty1 however1 did not 
satisfy the artisan2 and his wonted     
activity of mind rendered this model a  
subject of profound meditation1 and led 
him into a course of practical inquiry  
respecting it1 which formed the         
commencement of a most brilliant career 
of mechanical discovery4 ,the           
improvement--we might almost say the    
creation--of the steam engine1 by this  
great man1 must not therefore be        
regarded1 as so often happens with      
mechanical discoveries1 as the result of
 fortuitous observation1 or even of a   
felicitous momentary inspiration4 ,watt1

 on the other hand1 conducted his       
investigation by a course of deep       
thought1 and of experiments marked by   
the last refinement of delicacy and     
address4 ,if he had received a more     
extended and liberal education1 one     
would have thought that he had adopted  
for his guide the celebrated maxim of   
,bacon3--  ,to write1 speak1 meditate1  
or act1 when we are not provided with   
facts to direct our thoughts1 is to     
navigate a coast full of dangers without
 a pilot1 and to launch into the        
immensity of the ocean without either   
rudder or compass4  ,the model which he 
had repaired1 had a cylinder of only two
 inches diameter1 and six inches stroke4
 ,after he had put it in complete order1
 he found1 that although the boiler was 
much larger in proportion to the        
cylinder than those of real engines1    
yet1 that it was incapable of supplying 
the cylinder with steam in sufficient   
quantity to keep it at work4 ,to enable 
it to continue to move1 he found it     

necessary to lessen the quantity of     
water raised by its pump1 so as to      
,pg#jhe reduce the load on its piston   
very much below the proper standard     
according to the common rules for large 
engines4  ,he ascribed the great        
inferiority in the performance of the   
model1 compared with the performance of 
the large engines1 to the small size of 
the cylinder1 and to its material4 ,the 
cylinder of the model was brass1 while  
those of large engines were of cast     
iron2 and brass being a better conductor
 of heat than iron1 he concluded that   
more heat in proportion was lost from   
this cause in the model1 than in the    
larger engines4 ,he observed that the   
small cylinder was so heated when the   
steam was admitted into it1 that it     
could not be touched by the hand2 but1  
nevertheless1 that this heat contributed
 nothing to its performance1 inasmuch as
 before the piston descended1 the       
cylinder required to be cooled4   7#dg47
 ,his first attempt to improve the      

engine1 was by using a wooden cylinder  
instead of an iron one4 ,he accordingly 
made a model with a cylinder of wood1   
soaked in linseed oil1 and baked to     
dryness4 ,with this he made numerous    
experiments1 and found that it required 
a less quantity of water to be thrown   
into the cylinder to condense the steam1
 and that it was worked with a less     
supply of steam from the boiler than was
 necessary with the metallic cylinder4  
,still he found that the force with     
which the piston descended was          
considerably less than that which the   
atmospheric pressure ought to supply1   
supposing a tolerably perfect vacuum to 
be produced under the piston4 ,this led 
him to suspect that the water injected  
into the cylinder was not perfectly     
effectual in condensing the steam4 ,the 
experiments which he had previously made
 on the increased temperature at which  
water boils under pressures greater than
 that of the atmosphere1 led him by     
analogy to the conclusion that it would 

boil at lower temperatures if it were   
submitted to a pressure less than the   
atmosphere1 and he was aware that ,dr4  
,cullen and others had then recently    
discovered that in vacuo1 water would   
boil at so low a temperature as #ajj4   
,these notions suggested the probability
 that the water injected into the       
cylinder being heated by the condensed  
steam1 might produce vapour of a low    
temperature ,pg#jhf and reduced pressure
 under the piston1 which would account  
for the deficiency he observed in the   
power of the engine4  ,no means occurred
 to him by which he could ascertain1 by 
direct experiment1 the temperatures at  
which water would boil under pressures  
less than that of the atmosphere4 ,he   
sought1 however1 to determine it by the 
following method4 ,having ascertained1  
by repeating and multiplying the        
experiments which he had tried in #agfb1
 on high-pressure steam1 he obtained a  
table of the temperatures at which water
 boils at various pressures greater than

 that of the atmosphere4 ,these results 
he laid down in a series forming a      
curve1 of which the abscissa represented
 the temperatures1 and the ordinates the
 pressures4 ,he then continued this     
curve1 backwards as it were1 and        
obtained1 by analogy1 an approximation  
to the boiling temperatures1            
corresponding to pressures less than    
that of the atmosphere4 ,in other words1
 having obtained by his experiments a   
notion1 however imperfect1 of the law or
 rule observed by the temperatures at   
which water boils at different pressures
 greater than that of the atmosphere1 he
 calculated by the same law or rule what
 the pressures would be at different    
pressures less than that of the         
atmosphere4  ,applying these results to 
the interior of the cylinder of the     
atmospheric engine1 he obtained an      
approximation to the pressure of the    
vapour which would be produced from the 
warm water formed by the cold water     
injected into the cylinder1 and the     

steam condensed by it2 and he           
accordingly found that vapour1 having a 
pressure seriously injurious to the     
power of the engine would be produced in
 the cylinder1 unless considerably more 
water of injection was thrown in than   
was customary4  ,it was apparent that   
the actual quantity of steam usefully   
employed in the cylinder at each stroke1
 was only the quantity which filled the 
cylinder2 and therefore1 in order to    
ascertain the quantity of steam lost by 
the imperfections of the machine1 it was
 necessary to compare the actual        
quantity of steam transmitted by the    
boiler to the cylinder at each stroke1  
with the quantity which would just fill 
the cylinder4 ,the difference would of  
course be wasted4 ,but to determine     
,pg#jhg the actual quantity of steam    
supplied by the boiler to the cylinder1 
there was no other means than by        
observing the quantity of water         
evaporated in the boiler4 ,that being   
observed1 it was necessary to know the  

quantity of steam which that water      
formed2 and it was therefore necessary  
to determine the quantity or volume of  
steam which a given volume of water     
produced4   7#dh47 ,on considering more 
attentively the operation of the        
machine1 the following circumstances    
gradually unfolded themselves to him4   
,let us suppose the piston at the top of
 the cylinder1 and the space in the     
cylinder below it1 filled with steam so 
as to balance the pressure of the       
atmosphere above the piston4 ,under such
 circumstances the steam1 as will       
presently be explained1 must have the   
temperature of boiling water4 ,but that 
the steam should have1 and should       
maintain1 this temperature1 it was      
evidently necessary that the inner      
surface of the cylinder in contact with 
it should have the same temperature3 for
 if it had a lower temperature1 it would
 take heat from the steam1 and reduce   
the temperature of the latter4 ,now the 
cylinder being a mass of metal1 has a   

quality in virtue of which heat passes  
freely through its dimensions1 so that  
its inner surface could not be          
maintained at a temperature more        
elevated than that of its dimensions    
extending from the inner surface to the 
outer surface4 ,therefore1 to maintain  
the steam contained in the cylinder at  
the proper temperature1 it was essential
 that the whole of the solid metal      
composing the cylinder should be itself 
at that temperature4  ,things being in  
this state1 it was required that a      
vacuum should be produced under the     
piston to give effect to the atmospheric
 pressure above it1 by relieving it from
 the pressure below4 ,this1 indeed1     
would appear to have been attained by   
introducing as much cold water within   
the cylinder as would be sufficient to  
reconvert the steam contained in it into
 water2 but ,watt found1 in his         
experiments on the atmospheric model1   
that the piston would not descend with  
the proper force1 unless a vastly       

greater quantity of water were          
introduced into the cylinder than the   
quantity which he had ascertained to be 
,pg#jhh necessary for the reconversion  
of the steam into water4 ,the cause of  
this he perceived and fully explained4  
,if we suppose as much1 and no more1    
cold water introduced into the cylinder 
as would reconvert the steam contained  
in it into water1 then we should have in
 the bottom of the cylinder a quantity  
of warm water with a vacuum above it3   
but the entire mass of metal composing  
the cylinder itself1 which was          
previously at the temperature of boiling
 water1 would still be at the same      
temperature4 ,the warm water1 resting in
 contact with this metal in the bottom  
of the cylinder1 would be immediately   
heated by it1 and would rise in its     
temperature1 while the metal of the     
cylinder itself would be somewhat       
lowered in temperature by the heat which
 it would thus impart to the warm water 
contained in it4 ,under these           

circumstances1 as we shall presently    
explain1 steam would be produced from   
the water1 which would fill the         
cylinder2 and although such steam would 
not have a mechanical pressure equal in 
amount to the atmosphere1 and therefore 
would not altogether prevent the piston 
from descending if it had no load to    
move1 yet it would deprive the engine of
 so great a portion of its legitimate   
power as to render it altogether        
inefficient4 ,but this defect would be  
removed by throwing into the cylinder a 
sufficient quantity of cold water1 not  
only to destroy the steam contained in  
it1 but also to cool the entire mass of 
metal composing the cylinder itself1    
until it would be reduced to such a     
temperature that the vapour proceeding  
from the water contained in it would    
have so small a pressure that it would  
not seriously or injuriously obstruct   
the descent of the piston4  ,the piston 
being made to descend with such force as
 to render the machine practically      

efficient1 it would then be necessary   
again to make it ascend2 and to         
accomplish this1 ,watt found that the   
boiler should supply a quantity of steam
 many times greater than was necessary  
to fill the cylinder4 ,mature reflection
 on the circumstances which have been   
just explained1 enabled him to discover 
how this undue quantity of steam was    
rendered necessary4  ,let it be         
recollected1 that when the piston has   
reached the bottom of the cylinder1 the 
whole mass of the cylinder1 and ,pg#jhi 
the piston itself1 are reduced to so low
 a temperature that the vapour of water1
 having the same temperature1 has no    
pressure sufficiently great to obstruct 
the action of the machine4 ,when1 in    
order to make the piston ascend1 steam  
is introduced from the boiler into the  
cylinder under the piston1 this steam   
encounters1 in the first instance1 the  
cold surfaces of the metal forming the  
bottom of the cylinder and the bottom of
 the piston4 ,the first effect of this  

is to convert the steam which comes from
 the boiler into water1 an effect which 
is produced by that steam imparting its 
heat to the metal with which it comes   
into contact4 ,this destruction of steam
 continues until the metal exposed to   
contact with it has been heated up to   
the temperature of boiling water4 ,then1
 and not till then1 the steam below the 
piston will have a pressure equal to    
that of the atmosphere above it1 and the
 piston will begin to ascend4 ,as it    
ascends1 however1 the sides of the      
cylinder which it exposes to the contact
 of the steam are cold1 and partially   
destroy the steam4 ,steam1 therefore1   
must be supplied from the boiler to     
replace the steam thus destroyed2 nor   
can the piston reach the top of the     
cylinder until such a quantity of steam 
shall have flowed from the boiler into  
the cylinder1 as shall be sufficient not
 only to fill the cylinder under the    
piston1 but likewise1 by its            
condensation1 to raise the whole mass of

 the cylinder and piston to the         
temperature of boiling water4  ,such    
were the circumstances which forced     
themselves upon the attention of ,watt1 
in the course of repairing1 and         
subsequently trying1 the model of the   
atmospheric engine1 at ,glasgow4 ,being 
informed generally of the uses of the   
engine in the drainage of mines1 and of 
the vast expense attending its          
operation1 by reason of the quantity of 
fuel which it consumed1 he saw how      
important any improvement would be by   
which the extensive sources of waste    
which had thus presented themselves     
could be removed4 ,he saw also1 that all
 that portion of steam which was        
expended1 not in filling the cylinder   
under the piston1 but in heating the    
great mass of metal composing the       
cylinder and piston1 from a low         
temperature to that of boiling water1   
upon each stroke of the piston1 was so  
much heat lost1 and that the proportion 
of the fuel expended in evaporating the 

steam thus wasted would be saved1 if by 
any ,pg#jij expedient he could make the 
piston descend without cooling the      
cylinder4 ,but in order to estimate the 
full amount of this waste1 and to       
discover the most effectual means of    
preventing it1 it was necessary to      
investigate the quantity of heat        
necessary for the evaporation of a given
 quantity of water2 also1 the quantity  
of steam which a given quantity of water
 would produce1 as well as other        
circumstances connected with the        
temperature and pressure of steam4 ,he1 
therefore1 applied himself to make      
experiments with a view to elucidate    
these questions2 and succeeded in       
obtaining results which led to the      
discovery of some of the most important 
of those physical phenomena1 on the due 
application of which1 the efficacy of   
the steam engine1 which he afterwards   
invented1 depended1 and which also form 
striking facts in the general physics of
 heat4   7#di47 ,the first question to  

which he directed his experiments1 was  
the determination of the extent to which
 water enlarged its volume1 or          
magnitude1 when it passed into steam4   
,to ascertain this1 he filled a thin    
,florence flask with steam1 of a        
pressure equal to the atmosphere1 and   
weighed it accurately4 ,the same flask  
was then filled with water1 and weighed 
again4 ,finally1 the weight of the flask
 itself was ascertained4 ,it is evident1
 that by such means1 the exact weight of
 the steam which filled the flask1 and  
of the same bulk of water1 would be     
obtained4 ,he found that the water      
weighed about eighteen hundred times    
more than the steam2 from whence he     
inferred that the steam which filled the
 flask contained about eighteen hundred 
times less water than the flask would   
contain4#ag  ,pg#jia ,having once       
ascertained this point1 he was able1 by 
observing the quantity of water         
evaporated in the boiler of the         
atmospheric model1 to compute the volume

 of steam which was supplied to the     
cylinder4 ,it was evident1 that for     
every cubic inch of water evaporated in 
the boiler1 eighteen hundred cubic      
inches of steam were supplied to the    
cylinder4 ,having accurately observed   
the evaporation of the boiler for a     
short time1 and the number of strokes   
made by the piston in the same time1 he 
found that the quantity of water        
evaporated in the boiler would supply   
about four times as much steam as the   
cylinder would require4 ,he consequently
 inferred1 that about three-fourths of  
the steam produced was wasted4  ,the    
next question to which he directed his  
experiments1 was to ascertain the       
quantity of cold water necessary to be  
injected into the cylinder1 in order to 
condense the steam contained in it4 ,to 
ascertain this1 he attached a pipe to a 
boiler1 by which he was enabled to      
conduct the steam from the boiler into a
 glass jar containing cold water at     
fifty-two degrees of temperature4 ,the  

steam1 as it passed from the boiler     
through the pipe1 was condensed by the  
cold water1 and continued to be so      
condensed1 until1 by the heat which it  
imparted to the water1 the latter began 
to boil1 and would then condense no more
 steam4 ,on comparing the water in the  
glass jar1 when boiling1 with the water 
originally contained in it at fifty-two 
,pg#jib degrees1 the quantity was found 
to be increased in the proportion of six
 to seven1 very nearly2 from which he   
inferred1 that to reduce one ounce of   
steam to water1 it was necessary to mix 
about six ounces of cold water with it4 
,he was further led to the conclusion1  
that steam contains a vast quantity of  
heat1 by the following experiment4 ,he  
heated1 in a close digester1 a quantity 
of water several degrees above the      
common boiling point4 ,when thus heated1
 by opening a stop-cock1 he allowed the 
compressed steam to escape into a cold  
vessel2 in three or four seconds1 he    
found that the heat of the water in the 

digester was reduced from a very high   
temperature to the common boiling point2
 yet1 that all the steam which escaped  
from it1 and which carried off with it  
the superabundant heat1 formed only a   
few drops of water when condensed2 from 
which he inferred1 that this small      
quantity of water1 in the form of steam1
 contained as much heat as was          
sufficient to raise all the water in the
 digester from the boiling point to the 
temperature at which it was before the  
steam was allowed to escape4  ,having   
thus ascertained the exact quantity of  
cold water which ought to be injected   
into the cylinder in order to condense  
the steam which filled the cylinder1 he 
found1 on comparing the quantity        
necessary to be injected in order to    
enable the piston to descend1 that this 
quantity was about four times as great  
as that which was necessary to condense 
the steam4 ,this led him to the         
conclusion1 that about four times as    
much heat was destroyed in the cylinder 

as needed to be destroyed1 if the object
 were the mere condensation of the      
steam4 ,this result fully corroborated  
the other conclusion1 deduced1 from the 
proportion which he found between the   
quantity of steam supplied by the boiler
 and the actual contents of the         
cylinder4   7#ej47 ,watt was forcibly   
struck with these circumstances1 not    
only on account of their importance in  
an economical point of view1 when their 
relation to steam power was considered1 
but still more so1 as indicating        
phenomena in the physics of heat        
altogether novel to him4  ,he1          
therefore1 eagerly sought his friend    
,dr4 ,black1 to whom he communicated    
these results4 ,then1 for the first     
time1 he ,pg#jic was informed1 by       
,black1 of the theory of ,,latent       
,,heat1 which had recently been         
discovered by him1 and of which these   
very phenomena formed the basis4  ,some 
passages in the works of ,dr4 ,robison  
produced an erroneous impression1 that a

 large share of the merit of the        
discoveries of ,watt which have been    
just explained was due to ,dr4 ,black1  
to whose instructions on the subject of 
latent heat ,watt was represented to    
have owed the knowledge of those facts  
which led to his principal inventions   
and improvements4 ,we shall here give1  
in the words of ,watt himself1 his      
explanation of the circumstances which  
led to this error4 ,this explanation is 
given in a letter addressed by ,watt to 
,dr4 ,brewster1 in ,may #ahad1 and      
prefixed to the third volume of         
,brewster's edition of ,robison's       
,mechanical ,philosophy3--    ,the      
representations of friends whose        
opinions ,i highly value   induce me to 
avail myself of this opportunity of     
noticing an error   into which not only 
,dr4 ,robison1 but apparently also ,dr4 
,black1   has fallen1 in relation to the
 origin of my improvements upon   the   
steam engine1 and which not having been 
publicly controverted   by me1 has1 ,i  

am informed1 been adopted by almost     
every subsequent   writer upon the      
subject of latent heat4    ,dr4         
,robison1 in the article ,steam ,engine1
 after passing an   encomium upon me1   
dictated by the partiality of           
friendship1   qualifies me as the 'pupil
 and intimate friend of ,dr4 ,black1'--a
   description which not being there    
accompanied with any inference1   did   
not particularly strike me at the time  
of its first perusal4   ,he afterwards1 
in the dedication to me of his edition  
of ,dr4   ,black's lectures upon        
chemistry1 goes the length of supposing 
me   to have professed to owe my        
improvements upon the steam engine to   
the instructions and information ,i had 
received from that   gentleman1 which   
certainly was a misapprehension2 as1    
though ,i   have always felt and        
acknowledged my obligations to him for  
the   information ,i had received from  
his conversation1 and particularly   for
 the knowledge of the doctrine of latent

 heat1 ,i never did nor   could consider
 my improvements as originating in those
   communications4 ,he is also mistaken 
in his assertion 7p4 #h4 of the         
preface to the above work71 that ',i had
 attended two courses   ,pg#jid of the  
doctor's lectures2' for1 unfortunately  
for me1 the   necessary avocations of my
 business prevented me from attending   
his or any other lectures at college2   
and as ,dr4 ,robison was   himself      
absent from ,scotland for four years at 
the period referred   to1 he must have  
been misled by erroneous information4   
,in p4 #ahd4   of the lectures1 ,dr4    
,black says1 ',i have the pleasure of   
thinking   that the knowledge we have   
acquired concerning the nature of       
elastic vapours1 in consequence of my   
fortunate observation of   what happens 
in its formation and condensation1 has  
contributed in   no inconsiderable      
degree to the public good by suggesting 
to my   friend ,mr4 ,watt of            
,birmingham1 then of ,glasgow1 his      

improvement on   this useful engine'    
7meaning the steam engine of which he is
 then   speaking74 ,there can be no     
doubt from what follows in his          
description of the engine1 and from the 
very honourable mention   which he has  
made of me in various parts of his      
lectures1 that he   did not mean to     
lessen any merit that might attach to me
 as an   inventor2 but1 on the contrary1
 he was always disposed to give me      
fully as much praise as ,i deserved4    
,and were that otherwise doubtful1 it   
would1 ,i think1 be evident   from the  
following quotation from a letter of his
 to me1 dated   #acth ,february #aghc1  
where1 speaking of an intended          
publication by   a friend of mine1 on   
subjects connected with the history of  
steam1   he says1 ',i think it is very  
proper for you to give him a short      
account of your discoveries and         
speculations2 and particularly   to     
assert clearly and fully your sole right
 to the honour of   the improvements of 

the steam engine4' ,and in a written    
testimonial which he very kindly gave   
me1 on the occasion of a   trial at law 
against a piracy of my invention in     
#agif-g1 after   giving a short account 
of the invention1 he adds1 ',mr4 ,watt  
was   the sole inventor of the capital  
improvement and contrivance   above     
mentioned4'    ,under this conviction of
 his candour and friendship1 it is very 
painful to me to controvert any         
assertion or opinion of my revered      
friend2 yet1 in the present case ,i find
 it necessary to say1 that   he appears 
to me to have fallen into an error2 and 
,i hope1 in   addition to my assertion1 
to make that appear by the short history
   ,i have given of my invention1 in my 
,pg#jie notes upon ,dr4   ,robison's    
essay1 as well as by the following      
account of the state   of my knowledge  
previous to my receiving any explanation
 of the   doctrine of latent heat2 and  
also from that of the facts which       
principally guided me in the invention4 

,it was known very long before my time1 
that steam was condensed   by coming    
into contact with cold bodies1 and that 
it communicated   heat to them2 witness 
the common still1 c4 c4    ,it was      
known1 by some experiments of ,dr4      
,cullen and others1 that   water and    
other liquids boiled in vacuo at very   
low heats2 water   below #ajj4    ,it   
was known to some philosophers that the 
capacity or   equilibrium of heat1 as we
 then called it1 was much smaller in    
mercury and tin than in water4    ,it   
was also known that evaporation caused  
the cooling of the   evaporating liquid1
 and bodies in contact with it4    ,i   
had myself made experiments to determine
 the following facts3--    ,first1 the  
capacities of heat for iron1 copper1 and
 some sorts of   wood1 comparatively    
with water4    ,second1 the bulk of     
steam compared with that of water4      
,third1 the quantity of water evaporated
 in a certain boiler by a   pound of    
coals4    ,fourth1 the elasticities of  

steam at various temperatures greater   
than that of boiling water1 and an      
approximation to the law which   it     
followed at other temperatures4         
,fifth1 how much water in the form of   
steam was required every   stroke by a  
small ,newcomen's engine1 with a wooden 
cylinder six   inches diameter1 and     
twelve inches stroke4    ,sixth1 the    
quantity of cold water required in every
 stroke to   condense the steam in that 
cylinder1 so as to give it a working    
power of about #g lb4 on the inch4      
,here ,i was at a loss to understand how
 so much cold water could   be heated so
 much by so small a quantity of water in
 the form of   steam2 and ,i accordingly
 applied to ,dr4 ,black1 and then first 
understood what was called latent heat4 
,but this theory1 though useful in      
determining the quantity of   injection 
necessary where the quantity of water   
,pg#jif   evaporated by the boiler1 and 
used by the cylinder1 was known1 and    
in determining1 by the quantity and heat

 of the hot water emitted   by          
,newcomen's engines1 the quantity of    
steam required to work them   did not   
lead to the improvements ,i afterwards  
made in the engine4   ,these            
improvements proceeded upon the old     
established fact1 that   steam was      
condensed by the contact of cold bodies2
 and the later   known one1 that water  
boiled in vacuo at heats below #ajj1 and
   consequently that a vacuum could not 
be obtained unless the   cylinder and   
its contents were cooled every stroke to
 below that   heat4  ,illustration3     
,,loch ,,lomond4    ,,footnotes3    #af 
,we are indebted for many of the        
anecdotes of the life of   ,watt to the 
,eloge ,historique1 recently published  
by ,m4 ,arago1   who was furnished with 
all the documents and circumstances     
relating to this celebrated person which
 were considered proper   for           
publication1 by his son1 the present    
,james ,watt1 ,esq41 of   ,aston ,hall1 
near ,birmingham1 and to the notes added

 to this   memoir by ,mr4 ,muirhead1 a  
relative of ,mr4 ,watt4    #ag ,the     
following is the account of these       
experiments given   in ,watt's own      
words3--    ,it being evident that there
 was a great error in ,dr4              
,desagulier's calculations of ,mr4      
,beighton's experiments on the   bulk of
 steam1 a ,florence flask1 capable of   
containing about a   pound of water1 had
 about one ounce of distilled water put 
into it2 a glass tube was fitted into   
its mouth1 and the   joining made tight 
by lapping that part of the tube with   
packthread covered with glazier's putty4
 ,when the flask was   set upright1 the 
tube reached down near to the surface of
 the   water1 and in that position the  
whole was placed in a tin   reflecting  
oven before a fire until the water was  
wholly   evaporated1 which happened in  
about an hour1 and might have   been    
done sooner1 had ,i not wished the heat 
not much to exceed   that of boiling    
water4 ,as the air in the flask was     

heavier   than the steam1 the latter    
ascended to the top1 and expelled   the 
air through the tube4 ,when the water   
was all evaporated1   the oven and flask
 were removed from the fire1 and a blast
 of   cold air was directed against one 
side of the flask1 to   collect the     
condensed steam in one place4 ,when all 
was cold1   the tube was removed1 the   
flask and its contents were weighed     
with care2 and the flask being made hot1
 it was dried by   blowing into it by   
bellows1 and when weighed again was     
found   to have lost rather more than   
four grains1 estimated at #d-a_/c       
grains4 ,when the flask was filled with 
water1 it was found to   contain about  
#ag-a_/h ounces avoirdupois of that     
fluid which   gave about #ahjj for the  
expansion of water converted into       
steam of the heat of boiling water4     
,this experiment was repeated with      
nearly the same result1 and   in order  
to ascertain whether the flask had been 
wholly filled   with steam1 a similar   

quantity of water was for the third time
   evaporated2 and1 while the flask was 
still cold1 it was placed   inverted    
with its mouth 7contracted by the tube7 
immersed in a   vessel of water1 which  
it sucked in as it cooled1 until in the 
temperature of the atmosphere it was    
filled to within half an   ounce measure
 of water4    ,in repetitions of this   
experiment at a later date1 ,i          
simplified the apparatus by omitting the
 tube1 and laying the   flask upon its  
side in the oven1 partly closing its    
mouth by a   cork1 having a notch on one
 side1 and otherwise proceeding as   has
 been mentioned4  ,pg#jig               
,illustration3 ,,glasgow4  ,,chap4 ,,iv4
      ,,exposition ,,of ,,physical      
,,principles4 -- ,,thermometer4 --      
,,method ,,of     ,,graduating ,,it4 -- 
,,freezing ,,and ,,boiling ,,points4 -- 
,,latent ,,heat ,,of     ,,water4 --    
,,quantity ,,of ,,heat ,,necessary ,,to 
,,convert ,,ice ,,into ,,water4     --  
,,quantity ,,of ,,heat ,,given ,,out    

,,by ,,water ,,in ,,being ,,converted   
,,into     ,,ice4 -- ,,process ,,of     
,,boiling4 -- ,,of ,,reconversion ,,of  
,,steam ,,into     ,,water4 --          
,,quantity ,,of ,,heat ,,necessary ,,to 
,,convert ,,water ,,into     ,,steam4 --
 ,,boiling ,,point ,,of ,,water4 --     
,,different ,,in ,,different            
,,places4 -- ,,depends ,,on ,,the       
,,barometer4 -- ,,varies ,,with ,,the   
,,pressure4 -- ,,experimental ,,proof   
,,of ,,this4 -- ,,boils ,,at ,,lower    
,,temperatures ,,than #bab ,,under      
,,pressures ,,less ,,than ,,the         
,,atmosphere4 -- ,,sum ,,of ,,latent    
,,and ,,sensible ,,heat ,,of ,,steam    
,,always     ,,the ,,same4 -- ,,the     
,,fuel ,,necessary ,,to ,,evaporate     
,,water ,,the ,,same1     ,,whatever    
,,be ,,the ,,temperature ,,or ,,pressure
 ,,at ,,which ,,it ,,is                 
,,evaporated4 -- ,,mechanical ,,force   
,,obtained ,,by ,,evaporation4 -- ,,this
     ,,force ,,nearly ,,the ,,same      
,,under ,,all ,,circumstances4   7#ea47 

,we shall pause here to put the reader  
in possession of the physical and       
mechanical principles connected with the
 evaporation of water and other liquids1
 which are necessary to enable him to   
understand the full extent of the value 
and the merit of the discoveries of     
,watt1 and to comprehend the ,pg#jih    
structure and operation of the steam    
engine in its improved form1 as it has  
passed to us from his hands4  ,as we    
shall frequently have occasion to refer 
to the indications of a thermometer1 we 
shall first explain the principle of    
that instrument as it is commonly used  
in this country4  ,the thermometer is an
 instrument used for the purpose of     
measuring and indicating the temperature
 or sensible heat of material           
substances4  ,heat1 like all other      
physical agents1 can only be measured by
 its effects4 ,one of these effects best
 suited for this purpose1 is the change 
of dimension which all bodies undergo in
 consequence of their change of         

temperature4 ,in general1 when heat is  
applied to a material substance1 that   
substance undergoes an enlargement of   
bulk2 and if heat be abstracted from it1
 it suffers a diminution of bulk4 ,this 
variation of magnitude is not always in 
the same proportion as the increase or  
diminution of temperature2 but it is so 
when applied to certain substances and  
between certain limits4 ,one of the     
substances whose expansion and          
contraction through an extensive range  
of temperature has been found to be     
nearly uniform1 and which is attended   
with other convenient qualities for a   
thermometer1 is the liquid called       
mercury or quicksilver4 ,a mercurial    
thermometer is constructed in the       
following way3--  ,a glass tube is made 
with a small and uniform bore3 upon the 
end of this tube1 a bulb is blown1      
having a magnitude very great compared  
with the bore of the tube4 ,let us      
suppose this bulb and a part of the tube
 to be filled with mercury4 ,if the     

mercury contained in the bulb be heated1
 it will expand1 and being more         
susceptible of expansion than the glass 
which contains it1 the bulb will be too 
small for its augmented volume3 the     
mercury in the bulb can only1 therefore1
 obtain room for its increased bulk by  
pressing the mercury in the tube        
upwards1 which it will accordingly do4  
,the increase of volume which the       
mercury in the bulb therefore undergoes1
 will be exhibited by the increased     
length of the column in the tube4 ,since
 the bore of the tube is made so        
exceedingly minute compared with the    
magnitude of the bulb1 a very small     
quantity of mercury forced ,pg#jii from 
the bulb into the tube1 will cause a    
considerable increase of the length of  
the column4 ,small degrees of expansion 
will therefore be rendered very         
apparent1 and may be accurately         
measured4 ,the following is the method  
by which the thermometer called         
,fahrenheit's thermometer is graduated4 

,the tube and bulb being prepared and   
supplied with mercury1 as already       
explained1 let the instrument be plunged
 in a vessel of melting ice4 ,it will be
 found that the mercury will stand in   
the tube at a certain point1 from which 
it will not vary so long as any ice     
remains not completely melted in the    
vessel4 ,let a mark be made on the tube1
 or on a scale attached to the tube1 at 
the point corresponding to the top of   
the column3 the point thus marked is    
called the freezing point4  ,now let the
 instrument be immersed in a vessel of  
boiling water1 the barometer at the time
 having the height of thirty inches4 ,it
 will be found that so long as the water
 is kept boiling1 the column of mercury 
in the tube will remain stationary4 ,let
 the point corresponding with the top of
 the column be marked on the tube1 or on
 the scale attached to it4 ,this is     
called the boiling point4 ,let the space
 on the scale between the freezing and  
boiling points be now divided into #ahj 

equal parts3 each of these parts is     
called a degree4 ,let the same divisions
 be continued upon the scale below the  
freezing point1 until thirty-two        
divisions be taken2 let the lowest      
division be then marked #j1 and let the 
successive divisions upwards from that  
be numbered #a1 #b1 #c1 c4 ,in like     
manner1 let the same divisions be       
continued above the boiling point1 as   
far as the tube will admit4  ,it is     
evident that1 under these circumstances1
 the freezing point will be marked by   
#cb1 and the boiling point by #bab4 ,it 
is usual to express the degrees of a    
thermometer in the same manner as the   
degrees of a circle1 by placing a small 
above the number4 ,thus the freezing    
point is expressed by #cb1 and the      
boiling point by #bab4  ,the reason the 
degrees were commenced at #cb below the 
freezing point was1 because1 when the   
thermometer was invented1 that          
temperature was supposed to be the      
lowest degree of cold possible1 being   

that of a certain mixture of ,pg#ajj    
snow and salt4 ,this1 however1 has since
 been found to be an error1 very much   
lower temperatures being obtained by    
various physical expedients4  ,the      
temperature of a body is1 then1 that    
elevation to which the thermometer would
 rise when immersed in that body4 ,thus1
 if in plunging the thermometer in water
 we found the mercury to rise or fall to
 the division marked #ajj1 we should    
then say1 the temperature of the water  
was #ajj4  ,let us suppose a spirit     
lamp1 or other regular source of heat1  
applied to a bath of mercury1 so as to  
maintain the mercury at a fixed         
temperature of #bjj1 and let another    
vessel1 containing a quantity of ice at 
a temperature of #bj be immersed in the 
mercury4 ,let a thermometer be placed in
 the mercury1 and another in the ice4   
,the following effects will then ensue4 
,the thermometer immersed in the ice    
will be observed gradually to rise from 
#bj upwards1 until it indicates the     

temperature of #cb4 ,it will then become
 stationary1 and the ice which had      
hitherto remained in a solid state will 
begin to melt and be converted into     
water4 ,this process of liquefaction    
will continue for a considerable time1  
during which the thermometer immersed in
 the ice will constantly be maintained  
at #cb4 ,at the moment1 however1 when   
the last portion of ice is liquefied1   
the thermometer will begin again to     
rise4 ,the coincidence of this ascent of
 the thermometer with the completion of 
the liquefaction of the ice1 may be very
 easily observed1 because the ice being 
lighter1 bulk for bulk1 than water1 will
 float on the surface1 and so long as a 
particle of it remains unmelted it will 
be distinctly seen4  ,now it cannot be  
doubted that1 during the whole of this  
process1 the mercury1 supposed to be    
maintained at #bjj1 constantly imparts  
heat to the ice2 yet1 from the moment   
the liquefaction begins1 until it is    
completed1 no increased temperature is  

exhibited by the thermometer immersed in
 the melting ice4 ,if during this part  
of the process no heat were received by 
the ice from the mercury1 the           
consequence would be1 that the          
application of the lamp would cause the 
temperature of the mercury to rise above
 #bjj1 which may be easily demonstrated 
by withdrawing the vessel of ice from   
the mercurial bath during the process of
 liquefaction4 ,the moment ,pg#aja it is
 withdrawn1 the thermometer immersed in 
the mercury1 instead of remaining fixed 
at #bjj1 will begin to rise1 although   
the action of the lamp remains the same 
as before2 from which it is evident that
 the heat which now causes the mercury  
to rise above #bjj was before received  
by the melting ice4  ,the heat which    
thus enters ice in the process of       
liquefaction1 and which is not indicated
 by the thermometer1 is for this reason 
called latent heat4 ,it will be         
perceived that this phrase is the name  
of a fact1 and not of an hypothesis4    

,that heat really enters the water1 and 
is contained in it1 has been established
 by the experiments2 and to declare that
 it is present there1 is to declare an  
established fact4 ,to call it by the    
name latent heat1 is to declare another 
established fact1 viz41 that it is not  
sensible to the thermometer4  ,these    
facts show us that heat is capable of   
existing in bodies in two distinct      
states1 in one of which it is sensible  
to the thermometer1 and in the other    
not4 ,heat which is sensible to the     
thermometer is called1 for distinction1 
sensible or free heat4 ,it may be here  
observed1 that heat which is sensible to
 the thermometer is also perceptible by 
the senses1 and heat not sensible to the
 thermometer is not perceptible by the  
senses4 ,thus1 ice at #cb and water at  
#cb feel equally cold1 and yet we have  
seen that the latter contains           
considerably more heat than the former4 
,dr4 ,black1 who first noticed the      
remarkable fact to which we have now    

alluded1 inferred that ice is converted 
into water by communicating to it a     
certain quantity or dose of heat1 which 
enters into combination with it in a    
manner analogous to that which takes    
place when bodies combine chemically4   
,the heat1 thus combined with the solid 
ice1 loses its property of affecting the
 senses or the thermometer1 and the     
effects therefore bear a resemblance to 
those cases of chemical combination in  
which the constituent elements change   
their sensible properties when they form
 the compound4  ,the fact that the      
thermometer immersed in the ice remains 
stationary only as long as the process  
of liquefaction is going on1 shows that 
this absorption of heat is necessarily  
connected with that process1 and that1  
were it not for the conversion of       
,pg#ajb the solid ice into liquid water1
 the heat which is so received would be 
sensible1 and would cause the           
thermometer immersed in the ice to rise4
 ,before the time of ,black it was      

supposed that the slightest addition of 
heat would cause solid ice to be        
converted into water1 and that the      
thermometer would immediately pass from 
the freezing temperature to higher      
degrees4 ,the experiments above         
described1 however1 show the falsehood  
of such a supposition4 ,if1 while the   
mercurial bath1 in which the ice is     
immersed1 is maintained at the          
temperature of #bjj1 the length of time 
necessary to complete the liquefaction  
of the ice be observed1 it would be     
found that that time is about           
twenty-eight times the length of time   
which it would take to raise the liquid 
water from #cb to #cg2 and if it be     
assumed that the same quantity of heat  
is imparted to the ice1 during the      
process of liquefaction1 during each    
minute1 as is imparted to the water1    
during each minute1 in rising from #cb  
to #cg1 it will follow1 that to liquefy 
the ice requires twenty-eight times as  
much heat as is necessary to raise the  

water from #cb to #cg4 ,it appears1     
therefore1 that1 instead of a small     
quantity of heat being necessary to melt
 the ice1 a very considerable portion is
 absorbed in that process4  ,having     
ascertained the remarkable fact1 that   
heat is absorbed in a large quantity in 
the conversion of ice into water1       
without rendering the body so absorbing 
it warmer1 let us now inquire what the  
exact quantity of heat so absorbed is4  
,we have already stated that1 if the    
quantity communicated in equal times be 
the same1 the heat necessary to liquefy 
a given weight of ice would be          
twenty-eight times as much as would be  
necessary to raise the same weight of   
water from #cb to #cg2 or1 if the heat  
necessary to raise water through every  
#e be the same1 that quantity of heat   
would be sufficient to raise water from 
#cb to #agb3 and hence we infer1 that as
 much heat is absorbed in the           
liquefaction of a given quantity of ice 
as would raise the same quantity of     

water through #adj degrees of the       
thermometric scale4   7#eb47 ,let us now
 examine the analogous effects produced 
by the continued application of heat to 
water in the liquid state4  ,let a small
 quantity of water be placed in a glass 
flask of considerable size1 and then    
closed so as to prevent the escape      
,pg#ajc of any vapour4 ,let this vessel 
be now placed over the flame of a spirit
 lamp1 so as to cause the water it      
contains to boil4 ,for a considerable   
time the water will be observed to boil1
 and apparently to diminish in quantity1
 until at length all the water          
disappears1 and the vessel is apparently
 empty4 ,if the vessel be now removed   
from the lamp1 and suspended in a cool  
atmosphere1 the whole of the interior of
 its surface will presently appear to be
 covered with a dewy moisture2 and at   
length a quantity of water will collect 
in the bottom of it1 equal to that which
 had been in it at the commencement of  
the process4 ,that no water has at any  

period of the experiment escaped from   
it1 may be easily determined1 by        
performing the experiment with the glass
 flask suspended from the arm of a      
balance1 counterpoised by a sufficient  
weight suspended from the other arm4    
,the equilibrium will be preserved      
throughout1 and the vessel will be found
 to have the same weight1 when to all   
appearance it is empty1 as when it      
contains the liquid water4 ,it is       
evident1 therefore1 that the water      
exists in the vessel in every stage of  
the process1 but that it becomes        
invisible when the process of boiling   
has continued for a certain length of   
time2 and it may be shown that it will  
continue to be invisible1 provided the  
flask be exposed to a temperature       
considerably elevated4 ,thus1 for       
example1 if it be suspended in a vessel 
of boiling water1 the water which it    
contains will continue to be invisible2 
but the moment it is withdrawn from the 
boiling water1 and exposed to the cold  

air1 the water will again become        
visible1 as above mentioned1 forming a  
dew on the inner surface1 and finally   
collecting in the bottom1 as in the     
commencement of the experiment4  ,in    
fact1 the liquid has1 by the process of 
boiling1 been converted into vapour1 or 
steam1 which is a body similar in its   
leading properties to common air1 and1  
like it1 is invisible4 ,it will         
hereafter appear that it likewise       
possesses the property of elasticity1   
and other mechanical qualities enjoyed  
by gases in general4   7#ec47 ,again1   
let an open vessel be filled with water 
at #fj1 and placed in a mercurial bath1 
which is maintained1 by a fire or lamp  
applied to it1 at the temperature of    
#bcj4 ,place a thermometer in the water1
 and it will be observed gradually to   
,pg#ajd rise as the temperature of the  
water is increased by the heat which it 
receives from the mercury in which it is
 immersed4 ,the water will steadily rise
 in this manner until it attains the    

temperature of #bab2 but here the       
thermometer immersed in it will become  
stationary4 ,at the same time the water 
contained in the vessel will become     
agitated1 and its surface will present  
the same appearance as if bubbles of air
 were rising from the bottom1 and       
issuing at the top4 ,a cloudy vapour    
will be given off in large quantities   
from its surface4 ,this process is      
called ebullition or boiling4 ,if it be 
continued for any considerable time1 the
 quantity of water in the vessel will be
 sensibly diminished2 and at length     
every particle of it will disappear1 and
 the vessel will remain empty4 ,during  
the whole of this process1 the          
thermometer immersed in the water will  
remain stationary at #bab4  ,now1 it    
will be asked1 what has become of the   
water8 ,it cannot be imagined that it   
has been annihilated4 ,we shall be able 
to answer this by adopting means to     
prevent the escape of any particle of   
matter from the vessel containing the   

water1 into the atmosphere or elsewhere4
 ,let us suppose that the top of the    
vessel containing the water is closed1  
with the exception of a neck            
communicating with a tube1 and let that 
tube be carried into another close      
vessel removed from the cistern of      
heated mercury1 and plunged in another  
cistern of cold water4 ,such an         
apparatus is represented in fig4 #ae4   
,illustration3 ,fig4 #ae4  ,a is a      
cistern of heated mercury1 in which the 
glass vessel ,b1 containing water1 is   
immersed4 ,from the top of the vessel ,b
 proceeds a glass tube ,c1 inclining    
downwards1 and entering a glass vessel  
,d1 which is immersed in a cistern ,e of
 cold water4 ,if the process already    
described be continued until the water  
by constant ebullition has disappeared1 
as already mentioned1 ,pg#aje from the  
vessel ,b1 it will be found that a      
quantity of water will be collected in  
the vessel ,d2 and if this water be     
weighed1 it will be found to have       

exactly the same weight as the water had
 which was originally placed in the     
vessel ,b4 ,it is1 therefore1 quite     
apparent that the water has passed by   
the process of boiling from the one     
vessel to the other2 but1 in its        
passage1 it was not perceptible by the  
sight4 ,the tube ,c and the upper part  
of the vessel ,b1 had the same          
appearance1 exactly1 as if they had been
 filled with atmospheric air4 ,that they
 are not merely filled with atmospheric 
air may1 however1 be easily proved4     
,when the process of boiling first      
commences1 it will be found that the    
tube ,c is cold1 and the inner surface  
dry4 ,when the process of ebullition has
 continued a short time1 the tube ,c    
will become gradually heated1 and the   
inner surface of it covered with        
moisture4 ,after a time1 however1 this  
moisture disappears1 and the tube       
attains the temperature #bab4 ,in this  
state it continues until the whole of   
the water is discharged from the vessel 

,b to the vessel ,d4   7#ed47 ,these    
effects are easily explained4 ,the water
 in the vessel ,b is incapable of       
receiving any higher temperature than   
#bab1 consistently with its retaining   
the liquid form4 ,small portions1       
therefore1 are constantly converted into
 steam by the heat received from the    
surrounding mercury1 and bubbles of     
steam are formed on the bottom and sides
 of the vessel ,b4 ,these bubbles1 being
 very much lighter1 bulk for bulk1 than 
water1 rise rapidly through the water1  
just in the same manner as bubbles of   
air would1 and produce that peculiar    
agitation at its surface which has been 
taken as the external indication of     
boiling4 ,they escape from the surface1 
and collect in the upper part of the    
vessel4 ,the steam thus collected1 when 
it first enters the tube ,c1 is cooled  
below the temperature of #bab by the    
surface of the tube2 and consequently1  
being incapable of remaining in the     
state of vapour at any lower temperature

 than #bab1 it is reconverted into      
water1 and forms the dewy moisture which
 is observed in the commencement of the 
process on the interior of the tube ,c4 
,at length1 however1 the whole of the   
tube ,c is heated to the temperature of 
#bab1 and the moisture which was        
previously collected upon its inner     
,pg#ajf surface is again converted into 
steam4 ,as the quantity of steam evolved
 from the water in ,b increases1 it     
drives before it the steam previously   
collected in the tube ,c1 and forces it 
into the vessel ,b4 ,here it encounters 
the inner surface of this vessel1 which 
is kept constantly cold by being        
surrounded with the cold water in which 
it is immersed2 and the vapour1 being   
thus immediately reduced below the      
temperature of #bab1 is reconverted into
 water4 ,at first it collects in a dew  
on the surface of the vessel ,d2 but as 
this accumulates1 it drops into the     
bottom of the vessel1 and forms a more  
considerable quantity4 ,as the quantity 

of water is observed to be gradually    
diminished in the vessel ,b1 the        
quantity will be found to be gradually  
increased in the vessel ,d2 and if the  
operation be suspended at any stage of  
the process1 and the water in the two   
vessels weighed1 it will be found that  
the weight of the water in ,d is exactly
 equal to the weight which the water in 
,b has lost4   7#ee47 ,the demonstration
 is1 therefore1 perfect1 that the       
gradual diminution of the boiling water 
in the vessel ,b is produced by the     
conversion of that water into steam by  
the heat4 ,in the process first         
described1 when the top of the vessel ,b
 was supposed to be open1 this steam    
made its escape into the air1 where it  
was first dispersed1 and subsequently   
cooled in separate particles1 and was   
deposited in minute globules of moisture
 on the ground and on surrounding       
objects4   7#ef47 ,in reviewing this    
process1 we are struck by the fact1 that
 the continued application of heat to   

the vessel ,b is incapable of raising   
the temperature of the water contained  
in it above #bab4 ,this presents an     
obvious analogy to the process of       
liquefaction1 and leads to inquiries of 
a similar nature1 which are attended    
with a like result4 ,we must either     
infer1 that the water1 having arrived at
 #bab1 received no more heat from the   
mercury2 or that such heat1 if received1
 is incapable of affecting the          
thermometer2 or1 finally1 that the steam
 which passes off carries this heat with
 it4 ,that the water receive heat from  
the mercury1 will be proved by the fact1
 that1 if the vessel ,b be removed from 
the mercury1 other things remaining as  
before1 the temperature of the mercury  
will rapidly rise1 and if the fire be   
continued1 it will even boil2 but so    
long as the ,pg#ajg vessel ,b remains   
immersed1 it prevents the mercury from  
increasing in temperature4 ,it therefore
 receives that heat which would         
otherwise raise the temperature of the  

quicksilver4  ,illustration3 ,fig4 #af4 
,if a thermometer be immersed in the    
steam which collects in the upper part  
of the vessel ,b1 it will show the same 
temperature 7of #bab7 as the water from 
which it is raised4 ,the heat1          
therefore1 received from the mercury1 is
 clearly not imparted in a sensible form
 to the steam1 which has the same       
temperature in the form of steam as it  
had in the form of water4 ,what has been
 already explained respecting           
liquefaction would lead us1 by analogy1 
to suspect that the heat imparted by the
 mercury to the water has become latent 
in the steam1 and is instrumental to the
 conversion of water into steam1 in the 
same manner as heat has been shown to be
 instrumental to the conversion of ice  
into water4 ,as the fact was in that    
case detected by mixing ice with water1 
so we shall1 in the present instance1   
try it by a like test1 viz4 by mixing   
water with steam4 ,let about five ounces
 and a half of water1 at the temperature

 of #cb1 be placed in a vessel ,a 7fig4 
#af471 and let another vessel ,b1 in    
which water is kept constantly boiling  
at the temperature of #bab1 communicate 
with ,a by a pipe ,c proceeding from the
 top1 so that the steam may be conducted
 from ,b1 and escape from the mouth of  
the pipe at some depth below the surface
 of the water in ,a4 ,as the steam      
issues from the pipe1 it will be        
immediately reconverted into water by   
the cold water which it encounters2 and1
 by continuing this process1 the water  
in ,a will be gradually heated by the   
steam combined with it and received     
through the pipe ,c4 ,if this process be
 continued until the water in ,a is     
raised to the temperature of #bab1 it   
will boil4 ,let it then be weighed1 and 
it will be found to weigh six ounces and
 a half3 from whence we infer1 that one 
ounce of water has been received from   
the vessel ,b in the form of steam1 and 
has been reconverted into water by the  
inferior temperature of the water in ,a4

 ,now1 this ounce of water received in  
the form of steam into the vessel ,a    
had1 when in that form1 the temperature 
of #bab4 ,it is now ,pg#ajh converted   
into the liquid form1 and still retains 
the same temperature of #bab2 but it has
 caused the five ounces and a half of   
water with which it has been mixed1 to  
rise from the temperature of #cb to the 
temperature of #bab1--;and this1 without
 losing any temperature itself4 ,it     
follows1 therefore1 that1 in returning  
to the liquid state1 it has parted with 
as much heat as is capable of raising   
five times and a half its own weight of 
water from #cb to #bab4 ,this heat was  
combined with the steam1 though not     
sensible to the thermometer2 and was1   
therefore1 latent4 ,had it been sensible
 in the water in ,b1 it would have      
caused the water to have risen through a
 number of thermometric degrees1        
amounting to five times and a half the  
excess of #bab above #cb2 that is1      
through five times and a half #ahj2 for 

it has caused five times and a half its 
own weight of water to receive an equal 
increase of temperature4 ,but five times
 and a half #ahj is #iij1 or1 to use    
round numbers 7for minute accuracy is   
not here our object71 #ajjj4 ,it        
follows1 therefore1 that an ounce of    
water1 in passing from the liquid state 
at #bab to the state of steam at #bab1  
receives as much heat as would be       
sufficient to raise it through #ajjj    
thermometric degrees1 if that heat1     
instead of becoming latent1 had been    
sensible4   7#eg47 ,in order to derive  
all the knowledge from these experiments
 which they are capable of imparting1 it
 will be necessary to examine very      
carefully how water comports itself     
under a variety of different            
circumstances4  ,if water be boiled in  
an open vessel1 with a thermometer      
immersed1 on different days1 it will be 
observed that the fixed temperature     
which it assumes in boiling will be     
subject to a variation within certain   

small limits4 ,thus1 at one time1 it    
will be found to boil at the temperature
 of #baj2 while1 at others1 the         
thermometer immersed in it will rise to 
#bac2 and1 on different occasions1 it   
will fix itself at different points     
within these limits4 ,it will also be   
found1 if the same experiment be        
performed at the same time in distant   
places1 that the boiling points will be 
subject to a like variation4 ,now1 it is
 natural to inquire what cause produces 
this variation2 and we shall be led to  
the discovery of the cause1 by examining
 what other physical effects undergo a  
simultaneous change4 ,pg#aji  ,if we    
observe the height of the barometer at  
the time of making each experiment1 we  
shall find a very remarkable            
correspondence between it and the       
boiling temperature4 ,invariably1       
whenever the barometer stands at the    
same height1 the boiling temperature    
will be the same4 ,thus1 if the         
barometer stands at #cj inches1 the     

boiling temperature will be #bab4 ,if   
the barometer fall to #bi-a_/b inches1  
the thermometer stands at a small       
fraction above #baa4 ,if the barometer  
rise to #cj-a_/b inches1 the boiling    
temperature rises to nearly #bac4 ,the  
variation in the boiling temperature is1
 then1 accompanied by a variation in the
 pressure of the atmosphere indicated by
 the barometer2 and it is constantly    
found that the boiling point will remain
 unchanged1 so long as the atmospheric  
pressure remains unchanged1 and that    
every increase in the one causes a      
corresponding increase in the other4    
7#eh47 ,from these facts it must be     
inferred1 that the pressure excited on  
the surface of the water has a tendency 
to resist its ebullition1 and to make it
 necessary1 before it can boil1 that it 
should receive a higher temperature2    
and1 on the contrary1 that every        
diminution of pressure on the surface of
 the water will give an increased       
facility to the process of ebullition1  

or will cause that process to take place
 at a lower temperature4 ,as these facts
 are of the utmost importance in the    
theory of heat1 it may be useful to     
verify them by direct experiment4  ,if  
the variable pressure excited on the    
surface of the water by the atmosphere  
be the cause of the change in the       
boiling temperature1 it must happen1    
that any change of pressure produced by 
artificial means on the surface of the  
water must likewise change the boiling  
point1 according to the same law4 ,thus1
 if a pressure considerably greater than
 the atmospheric pressure be excited on 
a liquid1 the boiling point may be      
expected to rise considerably above     
#bab2 and1 on the other hand1 if the    
surface of the water be relieved from   
the pressure of the atmosphere1 and be  
submitted to a considerably diminished  
pressure1 the water would boil below    
#bab4  ,illustration3 ,fig4 #ag4  ,let  
,b 7fig4 #ag47 be a strong spherical    
vessel of brass1 supported on a stand   

,s1 under which is placed a large spirit
 lamp ,l1 or other means of heating it4 
,in the top of this vessel are three    
apertures1 in two of which are screwed a
 ,pg#aaj thermometer ,t1 the bulb of    
which enters the hollow brass sphere1   
and a stop-cock ,c1 which may be closed 
or opened at pleasure1 to confine the   
steam1 or allow it to escape4 ,in the   
third aperture at the top1 is screwed a 
long barometer tube1 open at both ends4 
,the lower end of this tube extends     
nearly to the bottom of the spherical   
vessel ,b4 ,in the bottom of this vessel
 is placed a quantity of mercury1 the   
surface of which rises to some height   
above the lower end of the tube ,a4     
,over the mercury is poured a quantity  
of water1 so as to half fill the vessel 
,b4 ,matters being thus arranged1 the   
screws are made tight1 so as to confine 
the water1 and the lamp is allowed to   
act on the vessel2 the temperature of   
the water is raised1 and steam is       
produced1 which1 being confined within  

the vessel1 exerts its pressure on the  
surface of the water1 and resists its   
ebullition4 ,the pressure of the steam  
acting on the surface of the water is   
communicated to the surface of the      
mercury1 and it forces a portion of the 
mercury into the tube ,a1 which         
presently rises above the point where   
the tube is screwed into the top of the 
vessel ,b4 ,as the action of the lamp   
continues1 the thermometer ,t exhibits a
 gradually increasing temperature2 while
 the column of mercury in ,a shows the  
force with which the steam presses on   
the surface of the water in ,b1--this   
column being balanced by the pressure of
 the steam4 ,thus1 the temperature and  
pressure of the steam at the same moment
 may always be observed by inspecting   
the thermometer ,t and the tube ,a4     
,when the column in the tube ,a has     
risen to the height of #cj inches above 
the level of the mercury in the vessel  
,b1 then the pressure of the steam will 
be equivalent to double the pressure of 

the atmosphere1 because1 the tube ,a    
being open at the top1 the atmosphere   
presses on the ,pg#aaa surface of the   
mercury in it4 ,the thermometer ,t will 
be observed gradually to rise until it  
attains the temperature of #bab2 but it 
will not stop there1 as it would do if  
immersed in water boiled in an open     
vessel4 ,it will1 on the other hand1    
continue to rise2 and when the column of
 mercury in ,a has attained the height  
of #cj inches1 the thermometer ,t will  
have risen to #bea1--;being #ci above   
the ordinary boiling point4  ,during the
 whole of this process1 the surface of  
the water being submitted to a          
constantly increasing pressure1 its     
ebullition is prevented1 and it         
continues to receive heat without       
boiling4 ,that it is the increased      
pressure which resists its ebullition1  
and causes it to receive a temperature  
above #bab1 may be easily shown4 ,let   
the stop-cock ,c be opened2 immediately 
the steam in ,b1 having a pressure      

considerably greater than that of the   
atmosphere1 will rush out1 and will     
continue to issue from ,c1 until its    
pressure is balanced by the atmosphere4 
,at the same time the column of mercury 
in ,a will be observed rapidly to fall1 
and to sink below the orifice by which  
it is inserted in the vessel ,b4 ,the   
thermometer ,t will also fall until it  
attains the temperature of #bab4 ,at    
that point1 however1 it will remain     
stationary2 and the water will now be   
distinctly heard to be in a state of    
rapid ebullition4 ,if the stop-cock ,c  
be once more closed1 the thermometer    
will begin to rise1 and the column of   
mercury ascending in ,a will be again   
visible4  ,if1 instead of a stop-cock   
being at ,c1 the aperture were made to  
communicate with a valve1 like the      
safety-valve of a steam engine1 loaded  
with a certain weight1--say at the rate 
of #ae lbs4 on the square inch1--then   
the thermometer ,t1 and the mercury in  
the tube ,a1 would not rise indefinitely

 as before4 ,the thermometer would      
continue to rise till it attained the   
temperature of #bea2 and the mercury in 
the tube ,a would rise to the height of 
#cj inches4 ,at this limit the          
resistance of the valve would be        
balanced by the pressure of the steam2  
and as fast as the water would have a   
tendency to produce steam of a higher   
pressure1 the valve would be raised and 
the steam suffered to escape2 the       
thermometer ,t and the column of mercury
 in ,a remaining stationary during this 
process4 ,if the valve were loaded more 
heavily1 the phenomena would be ,pg#aab 
the same1 only that the mercury in ,t   
and ,a would become stationary at       
certain heights4 ,but1 on the other     
hand1 if the valve were loaded at a less
 pressure than #ae lbs4 on the square   
inch1 then the mercury in the two tubes 
would become stationary at lower points4
   7#ei47 ,these experiments show that  
every increase of pressure above the    
ordinary pressure of the atmosphere     

causes an increase in the temperature at
 which water boils4 ,we shall now       
inquire whether a diminution of pressure
 will produce a corresponding effect on 
the boiling point4  ,this may be easily 
accomplished by the aid of an air pump4 
,let water at the temperature of #bjj be
 placed in a glass vessel under the     
receiver of an air pump1 and let the air
 be gradually withdrawn4 ,after a few   
strokes of the pump1 the water will     
boil2 and if the mercurial gauge of the 
pump be observed1 it will be found that 
its altitude will be about #bc-a_/b     
inches4 ,thus the pressure to which the 
water is submitted has been reduced from
 the ordinary pressure of the atmosphere
 expressed by the column of #cj inches  
of mercury1 to a diminished pressure    
expressed by #bc-a_/b inches2 and we    
find that the temperature at which the  
water boils has been lowered from #bab  
to #bjj4 ,let the same experiment be    
repeated with water at the temperature  
of #ahj1 and it will be found that a    

further rarefaction of the air is       
necessary1 but the water will at length 
boil4 ,if the gauge of the pump be now  
observed1 it will be found to stand at  
about fifteen inches1 showing1 that at  
the temperature of #ahj water will boil 
under half the ordinary pressure of the 
atmosphere4 ,these experiments may be   
varied and repeated2 and it will be     
always found1 that1 as the pressure is  
diminished or increased1 the temperature
 at which the water will boil will be   
also diminished or increased4   7#fj47  
,the same effects may be exhibited in a 
striking manner without an air pump1 by 
producing a vacuum by the condensation  
of steam4 ,let a small quantity of water
 be placed in a thin glass flask1 and   
let it be boiled by holding it over a   
spirit lamp4 ,when the steam is observed
 to issue abundantly from the mouth of  
the flask1 let it be quickly corked and 
removed from the lamp4 ,the process of  
boiling will then cease1 and the water  
will become quiescent2 but if the flask 

be plunged ,pg#aac in a vessel of cold  
water1 the water it contains will again 
pass into a state of violent ebullition1
 thus exhibiting the singular fact of   
water being boiled by cooling it4 ,this 
effect is produced by the cold medium in
 which the flask is immersed1 causing   
the steam above the surface of the water
 in it to be condensed1 and therefore   
relieving the water from its pressure4  
,the water1 under these circumstances1  
boils at a lower temperature than when  
submitted to the pressure of the        
uncondensed vapour4   7#fa47 ,there is  
no limit to the temperature to which    
water may be raised1 if it be submitted 
to a sufficient pressure to resist its  
tendency to take the vaporous form4 ,if 
a strong metallic vessel be nearly      
filled with water1 so as to prevent the 
liquid from escaping by any force which 
it can exert1 the water thus inclosed   
may be heated to any temperature        
whatever without boiling2 in fact1 it   
may be made red-hot2 and the temperature

 to which it may be raised will have no 
limit1 except the strength of the vessel
 containing it1 or the point at which   
the metal of which it is formed may     
begin to soften or to be fused4   7#fb47
 ,the following table will show the     
temperature at which water will boil    
under different pressures of the        
atmosphere corresponding to the         
altitudes of the barometer between #bf  
and #ca inches4    ,barometer4          
,boiling ,point4     #bf  inches        
#bjdia     #bfe             #bjegi      
#bg               #bjffg     #bge       
#bjgee     #bh               #bjhdc     
#bhe             #bjica     #bi         
#bajai     #bie             #baajg      
#cj               #bab     #cje         
#babhh     #ca               #bacgf     
,from this table it appears1 that1 for  
every tenth of an inch which the        
barometric column varies between these  
limits1 the boiling temperature changes 
by the fraction of a degree expressed by
 the decimal #agf1 or nearly by the     

vulgar fraction #a_/f4   7#fc47 ,in the 
experiment already described1 by which  
the latent ,pg#aad heat of steam was    
determined1 the water was supposed to be
 boiled under the ordinary pressure of  
the atmosphere4 ,having seen1 however1  
that water may boil at different        
temperatures1 under different pressures1
 the inquiry presents itself1 whether   
the heat absorbed in vaporisation at    
different temperatures1 and under       
different pressures1 is subject to any  
variation8 ,experiments of the same     
nature as those already described1      
instituted upon water in a state of     
ebullition at different temperatures1 as
 well below as above #bab1 have led to  
the discovery of a very remarkable fact 
in the theory of vapour4 ,it has been   
found that the heat absorbed by         
vaporisation is always less1 the higher 
the temperature at which the ebullition 
takes place2 and less1 by the same      
amount as the temperature of ebullition 
is increased4 ,thus1 if water boil at   

#cab1 the heat absorbed in ebullition   
will be less by #ajj than if it boiled  
at #bab2 and again1 if water be boiled  
under a diminished pressure1 at #aab1   
the heat absorbed in vaporisation will  
be #ajj more than the heat absorbed by  
water boiled at #bab4 ,it follows1      
therefore1 that the actual consumption  
of heat in the process of vaporisation  
must be the same1 whatever be the       
temperature at which the vaporisation   
takes place2 for whatever heat is saved 
in the sensible form1 is consumed in the
 latent form1 and vice vers4  ,let us   
suppose a given weight of water at the  
temperature of #cb to be exposed to any 
regular source by which heat may be     
supplied to it4 ,if it be under the     
ordinary atmospheric pressure1 the first
 #ahj of heat which it receives will    
raise it to the boiling point1 and the  
next #ajjj will convert it into steam4  
,thus1 in addition to the heat which it 
contains at #cb1 the steam at #bab      
contains #aahj of heat4 ,but if the same

 water be submitted to a pressure equal 
to half the atmospheric pressure1 then  
the first #adh of heat which it receives
 will cause it to boil1 and the next    
#ajcb will convert it into vapour4      
,thus1 steam at the temperature of #ahj 
contains a quantity of heat more than   
the same quantity of water at #cb1 by   
#ajcb added to #adh1 which gives a sum  
of #aahj4 ,steam1 therefore1 raised     
under the ordinary pressure of the      
atmosphere at #bab1 and steam raised    
under half that pressure at #ahj1       
contain the same quantity of heat1--with
 this difference ,pg#aae only--that the 
one has more latent heat1 and less      
sensible heat1 than the other4  ,from   
this fact1 that the sum of the latent   
and sensible heats of the vapour of     
water is constant1 it follows that the  
same quantity of heat is necessary to   
convert a given weight of water into    
steam1 at whatever temperature1 or under
 whatever pressure1 the water may be    
boiled4 ,it follows1 also1 that1 in the 

steam engine1 equal weights of          
high-pressure and low-pressure steam are
 produced by the same consumption of    
fuel2 and that1 in general1 the         
consumption of fuel is proportional to  
the quantity of water vaporised1        
whatever the pressure of the steam may  
be4#ah   7#fd47 ,having explained the   
conditions under which1 by supplying    
heat to water1 it is converted into     
steam1 and1 by abstracting heat from    
steam1 it may be reconverted into water1
 let us now consider the mechanical     
force which is developed in these       
phenomena4  ,illustration3 ,fig4 #ah4   
,let ,a ,b 7fig4 #ah47 be a tube1 or    
cylinder1 the base of which is equal to 
a square inch1 and let a piston ,p move 
in it so as to be steam-tight4 ,let it  
be supposed1 that under this piston     
there is1 in the bottom of the cylinder1
 a cubic inch of water between the      
bottom of the piston and the bottom of  
the tube2 let the piston be             
counterbalanced by a weight ,w acting   

over a pulley1 which will be just       
sufficient to counterpoise the weight of
 the piston1 so as leave no force       
tending to keep the piston down1 except 
the force of the atmosphere acting above
 it4 ,under the circumstances here      
supposed1 the piston being in contact   
with the water1 and all air being       
excluded1 it will be pressed down by the
 weight of the atmosphere1 which we will
 suppose to be fifteen pounds1 the      
magnitude of the piston being a square  
inch4 ,pg#aaf  ,now let the flame of a  
lamp be applied at the bottom of the    
tube2 the water under the piston having 
its temperature thereby gradually       
raised1 and being submitted to no       
pressure save that of the atmosphere    
above the piston1 it will begin to be   
converted into steam when it has        
attained the temperature of #bab4       
,according as it is converted into      
steam1 it will cause the piston to      
ascend in the tube until all the water  
has been evaporated4 ,if the tube were  

constructed of sufficient length1 the   
piston then would be found to have risen
 to the height of about seventeen       
hundred inches1 or one hundred and      
forty-two feet2 since1 as has been      
already explained1 water passing into   
steam under the ordinary pressure of the
 atmosphere undergoes an increase of    
bulk in the proportion of about         
seventeen hundred to one4  ,now in this 
process1 the air above the piston1 which
 presses on it with a force equal to    
fifteen pounds1 has been raised one     
hundred and forty-two feet4 ,it appears1
 therefore1 that1 by the evaporation of 
a cubic inch of water under a pressure  
equal to fifteen pounds per square inch1
 a mechanical force of this amount is   
developed4  ,it is evident that fifteen 
pounds raised one hundred and forty-two 
feet successively1 is equivalent to one 
hundred and forty-two times fifteen     
pounds raised one foot4 ,now1 one       
hundred and forty-two times fifteen is  
two thousand one hundred and thirty1 and

 therefore the force thus obtained is   
equal to two thousand one hundred and   
thirty pounds raised one foot high4     
,this being within about #aaj pounds of 
a ton1 it may be stated1 in round       
numbers1 that1 by the evaporation of a  
cubic inch of water under these         
circumstances1 a force is obtained equal
 to that which would raise a ton weight 
a foot high4  ,the augmentation of      
volume which water undergoes in passing 
into steam under the pressure here      
supposed1 may be easily retained in the 
memory1 from the accidental circumstance
 that a cubic inch of water is converted
 into a cubic foot of steam1 very       
nearly4 ,a cubic foot contains one      
thousand seven hundred and twenty-eight 
cubic inches1--which is little different
 from the proportion which steam bears  
to water1 when raised under the         
atmospheric pressure4 ,pg#aag   7#fe47  
,it will1 therefore1 be an advantage to 
retain in memory the following general  
facts3--  #a4 ,a cubic inch of water    

evaporated under the ordinary           
atmospheric pressure1 is converted into 
a cubic foot of steam4  #b4 ,a cubic    
inch of water evaporated under the      
atmospheric pressure1 gives a mechanical
 force equal to what would raise about a
 ton weight a foot high4   7#ff47 ,let  
us1 again1 suppose the piston ,p 7fig4  
#bc47 to be restored to its original    
position1 with the liquid water beneath 
it2 and1 in addition to the weight of   
the atmosphere which before pressed it  
down1 let us suppose another weight of  
fifteen pounds laid upon it1 so that the
 water below shall be pressed by double 
the weight of the atmosphere4 ,if the   
lamp were now applied1 and at the same  
time a thermometer were immersed in the 
water1 it would be found that the water 
would not begin to be converted into    
steam until it attained the temperature 
of about #bej4 ,the piston would then   
begin1 as before1 to ascend1 and the    
water to be gradually converted into    
vapour4 ,the water being completely     

evaporated1 it would be found that the  
piston would be raised to a height      
little more than half its former height1
 or #gb feet4 ,the mechanical effect1   
therefore1 thus obtained1 will be       
equivalent to double the former weight  
raised half the former height4  ,in like
 manner1 if the piston were loaded with 
thirty pounds in addition to the        
atmosphere1 the whole pressure on the   
water being then three times the        
pressure first supposed1 the piston     
would be raised to somewhat more than   
one third of its first height by the    
evaporation of the water4 ,this would   
give a mechanical force equivalent to   
three times the original weight raised a
 little more than one third of the      
original height4  ,in general1 as the   
pressure on the piston is increased1 the
 height to which the piston would be    
raised by the evaporation of the water  
will be diminished in a proportion      
somewhat less than the proportion in    
which the pressure on the piston is     

increased4 ,if the temperature at which 
the water is converted into steam under 
these different pressures were the same1
 then the height to which the piston    
would be raised by the evaporation of   
the water would be diminished in        
precisely ,pg#aah the same proportion as
 the pressure on the piston is          
increased2 and1 in that case1 the whole 
mechanical force developed by the       
evaporation of the water would remain   
exactly the same under whatever pressure
 the water might be boiled4 ,we shall   
explain hereafter the extent to which   
the variation of temperature in the     
water and steam corresponding to the    
variation of pressure modifies this law2
 but1 as the effect of the difference of
 temperatures is not considerable1 it   
will be convenient to register in the   
memory the following important practical
 conclusion3--   7#fg47 ,a cubic inch of
 water converted into steam will supply 
a mechanical force very nearly equal to 
a ton weight raised a foot high2 and    

this force will not be subject to       
considerable variation1 whatever be the 
temperature or pressure at which the    
water may be evaporated4  ,illustration3
 ,,glasgow4    ,,footnotes3    #ah ,the 
preceding paragraphs1 and some other    
parts of the   present volume on the    
general properties of ,heat1 are taken  
from my ,treatise on ,heat1 in the      
,cabinet ,cyclopdia1 to   which those   
who desire more detailed explanation and
 more   copious illustration should     
refer4  ,pg#aai     ,illustration3      
,,glasgow ,,college4  ,,chap4 ,v4       
,,watt ,,finds ,,that ,,condensation    
,,in ,,the ,,cylinder ,,is              
,,incompatible     ,,with ,a ,,due      
,,economy ,,of ,,fuel4 -- ,,conceives   
,,the ,,notion ,,of     ,,condensing    
,,out ,,of ,,the ,,cylinder4 --         
,,discovers ,,separate                  
,,condensation4 -- ,,invents ,,the      
,,air-,,pump4 -- ,,substitutes ,,steam  
,,pressure ,,for ,,atmospheric          
,,pressure4 -- ,,invents ,,the ,,steam  

,,case1     ,,or ,,jacket4 -- ,,his     
,,first ,,experiments ,,to ,,realise    
,,these     ,,inventions4 -- ,,his      
,,experimental ,,apparatus4 --          
,,difficulties ,,of     ,,bringing ,,the
 ,,improved ,,engines ,,into ,,use4 --  
,,watt ,,practises ,,as ,a     ,,civil  
,,engineer4 -- ,,his ,,partnership      
,,with ,,roebuck4 -- ,,his ,,first      
,,patent4 -- ,,description ,,of ,,his   
,,single-,,acting ,,steam ,,engine4     
7#fh47 ,at the period to which we have  
now brought the history of the invention
 of the steam engine1 ,watt had         
obtained1 chiefly by his own            
experiments1 a sufficient knowledge of  
the phenomena which have been just      
explained1 to enable him to arrive at   
the conclusion that a very small        
proportion of the whole mechanical      
effect attending the evaporation was    
really rendered available by the        
atmospheric engine2 and that1 ,pg#abj   
therefore1 extensive and injurious      
sources of waste existed in its         

machinery4  ,he perceived that the      
principal source of this wasteful       
expenditure of power consisted in the   
quantity of steam which was condensed at
 each stroke of the piston1 in heating  
the cylinder previous to the ascent of  
the piston4 ,yet1 as it was evident that
 that ascent could not be accomplished  
in a cold cylinder1 it was apparent that
 this waste of power must be inevitable1
 unless some expedient could be devised1
 by which a vacuum could be maintained  
in the cylinder1 without cooling it4    
,but1 to produce such a vacuum1 the     
steam must be condensed2 and1 to        
condense the steam1 its temperature must
 be lowered to such a point that the    
vapour proceeding from it shall have no 
injurious pressure2 yet1 if condensed   
steam be contained in a cylinder at a   
high temperature1 it will return to the 
temperature of the cylinder1 recover its
 elasticity1 and resist the descent of  
the piston4  ,having reflected on these 
circumstances1 it became apparent to    

,watt1 that a vice was inherent in the  
structure of the atmospheric engine1    
which rendered a large waste of power   
inevitable2 this vice arising from the  
fact1 that the condensation of the steam
 was incompatible with the condition of 
maintaining the elevated temperature of 
the cylinder in which that condensation 
took place4 ,it followed1 therefore1    
either that the steam must be           
imperfectly condensed1 or that the      
condensation could not take place in the
 cylinder4 ,it was in #agfe1 that1      
pondering on these circumstances1 the   
happy idea occurred to him1 that the    
production of a vacuum could be equally 
effected1 though the place where the    
condensation of the steam took place    
were not the cylinder itself4 ,he saw1  
that if a vessel in which a vacuum was  
produced were put into communication    
with another containing an elastic      
fluid1 the elastic fluid would rush into
 the vacuum1 and diffuse itself through 
the two vessels2 but if1 on rushing into

 such vacuum1 this elastic fluid1 being 
vapour1 were there condensed1 or        
restored to the liquid form1 that then  
the space within the two vessels would  
be equally rendered a vacuum2--that1    
under such circumstances1 one of the    
vessels might be maintained at any      
temperature1 however high1 while ,pg#aba
 the other might be kept at any         
temperature1 however low4 ,this         
felicitous conception formed the first  
step in that splendid career of         
invention and discovery which has       
conferred immortality on the name of    
,watt4 ,he used to say1 that the moment 
the idea of separate condensation       
occurred to him1--that is1 of           
condensing1 in one vessel kept cold1 the
 steam coming from another vessel kept  
hot1--all the details of his improved   
engine rushed into his mind in such     
rapid succession1 that1 in the course of
 a day1 his invention was so complete   
that he proceeded to submit it to       
experiment4  ,illustration3 ,fig4 #ai4  

,to explain the first conception of this
 memorable invention2 let a tube or     
pipe1 ,s 7fig4 #ai471 be imagined to    
proceed from the bottom of the cylinder 
,a ,b to a vessel1 ,c1 having a         
stop-cock1 ,d1 by which the             
communication between the cylinder and  
the vessel ,c may be opened or closed at
 pleasure4 ,if we suppose the piston ,p 
at the top of the cylinder1 and the     
space below it filled with steam1 the   
cylinder and steam being at the usual   
temperature1 while the vessel ,c is a   
vacuum1 and maintained at a low         
temperature4 ,then1 on opening the cock 
,d1 the steam will rush from the        
cylinder ,a ,b through the tube ,s1 and1
 passing into the cold vessel ,c1 will  
be condensed by contact with its cold   
sides4 ,this process of condensation    
will be rendered instantaneous if a jet 
of cold water is allowed to play in the 
vessel ,c4 ,when the steam thus rushing 
into ,c1 has been destroyed1 and the    
space in the cylinder ,a ,b becomes a   

vacuum1 then the pressure of the        
atmosphere being unobstructed1 the      
piston will descend with the force due  
to the excess of the pressure of the    
atmosphere above the friction4 ,when it 
has descended1 suppose the stop-cock ,d 
closed1 and steam admitted from ,pg#abb 
the boiler through a proper cock or     
valve below the piston1 the cylinder and
 piston being still at the same         
temperature as before4 ,the steam on    
entering the cylinder1 not being exposed
 to contact with any surface below its  
own temperature1 will not be condensed1 
and therefore will immediately cause the
 piston to rise1 and the piston will    
have attained the top of the cylinder   
when as much steam shall have been      
supplied by the boiler as will fill the 
cylinder4 ,when this has taken place1   
suppose the communication with the      
boiler cut off1 and the cock ,d once    
more opened3 the steam will again rush  
through the pipe ,s into the vessel ,c1 
where encountering the cold surface and 

the jet of cold water1 it will be       
condensed1 and the vacuum1 as before1   
will be produced in the cylinder ,a ,b2 
that cylinder still maintaining its     
temperature1 the piston will again      
descend1 and so the process may be      
continued4   7#fi47 ,having carried the 
invention to this point1 ,watt saw that 
the vessel ,c would gradually become    
heated by the steam which would be      
continually condensed in it4 ,to prevent
 this1 as well as to supply a constant  
jet of cold water1 he proposed to keep  
the vessel ,c submerged in a cistern of 
cold water1 from which a pipe should    
conduct a jet to play within the vessel1
 so as to condense the steam as it would
 pass from the cylinder4  ,but here a   
difficulty presented itself1 against    
which it was necessary to provide4 ,the 
cold water admitted through the jet to  
condense the steam1 mixed with the      
condensed steam itself1 would gradually 
collect in the vessel ,c1 and at length 
choke it4 ,to prevent this1 ,watt       

proposed to put the vessel ,c in        
communication with a pump ,f1 which     
might be wrought by the engine itself1  
and by which the water1 which would     
collect in the bottom of the vessel ,c1 
would be constantly drawn off4 ,this    
pump would be evidently rendered the    
more necessary1 since more or less      
atmospheric air1 always combined with   
water in its common state1 would enter  
the vessel ,c by the condensing jet4    
,this air would be disengaged in the    
vessel ,c by the heat of the steam      
condensed therein2 and it would rise    
through the tube ,s1 and vitiate the    
vacuum in the cylinder2--an effect which
 would be rendered the more injurious1  
,pg#abc inasmuch as1 unlike steam1 this 
elastic fluid would be incapable of     
being condensed by cold4 ,the pump ,f1  
therefore1 by which ,watt proposed to   
draw off the water from the vessel ,c1  
might also be made to draw off the air1 
or the principal part of it4  ,the      
vessel ,c was subsequently called a     

condenser2 and1 from the circumstances  
just adverted to1 the pump ,f has been  
called the air-pump4  ,these--namely1   
the cylinder1 the condenser1 and the    
air-pump--were the three principal parts
 in the invention1 as it first presented
 itself to the mind of ,watt--and even  
before it was reduced to a model1 or    
submitted to experiment4 ,but1 in       
addition to these1 other two            
improvements offered themselves in the  
very first stage of its progress4  ,in  
the atmospheric engine1 the piston was  
maintained steam-tight in the cylinder  
by supplying a stream of cold water     
above it1 by which the small interstices
 between the piston and cylinder would  
be stopped4 ,it is evident that the     
effect of this water as the piston      
descended would be to cool the cylinder1
 besides which any portion of it which  
might pass between the piston and       
cylinder and which would pass below the 
piston1 would boil the moment it would  
fall into the cylinder1 which itself    

would be maintained at the boiling      
temperature4 ,this water1 therefore1    
would produce steam1 the pressure of    
which would resist the descent of the   
piston4  ,watt perceived1 that even     
though this inconvenience were removed  
by the use of oil or tallow upon the    
piston1 still1 that as the piston would 
descend in the cylinder1 the cold       
atmosphere would follow it2 and would1  
to a certain extent1 lower the          
temperature of the cylinder4 ,on the    
next ascent of the piston1 this         
temperature would have to be again      
raised to #bab by the steam coming from 
the boiler1 and would entail upon the   
machine a proportionate waste of power4 
,if the atmosphere of the engine-house  
could be kept heated to the temperature 
of boiling water1 this inconvenience    
would be removed4 ,the piston would then
 be pressed down by air as hot as the   
steam to be subsequently introduced into
 it4 ,on further consideration1 however1
 it occurred to ,watt that it would be  

still more advantageous if the cylinder 
itself could be ,pg#abd worked in an    
atmosphere of steam1 having only the    
same pressure as the atmosphere4 ,such  
steam would press the piston down as    
effectually as the air would2 and it    
would have the further advantage over   
air1 that if any portion of it leaked   
through between the piston and cylinder1
 it would be condensed1 which could not 
be the case with atmospheric air4 ,he   
therefore determined on surrounding the 
cylinder by an external casing1 the     
space between which and the cylinder he 
proposed to be filled with steam        
supplied from the boiler4 ,the cylinder 
would thus be enclosed in an atmosphere 
of its own1 independent of the external 
air1 and the vessel so enclosing it     
would only require to be a little larger
 than the cylinder1 and to have a close 
cover at the top1 the centre of which   
might be perforated with a hole to admit
 the rod of the piston to pass through1 
the rod being made smooth1 and so fitted

 to the perforation that no steam should
 escape between them4 ,this method would
 be attended also with the advantage of 
keeping the cylinder and piston always  
heated1 not only inside but outside2 and
 ,watt saw that it would be further     
advantageous to employ the pressure of  
steam to drive the piston in its descent
 instead of the atmosphere1 as its      
intensity or force would be much more   
manageable2 for1 by increasing or       
diminishing the heat of the steam in    
which the cylinder was enclosed1 its    
pressure might be regulated at pleasure1
 and it might be made to urge the piston
 with any force that might be required4 
,the power of the engine would therefore
 be completely under control1 and       
independent of all variations in the    
pressure of the atmosphere4   7#gj47    
,this was a step which totally changed  
the character of the machine1 and which 
rendered it a ,,steam ,,engine instead  
of an ,,atmospheric ,,engine4 ,not only 
was the vacuum below the piston now     

produced by the property of steam1 in   
virtue of which it is reconverted into  
water by cold2 but the pressure which   
urged the piston into this vacuum was   
due to the elasticity of steam4  ,the   
external cylinder1 within which the     
working cylinder was enclosed1 was      
called ,,the ,,jacket1 and is still very
 generally used4  ,illustration3 ,fig4  
#bj4   7#ga47 ,the first experiment in  
which ,watt attempted to ,pg#abe        
realise1 on a small scale1 his          
conceptions1 was made in the following  
manner4 ,the cylinder of the engine was 
represented by a brass syringe ,a ,b    
7fig4 #bj47 an inch and a third in      
diameter1 and ten inches in length1 to  
which a top and a bottom of tin plate   
was fitted4 ,steam was conveyed by a    
pipe1 ,s1 from a small boiler into the  
lower end of this syringe1 a            
communication being made with the upper 
end of the syringe by a branch pipe ,d4 
,for the greater convenience of the     
experiment1 it was found desirable to   

invert the position of the cylinder1 so 
that the steam should press the piston  
,p upwards instead of downwards4 ,the   
piston-rod ,r therefore was presented   
downwards4 ,an eduction pipe ,e was also
 inserted in the top of the cylinder1   
which was carried to the condenser4 ,the
 piston-rod was made hollow1 or rather a
 hole was drilled longitudinally through
 it1 and a valve was fitted at its lower
 end1 to carry off the water produced by
 the steam1 which ,pg#abf would be      
condensed in the cylinder in the        
commencement of the process4 ,the       
condenser used in this experiment       
operated without injection1 the steam   
being condensed by the contact of cold  
surfaces4 ,it consisted of two thin     
pipes ,f1 ,g of tin1 ten or twelve      
inches in length1 and the sixth of an   
inch in diameter1 standing beside each  
other perpendicularly1 and communicating
 at the top with the eduction pipe1     
which was provided with a valve opening 
upwards4 ,at the bottom these two pipes 

communicated with another tube ,i of    
about an inch in diameter1 by a         
horizontal pipe1 having in it a valve1  
,m1 opening towards ,i1 fitted with a   
piston ,k1 which served the office of   
the air-pump1 being worked by the hand4 
,this piston1 ,k1 had valves in it      
opening upwards4 ,these condensing pipes
 and air-pump were immersed in a small  
cistern1 filled with cold water4 ,the   
steam was conveyed by the steam-pipe ,s 
to the bottom of the cylinder1 a        
communication between the top and bottom
 of the cylinder being occasionally     
opened by a cock1 ,c1 placed in the     
branch pipe4 ,the eduction pipe leading 
to the condenser also had a cock1 ,l1 by
 which the communication between the top
 of the cylinder and the condenser might
 be opened and closed at pleasure4 ,in  
the commencement of the operation1 the  
cock ,n admitting steam from the boiler1
 and the cock ,l opening a communication
 between the cylinder and the condenser1
 and the cock ,c opening a communication

 between the top and bottom of the      
cylinder1 being all open1 steam rushed  
from the boiler1 passing through all the
 pipes1 and filling the cylinder4 ,a    
current of mixed air and steam was thus 
produced through the eduction pipe ,e1  
through the condensing pipes ,f and ,g1 
and through the air-pump ,i1 which      
issued from the valve ,h in the eduction
 pipe1 and from the valve in the        
air-pump piston1 all of which opened    
upwards4 ,the steam also in the cylinder
 passed through the hole drilled in the 
piston-rod1 and escaped1 mixed with air1
 through the valve in the lower end of  
that rod4 ,this process was continued   
until all the air in the cylinder1      
pipes1 and condenser1 was blown out1 and
 all these spaces filled with pure      
steam4 ,the cocks ,l1 ,c1 and ,n1 were  
then closed1 and the atmospheric        
pressure closed the valve ,h and the    
valves in the air-pump piston4 ,the cold
 surfaces condensing the steam in       
,pg#abg the pipes ,f and ,g1 and in the 

lower part of the air-pump1 a vacuum was
 produced in these spaces4 ,the cock ,c 
being now closed1 and the cocks ,l and  
,n being open1 the steam in the upper   
part of the cylinder rushed through the 
pipe ,e into the condenser1 where it was
 reduced to water1 so that a vacuum was 
left in the upper part of the cylinder4 
,the steam from the boiler passing below
 the piston1 pressed it upwards with    
such force1 that it lifted a weight of  
eighteen pounds hung from the end of the
 piston-rod4 ,when the piston reached   
the top of the cylinder1 the cocks ,l   
and ,n were closed1 and the cock ,c     
opened4 ,all communication between the  
cylinder and the boiler1 as well as     
between the cylinder and the condenser1 
were now cut off1 and the steam in the  
cylinder circulated freely above and    
below the piston1 by means of the open  
tube ,d4 ,the piston1 being subject to  
equal forces upwards and downwards1     
would therefore descend by its own      
weight1 and would reach the bottom of   

the cylinder4 ,the air-pump piston      
meanwhile being drawn up1 the air and   
the condensed steam in the tubes ,f and 
,g were drawn into the air-pump ,i1     
through the open horizontal tube at the 
bottom4 ,its return was stopped by the  
valve ,m4 ,by another stroke of the     
air-pump1 this water and air were drawn 
out through valves in the piston1 which 
opened upwards4 ,the cock ,c was now    
closed1 and the cocks ,l and ,n opened1 
preparatory to another stroke of the    
piston4 ,the steam in the upper part of 
the cylinder rushed1 as before1 into the
 tubes ,f and ,g1 and was condensed by  
their cold surfaces1 while steam from   
the boiler coming through the pipe ,s1  
pressed the piston upwards4 ,the piston 
again ascended with the same force as   
before1 and in the same manner the      
process was continually repeated4       
7#gb47 ,the quantity of steam expended  
in this experimental model in the       
production of a given number of strokes 
of the piston was inferred from the     

quantity of water evaporated in the     
boiler2 and on comparing this with the  
magnitude of the cylinder and the weight
 raised by the pressure of the steam1   
the contrivance was proved to affect the
 economy of steam1 as far as the        
imperfect conditions of such a model    
could have permitted4 ,a larger model   
was next constructed1 having an outer   
cylinder1 or steam case1 surrounding the
 working cylinder1 and ,pg#abh the      
experiments made with it fully realised 
,watt's expectations1 and left no doubt 
of the great advantages which would     
attend his invention4 ,the weights      
raised by the piston proved that the    
vacuum in the cylinder produced by the  
condensation was almost perfect2 and he 
found that when he used water in the    
boiler which by long boiling had been   
well cleared of air1 the weight raised  
was not much less than the whole amount 
of the pressure of the steam upon the   
piston4 ,in this larger model1 the      
cylinder was placed in the usual        

position1 with a working lever and other
 apparatus similar to that employed in  
the ,atmospheric ,engine4   7#gc47 ,it  
was in the beginning of the year #agfe1 
,watt being then in the twenty-ninth    
year of his age1 that he arrived at     
these great discoveries4 ,the           
experimental models just described1 by  
which his invention was first reduced to
 a rude practical test1 were fitted up  
at a place called ,delft ,house1 in     
,glasgow4 ,it will doubtless1 at the    
first view1 be a matter of surprise that
 improvements of such obvious importance
 in the economy of steam power1 and     
capable of being verified by tests so   
simple1 were not immediately adopted    
wherever atmospheric engines were used4 
,at the time1 however1 referred to1     
,watt was an obscure artisan1 in a      
provincial town1 not then arrived at the
 celebrity to which it has since        
attained1 and the facilities by which   
inventions and improvements became      
public were much less than they have    

since become4 ,it should also be        
considered that all great and sudden    
advances in the useful arts are         
necessarily opposed by the existing     
interests with which their effects are  
in conflict4 ,from these causes of      
opposition1 accompanied with the usual  
influence of prejudice and envy1 ,watt  
was not exempt1 and was not therefore   
likely suddenly to revolutionise the    
arts and manufactures of the country by 
displacing the moving powers employed in
 them1 and substituting an engine1 the  
efficacy and power of which depended    
mainly on physical principles1 then     
altogether new and but imperfectly      
understood4  ,not having the command of 
capital1 and finding it impracticable to
 inspire those who had1 with the same   
confidence in the advantages of his     
invention which he himself felt1 he was 
,pg#abi unable to take any step towards 
the construction of engines on a large  
scale4 ,soon after this1 he gave up his 
shop in ,glasgow1 and devoted himself to

 the business of a ,civil ,engineer4 ,in
 this capacity he was engaged to make a 
survey of the river ,clyde1 and         
furnished an elaborate and valuable     
,report upon its projected improvements4
 ,he was also engaged in making a plan  
of the canal1 by which the produce of   
the ,monkland ,colliery was intended to 
be carried to ,glasgow1 and in          
superintending the execution of that    
work4 ,besides these1 several other     
engineering enterprises occupied his    
attention1 among which may be mentioned1
 the navigable canal across the isthmus 
of ,crinan1 afterwards completed by     
,rennie2 improvements proposed in the   
ports of ,ayr1 ,glasgow1 and ,greenock2 
the construction of the bridges at      
,hamilton1 and at ,rutherglen2 and the  
survey of the country through which the 
celebrated ,caledonian canal was        
intended to be carried4  ,if1 forgetful 
of my duties as the organ of this       
academy1 says ,m4 ,arago 7whose eloquent
 observations on the delays of this     

great invention1 addressed to the       
assembled members of the ,national      
,institute of ,france1 we cannot forbear
 to quote71 ,i could think of making you
 smile1 rather than expressing useful   
truths1 ,i would find here matter for a 
ludicrous contrast4 ,i would call to    
your recollection the authors1 who at   
our weekly sittings demand with all     
their might and main 7 cor et  cris7 an 
opportunity to communicate some little  
remark--some small reflection--some     
trifling note1 conceived and written the
 night before2 ,i would represent them  
to you cursing their fate1 when         
according to your rules1 the reading of 
their communication is postponed to the 
next meeting1 although during this cruel
 week1 they are assured that their      
important communication is deposited in 
our archives in a sealed packet4 ,on the
 other hand1 ,i would point out to you  
the creator of a machine1 destined to   
form an epoch in the annals of the      
world1 undergoing patiently and without 

murmur1 the stupid contempt of          
capitalists1--conscious of his exalted  
genius1 yet stooping for eight years to 
the common labour of laying down plans1 
taking levels1 and all the tedious      
calculations connected with the routine 
of common engineering4 ,while in this   
conduct you cannot fail to recognise the
 serenity1 ,pg#acj the moderation1 and  
the true modesty of his character1 yet  
such indifference1 however noble may    
have been its causes1 has something in  
it not altogether blameless4 ,it is not 
without reason that society visits with 
severe reprobation those who withdraw   
gold from circulation and hoard it in   
their coffers4 ,is he less culpable who 
deprives his country1 his fellow        
citizens1 his age1 of treasures a       
thousand times more precious than the   
produce of the mine2 who keeps to       
himself his immortal inventions1 sources
 of the most noble and purest enjoyment 
of the mind1 who abstains from          
conferring upon labour those powers1 by 

which would be multiplied in an infinite
 proportion the products of industry1   
and by which1 with advantage to         
civilisation and human nature1 he would 
smooth away the inequalities of the     
conditions of man4#ai   7#gd47 ,although
 ,watt was thus attracted by pursuits   
foreign to his recent investigations    
respecting the improvement of steam     
power1 he never lost sight of that      
object4 ,it was not until the year      
#agfh1 three years after his great      
discoveries1 that any step was taken to 
enable him to carry them into effect on 
a large scale4 ,at that time his friends
 brought him into communication with    
,dr4 ,roebuck1 the proprietor of the    
,carron ,iron ,works1 who rented        
extensive coal works at ,kinneal from   
the ,duchess of ,hamilton4 ,watt was    
first employed by ,roebuck as a civil   
engineer2 but when he made known to him 
the improvements he had projected in the
 steam engine1 ,roebuck proposed to take
 out a patent for an engine on the      

principle of the model which had been   
fitted up at ,delft ,house1 and to join 
,watt in a partnership1 for the         
construction of such engines4 ,sensible 
of the advantages to be derived from the
 influence of ,roebuck1 and from his    
command of capital1 ,watt agreed to cede
 to him two thirds of the advantages to 
be derived from the invention4 ,a patent
 was accordingly taken out on the fifth 
of ,january1 #agfi1 nearly four years   
after the invention had been completed2 
and an experimental engine on a large   
scale was constructed by him1 and fitted
 up at ,kinneal ,house4 ,in the first   
trial this machine more than fulfilled  
,watt's anticipations4 ,its ,pg#aca     
success was complete4 ,in the practical 
details of its construction1 however1   
some difficulties were still            
encountered1 the greatest of which      
consisted in packing the piston1 so as  
to be steam-tight4 ,the principle of the
 new engine did not admit of water being
 kept upon the piston1 to prevent       

leakage1 as in the old engines2 he was  
therefore obliged to have his cylinders 
much more accurately bored1 and more    
truly cylindrical1 and to try a great   
variety of soft substances for packing  
the piston1 which would make it         
steam-tight without great friction1 and 
maintain it so in a situation perfectly 
dry1 and at the temperature of boiling  
water4  ,while ,watt was endeavouring to
 overcome these and other difficulties1 
in the construction of the machine1 his 
partner1 ,dr4 ,roebuck1 became          
embarrassed1 by the failure of his      
undertaking in the ,borrowstowness coal 
and salt works2 and he was unable to    
supply the means of prosecuting with the
 necessary vigour the projected         
manufacture of the new engines4  ,the   
important results of ,watt's labours    
having happily at this time become more 
publicly known1 ,mr4 ,matthew ,boulton1 
whose establishment at ,soho1 near      
,birmingham1 was at that time the most  
complete manufactory for metal-work in  

,england1 and conducted with unexampled 
enterprise and spirit1 proposed to      
purchase ,dr4 ,roebuck's interest in the
 patent4 ,this arrangement was effected 
in the year #aggc1 and in the following 
year ,mr4 ,watt removed to ,soho1 where 
a portion of the establishment was      
allotted to him1 for the erection of a  
foundery1 and other works necessary to  
realise his inventions on a grand scale4
  ,the patent which had been granted in 
#agfi was limited to a period of        
fourteen years1 and would consequently  
expire about the year #aghc4 ,from the  
small progress which had hitherto been  
made in the construction of engines upon
 the new principle1 and from the many   
difficulties still to be encountered1   
and the large expenditure of capital    
which must obviously be incurred before 
any return could be obtained1 it was    
apparent that unless an extension of the
 patent right could be obtained1        
,boulton and ,watt could never expect   
any advantage adequate to the risk of   

their great ,pg#acb enterprise4 ,in the 
year #aggd an application was           
accordingly made to parliament for an   
extension of the patent1 which was      
supported by the testimony of ,dr4      
,roebuck1 ,mr4 ,boulton1 and others1 as 
to the merits and probable utility of   
the invention4 ,an ,act was accordingly 
passed1 in #agge1 extending the term of 
the patent until the year #ahjj4        
7#ge47 ,the following abstract of this  
,act may not be uninteresting at this   
time1 when the anticipations expressed  
in it have been so successfully and     
extensively realised3--  ,an ,act for   
vesting in ,james ,watt1 engineer1 his  
executors1 administrators1 and assigns1 
the sole use and property of certain    
steam engines1 commonly called fire     
engines1 of his invention1 throughout   
his majesty's dominions1 for a limited  
time3  ,and whereas the said ,james     
,watt hath employed many years1 and a   
considerable part of his fortune1 in    
making experiments upon steam engines1  

commonly called fire engines1 with a    
view to improve those very useful       
machines1 by which several very         
considerable advantages over the common 
steam engines are acquired2 but upon    
account of the many difficulties which  
always arise in the execution of such   
large and complex machines1 and of the  
long time requisite to make the         
necessary trials1 he could not complete 
his intention before the end of the year
 #aggd1 when he finished some large     
engines as specimens of his             
construction1 which have succeeded1 so  
as to demonstrate the utility of the    
said invention3  ,and whereas1 in order 
to manufacture these engines with the   
necessary accuracy1 and so that they may
 be sold at moderate prices1 a          
considerable sum of money must be       
previously expended in erecting mills   
and other apparatus2 and as several     
years and repeated proofs will be       
required before any considerable part of
 the public can be fully convinced of   

the utility of the invention1 and of    
their interest to adopt the same1 the   
whole term granted by the said letters  
patent may probably elapse before the   
said ,james ,watt can receive an        
advantage adequate to his labour and    
invention3  ,and whereas1 by furnishing 
mechanical power at much less expense1  
and in more convenient forms1 than has  
hitherto been done1 his engines may be  
of great utility1 in facilitating       
,pg#acc the operations in many great    
works and manufactures of this kingdom2 
yet it will not be in the power of the  
said ,james ,watt to carry his invention
 into that complete execution which he  
wishes1 and so as to render the same of 
the highest utility to the public of    
which it is capable1 unless the term    
granted by the said letters patent be   
prolonged1 and his property in the said 
invention secured for such time as may  
enable him to obtain an adequate        
recompense for his labour1 time1 and    
expense3  ,to the end1 therefore1 that  

the said ,james ,watt may be enabled and
 encouraged to prosecute and complete   
his said invention1 so that the public  
may reap all the advantages to be       
derived therefrom in their fullest      
extent3 it is enacted1  ,that from and  
after the passing of this ,act1 the sole
 privilege and advantage of making1     
constructing1 and selling the said      
engines hereinbefore particularly       
described1 within the kingdom of ,great 
,britain1 and his majesty's colonies and
 plantations abroad1 shall be1 and are  
hereby declared to be1 vested in the    
said ,james ,watt1 his executors1       
administrators1 and assigns1 for and    
during the term of twenty-five years1 c4
 c4   7#gf47 ,thus protected and        
supported1 ,watt now directed the whole 
vigour of his mind to perfect the       
practical details of his invention1 and 
the result was1 the construction on a   
large scale of the engine which has     
since been called his ,,single ,,acting 
,,steam ,,engine4  ,it is necessary to  

recollect1 that notwithstanding the     
extensive and various application of    
steam power in the arts and             
manufactures1 at the time to which our  
narrative has now reached1 the steam    
engine had never been employed for any  
other purpose save that of raising water
 by working pumps4 ,the motion1         
therefore1 which was required was merely
 an upward force1 such as was necessary 
to elevate the piston of a pump1 loaded 
with the column of water which it       
raised4 ,the following then is a        
description of the improved engine of   
,watt1 by which such work was proposed  
to be performed3--  ,illustration3 ,fig4
 #ba4  ,in the cylinder represented at  
,c 7fig4 #ba471 the piston ,p moves     
steam-tight4 ,it is closed at the top1  
and the piston ,pg#acd rod1 being       
accurately turned1 runs in a steam-tight
 collar1 ,b1 furnished with a           
stuffing-box1 and is constantly         
lubricated with melted tallow4 ,a funnel
 is screwed into the top of the         

cylinder1 through which1 by opening a   
stop-cock1 melted ,pg#ace tallow is     
permitted from time to time to fall upon
 the piston within the cylinder1 so as  
to lubricate it1 and keep it            
steam-tight4 ,two boxes1 ,a ,a1 called  
the upper and lower steam boxes1 contain
 valves by which steam from the boiler  
may be admitted and withdrawn4 ,these   
steam boxes are connected by a tube of  
communication ,t1 and they communicate  
with the cylinder at the top and bottom 
by short tubes represented in the       
figure4 ,the upper steam box ,a contains
 one valve1 by which a communication    
with the boiler may be opened or closed 
at pleasure4 ,the lower valve box       
contains two valves4 ,the lower valve ,i
 communicates with the tube ,t1 leading 
to the condenser ,d1 which being opened 
or closed1 a communication is made or   
cut off at pleasure1 between the        
cylinder ,c and the condenser ,d4 ,a    
second valve1 or upper valve ,h1 which  
is represented closed in the figure1 may

 be opened so as to make a free         
communication between the cylinder ,c   
and the tube ,t1 and by that means      
between the cylinder ,c1 below the      
piston and the space above the piston4  
,the condenser ,d is submerged in a     
cistern of cold water4 ,at the side     
there enters it a tube1 ,e1 governed by 
a cock1 which being opened or closed to 
any required extent1 a jet of cold water
 may be allowed to play in the          
condenser1 and may be regulated or      
stopped1 at pleasure4 ,this jet1 when   
playing1 throws the water upwards in the
 condenser towards the mouth of the tube
 ,t1 as water issues from the rose of a 
watering pot4 ,the tube ,s proceeds from
 the boiler1 and terminates in the steam
 box ,a1 so that the steam supplied from
 the boiler constantly fills that box4  
,the valve ,g is governed by levers1    
whose pivots are attached to the framing
 of the engine1 and is opened or closed 
at pleasure1 by raising or lowering the 
lever ,g4 ,the valve ,g1 when open1 will

 therefore allow steam to pass from the 
boiler through the short tube to the top
 of the piston1 and this steam will also
 fill the tube ,t4 ,if the lower valve  
,h be closed1 its circulation beyond    
that point will be stopped2 but if the  
valve ,h be open1 the valve ,i being    
closed1 then the steam will circulate   
equally in the cylinder1 above and below
 the piston4 ,if the valve ,i be open1  
then steam will rush through the tube ,t
 into the condenser2 but this escape of 
the steam will be ,pg#acf stopped1 if   
the valve ,i be closed4 ,the valve ,h is
 worked by the lever ,h1 and the valve  
,i by the lever ,i4  ,the valve ,g is   
called the upper steam valve1 ,h the    
lower steam valve1 ,i the exhausting    
valve1 and ,e the condensing valve4     
,from the bottom of the condenser ,d    
proceeds a tube leading to the air-pump1
 which is also submerged in the cistern 
of cold water4 ,in this tube is a valve 
,m1 which opens outwards from the       
condenser towards the air-pump4 ,in the 

piston of the air-pump ,n is a valve    
which opens upwards4 ,the piston-rod ,q 
of the air-pump is attached to a beam of
 wood called a plug frame1 which is     
connected with the working beam by a    
flexible chain playing on the small     
arch-head immediately over the air-pump4
 ,from the top of the air-pump barrel   
above the piston proceeds a pipe or     
passage leading to a small cistern1 ,b1 
called the hot well4 ,the pipe which    
leads to this well1 is supplied with a  
valve1 ,k1 which opens outwards from the
 air pump barrel towards the well4 ,from
 the nature of its construction1 the    
valve ,m admits the flow of water from  
the condenser towards the air-pump1 but 
prevents its return2 and1 in like       
manner1 the valve ,k admits the flow of 
water from the upper part of the        
air-pump barrel into the hot well ,b1   
but obstructs its return4  ,let us now  
consider how these valves should be     
worked in order to move the piston      
upwards and downwards with the necessary

 force4 ,it is in the first place       
necessary that all the air which fills  
the cylinder1 the tubes and the         
condenser shall be expelled4 ,to        
accomplish this it is only necessary to 
open at once the three valves ,g1 ,h1   
and ,i4 ,the steam then rushing from the
 boiler through the steam-pipe ,s1 and  
the open valve ,g will pass into the    
cylinder above the piston1 will fill the
 tube ,t1 pass through the lower steam  
valve ,h1 will fill the cylinder ,c     
below the piston1 and will pass through 
the open valve ,i into the condenser4   
,if the valve ,e be closed so that no   
jet shall play in the condenser1 the    
steam rushing into it will be partially 
condensed by the cold surfaces to which 
it will be exposed2 but if the boiler   
supply it through the pipe ,s in        
sufficient abundance1 it will rush with 
violence through the cylinder and all   
the passages1 and its pressure in the   
,pg#acg condenser ,d1 combined with that
 of the heated air with which it is     

mixed1 will open the valve ,m1 and it   
will rush through mixed with the air    
into the air-pump barrel ,n4 ,it will   
press the valves in the air-pump piston 
upwards1 and1 opening them1 will rush   
through1 and will collect in the        
air-pump barrel above the piston4 ,it   
will then1 by its pressure1 open the    
valve ,k1 and will escape into the      
cistern ,b4  ,throughout this process   
the steam1 which mixed with the air     
fills the cylinder1 condenser and       
air-pumps will be only partially        
condensed in the last two1 and it will  
escape mixed with air through the valve 
,k1 and this process will continue until
 all the atmospheric air which at first 
filled the cylinder1 tubes1 condenser   
and air-pump barrel shall be expelled   
through the valve ,k1 and these various 
spaces shall be filled with pure steam4 
,when that has happened let us suppose  
all the valves closed4 ,in closing the  
valve ,i the flow of steam to the       
condenser will be stopped1 and the steam

 contained in it will speedily be       
condensed by the cold surface of the    
condenser1 so that a vacuum will be     
produced in the condenser1 the condensed
 steam falling in the form of water to  
the bottom4 ,in like manner1 and for    
like reasons1 a vacuum will be produced 
in the air-pump4 ,the valve ,m1 and the 
valves in the air-pump piston will be   
closed by their own weight4  ,by this   
process1 which is called blowing        
through1 the atmospheric air1 and other 
permanent gases1 which filled the       
cylinder1 tubes1 condenser and air-pump 
are expelled1 and these spaces will be a
 vacuum4 ,the engine is then prepared to
 be started1 which is effected in the   
following manner3--,the upper steam     
valve ,g is opened1 and steam allowed to
 flow from the boiler through the       
passage leading to the top of the       
cylinder4 ,this steam cannot pass to the
 bottom of the cylinder1 since the lower
 steam valve ,h is closed4 ,the space in
 the cylinder below the piston being    

therefore a vacuum1 and the steam       
pressing above it the piston will be    
pressed downwards with a corresponding  
force4 ,when it has arrived at the      
bottom of the cylinder the steam valve  
,g must be closed1 and at the same time 
the valve ,h opened4 ,the valve ,i      
leading to the condenser being also     
closed1 the steam ,pg#ach which fills   
the cylinder above the piston is now    
admitted to circulate through the open  
valve ,h below the piston1 so that the  
piston is pressed equally upwards and   
downwards by steam1 and there is no     
force to resist its movement save its   
friction with the cylinder4 ,the weight 
of the pump rods on the opposite end of 
the beam being more than equivalent to  
overcome this the piston is drawn to the
 top of the cylinder1 and pushes before 
it the steam which is drawn through the 
tube ,t1 and the open valve ,h1 and     
passes into the cylinder ,c below the   
piston4  ,illustration3 ,fig4 #bb4      
,when the piston has thus arrived once  

more at the top of the cylinder1 let the
 valve ,h be closed1 and at the same    
time the valves ,g and ,i opened1 and   
the condensing cock ,e also opened1 so  
as to admit the jet to play in the      
condenser4 ,the steam which fills the   
cylinder ,c below the piston1 will now  
rush through the open valve ,i into the 
condenser which has been hitherto a     
vacuum1 and there encountering the jet1 
will be instantly converted into water1 
and a mixture of condensed steam and    
injected water will collect in the      
bottom of the condenser4 ,at the same   
time1 the steam proceeding from the     
boiler by the steam pipe ,s to the upper
 steam box ,a1 will pass through the    
open steam valve ,g to the top of the   
piston1 but cannot pass below it because
 of the lower steam valve ,h being      
closed4 ,the piston1 thus acted upon    
above by the pressure of the steam1 and 
the space in the cylinder below it being
 a vacuum1 its downward motion is       
resisted by no force but the friction1  

and it is therefore driven to the bottom
 of the cylinder4 ,during its descent   
the valves ,g1 ,i1 and ,e remained open4
 ,at the moment it arrives at the bottom
 of the cylinder1 all these three valves
 are closed1 and the valve ,h opened4   
,the steam which fills the cylinder     
above the piston is now permitted to    
circulate below it1 by the open valve   
,h1 and the piston being consequently   
pressed equally upwards and downwards   
will be drawn upwards as before by the  
preponderance of the pump rods at the   
opposite end of the beam4 ,the weight of
 these rods must also be sufficiently   
great to draw the air-pump piston ,n    
upwards4 ,as this piston rises in the   
air-pump1 it leaves a vacuum below it   
into which the water and air collected  
in the condenser will be drawn through  
the valve ,m1 which opens outwards4     
,when the ,pg#aci air-pump piston has   
arrived at the top of the barrel1 which 
it will do at the same time that the    
steam piston arrives at the top of the  

cylinder1 the water and the chief part  
of the air or other fluids which may    
have been in the condenser will be drawn
 into the barrel of the air-pump1 and   
the valve ,m being closed by its own    
weight1 assisted by the pressure of     
these fluids they cannot return into the
 condenser4 ,at the moment the steam    
piston arrives at the top of the        
cylinder1 the valve ,h is closed1 and   
the three valves ,g1 ,i1 and ,e are     
opened4 ,the effect of this change is   
the same as was already described in the
 former case1 and the piston will in the
 same manner and from the same causes be
 driven downwards4 ,the air-pump piston 
will at the same time descend by the    
force of its own weight1 aided by the   
weight of the plug-frame attached to its
 rod4 ,as it descends1 the air below it 
will be gradually compressed above the  
surface of the water in the bottom of   
the barrel1 until its pressure becomes  
sufficiently great to open the valves in
 the air-pump piston4 ,when this        

happens1 the valves in the air-pump     
piston1 as represented on a large scale 
in fig4 #bb41 will be opened1 and the   
air will pass through them above the    
piston4 ,when the piston comes in       
contact with the water in the bottom of 
the barrel1 this water will likewise    
pass through the open valves4 ,when the 
piston has arrived at the bottom of the 
air-pump barrel1 the valves in it will  
be closed by the pressure of the fluids 
above them4 ,the next ascent of the     
steam piston will draw up the air-pump  
piston1 and with it the fluids in the   
pump barrel above it4 ,as the air-pump  
,pg#adj piston approaches the top of its
 barrel1 the air and water above it will
 be drawn through the valve ,k into the 
hot cistern ,b4 ,the air will escape in 
bubbles through the water in that       
cistern1 and the warm water will be     
deposited in it4  ,the magnitude of the 
opening in the condensing valve ,e1 must
 be regulated by the quantity of steam  
admitted to the cylinder4 ,as much water

 ought to be supplied through the       
injection valve as will be sufficient to
 condense the steam contained in the    
cylinder1 and also to reduce the        
temperature of the water itself1 when   
mixed with the steam1 to a sufficiently 
low degree to prevent it from producing 
vapour of a pressure which would        
injuriously affect the working of the   
piston4 ,it has been shown1 that five   
and a half cubic inches of ice-cold     
water mixed with one cubic inch of water
 in the state of steam would produce six
 and a half cubic inches of water at the
 boiling temperature4 ,if then the      
cylinder contained one cubic inch of    
water in the state of steam1 and only   
five and a half cubic inches of water   
were admitted through the condensing    
jet1 supposing this water1 when         
admitted1 to be at the temperature of   
#cb1 then the consequence would be that 
six and a half cubic inches of water at 
the boiling temperature would be        
produced in the condenser4 ,steam would 

immediately arise from this1 and at the 
same time the temperature of the        
remaining water would be lowered by the 
amount of the latent heat taken up by   
the steam so produced4 ,this vapour     
would rise through the open exhausting  
valve ,i1 would fill the cylinder below 
the piston1 and would impair the        
efficiency of the steam above pressing  
it down4 ,the result of the inquiries of
 ,watt respecting the pressure of steam 
at different temperatures1 showed1 that 
to give efficiency to the steam acting  
upon the piston it would always be      
necessary to reduce the temperature of  
the water in the condenser to #ajj4     
,let us then see what quantity of water 
at the common temperature would be      
necessary to produce these effects4  ,if
 the latent heat of steam be taken at   
#ajjj1 a cubic inch of water in the     
state of steam may be considered for the
 purposes of this computation1 as       
equivalent to one cubic inch of water at
 #abab4 ,now the question is1 how many  

cubic inches of water at #fj must be    
mixed with this1 in order that the      
,pg#ada mixture may have the temperature
 of #ajj8 ,this will be easily computed4
 ,as the cubic inch of water at #abab is
 to be reduced to #ajj1 it must be      
deprived of #aaab of its temperature4   
,on the other hand1 as many inches of   
water at #fj as are to be added1 must be
 raised in the same mixture to the      
temperature of #ajj1 and therefore each 
of these must receive #dj of            
temperature4 ,the number of cubic inches
 of water necessary to be added will    
therefore be determined by finding how  
often #dj are contained in #aaab4 ,if   
#aaab be divided by #dj1 the quotient   
will be #bgh4 ,hence it appears1 that to
 reduce the water in the condenser to   
the temperature of #ajj1 supposing the  
temperature of the water injected to be 
#fj1 it will be necessary to supply by  
the injection cock very nearly          
twenty-eight times as much water as     
passes through the cylinder in the state

 of steam2 and therefore if it be       
supposed that all the water evaporated  
in the boiler passes through the        
cylinder1 it follows that about         
twenty-eight times as much water must be
 thrown into the condenser as is        
evaporated in the boiler4  ,from these  
circumstances it will be evident that   
the cold cistern in which the condenser 
and air-pump are submerged1 must be     
supplied with a considerable quantity of
 water4 ,independently of the quantity  
drawn from it by the injection valve1 as
 just explained1 the water in the       
cistern itself must be kept down to a   
temperature of about #fj4 ,the interior 
of the condenser and air-pump being     
maintained by the steam condensed in    
them at a temperature not less than     
#ajj2 the outer surfaces of these       
vessels consequently impart heat to the 
water in the cold cistern1 and have     
therefore a tendency to raise the       
temperature of that water4 ,to prevent  
this1 a pump called the cold pump1      

represented at ,l in fig4 #ba41 is      
provided4 ,by this pump water is raised 
from any convenient reservoir1 and      
driven through proper tubes into the    
cold cistern4 ,this cold pump is wrought
 by the engine1 the rod being attached  
to the beam4 ,water being1 bulk for     
bulk1 heavier the lower its temperature1
 it follows that the water supplied by  
the cold pump to the cistern will have a
 tendency to sink to the bottom1        
pressing upwards the warmer water       
contained in it4 ,a waste-pipe is       
provided1 by which this ,pg#adb water is
 drained off1 and the cistern therefore 
maintained at the necessary temperature4
  ,from what has been stated1 it is also
 evident that the hot well ,b1 into     
which the warm water is thrown by the   
air-pump1 will receive considerably more
 water than is necessary to feed the    
boiler4 ,a waste-pipe1 to carry off     
this1 is also provided2 and the quantity
 necessary to feed the boiler is pumped 
up by a small pump1 ,o1 the rod of which

 is attached to the beam1 as represented
 in fig4 #ba41 and which is worked by   
the engine4 ,the water raised by this   
pump is conducted to a reservoir from   
which the boiler is fed1 by means which 
will be hereafter explained4  ,we shall 
now explain the manner in which the     
machine is made to open and close the   
valves at the proper times4 ,by         
referring to the explanation already    
given1 it will be perceived that at the 
moment the piston reaches the top of the
 cylinder1 the upper steam valve ,g must
 be open1 to admit the steam to press it
 down2 while the exhausting valve ,i    
must be opened1 to allow the steam to   
pass to the condenser2 and the          
condensing valve ,e must be opened1 to  
let in the water necessary for the      
condensation of the steam2 and at the   
same time the lower steam valve ,h must 
be closed1 to prevent the passage of the
 steam which has been admitted through  
,g4 ,the valves ,g1 ,i1 and ,e must be  
kept open1 and the valve ,h kept closed1

 until the piston arrives at the bottom 
of the cylinder1 when it will be        
necessary to close all the three valves1
 ,g1 ,i1 and ,e1 and to open the valve  
,h1 and the same effects must be        
produced each time the piston arrives at
 the top and bottom of the cylinder4    
,all this is accomplished by a system of
 levers1 which are exhibited in fig4    
#ba4 ,the pivots on which these levers  
play are represented on the framing of  
the engine1 and the arms of the levers  
,g1 ,h1 and ,i1 communicating with the  
corresponding valves ,g1 ,h1 and ,i1 are
 represented opposite a bar attached to 
the rod of the air-pump1 called the plug
 frame4 ,this bar carries certain pegs  
and detents1 which act upon the arms of 
the several levers in such a manner     
that1 on the arrival of the beam at the 
extremities of its play upwards and     
downwards1 the levers are so struck that
 the valves are opened and closed at the
 proper ,pg#adc times4 ,it is needless  
to explain all the details of this      

arrangement4 ,let it be sufficient1 as  
an example of all1 to explain the method
 of working the upper steam valve ,g4   
,when the piston reaches the top of the 
cylinder1 a pin strikes the arm of the  
lever ,g1 and throws it upwards3 this1  
by means of the system of levers1 pulls 
the arm of the valve ,g downwards1 by   
which the upper steam valve is raised   
out of its seat1 and a passage is opened
 from the steam pipe to the cylinder4   
,the valve is maintained in this state  
until the piston reaches the bottom of  
the cylinder1 when the arm ,g is pressed
 downwards1 by which the arm ,g is      
pressed upwards1 and the valve restored 
to its seat4 ,by similar methods the    
levers governing the other three valves1
 ,h1 ,i1 and ,e1 are worked4            
,illustration3 ,fig4 #bc4               
,illustration3 ,fig4 #bd4  ,the valves  
used in these engines were of the kind  
called spindle valves4 ,they consisted  
of a flat circular plate of bell metal1 
,a ,b1 fig4 #bc41 with a round spindle  

passing perpendicularly through its     
centre1 and projecting above and below  
it4 ,this valve1 having a conical form1 
was fitted very exactly1 by grinding    
into a corresponding circular conical   
seat1 ,a ,b ,c ,d1 fig4 #bd41 which     
forms the passage which it is the office
 of the valve to open and close4 ,when  
the valve falls into its seat1 it fits  
the aperture like a plug1 so as entirely
 to stop it4 ,the spindle plays in      
sockets or holes1 one above and the     
other below the aperture which the valve
 stops2 these holes keep the valve in   
its proper position1 so as to cause it  
to drop exactly into its place4  ,in the
 experimental engine made by ,mr4 ,watt 
at ,kinneal1 he used cocks1 and         
sometimes sliding covers1 like the      
regulator described in the old engines2 
but these he found very soon to become  
leaky4 ,he was1 therefore1 obliged to   
change them for the spindle valves just 
described1 which1 being truly ,pg#add   
ground1 and accurately fitted in the    

first instance1 were not so liable to go
 out of order4 ,these valves are also   
called puppet clacks1 or button valves4 
,in the earlier engines constructed by  
,watt1 the condensation was produced by 
the contact of cold surfaces1 without   
injection4 ,the reason of rejecting the 
method of condensing by injection was1  
doubtless1 to avoid the injurious       
effects of the air1 which would always  
enter the condenser1 in combination with
 the water of condensation1 and vitiate 
the vacuum4 ,it was soon found1 however1
 that a condenser acting by cold        
surfaces without injection1 being       
necessarily composed of narrow pipes or 
passages1 was liable to incrustation    
from bad water1 by which the conducting 
power of the material of the condenser  
was diminished2 so that1 while its outer
 surface was kept cold by the water of  
the cold cistern1 the inner surface     
might1 nevertheless1 be so warm that a  
very imperfect condensation would be    
produced4  ,illustration3 ,,soho1       

,,birmingham4    ,,footnotes3    #ai    
,eloge1 p4 #cjh4  ,pg#ade               
,illustration3 ,,birmingham4  ,,chap4   
,,vi4      ,,correspondence ,,of ,,watt 
,,with ,,smeaton4 -- ,,failure ,,of     
,,condensation     ,,by ,,surface4 --   
,,improvements ,,in ,,construction ,,of 
,,piston4 -- ,,method     ,,of          
,,packing4 -- ,,improvements ,,in       
,,boring ,,the ,,cylinders4 --          
,,disadvantages ,,of ,,the ,,new        
,,compared ,,with ,,the ,,old ,,engines4
 --     ,,greatly ,,increased ,,economy 
,,of ,,fuel4 -- ,,expedients ,,to       
,,force ,,the     ,,new ,,engines ,,into
 ,,use4 -- ,,correspondence ,,with      
,,smeaton4 --     ,,efficiency ,,of     
,,fuel ,,in ,,the ,,new ,,engines4 --   
,,discovery ,,of ,,the     ,,expansive  
,,action ,,of ,,steam4 -- ,,watt        
,,states ,,it ,,in ,a ,,letter ,,to     
,,dr4     ,,small4 -- ,,its ,,principle 
,,explained4 -- ,,mechanical ,,effect   
,,resulting ,,from ,,it4 -- ,,computed  
,,effect ,,of ,,cutting ,,off ,,steam   

,,at     ,,different ,,portions ,,of    
,,the ,,stroke4 -- ,,produces ,a        
,,variable ,,power4     -- ,,expedients 
,,for ,,equalising ,,the ,,power4 --    
,,limitation ,,of ,,the     ,,expansive 
,,principle ,,in ,,watt',s ,,engines4 --
 ,,its ,,more ,,extensive               
,,application ,,in ,,the ,,cornish      
,,engines4   7#gg47 ,in a letter        
addressed by ,watt to ,smeaton1 dated   
,april1 #agff1 ,watt refers to some of  
these practical difficulties which he   
had to encounter4 ,i have been1 says he1
 tormented with exceedingly bad health1 
resulting from the operation of an      
anxious mind1 the natural consequence of
 staking everything ,pg#adf upon the    
cast of a die2 for in that light ,i look
 upon every project which has not       
received the sanction of repeated       
success4  ,i have made considerable     
alterations in our engine lately1       
particularly in the condenser4 ,that    
which ,i used at first was liable to be 
impaired1 from incrustations from bad   

water2 therefore we have substituted one
 which works by an injection4 ,in       
pursuing this idea ,i have tried several
 kinds1 and have at last come to one1   
which ,i am not inclined to alter4 ,it  
consists of a jack-head pump1 shut at   
bottom1 with a common clack bucket1 and 
a valve in the cover of the pump1 to    
discharge the air and water4 ,the       
eduction steam pipe1 which comes from   
the cylinder1 communicates with this    
pump both above and below the bucket1   
and has valves to prevent anything from 
going back from the pump to the eduction
 pipe4 ,the bucket descends by its own  
weight1 and is raised by the engine when
 the great piston descends1 being hung  
to the outer end of the great lever3 the
 injection is made both into the upper  
part of this pump and into the eduction 
pipe1 and operates beyond my ideas in   
point of quickness and perfection4      
,besides the difficulty arising from    
incrustation1 ,watt found the tubulated 
condensers1 and indeed all other        

expedients for condensing by cold       
surfaces1 subject to a fatal objection4 
,they did not condense instantaneously1 
and although they were capable of       
ultimately effecting the condensation1  
yet that process was not completed until
 a great part of the stroke of the      
piston was made4 ,thus during more or   
less of the stroke the uncondensed steam
 resisted the piston1 and robbed the    
moving power of a part of its effect4   
,this objection has ever attended       
condensation by surface4  ,illustration3
 ,fig4 #be4  ,illustration3 ,fig4 #bf4  
7#gh47 ,another source of difficulty    
arose from the necessity of constructing
 the piston and cylinder with greater   
precision than had been usual in the old
 engines4 ,to fit the cover to the      
cylinder so as to be steam-tight2 to    
construct the piston rod so as to move  
through it without allowing the escape  
of steam1 and yet at the same time      
without injurious friction2 to connect  
the piston rod with the piston1 so as to

 drive the ,pg#adg latter through the   
cylinder with a perfectly straight and  
parallel motion2 to make such connection
 perfectly centrical and firm1 and yet  
to allow the piston in its ascent to    
come nearly into contact with the cover 
of the cylinder--were all difficulties  
peculiar to the new engine4 ,in the     
atmospheric engine the shank of the     
piston rod was rough and square1 and the
 rod was secured to the piston by two or
 four branches or stays1 as represented 
in fig4 #be4 ,it is evident that such a 
construction would be inadmissible in an
 engine in which the piston in its      
ascent must be brought nearly into      
contact with the close cover of the     
cylinder4 ,besides this the piston rod  
of an atmospheric engine might          
throughout its whole length have any    
form which was most convenient1 and     
required no other property than the     
strength necessary to work the beam4 ,in
 the new engine1 on the contrary1 it was
 necessary that it should be accurately 

turned and finely polished1 so as to    
pass through the hole in the top of the 
cylinder1 and be maintained in it       
steam-tight4 ,this was effected by a    
contrivance called a stuffing-box ,b1   
represented in fig4 #bf4 ,a hole is made
 in the cover of the cylinder very      
little greater in magnitude than the    
diameter of the piston rod4 ,above this 
hole is a cup in which1 around the      
piston1 is placed a stuffing of hemp or 
tow1 which is saturated with oil or     
melted tallow4 ,this collar of hemp is  
pressed down by another piece1 also     
perforated with a hole through which the
 piston rod plays1 and which is screwed 
down on the said collar of hemp4        
7#gi47 ,although the imperfect manner in
 which the interior of the cylinders was
 then formed impaired the efficiency of 
the ,pg#adh new engines1 yet such       
imperfections were not so injurious as  
in the old atmospheric engines4 ,any    
imperfection of form of the inner       
surface of the cylinder would           

necessarily cause more or less steam or 
air to escape between the piston and    
cylinder4 ,in the improved engine this  
steam passing into the vacuum below the 
piston would rush into the condenser1   
and be there condensed1 so that its     
effect in resisting the motion of the   
piston would necessarily be trifling4   
,but on the other hand1 any escape of   
air between the piston and cylinder of  
an atmospheric engine would introduce an
 elastic fluid under the piston1 which  
would injuriously affect the action of  
the machine4  ,illustration3 ,fig4 #bg4 
,to make the pistons move sufficiently  
steam-tight in these early imperfect    
cylinders1 ,watt contrived a packing    
formed of a collar of hemp1 or tow1 as  
represented in fig4 #bg4 ,the bottom of 
the piston was formed of a circular     
plate of a diameter nearly1 but not     
altogether equal to the interior        
diameter of the cylinder4 ,the part of  
the piston above this was considerably  
less in diameter1 so that the piston was

 surrounded by a circular groove or     
channel two inches wide1 into which hemp
 or soft rope1 called gasket1 was run1  
so as to form the packing4 ,the top of  
the piston was placed over this1 having 
a rim or projecting part1 which entered 
the circular groove and pressed upon the
 packing1 the cover being pressed       
downwards by screws passing through the 
piston4 ,the lower part of the groove   
round the piston was rounded with a     
curve1 so that the pressure on the      
packing might force the latter against  
the inner surface of the cylinder4 ,this
 packing was kept supplied with melted  
tallow1 as already described1 from the  
funnel1 screwed into the top of the     
cylinder4 ,the metallic edges of the    
piston were by this means prevented from
 coming into contact with the surface of
 the cylinder1 which was only pressed   
upon by the stuffing or packing         
projecting beyond these4   7#hj47       
,improved methods of boring soon1       
however1 relieved ,pg#adi the engine    

from a part of these imperfections1 and 
,watt writes to ,mr4 ,smeaton in the    
letter above quoted as follows3--  ,mr4 
,wilkinson has improved the art of      
boring cylinders2 so that ,i promise1   
upon a #gb inch cylinder1 being not     
further distant from absolute truth than
 the thickness of a thin sixpence in the
 worst part4 ,i am labouring to improve 
the regulators2 my scheme is to make    
them acute conical valves1 shut by a    
weight1 and opened by the force of the  
steam4 ,they bid fair for success1 and  
will be tried in a few days4  ,the      
person here alluded to was ,mr4 ,john   
,wilkinson1 of ,bersham near ,chester1  
who1 about the year #agge1 contrived a  
new machine for accurately boring the   
insides of cylinders4 ,the cylinder     
being first obtained from the foundery  
with a surface as accurate as the       
process of casting would admit1 had its 
inner surface reduced to still greater  
accuracy by this machine1 which consists
 of a straight central bar extended     

along the axis of the cylinder1 which   
was made to revolve slowly round it4    
,during the operation of boring1 the    
borer or cutter was fitted to slide     
along this bar1 which being perfectly   
straight1 served as a sort of ruler to  
guide the borer or cutter in its        
progress through the cylinder4 ,in this 
manner the interior surface of the      
cylinder was rendered not only true and 
straight in its longitudinal direction1 
but also perfectly circular in its cross
 section4  ,the grease found to be most 
eligible for lubrication was the tallow 
of beef or mutton2 but in the earlier   
cylinders this was soon consumed by     
reason of the imperfection of the       
boring1 and the piston being left dry   
ceased to be steam-tight4 ,to prevent   
this1 ,watt sought for some substance1  
which while it would thicken the tallow1
 and detain it around the piston1 would 
not be subject to decomposition by heat4
 ,black lead dust was used for this     
purpose1 but was soon found to wear the 

cylinder4 ,in the mean while1 however1  
the improved method of boring supplied  
cylinders which rendered this expedient 
unnecessary4  ,when the inner surface of
 the cylinder is perfectly true and     
smooth1 the packing of the piston is    
soon rendered solid and hard1 being     
moulded to the cylinder by working1 so  
as to fit it perfectly4 ,when by wear it
 became loose1 it was ,pg#aej only      
necessary to tighten the screws by which
 the top and bottom of the piston were  
held together4 ,the packing being       
compressed by those means1 was forced   
outwards towards the surface of the     
cylinder1 so as to be rendered          
steam-tight4   7#ha47 ,it was not until 
about the year #aggh1 nine years after  
the date of the patent1 and thirteen    
after the invention of separate         
condensation1 that any impression was   
produced on the mining interests by the 
advantages which were presented to them 
by these vast improvements4 ,this long  
interval1 however1 had not elapsed      

without considerable advantage2 for     
although all the great leading          
principles of the contrivance were      
invented so early as the year #agfe1 yet
 the details of construction had been in
 a state of progressive and continued   
improvement from the time ,watt joined  
,dr4 ,roebuck1 in #agfi1 to the period  
now adverted to4  ,the advantages which 
the engine offered in the form in which 
it has been just described1 were        
numerous and important1 as compared even
 with the most improved form of the     
atmospheric engine2 and it should be    
remembered1 that that machine had also  
gone on progressively improving1 and was
 probably indebted for some of its      
ameliorations to hints derived from the 
labours of ,watt1 and to the adoption of
 such of his expedients as were         
applicable to this imperfect machine1   
and could be adopted without an         
infraction of his patent4  ,in the most 
improved forms to which the atmospheric 
engine had then attained1 the quantity  

of steam wasted at each stroke of the   
piston was equal to the contents of the 
cylinder4 ,such engines1 therefore1     
consumed twice the fuel which would be  
requisite1 if all sources of waste could
 have been removed4 ,in ,watt's engines1
 the steam consumed at each stroke of   
the piston amounted only to #a-a_/d     
times the contents of the cylinder4 ,the
 waste steam1 therefore1 per stroke1 was
 only a quarter of what was usefully    
employed4 ,the absolute waste1          
therefore1 of the best atmospheric      
engines was four times that of the      
improved engine1 and consequently the   
saving of fuel in the improved engines  
amounted to about three eighths of all  
the fuel consumed in atmospheric engines
 of the same power4 ,pg#aea   7#hb47    
,but independently of this saving of    
steam1 which would otherwise be wasted1 
the power of ,watt's engine1 as compared
 with the atmospheric engine1 was so    
much augmented that the former would    
work against a resistance of ten pounds 

on the square inch under the same       
circumstances in which the latter would 
not move against more than seven pounds4
 ,the cause of this augmentation of     
power is easily explained4 ,in the      
atmospheric engine the temperature of   
the condensed steam could not be reduced
 below #aeb without incurring a greater 
loss than would be compensated by the   
advantage to be obtained from any higher
 degree of condensation4 ,now steam     
raised from water at #aeb has a pressure
 of nearly four pounds per square inch4 
,this pressure1 therefore1 acted below  
the piston resisting the atmospheric    
pressure above4 ,in ,watt's engine1     
however1 the condenser was kept at a    
temperature of about #ajj1 at which     
temperature steam has a pressure of less
 than one pound per square inch4 ,a     
resisting force upon the piston of three
 pounds per square inch was therefore   
saved in ,watt's engine as compared with
 the atmospheric engine4   7#hc47       
,besides these direct sources of        

economy1 there were other advantages    
incidental to ,watt's engine4 ,an       
atmospheric engine possessed very       
limited power of adaptation to a varying
 load4 ,the moving power being the      
atmospheric pressure1 was not under     
control1 and1 on the other hand1 was    
subject to variations from day to day   
and from hour to hour1 according to the 
changes of the barometer4 ,in the first 
construction of such an engine1         
therefore1 its power being necessarily  
adapted to the greatest load which it   
would have to move1 whenever the load   
upon its pumps was diminished1 the      
motion of the piston in descending would
 be rapidly accelerated in consequence  
of the moving power exceeding the       
resistance4 ,by this the machinery would
 be subject to sudden shocks1 which were
 productive of rapid wear1 and exposed  
the machinery to the danger of fracture4
 ,to remedy this inconvenience1 the     
following expedient was provided in the 
atmospheric engine3 whenever the load on

 the engine was materially diminished1  
the quantity of water admitted through  
the injection valve to condense the     
steam was proportionally ,pg#aeb        
diminished4 ,an imperfect condensation  
being therefore produced1 vapour        
remained in the cylinder under the      
piston1 the pressure of which resisted  
the atmosphere1 and mitigated the force 
of the machine4 ,besides this1 a cock   
was provided in the bottom of the       
cylinder1 called an air cock1 by which  
atmospheric air could be admitted to    
resist the piston whenever the motion   
was too rapid4  ,these expedients1      
however1 were all attended with a waste 
of fuel in relation to the work done by 
the engine2 for it is evident that the  
consumption of steam was necessarily the
 same1 whether the engine was working   
against its full load or against a      
reduced resistance4  ,on the other hand1
 in the improved engine of ,watt1 when  
the load1 to work against which the     
engine exerted its full power1 was      

diminished1 a cock or valve was provided
 in the steam pipe leading from the     
boiler1 which was called a throttle     
valve1 by adjusting which the passage in
 that pipe could be more or less        
contracted4 ,by regulating this cock the
 supply of steam from the boiler was    
checked1 and the quantity transmitted to
 the cylinder diminished1 so that its   
effect upon the piston might be rendered
 equal to the amount of the diminished  
resistance4 ,by this means the quantity 
of steam transmitted to the cylinder was
 rendered exactly proportional to the   
work which the engine had to perform4   
,if1 under such circumstances1 the      
boiler was worked to its full power1 so 
as to produce steam as fast as it would 
when the engine was working at full     
power1 then no saving of fuel would be  
effected1 since the surplus steam       
produced in the boiler would necessarily
 escape at the safety valve4 ,but in    
such case the fireman was directed to   
limit the fuel of the furnace until the 

discharge at the safety valve ceased4   
,by these expedients1 the actual        
consumption of fuel in one of these     
improved engines was always in the exact
 proportion of the work which it        
performed1 whether it worked at full    
power or at any degree under its regular
 power4   7#hd47 ,notwithstanding these 
and other advantages attending the new  
engines1 ,boulton and ,watt experienced 
difficulties all but insurmountable in  
getting them into use4 ,no manufactory  
existed in the country possessing       
machinery capable of ,pg#aec executing  
with the necessary precision the valves 
and other parts which required exact    
execution1 and the patentees were       
compelled to construct machinery at     
,soho for this purpose2 and even after  
they succeeded in getting the cylinders 
properly bored1 the piston rods exactly 
turned and polished1 the spindle valves 
constructed so as to be steam-tight1 and
 every other arrangement completed which
 was necessary for the efficiency of the

 machine1 the novelty of the engine1 and
 the difficulty which was supposed to   
attend its maintenance in good working  
order1 formed strong objections to its  
adoption4  ,to remove such objections1  
great sacrifices were necessary on the  
part of ,boulton and ,watt2 and they    
accordingly resolved to undertake the   
construction of the new engines without 
any profit1 giving them to the parties  
requiring their use at first cost1 on   
the condition of being remunerated by a 
small share of what they would save in  
fuel4  ,we have no objection1 writes    
,mr4 ,boulton1 to contract with the     
,carron ,company to direct the making of
 an engine to return the water for their
 mills4 99 99 99 99 ,we do not aim at   
profits in engine building1 but shall   
take our profits out of the saving of   
fuel2 so that if we save nothing1 we    
shall take nothing4 ,our terms are as   
follows3 we will make all the necessary 
plans1 sections1 and elevations for the 
building1 and for the engine with its   

appurtenances1 specifying all cast and  
forged iron work1 and every other       
particular relative to the engine4 ,we  
will give all necessary directions to   
your workmen1 which they must implicitly
 obey4 ,we will execute1 for a          
stipulated price1 the valves1 and all   
other parts which mayrequire exact      
execution1 at ,soho2 we will see that   
all the parts are put together1 and set 
to work1 properly2 we will keep our own 
work in repair for one year1 and we have
 no other objection to seven years than 
the inconvenience of the distance4 ,we  
will guarantee that the engine so       
constructed shall raise at least #bj1jjj
 cubic feet of water twenty-four feet   
high with each hundred weight of coals  
burnt4  ,when all this is done1 a fair  
and candid comparison shall be made     
between it1 and your own engine1 or any 
other engine in ,scotland1 from which   
comparison the amount of savings in fuel
 shall be estimated1 and that amount    
being ,pg#aed divided into three parts1 

we shall be entitled to one of those    
parts1 in recompense for our patent     
licence1 our drawings1 c4 c4 ,our own   
share of savings shall be estimated in  
money1 according to the value of your   
coals delivered under the boiler1 and   
you shall annually pay us that sum1     
during twenty-five years from the day   
you begin to work2 provided you continue
 the use of the engine so long4 ,and in 
case you sell the engine1 or remove it  
to any other place1 you must previously 
give us notice1 for we shall then be    
entitled to our third of the savings of 
fuel1 according to the value of coals at
 such new place4 ,this is a necessary   
condition1 otherwise the engine which we
 make for you at an expense of two      
thousand pounds may be sold in ,cornwall
 for ten thousand pounds4  ,such parts  
of the engine as we execute at ,soho we 
will be paid for at a fair price2 ,i    
conclude1 from all the observations ,i  
have had an opportunity of making1 that 
our engines are four times better than  

the common engines4 ,in boilers1 which  
are a very expensive article1 the       
savings will be in proportion to the    
savings of coal4 ,if you compare our    
engine with the common engine 7not in   
size1 but in power71 you will find the  
original expense of erecting one to be  
nearly the same4  ,mr4 ,wilkinson has   
bored us several cylinders1 almost      
without error2 that of fifty inches     
diameter1 which we put up at ,tipton1   
does not err the thickness of an old    
shilling in any part2 so that you must  
either improve your method of boring1 or
 we must furnish the cylinder to you4   
,the reluctance of mining companies to  
relinquish the old engines1 even on     
these terms1 led them to propose to ,mr4
 ,watt to grant them a licence for the  
use of his condenser1 to be applied to  
the atmospheric engine1 without the     
introduction of other improvements4     
,such a proposition was made to him by  
,mr4 ,smeaton1 in the year #aggh1 to    
which he returned the following         

answer3--  ,i have several times        
considered the propriety of the         
application of my condensers to common  
engines1 and have made experiments with 
that view upon our engine at ,soho1 but 
have never found such results as would  
induce me to try ,pg#aee it any where   
else2 and1 in consequence1 we refused to
 make that application to ,wheal ,virgin
 engines in ,cornwall1 and to some      
others2 our reasons were1 that though it
 might have enabled them to have gone   
deeper with their present engines1 yet1 
the savings of fuel would not have been 
great1 in comparison to the complete    
machine4 ,by adding condensers to       
engines that were not in good order1 our
 engine would have been introduced into 
that country 7which we look upon as our 
richest mine7 in an unfavourable point  
of view1 and without such profits as    
would have been satisfactory either to  
us or to the adventurers2 and if we had 
granted the use of condensers to one1 we
 must have done so to all1 and thereby  

have curtailed our profits1 and perhaps 
injured our reputation4 ,besides1 where 
a new engine is to be erected1 and to be
 equally well executed in point of      
workmanship and materials1 an engine of 
the same power cannot be constructed    
materially cheaper on the old plan than 
on ours2 for our boiler and cylinder are
 much smaller1 and the building1 the    
lever1 the chains1 together with all the
 pump and pit work1 are only the same4  
99 99 99 99  ,we charge our profits in  
proportion to the saving made in fuel by
 our engine1 when compared with a common
 one which burns the same kind of coals2
 we ask one third of these savings to be
 paid us annually1 or half yearly2 the  
payment being redeemable in the option  
of our employer1 at ten years' purchase2
 and when the coals are low priced1 we  
should also make some charge as         
engineers4 ,in all these comparisons our
 own interest has made us except your   
7,mr4 ,smeaton7 improved engines1 unless
 we were allowed a greater proportion of

 the savings4  ,their exertions to      
improve the manufacture of engines at   
,soho is shown by the following letter  
from ,mr4 ,boulton1 in the same         
correspondence to ,mr4 ,smeaton3--  ,we 
are systematising the business of engine
 making1 as we have done before in the  
button manufactory2 we are training up  
workmen1 and making tools and machines  
to form the different parts of ,mr4     
,watt's engines with more accuracy1 and 
at a cheaper rate than can possibly be  
done by the ordinary methods of working4
 ,our workshop and apparatus will be of 
,pg#aef sufficient extent to execute all
 the engines which are likely to be soon
 wanted in this country2 and it will not
 be worth the expense for any other     
engineers to erect similar works1 for   
that would be like building a mill to   
grind a bushel of corn4  ,i can assure  
you from experience1 that our small     
engine at ,soho is capable of raising   
#ejj1jjj cubic feet of water #a foot    
high with every #aab lbs4 of coals1 and 

we are in hopes of doing much more4 ,mr4
 ,watt's engine has a very great        
advantage in mines1 which are           
continually working deeper3 suppose1 for
 instance1 that a mine is #ej fathoms   
deep1 you may have an engine which will 
be equal to draining the water when the 
mine is worked1 to #ajj fathoms deep1   
and yet you can constantly adapt the    
engine to its load1 whether it be #ej or
 #ajj fathoms1 or any intermediate      
depth2 and the consumption of coals will
 be less in proportion when working at  
the lesser than at the greater depths2  
supposing it works1 as our engines      
generally do1 at #aa lbs4 per square    
inch1 when the mine becomes #ajj fathoms
 deep4   7#he47 ,the great improvement  
which has been introduced within the    
last half century1 in the details of    
,watt's steam engine1 will be rendered  
manifest by comparing the effects of a  
given weight of fuel here supplied by   
,mr4 ,boulton with the effects which the
 same weight of fuel is now known to    

produce in the best pumping engines     
worked in ,cornwall4 ,one of these      
engines1 in good working order1 has been
 known to raise #abe1jjj1jjj lbs4 #a    
foot high1 by the combustion of a bushel
 of coals4 ,but the average performance 
of even the best engines is below this  
amount4 ,if we take it at #ij1jjj1jjj1  
this will be equivalent to the weight of
 about #a-a_/b million cubic feet of    
water1 a bushel of coals being #c_/d    
cwt4 ,it will therefore follow that1    
with the present engines1 one hundred   
weight of coals is capable of raising   
about two million cubic feet of water   
one foot high1 being a duty four times  
that assigned to the early engines by   
,mr4 ,boulton4   7#hf47 ,at the time    
that ,watt1 in conjunction with ,dr4    
,roebuck1 obtained the patent for his   
improved engine1 the idea occurred to   
him1 that the steam which had impelled  
the piston in its descent rushed from   
the cylinder with a mechanical force    
much more than sufficient to overcome   

any resistance ,pg#aeg which it had to  
encounter in its passage to the         
condenser2 and that such force might be 
rendered available as a moving power1 in
 addition to that already obtained from 
the steam during the stroke of the      
piston4 ,this notion involved the whole 
principle of the expansive action of    
steam1 which subsequently proved to be  
of such importance in the performance of
 steam engines4 ,watt was1 however1 so  
much engrossed at that time1 and        
subsequently1 by the difficulties he had
 to encounter in the construction of his
 engines1 that he did not attempt to    
bring this principle into operation4 ,it
 was not until after he had organised   
that part of the establishment at ,soho 
which was appropriated to the           
manufacture of steam engines1 that he   
proceeded to apply the expansive        
principle4 ,since the date of the patent
 which he took out for this 7#aghb71 was
 subsequent to the application of the   
same principle by another engineer1     

named ,hornblower1 it is right to state1
 that the claim of ,mr4 ,watt to this   
important step in the improvement of the
 steam engine1 is established by a      
letter addressed by him to ,dr4 ,small1 
of ,birmingham1 dated ,glasgow1 ,may1   
#agfi3--  ,i mentioned to you a method  
of still doubling the effect of the     
steam1 and that tolerably easy1 by using
 the power of steam rushing into a      
vacuum1 at present lost4 ,this would do 
little more than double the effect1 but 
it would too much enlarge the vessels to
 use it all3 it is peculiarly applicable
 to wheel engines1 and may supply the   
want of a condenser1 where the force of 
steam only is used2 for open one of the 
steam valves1 and admit steam until one 
fourth of the distance between it and   
the next valve is filled with steam1    
then shut the valve1 and the steam will 
continue to expand1 and to press round  
the wheel1 with a diminishing power1    
ending in one fourth of its first       
exertion4 ,the sum of the series you    

will find greater than one half1 though 
only one fourth of steam was used4 ,the 
power will indeed be unequal1 but this  
can be remedied by a fly1 or by several 
other means4  ,in #aggf the engine1     
which had been then recently erected at 
,soho1 was adapted to act upon the      
principle of expansion4 ,when the piston
 had been pressed down in the cylinder  
for a certain portion of the stroke1 the
 further supply of steam ,pg#aeh from   
the boiler was cut off1 by closing the  
upper steam valve1 and the remainder of 
the stroke was accomplished by the      
expansive power of the steam which had  
already been introduced into the        
cylinder4   7#hg47 ,to make this method 
of applying the force of steam          
intelligible1 some previous explanation 
of mechanical principles will be        
necessary4  ,if a body which offers a   
certain resistance be urged by a certain
 moving force1 the motion which it will 
receive will depend on the relation     
between the energy of the moving force  

and the amount of the resistance opposed
 to it4 ,if the moving force be         
precisely equal to the resistance1 the  
motion which the body will receive will 
be perfectly uniform4  ,if the energy of
 the moving force be greater than the   
resistance1 then its surplus or excess  
above the amount of resistance will be  
expended in imparting momentum to the   
mass of the body moved1 and the latter  
will1 consequently1 continually acquire 
augmented speed4 ,the motion of the body
 will1 therefore1 be in this case       
accelerated4  ,if the energy of the     
moving force be less in amount than the 
resistance1 then all that portion of the
 resistance which exceeds the amount of 
the moving force will be expended in    
depriving the mass of the body of       
momentum1 and the body will therefore be
 moved with continually diminished speed
 until it be brought to rest4   7#hh47  
,whenever1 therefore1 a uniform motion  
is produced in a body1 it may be taken  
as an indication of the equality of the 

moving force to the resistance2 and1 on 
the other hand1 according as the speed  
of the body is augmented or diminished1 
it may be inferred that the energy of   
the moving force has been greater or    
less than the resistance4  ,it is an    
error to suppose that rest is the only  
condition possible for a body to assume 
when under the operation of two or more 
mechanical forces which are in          
equilibrium4 ,by the laws of motion the 
state of a body which is not under the  
operation of any external force must be 
either in a state of rest or of uniform 
motion4 ,whichever be its state1 it will
 suffer no change if the body be brought
 under the operation of two or more     
forces which are in equilibrium2 for to 
suppose ,pg#aei such forces to produce  
any change in the state of the body1    
whether from rest to motion1 or vice    
vers1 or in the velocity of the motion  
which the body may have previously had1 
would be equivalent to a supposition    
that the forces applied to the body     

being in equilibrium were capable of    
producing a dynamical effect1 which     
would be a contradiction in terms4      
,this1 though not always clearly        
understood by mere practical men1 or by 
persons superficially informed1 is1 in  
fact1 among the fundamental principles  
of mechanical science4   7#hi47 ,when   
the piston is at the top of the         
cylinder1 and about to commence its     
motion downwards1 the steam acting upon 
it will have not only to overcome the   
resistance arising from the friction of 
the various parts of the engine1 but    
will also have to put in motion the     
whole mass of matter of the piston pump 
rods1 pump pistons1 and the column of   
water in the pump barrels4 ,besides     
imparting to this mass the momentum     
corresponding to the velocity with which
 it will be moved1 it will also have to 
encounter the resistance due to the     
preponderance of the weight of the water
 and pump rods over that of the steam   
piston4 ,the pressure of steam1         

therefore1 upon the piston at the       
commencement of the stroke must1 in     
accordance with the mechanical          
principles just explained1 have a       
greater force than is equal to all the  
resistances which it would have to      
overcome1 supposing the mass to be      
moving at a uniform velocity4 ,the      
moving force1 therefore1 being greater  
than the resistance1 the mass1 when put 
in motion1 will necessarily move with a 
gradually augmented speed1 and the      
piston of the engine which has been     
described in the last chapter would     
necessarily move from the top to the    
bottom of the cylinder with an          
accelerated motion1 having at the moment
 of its arrival at the bottom a greater 
velocity than at any other part of the  
stroke4 ,as the piston and all the      
matter which it has put in motion must  
at this point come to rest1 the momentum
 of the moving mass must necessarily    
expend itself on some part of the       
machinery1 and would be so much         

mechanical force lost4 ,it is evident1  
therefore1 independently of any         
consideration of the expansive          
principle1 to which we shall presently  
refer1 that the action of the ,pg#afj   
moving power in the descent of the      
piston ought to be suspended before the 
arrival of the piston at the bottom of  
the cylinder1 in order to allow the     
momentum of the mass which is in motion 
to expend itself1 and to allow the      
piston to come gradually to rest at the 
termination of the stroke4  ,thus1 if we
 were to suppose that after the piston  
had descended through three fourths of  
the whole length of the cylinder1 and   
had acquired a certain velocity1 the    
steam above it were suddenly condensed1 
so as to leave a vacuum both above and  
below it1 the piston1 being then subject
 to no impelling force1 would still move
 downwards1 in virtue of the momentum it
 had acquired1 until the resistance     
would deprive it of that momentum1 and  
bring it to rest2 and if the remaining  

fourth part of the cylinder were        
necessary for the accomplishment of     
this1 then it is evident that that part 
of the stroke would be accomplished     
without further expenditure of the      
moving power4  ,in fact1 this part of   
the stroke would be made by the         
expenditure of that excess of moving    
power1 which1 at the commencement of the
 stroke1 had been employed in putting   
the machinery and its load in motion1   
and in subsequently accelerating that   
motion4  ,although under such           
circumstances the resistance1 during the
 operation of the moving power1 shall   
not have been at any time equal to the  
moving power1 since while the motion was
 accelerated it was less1 and while     
retarded greater than that power1 yet as
 the whole moving power has been        
expended upon the resistance1 the       
mechanical effect which the moving power
 has produced under such circumstances  
will be equal to the actual amount of   
that power4 ,if in an engine of this    

kind the steam was not cut off till the 
conclusion of the stroke1 a part of the 
moving power would be lost upon those   
fixed points in the machinery which     
would sustain the shock produced by the 
instantaneous cessation of motion at the
 end of the stroke4  ,independently1    
therefore1 of any consideration of the  
expansive principle1 it appears that1 in
 an engine of this kind1 the steam ought
 to be cut off before the completion of 
the stroke4 ,pg#afa  ,illustration3     
,fig4 #bh4   7#ij47 ,to render the      
expansive action of steam intelligible1 
let ,a ,b 7fig4 #bh47 represent a       
cylinder whose area we will suppose1 for
 the sake of illustration1 to be a      
square foot1 and whose length1 ,a ,b1   
shall also be a foot4 ,if steam of a    
pressure equal to the atmosphere be     
supplied to this cylinder1 it will exert
 a pressure of about one ton on the     
piston2 and if such steam be uniformly  
supplied from the boiler1 the piston    
will be moved from ,a to ,b with the    

force of one ton1 and that motion will  
be uniform if the piston be opposed     
throughout the same space by a          
resistance equal to a ton4 ,when the    
piston has arrived at ,b1 let us suppose
 that the further supply of steam from  
the boiler is stopped by closing the    
upper steam valve1 and let us also      
suppose the cylinder to be continued    
downwards so that ,b ,c shall be equal  
to ,a ,b1 and suppose that ,b ,c has    
been previously in communication with   
the condenser1 and is therefore a       
vacuum4 ,the piston at ,b will then be  
urged with a force of one ton downwards1
 and as it descends the steam above it  
will be diffused through an increased   
volume1 and will consequently acquire a 
diminished pressure4 ,we shall1 for the 
present1 assume that this diminution of 
pressure follows the law of elastic     
fluids in general2 that it will be      
decreased in the same proportion as the 
volume of the steam is augmented4 ,while
 the piston1 therefore1 moves from ,b   

downwards it will be urged by a         
continually decreasing force4 ,let us   
suppose1 that by some expedient1 it is  
also subject to a continually decreasing
 resistance1 and that this resistance   
decreases in the same proportion as the 
force which urges the piston4 ,in that  
case the motion of the piston would     
continue uniform4 ,when the piston would
 arrive at ,p1 the middle of the second 
cylinder1 then the space occupied by the
 steam being increased in the proportion
 of #b to #c1 the pressure on the piston
 would be diminished in the proportion  
of #c to #b1 and the pressure at ,b     
being one ton1 it would be two-thirds of
 a ton at ,p4 ,in like manner when the  
piston would arrive at ,c1 the space    
occupied by the steam being double that 
which ,pg#afb it occupied when the      
piston was at ,b1 the pressure of the   
steam would be half its pressure at ,b1 
and therefore at the termination of the 
stroke1 the pressure on the piston would
 be half a ton4  ,if the space from ,b  

to ,c1 through which the steam is here  
supposed to act expansively1 be divided 
into ten equal parts1 the pressure on   
the piston at the moment of passing each
 of those divisions would be calculated 
upon the same principle as in the cases 
now mentioned4 ,after moving through the
 first division1 the volume of the steam
 would be increased in the proportion of
 #aj to #aa1 and therefore its pressure 
would be diminished in the proportion of
 #aa to #aj4 ,the pressure1 therefore1  
driving the piston at the end of the    
first of these ten divisions would be   
#aj_/aaths of a ton4 ,in like manner1   
its pressure at the second of the       
divisions would be #aj_/abths of a ton1 
and the third #aj_/acths of a ton2 and  
so on1 as indicated in the figure4  ,now
 if the pressure of the steam through   
each of these divisions were to continue
 uniform1 and1 instead of gradually     
diminishing1 to suffer a sudden change  
in passing from one division to another1
 then the mechanical effect produced    

from ,b to ,c would be obtained by      
taking a mean or average of the several 
pressures throughout each of the ten    
divisions4 ,in the present case it has  
been supposed that the force on the     
piston at ,b was #bbdj pounds4 ,to      
obtain the pressure in pounds           
corresponding to each of the successive 
divisions1 it will therefore only be    
necessary to multiply #bbdj by #aj1 and 
to divide it successively by #aa1 #ab1  
#ac1 c4 ,the pressures1 therefore1 in   
pounds1 at each of the ten divisions1   
will be as follows3--     #ast          
#bjcfc    #b;d      #ahfff    #c;d      
#agbca    #dth     #afjjj    #eth       
#adicc    #fth     #adjjj    #gth       
#acagf    #hth     #abddd    #ith       
#aagij   #ajth     #aabjj  ,if the mean 
of these be taken by adding them        
together ,pg#afc and dividing by #aj1 it
 will be found to be #adih pounds4 ,it  
appears1 therefore1 that the pressures  
through each of the ten divisions being 
supposed to be uniform 7which however1  

strictly1 they are not17 the mechanical 
effect of the steam from ,b to ,c would 
be the same as if it acted uniformly    
throughout that space upon the piston   
with a force of about #aejj pounds1     
being rather less than three-fourths of 
its whole effect from ,a to ,b4  ,but it
 is evident that this principle will be 
equally applicable if the second        
cylinder had any other proportion to the
 first4 ,thus it might be twice the     
length of the first2 and in that case1 a
 further mechanical effect would be     
obtained from the expansion of the      
steam4  ,the more accurate method of    
calculating the effect of the expansion 
from ,b to ,c1 would involve more       
advanced mathematical principles than   
could properly be introduced here2 but  
the result of such a computation would  
be that the actual average effect of the
 steam from ,b to ,c would be equal to a
 uniform pressure through that space1   
amounting to one thousand five hundred  
and forty-five pounds1 being greater    

than the result of the above            
computation1 the difference being due to
 the expansive action through each of   
the ten divisions1 which was omitted in 
the above computation4   7#ia47 ,it is  
evident that the expansive principle1 as
 here explained1 involves the condition 
of a variation in the intensity of the  
moving power4 ,thus1 if the steam act   
with a uniform energy on the piston so  
long as its supply from the boiler      
continues1 the moment that supply is    
stopped1 by closing the steam valve1 the
 steam contained in the cylinder will   
fill a gradually increasing volume by   
the motion of the piston1 and therefore 
will act above the piston with a        
gradually decreasing energy4 ,if the    
resistance to the moving power produced 
by the load1 friction1 c4 be not subject
 to a variation corresponding precisely 
to such variation in the moving power1  
then the consequence must be that the   
motion imparted to the load will cease  
to be uniform4 ,if the energy of the    

moving power at any part of the stroke  
be greater than the resistance1 the     
motion produced will be accelerated2 if 
it be less1 the motion will be retarded2
 and if it be at one time greater1 and  
another ,pg#afd time less1 as will      
probably happen1 then the motion will be
 alternately accelerated and retarded4  
,this variation in the speed of the body
 moved will not1 however1 affect the    
mechanical effect produced by the power1
 provided that the momentum imparted to 
the moving mass be allowed to expend    
itself at the end of the stroke1 so that
 the piston may be brought to rest as   
nearly as possible by the resistance of 
the load1 and not by any shock on any   
fixed points in the machine4 ,this is an
 object which1 consequently1 should be  
aimed at with a view to the economy of  
power1 independently of other           
considerations connected with the wear  
and tear of the machinery4 ,so long as  
the engine is only applied to the       
operation of pumping water1 great       

regularity of motion is not essential1  
and1 therefore1 the variation of speed  
which appears to be an almost inevitable
 consequence of any extensive           
application of the expansive principle1 
is of little importance4 ,in the patent 
which ,watt took out for the application
 of the expansive principle1 he         
specified several methods of producing a
 uniform effect upon a uniform          
resistance1 notwithstanding the         
variation of the energy of the power    
which necessarily attended the expansion
 of the steam4 ,this he proposed to     
accomplish by various mechanical means1 
some of which had been previously       
applied to the equalisation of a varying
 power4 ,one consisted in causing the   
piston to act on a lever1 which should  
have an arm of variable length1 the     
length increasing in the same proportion
 as the energy of the moving power      
diminished4 ,this was an expedient which
 had been already applied in mechanics  
for the purpose of equalising a varying 

power4 ,a well-known example of it is   
presented in the main-spring and fuzee  
of a watch4 ,according as the watch goes
 down1 the main-spring becomes relaxed1 
and its force is diminished2 but1 at the
 same time1 the chain by which it drives
 the fuzee acts upon a wheel or circle1 
having a diameter increased in the same 
proportion as the energy of the spring  
is diminished4  ,another expedient      
consisted in causing the moving power1  
when acting with greatest energy1 to    
lift a weight which should be allowed to
 descend again1 assisting the piston    
when the energy of the moving force was 
diminished4 ,pg#afe  ,another method    
consisted in causing the moving force1  
when acting with greatest energy1 to    
impart momentum to a mass of inert      
matter1 which should be made to restore 
the same force when the moving power was
 more enfeebled4 ,we shall not more than
 allude here to these contrivances      
proposed by ,watt1 since their          
application has never been found        

advantageous in cases where the         
expansive principle is used4   7#ib47   
,the application of the expansive       
principle in the engines constructed by 
,boulton and ,watt1 was always very     
limited1 by reason of their confining   
themselves to the use of steam having a 
pressure not much exceeding that of the 
atmosphere4 ,if the principle of        
expansion1 as above explained1 be       
attentively considered1 it will be      
evident that the extent of its          
application will mainly depend on the   
density and pressure of the steam       
admitted from the boiler4 ,if the       
density and pressure be not considerable
 when the steam is cut off1 the extent  
of its subsequent expansion will be     
proportionally limited4 ,it was in      
consequence of this1 that this principle
 from which considerable economy of     
power has been derived1 was applied with
 much less advantage by ,mr4 ,watt than 
it has since been by others1 who have   
adopted the use of steam of much higher 

pressure4 ,in the engines of ,boulton   
and ,watt1 where the expansive principle
 was applied1 the steam was cut off     
after the piston had performed from one 
half to two thirds of the stroke1       
according to the circumstances under    
which the engine was worked4 ,the       
decreasing pressure produced by         
expansion was1 in this case1 especially 
with the larger class of engines1 little
 more than would be necessary to allow  
the momentum of the mass moved to spend 
itself1 before the arrival of the piston
 at the end of the stroke4              
,subsequently1 however1 boilers         
producing steam of much higher pressure 
were applied1 and the steam was cut off 
when the piston had performed a much    
smaller part of the whole stroke4 ,the  
great theatre of these experiments and  
improvements has been the mining        
districts in ,cornwall1 where1 instead  
of working with steam of a pressure not 
much exceeding that of the atmosphere1  
it has been found advantageous to use   

steam whose pressure is at least four   
times as great as ,pg#aff that of the   
atmosphere2 and instead of limiting its 
expansion to the last half or fourth of 
the stroke1 it is cut off after the     
piston has performed one fourth part of 
the stroke or less1 all the remainder of
 the stroke being accomplished by the   
expansive power of the steam1 and by    
momentum4  ,illustration3 ,,bridge      
,,over ,,the ,,clyde ,,at ,,hamilton1   
,,designed ,,by ,,watt4  ,pg#afg        
,illustration3 ,,double-,,acting        
,,engine1 ,,zinc ,,works1 ,,city ,,road1
 ,,london4  ,,chap4 ,,vii4              
,,properties ,,of ,,steam4 -- ,,common  
,,steam4 -- ,,superheated ,,steam4 --   
,,law ,,of ,,dalton ,,and ,,gay         
,,lussac4 -- ,,law ,,of ,,mariotte4 --  
,,relation     ,,between ,,temperature  
,,and ,,pressure ,,of ,,common ,,steam4 
-- ,,effects ,,of     ,,the ,,expansion 
,,of ,,common ,,steam4 -- ,,mechanical  
,,effects ,,of ,,steam4     -- ,,method 
,,of ,,equalising ,,the ,,expansive     

,,force4 -- ,,hornblower',s             
,,engine4 -- ,,woolf',s ,,engine4 --    
,,watt',s ,,attempts ,,to ,,extend ,,the
     ,,steam ,,engine ,,to              
,,manufactures4 -- ,,papin',s           
,,projected ,,applications     ,,of     
,,the ,,steam ,,engine4 -- ,,savery',s  
,,applications ,,of ,,the ,,engine ,,to 
,,move ,,machinery4 -- ,,jonathan       
,,hull',s ,,application ,,to ,,water    
,,wheels4     -- ,,stewart',s           
,,application ,,of ,,the ,,engine ,,to  
,,mill ,,work4 --     ,,washborough',s  
,,application ,,of ,,the ,,fly ,,wheel  
,,and ,,crank4 -- ,,watt',s     ,,second
 ,,patent4 -- ,,double-,,action         
,,valves4   7#ic47 ,since the           
application of the expansive action of  
steam involves the consideration of its 
properties when it ceases to be in      
contact with the water from which it was
 produced1 and likewise the variation of
 its pressure in different states of    
,pg#afh density and at different        
temperatures1 it is necessary here to   

explain some of the most important of   
these properties of vapour4  ,steam may 
exist in two states1 distinguished from 
each other by the following             
circumstances3--  #ast4 ,it may be such 
that the abstraction from it of any     
portion of heat1 however small1 will    
cause its partial condensation4  #b;d4  
,it may be such as to admit of the      
abstraction of heat from it without     
undergoing any other change than that   
which air would undergo under like      
circumstances1 viz4 a diminution of     
temperature and pressure4   7#id47 ,we  
shall call1 for distinction1 the former 
,common ,steam1 and the latter          
,superheated ,steam4  ,illustration3    
,fig4 #bi4  ,to explain the             
circumstances out of which these        
properties arise1 let ,b 7fig4 #bi47 be 
imagined to be a vessel filled with     
water1 communicating by a pipe and      
stopcock with another vessel ,a1 which  
in the commencement of the process may  
be conceived to be filled with air4 ,let

 ,d be a pipe and stopcock at the top of
 this vessel4 ,if the vessel ,b be      
heated1 and the two cocks be opened1 the
 steam proceeding from the water in ,b  
will blow the air out of the vessel ,a  
through the open stopcock ,d1 in the    
same manner as air is blown from a steam
 engine4 ,when the vessel ,a by these   
means has been filled with pure steam1  
let both stopcocks be closed4 ,if the   
steam in ,a1 under these circumstances1 
have a pressure of #ae lbs4 per square  
inch1 its temperature will be found to  
be #bac4 ,now1 if any heat be abstracted
 from this steam1 its temperature will  
fall1 and a portion of it will be       
reconverted into water4  ,again1 suppose
 the vessel ,a to be filled with pure   
steam which has been produced from the  
heated water in ,b1 the stopcock ,c     
being open4 ,let the stopcock ,c be then
 closed1 and the water in ,b be heated  
to a higher temperature1 the temperature
 and pressure of the steam in ,a being  
observed4 ,if the stopcock ,c be now    

opened1 the steam in ,a will be         
immediately observed to rise to the more
 elevated temperature which has been    
imparted to the water in ,b1 and at the 
same time it will acquire an increased  
pressure4 ,pg#afi  ,the increase of     
temperature which it has received would 
of itself produce an increased pressure2
 but that this is not the sole cause of 
the augmented pressure in the present   
case might be proved by weighing the    
vessel ,a4 ,it would be found to have   
increased weight1 which could only arise
 from its having received from the water
 in ,b an additional quantity of vapour4
 ,the increased pressure therefore1     
which the steam in ,a has acquired1 is  
due conjointly to its increased density 
and its increased temperature4 ,in      
general1 if the water in the vessel ,b  
be raised or lowered in temperature1 the
 steam in the vessel ,a will rise and   
fall in temperature in a corresponding  
manner1 always having the same          
temperature as the water in ,b4 ,if the 

weight of the vessel ,a were observed1  
it would be found to increase with every
 increase of temperature1 and to        
diminish with every diminution of       
temperature1 proving that the augmented 
temperature of the water in ,b produces 
an augmented density of the steam in ,a4
 ,the same pressure would be found      
always to correspond to the same        
temperature and density1 so that if the 
numerical amount of any one of the three
 quantities1 the temperature1 the       
pressure1 or the density1 were known1   
the other two must necessarily be       
determined1 the same temperature always 
corresponding to the same pressure1 and 
vice vers4 ,and in like manner1 steam   
produced under these circumstances of   
the same density cannot have different  
pressures4 ,it must be observed that the
 steam here produced receives all the   
heat which it possesses from the water  
from which it is raised4 ,now it is     
easily demonstrable1 that this is the   
least quantity of heat which is         

compatible with the steam maintaining   
the vaporous form2 for if the stopcock  
,c be closed so as to separate the steam
 in ,a from the water in ,b1 and that   
any portion of heat1 however small1 be  
then abstracted from the steam in ,a1   
some portion of the steam will be       
reconverted into water4  ,this then1    
according to the definition already     
given1 is ,common ,steam4   7#ie47 ,let 
us now suppose that the vessel ,a1 being
 in communication with the vessel ,b by 
the open stopcock1 has been filled with 
pure steam of any given temperature4    
,the steam which it thus contains will  
be common steam1 and1 as has been       
,pg#agj shown 7#id471 it cannot lose any
 portion of heat1 however small1 without
 being partially condensed2 but let the 
stopcock ,c be closed1 and let the steam
 in ,a be then exposed to any source of 
heat by which its temperature may be    
raised any required number of degrees4  
,from the steam thus obtained heat may  
be abstracted without producing any     

condensation2 and such abstraction of   
heat may be continued without producing 
condensation1 until the steam is cooled 
down to that temperature at which it was
 raised from the water in ,b1 when the  
stopcock ,c was opened4 ,any further    
reduction of temperature would be       
attended with condensation4  ,if after  
increasing the temperature of the steam 
in ,a1 the stopcock ,c being shut so as 
to render it superheated steam1 its     
pressure be observed1 the pressure will 
be found to be increased1 but not to    
that amount which it would have been    
increased had the steam in ,a been      
raised to the same temperature by       
heating the water in ,b to that         
temperature1 and keeping the stopcock   
open4 ,in fact1 its present augmented   
pressure will be due only to its        
increased temperature1 since its density
 remains unchanged4 ,but if in these    
circumstances the stopcock ,c be        
suddenly opened1 the pressure of the    
steam in ,a will as suddenly rise to    

that pressure which in common steam     
corresponds to its temperature2 and if  
the vessel ,a were weighed1 it would be 
found to have increased in weight1      
proving that the steam contained in it  
has received increased density by an    
increased quantity of vapour proceeding 
from the water in ,a4 ,in fact1 by      
opening the stopcock the steam which was
 before superheated steam1 has become   
common steam4 ,it has the greatest      
density which steam of that temperature 
can have2 and consequently1 if any heat 
be abstracted from it1 a partial        
condensation will ensue4  ,to render    
these general principles more           
intelligible1 let us suppose that the   
water in ,b is raised to the temperature
 of #bac1 the stopcock ,c being open2   
the vessel ,a will then be filled with  
steam of the same temperature1 and      
having a pressure of #ae lbs4 per square
 inch4 ,this will be common steam4 ,if  
the stopcock be now closed1 and the     
whole apparatus be exposed to the       

temperature of #bdc2 the steam in ,a    
will preserve the same density1 but its 
pressure will be ,pg#aga increased from 
#ae lbs4 to a little more than #af lbs4 
per square inch4 ,let the stopcock ,c be
 then opened and while the temperature  
of the steam in ,a shall continue to be 
#bdc1 the pressure will suddenly rise   
from #af lbs4 to about #bf lbs4 per     
square inch4 ,the weight of the steam in
 ,a will be at the same time increased  
in the same proportion of #af to #bf as 
its pressure4 ,the steam thus produced  
in ,a will then be common steam1 and any
 abstraction of heat from it would be   
attended with partial condensation4     
7#if47 ,the law1 according to which the 
pressure of elastic fluids in general1  
whether gases or vapours1 increases with
 their temperature1 was simultaneously  
discovered by ,dalton and ,gay ,lussac4 
,if the pressure which the gas or vapour
 would have at the temperature of       
melting ice1 were expressed by #aj1jjj1 
then the increase of pressure which it  

would receive for every degree of       
temperature by which it would be raised1
 its volume being supposed to be        
preserved1 would be expressed by        
#bjh-a_/c4 ,thus1 if the pressure of    
gas1 or vapour1 on a surface of a       
certain magnitude at the temperature of 
#cb were #aj1jjj ounces1 then the same  
gas or vapour would acquire an          
additional pressure of #bjh-a_/c ounces 
for every degree of temperature which   
would be imparted to it above #cb4 ,this
 law is common to all gases and vapours4
  ,it may be objected that water cannot 
exist in the state of vapour under the  
usual pressures at so low a temperature 
as melting ice4 ,this1 however1 does not
 hinder the application of the above    
law1 for that law will equally hold good
 by computing the pressure which the    
vapour would have if it were a permanent
 gas1 and if it could therefore exist in
 the elastic form at that low           
temperature4   7#ig47 ,another law1     
common to all elastic fluids1 and of    

equal importance with the former1 was   
discovered by ,mariotte4 ,by this law it
 appears that every gas or vapour1 so   
long as its temperature is unchanged1   
will have a pressure directly           
proportional to its density4 ,if        
therefore1 while we compress steam into 
half its volume1 we could preserve its  
temperature unaltered1 we should        
increase its pressure in a two-fold     
proportion2 but if the process of       
compression should cause its temperature
 to increase1 ,pg#agb then its increase 
of pressure will be greater than its    
increase of density1 since it will be   
due conjointly to the increase of       
density and to the increase of          
temperature4 ,in this case the increased
 pressure may be deduced from the       
combined application of the two laws    
just explained2 that of ,mariotte will  
determine that increase of pressure     
which is due to the increase of density1
 and that of ,dalton and ,gay ,lussac   
will determine the further increase of  

pressure which will be due to the       
increase of temperature4 ,the full      
investigation of these effects1 and the 
formul expressing them1 will be found in
 the ,appendix to this volume4   7#ih47 
,the fixed relations which exist between
 the temperatures of common steam and   
its pressure and density1 have never    
been discovered from any general        
physical principles4 ,the pressures and 
the densities however1 which correspond 
to a great variety of temperatures      
throughout the thermometric scale1 have 
been ascertained by extensive series of 
experiments instituted by philosophers  
of this and other countries4 ,from a    
comparison of the temperatures and      
pressures thus found by experiment1     
empirical formul have been constructed1 
which exhibit1 with an approximation    
sufficiently close for practice1 this   
relation2 and these formul may          
accordingly be used for the computation 
of tables exhibiting the pressures1     
temperatures1 and densities of common   

steam2 and such tables will have        
sufficient numerical accuracy for all   
practical purposes4 ,these formul1 and  
the tables resulting from them1 will be 
found in the ,appendix to this volume4  
7#ii47 ,it has been explained1 that to  
effect the conversion of water into     
steam1 it is only necessary to impart to
 it as much heat as1 added to the       
temperature which it has1 would1 if it  
continued in the liquid form1 raise it  
to the temperature of #abab4 ,this      
condition is necessary1 and sufficient  
to effect the transition of water into  
vapour4 ,if1 for example1 as much heat  
were imparted to the water evaporated1  
as would maintain it in the liquid state
 to #acjj1 then the steam so produced   
would be superheated steam1 having #hj  
of heat more than is necessary to       
maintain it in the vaporous form4 ,from 
such steam1 therefore1 #hj of heat may  
be abstracted without producing any     
condensation4 ,pg#agc   7#ajj47 ,common 
steam being raised from water at any    

pressure and temperature1 and being     
afterwards separated from the water1 if 
the same steam be compressed into a     
small volume1 or allowed to expand into 
a greater volume1 it will still maintain
 its quality of common steam1 and will  
have the same pressure and temperature1 
whatever volume it may assume1 as it    
would have if immediately raised from   
water at that pressure4 ,thus if steam  
be raised from water under a pressure of
 #cj lbs4 per square inch1 and1 being   
separated from the water1 be allowed to 
dilate1 until its pressure is reduced to
 #ae lbs4 per square inch1 its          
temperature will then be reduced to     
#bac1 which is that temperature which it
 would have if immediately raised from  
water under a pressure of #ae lbs4 per  
square inch2 and if any heat be         
abstracted from such steam1 whether     
under its original pressure1 or under   
the diminished pressure of #ae lbs4 per 
square inch1 a condensation will be     
produced1 the amount of which will be   

the same1 if the same quantity of heat  
be abstracted from the steam4 ,these are
 consequences which immediately flow    
from the fact1 that the sum of the      
latent and sensible heats of steam is   
always the same4#bj  ,it appears1       
therefore1 that supposing the steam used
 in an engine to receive no additional  
heat after it leaves the boiler1 however
 it may be changed in its density by    
subsequent expansion1 it will still     
retain its character of common steam1   
and cannot lose any portion of heat1    
however small1 without suffering partial
 condensation4 ,the mechanical force    
also exerted by such steam1 after       
expansion1 must be computed in the same 
manner as if it were raised immediately4
   7#aja47 ,if the law of ,mariotte were
 strictly applicable to steam1 its      
mechanical effect would be the same as  
has been already explained in all states
 of density2 but since its temperature  
will rise and fall as its density is    
increased or diminished1 a corresponding

 change will be produced in its ,pg#agd 
mechanical efficacy4 ,it is therefore   
necessary in the calculation of the     
mechanical effect of steam1 whether it  
be used at a uniform pressure without   
the principle of expansion1 or with the 
application of that principle to any    
given extent1 to take into account the  
combined operation of the laws of       
,mariotte and ,dalton4 ,formul          
exhibiting the relation between the     
temperatures1 pressures1 volumes1 and   
densities of steam1 and the mechanical  
effect produced by the evaporation of   
water1 whether acting with or without   
expansion1 together with the tables     
necessary for the practical application 
of these1 will be found in the          
,appendix4   7#ajb47 ,one of the methods
 of equalising the varying force of     
expanding steam1 would be to work it at 
the same time in two cylinders connected
 with the same beam2 so that while its  
force in one would be augmented1 its    
force in the other would be diminished1 

the combination of the two producing a  
uniform effect4 ,soon after the         
expansive principle was promulged by    
,mr4 ,watt1 this expedient was          
accordingly resorted to by an engineer  
named ,hornblower4  ,illustration3 ,fig4
 #cj4  ,in the year #agha1 ,hornblower  
conceived the notion of working an      
engine with two cylinders of different  
sizes1 by allowing the steam to flow    
freely from the boiler until it fills   
the smaller cylinder1 and then          
permitting it to expand into the greater
 one1 employing it thus to press down   
two pistons in the following manner4    
,let ,c1 fig4 #cj41 be the centre of the
 great working-beam1 carrying two arch  
heads1 on which the chains of the piston
 rods play4 ,the distances of these arch
 heads from the centre ,c must be in the
 same proportion as the length of the   
cylinders1 in order that the same play  
of the beam may correspond to ,pg#age   
the plays of both pistons4 ,let ,f be   
the steam-pipe from the boiler1 and ,g a

 valve to admit the steam above the     
lesser piston4 ,h is a tube by which a  
communication may be opened by the valve
 ,i1 between the top and bottom of the  
lesser cylinder ,b4 ,k is a tube        
communicating by the valve ,l1 between  
the bottom of the lesser cylinder ,b and
 the top of the greater cylinder ,a4 ,m 
is a tube communicating1 by the valve   
,n1 between the top and bottom of the   
greater cylinder ,a2 and ,p a tube      
leading to the condenser by the         
exhausting valve ,o4  ,at the           
commencement of the operation1 suppose  
all the valves opened1 and steam allowed
 to flow through the engine until the   
air be completely expelled1 and then let
 all the valves be closed4 ,to start the
 engine1 let the exhausting valve ,o and
 the steam valves ,g and ,l be opened1  
as in fig4 #cj4 ,the steam will flow    
freely from the boiler1 and press upon  
the lesser piston1 and at the same time 
the steam below the greater piston will 
flow into the condenser1 leaving a      

vacuum in the greater cylinder4 ,the    
valve ,l being opened1 the steam which  
is under the piston in the lesser       
cylinder will flow through ,k1 and press
 on the greater piston1 which1 having a 
vacuum beneath it1 will consequently    
descend4 ,at the commencement of the    
motion1 the lesser piston is as much    
resisted by the steam below it1 as it is
 urged by the steam above it2 but after 
a part of the descent has been effected1
 the steam below the piston1 in the     
lesser cylinder1 passing into the       
greater1 expands into an increased      
space1 and therefore loses part of its  
elastic force4 ,the steam above the     
lesser piston retaining its full force  
by having a free communication with the 
boiler by the valve ,g1 the lesser      
piston will be urged by a force equal to
 the excess of the pressure of this     
steam above the diminished pressure of  
the expanded steam below it4 ,as the    
pistons descend1 the steam which is     
between them is continually increasing  

in its bulk1 and therefore decreasing in
 its pressure1 from whence it follows1  
that the force which resists the lesser 
piston is continually decreasing1 while 
that which presses it down remains the  
same1 and therefore the effective force 
which impels it must be continually     
increasing4 ,pg#agf  ,on the other hand1
 the force which urges the greater      
piston is continually decreasing1 since 
there is a vacuum below it1 and the     
steam which presses it is continually   
expanding into an increased bulk4       
,illustration3 ,fig4 #ca4  ,impelled in 
this way1 let us suppose the pistons to 
have arrived at the bottoms of the      
cylinders1 and let the valves ,g1 ,l1   
and ,o1 be closed1 and the valves ,i and
 ,n opened4 ,no steam is allowed to flow
 from the boiler1 ,g being closed1 nor  
any allowed to pass into the condenser1 
since ,o is closed1 and all             
communication between the cylinders is  
stopped by closing ,l4 ,by opening the  
valve ,i1 a free communication is made  

between the top and bottom of the lesser
 piston through the tube ,h1 so that the
 steam which presses above the lesser   
piston will exert the same pressure     
below it1 and the piston is in a state  
of indifference4 ,in the same manner the
 valve ,n being open1 a free            
communication is made between the top   
and bottom of the greater piston1 and   
the steam circulates above and below the
 piston1 and leaves it free to rise4 ,a 
counterpoise attached to the pump-rods1 
in this case1 draws up the piston1 as in
 ,watt's single engine2 and when they   
arrive at the top1 the valves ,i and ,n 
are closed1 and ,g1 ,l1 and ,o1 opened1 
and the next descent of the pistons is  
produced in the manner already          
described1 and so the process is        
continued4  ,the valves are worked by   
the engine itself1 by means similar to  
some of those already described4 ,by    
computation1 we find the power of this  
engine to be nearly the same as a       
similar engine on ,watt's expansive     

principle4 ,it does not1 however1       
appear1 that any adequate advantage was 
gained by this modification of the      
principle1 since no engines of this     
construction are now made4   7#ajc47    
,the use of two cylinders was revived by
 ,arthur ,woolf in #ahjd1 who1 in this  
and the succeeding year1 obtained       
patents for the application of steam    
raised under a high pressure to         
double-cylinder engines4 ,the           
specification of his patent states1 that
 he has proved by experiment that steam 
raised ,pg#agg under a safety-valve     
loaded with any given number of pounds  
upon the square inch will1 if allowed to
 expand into as many times its bulk as  
there are pounds of pressure on the     
square inch1 have a pressure equal to   
that of the atmosphere4 ,thus1 if the   
safety-valve be loaded with four pounds 
on the square inch1 the steam1 after    
expanding into four times its bulk1 will
 have the atmospheric pressure2 if it be
 loaded with #e1 #f1 or #aj lbs4 on the 

square inch1 it will have the           
atmospheric pressure when it has        
expanded into #e1 #f1 or #aj times its  
bulk1 and so on4 ,it was1 however1      
understood in this case1 that the vessel
 into which it was allowed to expand    
should have the same temperature as the 
steam before it expands4  ,it is very   
unaccountable how a person of ,mr4      
,woolf's experience in the practical    
application of steam could be led into  
errors so gross as those involved in the
 averments of this patent2 and it is    
still more unaccountable how the        
experiments could have been conducted   
which led him to conclusions not only   
incompatible with all the established   
properties of elastic fluids1 but even  
involving in themselves palpable        
contradiction and absurdity4 ,if it were
 admitted that every additional pound   
avoirdupois which should be placed upon 
the safety-valve would enable steam1 by 
its expansion into a proportionally     
enlarged space1 to attain a pressure    

equal to the atmosphere1 the obvious    
consequence would be1 that a physical   
relation would subsist between the      
atmospheric pressure and the pound      
avoirdupois6 ,it is wonderful that it   
did not occur to ,mr4 ,woolf1 that1     
granting his principle to be true at any
 given place1 it would necessarily be   
false at another place1 where the       
barometer would stand at a different    
height6 ,thus1 if the principle were    
true at the foot of a mountain1 it would
 be false at the top of it2 and if it   
were true in fair weather1 it would be  
false in foul weather1 since these      
circumstances would be attended by a    
change in the atmospheric pressure1     
without making any change in the pound  
avoirdupois4#ba  ,pg#agh   7#ajd47 ,for 
several years after the extension of    
,watt's first patent had been obtained  
from parliament1 he was altogether      
engrossed by the labour of bringing to  
perfection the application of the       
steam-engine to the drainage of mines1  

and in surmounting the numerous         
difficulties which presented themselves 
to its general adoption1 even after its 
manifold advantages were established and
 admitted4 ,when1 however1 these        
obstacles had been overcome1 and the    
works for the manufacture of engines for
 pumping water1 at ,soho1 had been      
organised and brought into active       
operation1 he was relieved from the     
pressure of these anxieties1 and was    
enabled to turn his attention to the far
 more extensive and important uses of   
which he had long been impressed with   
the conviction that the engine was      
capable4 ,his sagacious mind enabled him
 to perceive that the machine he had    
created was an infant force1 which by   
the fostering influence of his own      
genius would one day extend its vast    
power over the arts and manufactures1   
the commerce and the civilisation of the
 world4 ,filled with such aspirations1  
he addressed his attention about the    
year #aggi1 to the adaptation of the    

steam-engine to move machinery1 and     
thereby to supersede animal power1 and  
the natural agents1 wind and water4     
,the idea that steam was capable of     
being applied extensively as a prime    
mover1 had prevailed from a very early  
period2 and now that we have seen its   
powers so extensively brought to bear1  
it will not be uninteresting to revert  
to the faint traces by which its agency 
was sketched in the crude speculations  
of the early mechanical inventors4      
7#aje47 ,papin1 to whom the credit of   
discovering the method of producing a   
vacuum by the condensation of steam is  
due1 was the earliest and most          
remarkable of those projectors4 ,with   
very limited powers of practical        
application1 he was1 nevertheless1      
peculiarly happy in his mechanical      
conceptions2 and had his experience and 
opportunities been proportionate to the 
clearsighted character of his mind1 he  
would doubtless have anticipated some of
 the most memorable of his successors in

 the progressive improvement of the     
steam engine4  ,in his work already     
cited1 after describing his method of   
imparting an alternate motion to a      
piston by the atmospheric ,pg#agi       
pressure acting against a vacuum        
produced by the condensation of steam1  
he stated that his invention1 besides   
being applicable to pumping water1 could
 be available for rowing vessels against
 wind and tide1 which he proposed to    
accomplish in the following manner4     
,paddle-wheels1 such as have since been 
brought into general use1 were to be    
placed at the sides1 and attached to a  
shaft extending across the vessel4      
,within the vessel1 and under this      
shaft1 he proposed to place several     
cylinders supplied with pistons1 to be  
worked by the atmospheric pressure4 ,on 
the piston-rods were to be constructed  
racks furnished with teeth3 these teeth 
were to work in the teeth of wheels or  
pinions1 placed on the shaft of the     
paddle-wheels4 ,these pinions were not  

to be fixed on the shaft1 but to be     
connected with it by a ratchet2 so that 
when they turned in one direction1 they 
would revolve without causing the shaft 
to revolve2 but when driven in the other
 direction1 the catch of the            
ratchet-wheel would act upon the shaft  
so as to compel the shaft and           
paddle-wheels to revolve with the motion
 of the pinion or wheel upon it4 ,by    
this arrangement1 whenever the piston of
 any cylinder was forced down by the    
atmospheric pressure1 the rack          
descending would cause the corresponding
 pinion of the paddle-shaft to revolve2 
and the catch of the ratchet wheel1     
being thus in operation1 would cause the
 paddle-shaft and paddle-wheels also to 
revolve2 but whenever the piston would  
rise1 the rack driving the pinion in the
 opposite direction1 the catch of the   
ratchet wheel would merely fall from    
tooth to tooth1 without driving the     
paddle-shaft4  ,it is evident that by   
such an arrangement a single cylinder   

and piston would give an intermitting   
motion to the paddle-shaft1 the motion  
of the wheel being continued only during
 the descent of the piston2 but if      
several cylinders were provided1 then   
their motion might be so managed1 that  
when one would be performing its        
ascending stroke1 and therefore giving  
no motion to the paddle-shaft1 another  
should be performing its descending     
stroke1 and therefore driving the       
paddle-shaft4 ,as the interval between  
the arrival of the piston at the bottom 
of the cylinder and the commencement    
,pg#ahj of its next descent would have  
been1 in the imperfect machine conceived
 by ,papin1 much longer than the time of
 the descent1 it was evident that more  
than two cylinders would be necessary to
 insure a constantly acting force on the
 paddle-shaft1 and1 accordingly1 ,papin 
proposed to use several cylinders4  ,in 
addition to this1 ,papin proposed to    
construct a boiler having a fireplace   
surrounded on every side by water1 so   

that the heat might be imparted to the  
water with such increased rapidity as to
 enable the piston to make four strokes 
per minute4 ,these projects were        
promulged in #afij1 but it does not     
appear that they were ever reduced to   
experiment4   7#ajf47 ,savery proposed1 
in his original patent1 in #afih1 to    
apply his steam engine as a general     
prime mover for all sorts of machinery1 
by causing it to raise water to make an 
artificial fall1 by which overshot      
water-wheels might be driven4 ,this     
proposal was not acted on during the    
lifetime of ,savery1 but it was at a    
subsequent period partially carried into
 effect4 ,mr4 ,joshua ,rigley erected   
several steam engines on this principle 
at ,manchester1 and other parts of      
,lancashire1 to impel the machinery of  
some of the earliest manufactories and  
cotton mills in that district4 ,the     
engines usually raised the water from   
sixteen to twenty feet high1 from whence
 it was conveyed to an overshot wheel1  

to which it gave motion4 ,the same water
 was repeatedly elevated by the engine1 
so that no other supply was necessary1  
save what was sufficient to make good   
the waste4 ,these engines continued in  
use for some years1 until superseded by 
improved machines4#bb   7#ajg47 ,in     
#agcf1 ,jonathan ,hulls obtained a      
patent for a method of towing ships into
 or out of harbour against wind and     
tide4 ,this method was little more than 
a revival of that proposed by ,papin in 
#afij4 ,the motion1 however1 was to be  
communicated to the paddle-shaft by a   
rope passing over a pulley fixed on an  
axis1 and was to be maintained during   
the returning stroke of the piston by   
the descent of a weight which was       
elevated during the descending stroke4  
,there is no record1 however1 of this   
plan1 any more than that of ,papin1 ever
 having been reduced to experiment4     
7#ajh47 ,during the early part of the   
last century the ,pg#aha manufactures of
 this country had not attained to such  

an extent as to render the moving power 
supplied by water insufficient or       
uncertain to any inconvenient degree2   
and accordingly mills1 and other works  
in which machinery required to be driven
 by a moving power1 were usually built  
along the streams of rivers4 ,about the 
year #agej the general extension of     
manufactures1 and their establishment in
 localities where water power was not   
accessible1 called the steam engine into
 more extensive operation4 ,in the year 
#ageb1 ,mr4 ,champion1 of ,bristol1     
applied the atmospheric engine to raise 
water1 by which a number of overshot    
wheels were driven4 ,these were applied 
to move extensive brass-works in that   
neighbourhood1 and this application was 
continued for about twenty years1 but   
ultimately given up on account of the   
expense of fuel and the improved        
applications of the steam engine4       
,about this time ,smeaton applied       
himself with great activity and success 
to the improvement of wind and water    

mills1 and succeeded in augmenting their
 useful effect in a twofold proportion  
with the same supply of water4 ,from the
 year #agej until the year #aghj he was 
engaged in the construction of his      
improved water mills1 which he erected  
in various parts of the country1 and    
which were imitated so extensively that 
the improvement of such mills became    
general4 ,in cases where a summer       
drought suspended the supply of water1  
horse machinery was provided1 either to 
work the mill or to throw back the      
water4 ,these improvements necessarily  
obstructed for a time the extension of  
steam power to mill work2 but the       
increase of manufactures soon created a 
demand for power greatly exceeding what 
could be supplied by such limited means4
  ,in the manufacture of iron1 it is of 
great importance to keep the furnaces   
continually blown1 so that the heat may 
never be abated by day or night4 ,in the
 extensive ironworks at ,colebrook      
,dale1 several water-wheels were used in

 the different operations of the        
manufacture of iron1 especially in      
driving the blowers of the iron         
furnaces4 ,these wheels were usually    
driven by the water of a river1 but in  
the summer months the supply became so  
short that it was insufficient to work  
them all4 ,steam engines were           
accordingly erected to ,pg#ahb return   
the water for driving these wheels4     
,this application of the engine as an   
occasional power for the supply of      
water-wheels having been found so       
effectual1 returning engines were soon  
adopted as the permanent and regular    
means of supplying water-wheels4 ,the   
first attempt of this kind is recorded  
to have been made by ,mr4 ,oxley1 in    
#agfb1 who constructed a machine to draw
 coals out of a pit at ,hartley         
colliery1 in ,northumberland4 ,it was   
originally intended to turn the machine 
by a continuous circular motion received
 from the beam of the engine2 but that  
method not being successful1 the engine 

was applied to raise water for a wheel  
by which the machine was worked4 ,this  
engine was continued in use for several 
years1 and though it was at length      
abandoned1 on account of its defective  
construction1 it nevertheless           
established the practicability of using 
steam power as a means of driving water 
wheels4#bc   7#aji47 ,in the year #aggg1
 ,mr4 ,john ,stewart read a paper before
 the ,royal ,society1 describing a      
method for obtaining a continued        
circular motion for turning all kinds of
 mills from the reciprocating motion of 
a steam engine4 ,he proposed to         
accomplish this by means of two endless 
chains passing over pulleys1 which      
should be moved upwards and downwards by
 the motion of the engine1 in the manner
 of a window sash4 ,the joint pins of   
the links of the two chains worked in   
teeth at the opposite sides of a cog    
wheel1 to which they imparted a circular
 motion1 first by one chain1 and then by
 the other1 acting alternately on       

opposite sides of the wheel4 ,one chain 
impelled it during the descent of the   
piston1 and the other during the ascent2
 but one of these chains always passed  
over its pulleys so as to produce no    
effect on one side of the cog wheel1    
whilst the other chain worked on the    
opposite side to turn it round4 ,for    
this purpose each chain was provided    
with a catch1 to prevent its circulating
 over its pulleys in one direction1 but 
to allow it free motion in the other4   
,the cog wheel thus kept in revolution  
might be applied to the axis of any mill
 which the engine was required to work4 
,thus1 if it were applied to a          
flour-mill1 the millstone itself would  
perform the office of a fly-wheel to    
regulate the intermission of ,pg#ahc the
 power1 and in other mills a fly-wheel  
might be added for this purpose4  ,the  
hints obtained by ,mr4 ,stewart from    
,papin's contrivance1 before mentioned1 
will not fail to be perceived4 ,in ,mr4 
,stewart's paper he notices indirectly  

the method of obtaining a continued     
circular motion from a reciprocating    
motion by means of a crank or winch1    
which1 he says1 occurs naturally in     
theory1 but in practice would be        
impossible1 from the nature of the      
motion of the engine1 which depends on  
the force of the steam1 and cannot be   
ascertained in its length4 ,therefore1  
on the first variation1 the machine     
would be either broken in pieces or     
turned back4 ,such an opinion1          
pronounced by a man of considerable     
mechanical knowledge and ingenuity1     
against a contrivance which1 as will    
presently appear1 proved in practice1   
not less than in theory1 to be the most 
effectual means of accomplishing the end
 here pronounced to be impossible1 is   
sufficiently remarkable4 ,it might cast 
some doubt on the extent of ,mr4        
,stewart's practical knowledge1 if it   
did not happen to be in accordance with 
a judgment so generally unimpeachable as
 that of ,mr4 ,smeaton4 ,this paper of  

,mr4 ,stewart's was referred by the     
council of the ,royal ,society to ,mr4  
,smeaton1 who remarked upon the         
difficulty arising from the absolute    
stopping of the whole mass of moving    
power1 whenever the direction of the    
motion is changed2 and observed1 that   
although a fly-wheel might be applied to
 regulate the motion1 it must be such a 
large one as would not be readily       
controlled by the engine itself2 and he 
considered that the use of such a       
fly-wheel would be a greater incumbrance
 to a mill than a water-wheel to be     
supplied by water pumped up by the      
engine4 ,this engineer1 illustrious as  
he was1 not only fell into the error of 
,mr4 ,stewart in respect of the crank1  
but committed the further blunder of    
condemning the very expedient which has 
since rendered the crank effectual4 ,it 
will presently appear that the          
combination of the crank and fly-wheel  
have been the chief means of            
establishing the dominion of the steam  

engine over manufactures4   7#aaj47 ,in 
#aggi1 ,mr4 ,matthew ,wasbrough1 an     
engineer at ,bristol1 took out a patent 
for the application of a steam engine   
,pg#ahd to produce a continuous circular
 motion by means of ratchet wheels1     
similar to those previously used by ,mr4
 ,oxley1 at ,hartley colliery2 to which1
 however1 ,mr4 ,wasbrough added a       
fly-wheel to maintain and regulate the  
motion4 ,several machines were          
constructed under this patent2 and among
 others1 one was erected at ,mr4        
,taylor's saw-mills and block           
manufactory at ,southampton4 ,in #aghj1 
one was erected at ,birmingham1 where   
the ratchet work was found to be subject
 to such objections1 that one of the    
persons about the works substituted for 
it the simple crank1 which has since    
been invariably used4 ,a patent was     
taken out for this application of the   
crank in the same year1 by ,mr4 ,james  
,pickard1 of ,birmingham4 ,it will      
presently appear1 however1 that the     

suggestion of this application of the   
crank was derived from the proceedings  
of ,watt1 who was at the same time      
engaged in similar experiments4         
7#aaa47 ,the single-acting steam engine1
 as constructed by ,watt1 was not       
adapted to produce continuous uniform   
motion of rotation1 for the following   
reasons3--  ,first4 ,the effect required
 was that of an uniformly acting force4 
,the steam engine1 on the other hand1   
supplied an intermitting force4 ,its    
operation was continued during the      
descending motion of the piston1 but it 
was suspended during the ascent of the  
piston4 ,to produce the continued effect
 now required1 either its principle of  
operation should be altered1 or some    
expedient should be devised for         
maintaining the motion of the revolving 
shaft during the ascent of the piston1  
and the consequent suspension of the    
moving power4  ,secondly4 ,the action of
 the steam engine was rectilinear4 ,it  
was a power which acted in a straight   

line1 viz41 in the direction of the     
cylinder4 ,the motion1 however1 required
 to be produced1 was a circular         
motion--a motion of rotation around the 
axis or shaft of the mill4  ,the steps  
by which ,watt proceeded to accomplish  
these objects have been recorded by     
himself as follows1 in his notes upon   
,dr4 ,robison's article on the steam    
engine3--  ,i had very early turned my  
mind to the producing of continued      
motion round an axis2 and it will be    
seen1 by reference to my first          
specification in #agfi1 that ,i there   
described ,pg#ahe a steam wheel1 moved  
by the force of steam1 acting in a      
circular channel against a valve on one 
side1 and against a column of mercury1  
or some other fluid metal1 on the other 
side4 ,this was executed upon a scale of
 about six feet diameter at ,soho1 and  
worked repeatedly1 but was given up1 as 
several practical objections were found 
to operate against it2 similar          
objections lay against other rotative   

engines1 which had been contrived by    
myself and others1 as well as to the    
engines producing rotatory motions by   
means of ratchet wheels4  ,having made  
my single reciprocating engines very    
regular in their movements1 ,i          
considered how to produce rotative      
motions from them in the best manner2   
and amongst various schemes which were  
subjected to trial1 or which passed     
through my mind1 none appeared so likely
 to answer the purpose as the           
application of the crank1 in the manner 
of the common turning lathe2 but as the 
rotative motion is produced in that     
machine by impulse given to the crank in
 the descent of the foot only1 it       
requires to be continued in its ascent  
by the energy of the wheel1 which acts  
as a fly2 being unwilling to load my    
engine with a fly-wheel heavy enough to 
continue the motion during the ascent of
 the piston 7or with a fly-wheel heavy  
enough to equalise the motion1 even if a
 counterweight were employed to act     

during that ascent71 ,i proposed to     
employ two engines1 acting upon two     
cranks fixed on the same axis1 at an    
angle of #abj to one another1 and a     
weight placed upon the circumference of 
the fly-wheel at the same angle to each 
of the cranks1 by which means the motion
 might be rendered nearly equal1 and    
only a very light fly-wheel would be    
requisite4  ,this had occurred to me    
very early2 but my attention being fully
 employed in making and erecting engines
 for raising water1 it remained in petto
 until about the year #aggh or #aghi1   
when ,mr4 ,wasbrough erected one of his 
ratchet-wheel engines at ,birmingham1   
the frequent breakages and              
irregularities of which recalled the    
subject to my mind1 and ,i proceeded to 
make a model of my method1 which        
answered my expectations2 but having    
neglected to take out a patent1 the     
invention was communicated by a workman 
employed to ,pg#ahf make the model1 to  
some of the people about ,mr4           

,wasbrough's engine1 and a patent was   
taken out by them for the application of
 the crank to steam engines4 ,this fact 
the said workman confessed1 and the     
engineer who directed the works         
acknowledged it2 but said1 nevertheless1
 that the same idea had occurred to him 
prior to his hearing of mine1 and that  
he had even made a model of it before   
that time2 which might be a fact1 as the
 application to a single crank was      
sufficiently obvious4  ,in these        
circumstances1 ,i thought it better to  
endeavour to accomplish the same end by 
other means1 than to enter into         
litigation2 and if successful1 by       
demolishing the patent1 to lay the      
matter open to every body4 ,accordingly1
 in #agha1 ,i invented and took out a   
patent for several methods of producing 
rotative motions from reciprocating     
ones2 amongst which was the method of   
the sun-and-planet wheels4 ,this        
contrivance was applied to many engines1
 and possesses the great advantage of   

giving a double velocity to the         
fly-wheel2 but is perhaps more subject  
to wear1 and to be broken under great   
strains1 than a simple crank1 which is  
now more commonly used1 although it     
requires a fly-wheel of four times the  
weight1 if fixed upon the first axis2 my
 application of the double engine to    
these rotative machines rendered the    
counterweight unnecessary1 and produced 
a more regular motion4   7#aab47 ,watt's
 second patent here referred to1 was    
dated #beth ,october1 #agha1 and was    
entitled ,a patent for certain new      
methods of applying the vibrating or    
reciprocating motions of steam or fire  
engines to produce a continued rotative 
or circular motion round an axis or     
centre1 and thereby to give motion to   
the wheels of mills and other machines4 
,all the methods specified in this      
patent were intended to be worked by the
 single-acting engine1 already          
described1 a counterweight being applied
 to impel the machinery during the      

returning stroke of the engine1 which   
weight would be elevated during the     
descent of the piston4 ,there were five 
different expedients proposed in the    
specification for producing a rotatory  
motion2 but1 of these five1 two only    
were ever applied in practice4 ,pg#ahg  
7#aac47 ,suppose a rod or bar attached  
by a pin or joint at the upper extremity
 to the working end of the beam of the  
engine1 and by a similar pin or joint at
 the lower extremity to an iron wheel   
fixed on the extremity of the axis of   
the fly-wheel4 ,one half of this wheel  
is formed of a solid semicircle of cast 
iron1 while the other half is           
constructed of open spokes1 so as to be 
as light as is consistent with strength4
 ,the position of the wheel on the axis 
is such that during the returning stroke
 of the piston1 when the operation of   
the steam is suspended1 the heavy       
semicircle of the wheel will be         
descending1 and by its weight will draw 
down the connecting bar1 and thereby    

draw down the working end of the beam1  
and draw up the piston in the cylinder4 
,when the piston descends and is driven 
by the power of the steam1 the heavy    
semicircle of the above-mentioned wheel 
will be drawn upwards1 and in the same  
way the motion will be continued4       
,illustration3 ,fig4 #cb4   7#aad47 ,the
 second method of producing a rotatory  
motion1 which was subsequently continued
 for many years in practical operation1 
was that which was called the           
,sun-and-planet ,wheels4 ,a toothed     
wheel ,a 7fig4 #cb471 called the sun    
wheel1 was fixed on the axle of the     
fly-wheel1 to which rotation was to be  
imparted4 ,the wheel ,b1 called the     
planet wheel1 having an equal diameter1 
was fastened on the end ,i of the       
connecting rod ,h ,i1 so as to be       
incapable of revolving4 ,during the     
descent of the piston1 the working end  
of the beam was drawn upwards1 and the  
end ,i of the connecting rod travelled  
from ,c to ,d1 through the dotted       

semicircle ,c ,i ,d4 ,the wheel ,b not  
being capable of revolving on the centre
 ,i1 would1 during this motion1 drive   
the sun wheel ,a4 ,during the ascent of 
the steam piston1 the working end of the
 beam would descend1 and the centre ,i  
of ,pg#ahh the planet wheel ,b would be 
driven downwards from ,d to ,c1 through 
the other dotted semicircle1 and would  
consequently continue to drive the sun  
wheel round in the same direction4      
,this contrivance1 although in the main 
inferior to the more simple one of the  
crank1 is not without some advantages2  
among others1 it gives to the sun wheel 
double the velocity which would be      
communicated by the crank2 for in the   
crank one revolution only on the axle is
 produced by one revolution of the      
crank1 but in the sun-and-planet wheel1 
two revolutions of the sun wheel are    
produced by one of the planet wheel2    
thus a double velocity is obtained from 
the same motion of the beam4 ,this will 
be evident from considering that when   

the planet wheel is in its highest      
position1 its lowest tooth is engaged   
with the highest tooth of the sun wheel2
 as the planet wheel passes from the    
highest position1 its teeth drive those 
of the sun wheel before them1 and when  
it comes into the lowest position1 the  
highest tooth of the planet wheel is    
engaged with the lowest of the sun      
wheel3 but then half of the sun wheel   
has rolled off the planet wheel1 and1   
therefore1 the tooth which was engaged  
with it in its highest position1 must   
now be distant from it by half the      
circumference of the wheel1 and must1   
therefore1 be again in the highest      
position2 so that while the planet wheel
 has been carried from the top to the   
bottom1 the sun wheel has made a        
complete revolution4  ,this advantage of
 giving an increased velocity may be    
obtained also by the crank1 by placing  
toothed wheels on its axle4             
,independently of the greater expense   
attending the construction of the       

sun-and-planet wheel1 its liability to  
go out of order1 and the rapid wear of  
the teeth1 and other objections1        
rendered it inferior to the crank1 which
 has entirely superseded it4   7#aae47  
,although by these contrivances ,watt   
succeeded in obtaining a continuous     
circular motion from the reciprocating  
motion of the steam engine1 the machine 
was still one of intermitting1 instead  
of continuous action4 ,the expedient of 
a counterweight1 elevated during the    
descending stroke1 and giving back the  
power expended on it in the interval of 
the returning stroke1 did not satisfy   
the ,pg#ahi fastidious mechanical taste 
of ,watt4 ,he soon perceived that all   
which he proposed to accomplish by the  
application of two cylinders and pistons
 working alternately1 could be attained 
with greater simplicity and effect by a 
single cylinder1 if he could devise     
means by which the piston might be      
impelled by steam upwards as well as    
downwards4 ,to accomplish this1 it was  

only necessary to throw the lower end of
 the cylinder into alternate            
communication with the boiler1 while the
 upper end would be put into            
communication with the condenser4 ,if1  
for example1 during the descent of the  
piston1 the upper end of the cylinder   
communicated with the boiler1 and the   
lower end with the condenser2 and1 on   
the other hand1 during the ascent of the
 piston1 the lower end communicated with
 the boiler1 and the upper end with the 
condenser2 then the piston would be     
driven continually1 whether upwards or  
downwards1 by the power of steam acting 
against a vacuum4 ,watt obtained his    
third patent for this contrivance1 on   
the #abth of ,march1 #aghb4  ,this      
change in the principle of the machine  
involved several other changes in the   
details of its mechanism4               
,illustration3 ,fig4 #cc4   7#aaf47 ,it 
was necessary1 in the first place1 to   
provide means for admitting and         
withdrawing the steam at either end of  

the cylinder4 ,for this purpose let ,b  
and ,b 7fig4 #cc47 be two steam-boxes1  
,b the upper1 and ,b the lower1         
communicating respectively with the top 
and bottom of the cylinder by proper    
passages ,d ,d4 ,let two valves be      
placed in ,b1 one1 ,s1 above the passage
 ,d1 and the other1 ,c1 below it2 and in
 like manner two other valves in the    
lower valve-box1 ,b1 one1 ,s1 above the 
passage ,d1 and the other1 ,c1 below it4
 ,above the valve ,s in the upper       
steam-box is an opening at which the    
steam-pipe from the boiler enters1 and  
below the valve ,c is another opening1  
at which enters the exhausting-pipe     
leading to the condenser4 ,in like      
manner1 above the valve ,s in the lower 
steam-box enters a steam-pipe leading   
from the boiler1 and below the valve ,c 
enters an exhausting-pipe leading to    
,pg#aij the condenser4 ,it is evident1  
therefore1 that steam can always be     
admitted above the piston by opening the
 valve ,s1 and below it by opening the  

valve ,s2 and1 in like manner1 steam can
 be withdrawn from the cylinder above   
the piston1 and allowed to pass to the  
condenser1 by opening the valve ,c1 and 
from below it by opening the valve ,c4  
,illustration3 ,fig4 #cd4  ,supposing   
the piston ,p to be at the top of the   
cylinder1 and the cylinder below the    
piston to be filled with pure steam1 let
 the valves ,s and ,c be opened1 the    
valves ,c and ,s being closed as        
represented in fig4 #cd4 ,steam from the
 boiler will1 therefore1 flow in through
 the open valve ,s1 and will press the  
piston downwards1 while the steam that  
has filled the cylinder below the piston
 will pass through the open valve ,c    
into the exhausting-pipe leading to the 
condenser1 and being condensed will     
leave the cylinder below the piston a   
vacuum4 ,the piston will1 therefore1 be 
pressed downwards by the action of the  
steam above it1 as in the single-acting 
engine4 ,having arrived at the bottom of
 the cylinder1 let the valves ,s and ,c 

be both closed1 and the valves ,s and ,c
 be opened1 as represented in fig4 #cd4 
,steam will now be admitted through the 
open valve ,s and through the passage ,d
 below the piston1 while the steam which
 has just driven the piston downwards1  
filling the cylinder above the piston1  
will be drawn off through the open valve
 ,c1 and the exhausting-pipe1 into the  
condenser1 leaving the cylinder above   
the piston a vacuum4 ,the piston will1  
therefore1 be pressed upwards by the    
action of the steam below it1 against   
the vacuum above it1 and will ascend    
with the same force as that with which  
it had descended4  ,this alternate      
action of the piston upwards and        
downwards may evidently be continued by 
opening and closing the valves          
alternately in pairs4 ,whenever the     
piston is at the top of the cylinder1 as
 represented in fig4 #cc41 the valves ,s
 and ,c1 that is1 the upper steam-valve 
and the lower exhausting-valve1 are     
opened1 and the valves ,c and ,s1 that  

is1 the upper exhausting-valve and the  
lower steam-valve1 are closed2 and      
,pg#aia when the piston has arrived at  
the bottom of the cylinder1 as          
represented in fig4 #cd41 the valves ,c 
and ,s1 that is1 the upper              
exhausting-valve and the lower          
steam-valve1 are opened1 and the valves 
,s and ,c1 that is1 the upper           
steam-valve and the lower               
exhausting-valve1 are closed4  ,if these
 valves1 as has been here supposed1 be  
opened and closed at the moments at     
which the piston reaches the top and    
bottom of the cylinder1 it is evident   
that they may be all worked by a single 
lever connected with them by proper     
mechanism4 ,when the piston arrives at  
the top of the cylinder1 this lever     
would be made to open the valves ,s and 
,c1 and at the same time to close the   
valves ,s and ,c2 and when it arrives at
 the bottom of the cylinder1 it would be
 made to close the valves ,s and ,c1 and
 to open the valves ,s and ,c4  ,if1    

however1 it be desired to cut off the   
steam before the arrival of the piston  
at the termination of its stroke1       
whether upwards or downwards1 then the  
steam-valves must be closed before the  
arrival of the piston at the end of its 
stroke2 and as the exhausting-valve     
ought to be left open until the stroke  
is completed1 these valves ought to be  
moved at different times4 ,in that case 
separate levers should be provided for  
the different valves4 ,we shall1        
however1 return again to the subject of 
the valves which regulate the admission 
of steam to the cylinder and its escape 
to the condenser4   7#aag47 ,it will be 
remembered that in the single-acting    
engine the process of condensation was  
suspended while the piston ascended in  
the cylinder1 and therefore the play of 
the jet of cold water in the condenser  
was stopped during this interval4 ,in   
the double-acting engine1 however1 the  
flow of steam from the cylinder to the  
condenser is continued1 whether the     

piston ascends or descends1 and         
therefore a constant condensation of    
steam must be produced4 ,the condensing 
jet1 therefore1 does not in this case1  
as in the former1 play with intervals of
 intermission4 ,a constant jet of cold  
water must be maintained in the         
condenser4  ,it will presently appear   
that in the double-acting engine applied
 to manufactures1 the motion of the     
piston was subject to more or less      
variation of speed1 and the quantity of 
steam ,pg#aib admitted to the cylinder  
was subject to a corresponding change4  
,the quantity of steam1 therefore1 drawn
 into the condenser was subject to      
variation1 and required a considerable  
change in the quantity of cold water    
admitted through the jet to condense it4
 ,to regulate this1 the valve or cock by
 which the water was admitted into the  
condenser was worked in the             
double-acting engine by a lever         
furnished with an index1 by which the   
quantity of condensing water admitted   

into the condenser could be regulated4  
,this index played upon a graduated     
arch1 by which the engine-man was       
enabled to regulate the supply4         
,illustration3 ,,heathfield ,,house1    
,,near ,,birmingham1 ,,the ,,residence  
,,of ,,watt4    ,,footnotes3    #bj     
,these effects are explained in my      
,treatise on ,heat2 and   they have     
lately been verified by experiments made
 with   locomotive engines by ,m4 de    
,pambour1 who found that the steam      
raised from the boiler of a locomotive  
engine1 under a   pressure of above #ej 
lbs4 per square inch1 was in the state  
of   common steam as it issued from the 
chimney at a very diminished   pressure 
and at a lower pressure4    #ba ,it is  
strange that this absurdity has been    
repeatedly   given as unquestionable    
fact in various encyclopdias1 as well   
as in by far the greater number of      
treatises expressly on the   subject4   
#bb ,farey1 ,treatise on the ,steam     
,engine1 p4 #abb4    #bc ,farey on the  

,steam ,engine1 p4 #big4  ,pg#aic       
,illustration3 ,,double-,,acting        
,,engine4--,,city ,,saw-,,mills4        
,,chap4 ,,viii4      ,,methods ,,of     
,,connecting ,,the ,,piston-,,rod ,,and 
,,beam ,,in ,,the     ,,double-,,acting 
,,engine4 -- ,,rack ,,and ,,sector4 --  
,,parallel ,,motion4 --     ,,connecting
 ,,rod ,,and ,,crank4 -- ,,fly-,,wheel4 
-- ,,throttle-,,valve4 --               
,,governor4 -- ,,construction ,,and     
,,operation ,,of ,,the ,,double-,,acting
     ,,engine4 -- ,,eccentric4 --       
,,cocks ,,and ,,valves4 --              
,,single-,,clack ,,valve4     --        
,,double-,,clack ,,valve4 -- ,,conical  
,,valves4 -- ,,slide ,,valves4 --       
,,murray',s ,,slides4 -- ,,the ,d       
,,valve4 -- ,,seaward',s ,,slides4 --   
,,single     ,,cock4 -- ,,four-,,way    
,,cock4 -- ,,pistons4 -- ,,common       
,,hemp-,,packed ,,piston4     --        
,,woolfe',s ,,piston4 -- ,,metallic     
,,pistons4 -- ,,cartwright',s ,,engine4 
-- ,,cartwright',s ,,piston4 --         

,,barton',s ,,piston4   7#aah47 ,in the 
single-acting engine1 the force of the  
piston acted on the beam only during its
 descent2 and this force was transmitted
 from the piston to the beam1 as we have
 seen1 by a flexible chain1 extended    
from the end of the piston-rod1 ,pg#aid 
and playing upon the arch head of the   
beam4 ,in the double-acting engine1     
however1 the force of the steam pressing
 the piston upwards must likewise be    
transmitted to the beam1 so as to drive 
the latter upwards while the piston     
ascends4 ,this action could not be      
accomplished by a chain connecting the  
piston with the arch head of the beam4  
,where the mechanical action to be      
transmitted is a pull1 and not a push1 a
 flexible chain1 cord1 or strap1 is     
sufficient2 but if a push or thrust is  
required to be transmitted1 then the    
flexibility of the medium of mechanical 
communication afforded by a chain       
renders it inapplicable4 ,in the        
double-acting engine1 during the        

descent1 the piston-rod still pulls the 
beam down2 and so far a chain connecting
 the piston-rod with the beam would be  
sufficient to transmit the action of the
 one to the other2 but in the ascent1   
the beam no longer pulls up the         
piston-rod1 but is pushed up by it4 ,a  
chain from the piston-rod to the arch   
head1 as described in the single-acting 
engine1 would fail to transmit this     
force4 ,if such a chain were used with  
the double engine1 where there is no    
counterweight on the opposite end of the
 beam1 the consequence would be1 that in
 the ascent of the piston the chain     
would slacken1 and the beam would still 
remain depressed4 ,it is therefore      
necessary that some other mechanical    
connection be contrived between the     
piston-rod and the beam1 of such a      
nature that in the descent the          
piston-rod may pull the beam down1 and  
may push it up in the ascent4           
,illustration3 ,fig4 #ce4  ,watt first  
proposed to effect this by attaching to 

the end of the piston-rod a straight    
rack1 faced with teeth1 which should    
work in corresponding teeth raised on   
the arch head of the beam1 as           
represented in fig4 #ce4 ,if his        
improved steam engines required no      
further precision of operation and      
construction than the atmospheric       
engines1 this might have been           
sufficient2 but in these engines it was 
indispensably necessary that the        
piston-rod should be guided with a      
smooth and even motion through the      
stuffing-box in the top of the cylinder1
 otherwise any shake or irregularity    
would cause it to work loose in the     
stuffing-box1 and either to admit the   
air1 or to let the steam escape4 ,under 
these circumstances1 the motion of      
,pg#aie the rack and toothed arch head  
were inadmissible1 since it was         
impossible by such means to impart to   
the piston-rod that smooth and equable  
motion which was requisite4 ,another    
contrivance which occurred to ,watt was1

 to attach to the top of the piston-rod 
a bar1 which should extend above the    
beam1 and to use two chains or straps1  
one extending from the top of the bar to
 the lower end of the arch head1 and the
 other from the bottom of the bar to the
 upper end of the arch head4 ,by such   
means the latter strap would pull the   
beam down when the piston would descend1
 and the former would pull the beam up  
when the piston would ascend4 ,these    
contrivances1 however1 were superseded  
by the celebrated mechanism since called
 the ,parallel ,motion1 one of the most 
ingenious mechanical combinations       
connected with the history of the steam 
engine4   7#aai47 ,it will be observed  
that the object was to connect by some  
inflexible means the end of the         
piston-rod with the extremity of the    
beam1 and so to contrive the mechanism1 
that while the end of the beam would    
move alternately up and down in part of 
a circle1 the end of the piston-rod     
connected with the beam should move up  

and down in a straight line4 ,if the end
 of the piston-rod were fastened upon   
the end of the beam by a pivot without  
any other connection1 it is evident     
that1 being moved up and down in the    
arch of a circle1 it would be drawn to  
the left and the right alternately1 and 
would consequently either be broken or  
bent1 or would work loose in the        
stuffing-box4 ,instead of connecting the
 end of the rod immediately with the end
 of the beam by a pivot1 ,watt proposed 
to connect them by certain moveable     
rods1 so arranged that1 as the end of   
the beam would move up and down in the  
circular arch1 the rods would so        
accommodate themselves to that motion1  
that the end connected with the         
piston-rod should not be disturbed from 
its rectilinear course4  ,to explain the
 principle of the mechanism called the  
parallel motion1 let us suppose that ,o 
,p 7fig4 #cf47 is a rod or lever        
moveable on a centre ,o1 and that the   
end ,p of this rod shall move through a 

circular arch ,p ,p ,p ,p a vertical    
plane1 and let its play be limited by   
two stops ,s1 which shall prevent its   
ascent above the point ,p1 and its      
descent below ,pg#aif the point ,p4 ,let
 the position of the rod and the        
limitation of its play be such that the 
straight line ,a ,b drawn through ,p and
 ,p1 the extreme positions of the lever 
,o ,p1 shall be a vertical line4        
,illustration3 ,fig4 #cf4  ,let o be a  
point on the other side of the vertical 
line ,a ,b1 and let the distance of ,o  
to the right of ,a ,b be the same as the
 distance of o to the left of ,a ,b4    
,let o p be a rod equal in length to ,o 
,p1 moving like ,o ,p on the centre o1  
so that its ,pg#aig extremity p shall   
play upwards and downwards through the  
arch p p p p1 its play being limited in 
like manner by stops s4  ,now1 let us   
suppose that the ends ,p p of these two 
rods are joined by a link ,p p1 the     
connection being made by a pivot1 so    
that the angles formed by the link and  

the rods shall be capable of changing   
their magnitude4 ,this link will make   
the motion of one rod depend on that of 
the other1 since it will preserve their 
extremities ,p p always at the same     
distance from each other4 ,if1          
therefore1 we suppose the rod ,o ,p to  
be moved to the position ,o ,p1 its     
extremity ,p tracing the arch ,p ,p ,p  
,p1 the link connecting the rods will at
 the same time drive the extremity p of 
the rod o p through the arch p p p p so 
that when the extremity of the one rod  
arrives at ,p1 the extremity of the     
other rod will arrive at p4 ,by this    
arrangement1 in the simultaneous motion 
of the rods1 whether upwards or         
downwards1 through the circular arches  
to which their play is limited1 the     
extremities of the link joining them    
will deviate from the vertical line ,a  
,b in opposite directions4 ,at the      
limits of their play1 the extremities of
 the link will always be in the line ,a 
,b2 but in all intermediate positions1  

the lower extremity of the link will be 
to the right of ,a ,b1 and its upper    
extremity to the left of ,a ,b4 ,so far 
as the derangement of the lower         
extremity of the link is concerned1 the 
matter composing the link would be      
transferred to the right of ,a ,b1 and  
so far as the upper extremity of the    
link is concerned1 the matter composing 
it would be transferred to the left of  
,a ,b4  ,by the combined effects of     
these contrary derangements of the      
extremities of the link from the        
vertical line1 it might be expected that
 a point would exist1 in the middle of  
the link1 where the two contrary        
derangements would neutralise each      
other1 and which point would therefore  
be expected to be disturbed neither to  
the right nor to the left1 but to be    
moved upwards and downwards in the      
vertical line ,a ,b4 ,such is the       
principle of the parallel motion2 and in
 fact the middle point of the link will 
move for all practical purposes         

accurately in the vertical line ,a ,b1  
provided that the angular play of the   
levers ,o ,p and o p does not exceed a  
certain ,pg#aih limit1 within which1 in 
practice1 their motion may always be    
restrained4  ,to trace the motion of the
 middle point of the link more minutely1
 let ,p ,p ,p ,p be four positions of   
the lever ,o ,p1 and let p p p p be the 
four corresponding positions of the     
lever o p4 ,in the positions ,o ,p o p1 
the link will take the position ,p p1 in
 which the entire link will be vertical1
 and its middle point x will therefore  
be in the vertical line ,a ,b4  ,when   
the one rod takes the position ,o ,p1   
the other rod will have the position o  
p2 and the link will have the position  
,p p4 ,the middle point of the link will
 be at x1 which will be found to be on  
the vertical line ,a ,b4 ,thus one half 
of the link ,p x will be to the left of 
the vertical line ,a ,b2 while the other
 half1 p x1 will be to the right of the 
vertical line2 the derangement from the 

vertical line affecting each half of the
 link in contrary directions4  ,again1  
taking the one rod in the position ,o   
,p1 the corresponding position of the   
other rod will be o p1 and the position 
of the link will be ,p p4 ,if the middle
 point of the link in this position be  
taken1 it will be found to be at x1 on  
the vertical line ,a ,b2 and1 as before1
 one half of the link ,p x will be      
thrown to the left of the vertical line1
 while the other half p x1 will be      
thrown to the right of the vertical     
line4  ,finally1 let the one rod be in  
its lowest position1 ,o ,p1 while the   
other rod shall take the corresponding  
position1 o p4 ,the direction of the    
link ,p p will now coincide with the    
vertical line2 and its middle point x   
will therefore be upon that line4 ,the  
previous derangement of the extremities 
of the rod1 to the right and to the     
left1 are now redressed1 and all the    
parts of the rod have assumed the       
vertical position4  ,it is plain1       

therefore1 that by such means the       
alternate motion of a point such as ,p  
or p1 upwards and downwards in a        
circular arch1 may be made to produce   
the alternate motions of another point  
x1 upwards and downwards in a straight  
line4   7#abj47 ,although the guidance  
of the air-pump rod in a true vertical  
line is not so necessary as that of the 
steam piston1 ,pg#aii and as the        
air-pump piston is always brought down  
by its own weight and that of its rod1  
the connection of the air-pump          
piston-rod with the beam1 by any        
contrivance of the kind now described1  
was not so necessary4 ,nevertheless1 by 
a slight addition to the mechanical     
contrivance which has been just         
described1 ,watt obtained the means of  
at once preserving the true rectilinear 
motion of both piston-rods4             
,illustration3 ,fig4 #cg4  ,let the     
lever represented by ,o ,p in fig4 #cf4 
be conceived to be prolonged to twice   
its length1 as represented in fig4 #cg41

 so that ,o ,p shall be twice ,o ,p4    
,let the points ,p p be connected by a  
link as before4 ,let a link ,p x1 equal 
in length to the link ,p p be attached  
to the point ,p1 and let the extremity x
 of this link be connected with the     
point p by another link1 equal in length
 to ,p ,p1 by pivots at x and p1 so that
 the figure ,p ,p x p shall be a jointed
 parallelogram1 the angles of which will
 be capable of altering their magnitude 
with every change of position of the    
rods o p and ,o ,p4 ,thus1 when the rod 
,o ,p descends1 the angles of the       
parallelogram at ,p and x will be       
diminished in magnitude1 while the      
angles at ,p and p will be increased in 
magnitude4 ,now1 let a line be conceived
 to be drawn from ,o to x4 ,it is       
evident that that line will pass through
 the middle point of the link p ,p1 for 
the triangle ,o ,p x is in all respects 
similar to the greater triangle ,o ,p x 
only on half the scale1 so that every   
side of the one is ,pg#bjj half the     

corresponding side of the other4        
,therefore ,p x is half the length of ,p
 x2 but ,p x was made equal to ,p p1 and
 therefore p x is half of ,p p1 that is 
to say1 x is the middle point of ,p p4  
,it has been already shown1 that in the 
alternate motion of the rods o p1 ,o ,p 
in ascending and descending1 the point x
 is moved upwards and downwards in a    
true vertical line4 ,now since the      
triangle ,o ,p x is in all respects     
similar to ,o ,p x1 and subject to a    
similar motion during the ascent and    
descent of the rods1 it is apparent that
 the point x must be subject to a motion
 in all respects similar to that which  
affects the points x1 except that the   
point x will move through double the    
space4 ,in fact1 the principle of the   
mechanism is precisely similar to that  
of the common pantograph1 where two rods
 are so connected as that the motion of 
the one governs the motion of the other1
 so that whatever line or figure may be 
described by one1 a similar line or     

figure must be described by the other4  
,since1 then1 the point x is moved      
upwards and downwards in a vertical     
straight line1 the point x will also be 
moved in a vertical straight line of    
double the length4  ,if such an         
arrangement of mechanism as has been    
here described can be connected with the
 beam of the steam engine1 so that while
 the point x is attached to the top of  
the steam piston1 and the space through 
which it ascends and descends shall be  
equal to the length of the stroke of    
that piston1 the point x shall be       
attached to the rod of the air-pump     
piston1 the stroke of the latter being  
half that of the steam piston1 then the 
points x and x will guide the motion of 
the two pistons so as to preserve them  
in true vertical straight lines4  ,the  
manner in which these ideas are reduced 
to practice admits of easy explanation3 
let the point ,o be the centre of the   
great working beam1 and let ,o ,p be the
 arm of the beam on the side of the     

steam cylinder4 ,let ,p be a pivot upon 
the beam1 at the middle point between   
its centre ,o and its extremity ,p2 and 
let the links ,p p1 ,p x1 and ,p p be   
jointed together1 as already described4 
,let the point or pivot o be attached to
 some part of the fixed framing of the  
engine or engine house1 and let the rod 
o p1 equal to half the arm of the beam1 
be attached by a pivot to the corner of 
the parallelogram at ,pg#bja p4 ,let the
 end of the steam piston-rod be attached
 to the corner of the parallelogram x1  
and let the end of the air-pump be      
attached to the middle point x of the   
link ,p p2 by which arrangement it is   
evident that the rectilinear motion of  
the two piston-rods will be rendered    
compatible with the alternate circular  
motions of the points ,p and ,p on the  
beam4  ,among the many mechanical       
inventions produced by the fertile      
genius of ,watt1 there is none which has
 excited such universal1 such           
unqualified1 and such merited admiration

 as that of the parallel motion4 ,it is 
indeed impossible1 even for an eye      
unaccustomed to view mechanical         
combinations1 to behold the beam of a   
steam engine moving the pistons1 through
 the instrumentality of the parallel    
motion1 without an instinctive feeling  
of pleasure at the unexpected fulfilment
 of an end by means having so little    
apparent connection with it4 ,when this 
feeling was expressed to ,watt himself1 
by those who first beheld the           
performance of this exquisite mechanism1
 he exclaimed with his usual vivacity1  
that he himself1 when he first beheld   
his own contrivance in action1 was      
affected by the same sense of pleasure  
and surprise at its regularity and      
precision4 ,he said1 that he received   
from it the same species of enjoyment   
that usually accompanies the first view 
of the successful invention of another  
person4  ,among the parts composing the 
steam engine1 you have doubtless1 says  
,m4 ,arago1 observed a certain          

articulated parallelogram4 ,at each     
ascent and descent of the piston1 its   
angles open and close with the          
sweetness--,i had almost said with the  
grace--which charms you in the gestures 
of a consummate actor4 ,follow with your
 eye alternately the progress of its    
successive changes1 and you will find   
them subject to the most curious        
geometrical conditions4 ,you will see1  
that of the four angles of the jointed  
parallelogram1 three describe circular  
arches1 but the fourth which holds the  
piston-rod is moved nearly in a straight
 line4 ,the immense utility of this     
result strikes mechanicians with even   
less force than the simplicity of the   
means by which ,watt has attained it4   
,the parallel motion1 of which there are
 several other varieties1 depending1    
however1 generally upon the same ,pg#bjb
 principle1 formed part of a patent     
which ,mr4 ,watt obtained in the year   
#aghd1 another part of which patent was 
for a locomotive engine1 by which a     

carriage was to be propelled on a road4 
,in a letter to ,mr4 ,smeaton dated     
#bb;d ,october1 in the same year1 ,watt 
says1--  ,i have lately contrived       
several methods of getting entirely rid 
of all the chains and circular arches   
about the great levers of steam engines1
 and nevertheless making the piston-rods
 ascend and descend perpendicularly1    
without any sliding motions or          
right-lined guides1 merely by           
combinations of motions about centres2  
and with this further advantage1 that   
they answer equally well to push upwards
 as to pull downwards1 so that this     
method is applicable to our double      
engines which act both in the ascent and
 descent of their pistons4  ,a rotative 
engine of this species with the new     
motion which is now at work in our      
manufactory 7but must be sent away very 
soon7 answers admirably4 ,it has cost   
much brain work to contrive proper      
working gear for these double engines1  
but ,i have at last done it tolerably   

well1 by means of the circular valves1  
placed in an inverted position1 so as to
 be opened by the force of the steam2   
and they are kept shut by the working   
gear4 ,we have erected an engine at     
,messrs4 ,goodwyne and ,co4's brewery1  
,east ,smithfield1 ,london4             
,illustration3 ,fig4 #ch4   7#aba47 ,by 
the contrivance which has been explained
 above1 the force of the piston in      
ascending and descending would be       
conveyed to the working end of the beam2
 and the next problem which ,watt had to
 solve was1 to produce by the force     
exerted by the working end of the beam  
in ascending and descending a continuous
 motion of rotation4 ,in the first      
instance he proposed to accomplish this 
by a crank placed upon the axle to which
 rotation was to be imparted1 and driven
 by a rod connecting it with the working
 end of the beam4 ,let ,k 7fig4 #ch47 be
 the centre1 to which motion is to be   
imparted by the working end ,h of the   
beam4 ,on the axle ,k suppose a short   

lever ,k ,i to be fixed so that when ,k 
,i is turned round the centre ,k1 the   
axle must turn with it4 ,let an iron    
rod1 the weight of which shall balance  
the piston and piston-rod at the other  
end of the beam1 be connected by joints 
with the working end ,h of the beam1 and
 the extremity ,i of the ,pg#bjc lever  
,k ,i4 ,as the end ,h of the beam is    
moved upwards and downwards1 the lever  
,k ,i will be turned round the centre   
,k1 taking successively the positions   
represented by faint lines in the       
figure2 and thus a motion of continued  
rotation will be imparted to the axle   
,k4  ,this simple and effectual         
expedient of producing a continued      
rotatory motion by a crank was abandoned
 by ,watt1 as already explained1 by     
reason of a patent having been obtained 
upon information of his experiments     
surreptitiously procured4 ,to avoid     
litigation1 he therefore substituted for
 the crank the sun and planet wheel     
already described2 but at the expiration

 of the patent1 which restricted the use
 of the crank1 the sun and planet wheel 
was discontinued in ,watt's engine1 and 
the crank restored4   7#abb47 ,whether  
the crank or the sun and planet wheel be
 used1 there is still a difficulty in   
the maintenance of a regular motion of  
rotation4 ,in the various positions     
which the crank and connecting rod      
assume throughout a complete revolution1
 there are two in which the moving power
 loses all influence in impelling the   
crank4 ,these positions are those which 
the crank assumes when the piston is at 
the top and bottom of the ,pg#bjd       
cylinder1 and is just about to change   
the direction of its motion4 ,when the  
piston is at the bottom of the cylinder1
 the pivot ,i 7fig4 #ch471 by which the 
connecting rod ,h ,i is attached to the 
end of the crank1 is immediately over   
the axle ,k of the crank1 and under the 
pivot ,h1 which joins the upper end of  
the connecting rod with the beam4 ,in   
fact1 in this position the connecting   

rod and crank are in the same straight  
line1 extending from the end of the beam
 to the axle of the crank4 ,the steam1  
on entering the cylinder below the      
piston1 and pressing it upwards1 would  
produce a corresponding downward force  
on the connecting rod at ,h1 which would
 be continued along the connecting rod  
and crank to the axle ,k4 ,it is evident
 that such a force could have no        
tendency to turn the crank round1 but   
would expend its whole energy in        
pressing the axle ,k downwards4  ,the   
other position in which the power loses 
its effect upon the crank is when the   
piston is at the top of the cylinder4   
,in this case1 the working end of the   
beam will be at the lowest point of its 
play1 and the crank-pin ,i will be      
immediately below the axle ,k2 so that  
,k will be placed immediately between ,h
 and ,i4 ,when the steam presses on the 
top of the piston1 it will expend its   
force in drawing the end ,h of the      
connecting rod upwards1 by which the    

crank-pin ,i will likewise be drawn     
upwards4 ,it is evident that this force 
can have no effect in turning the crank 
round1 but will expend its whole energy 
in producing an upward strain on the    
axle ,k4  ,if the crank were absolutely 
at rest in either of the positions above
 described1 it is apparent that the     
engine could not be put in motion by the
 steam2 but if the engine has been      
previously in motion1 then the mass of  
matter forming the crank1 and the axle  
on which the crank is formed1 having    
already had a motion of rotation1 will  
have a tendency to preserve the momentum
 it has received1 and this tendency will
 be sufficient to throw the crank ,k ,i 
out of either of those critical         
positions which have been described4    
,having once escaped these dead points1 
then the connecting rod forming an      
angle1 however obtuse or acute1 with the
 crank1 the pressure or pull upon the   
former will have a tendency to produce  
rotation in the latter4 ,as the crank   

revolves1 however1 the influence ,pg#bje
 of the connecting rod upon it will vary
 according to the angle formed by the   
connecting rod and crank4 ,when that    
angle is a right angle1 then the effect 
of the connecting rod on the crank is   
greatest1 since the force upon it has   
the advantage of the whole leverage of  
the crank2 but according as the angle   
formed by the crank and connecting rod  
becomes more or less acute or obtuse in 
the successive attitudes which they     
assume in the revolution of the crank1  
the influence of the connecting rod over
 the crank varies1 changing from nothing
 at the two dead points already         
described1 to the full effect produced  
in the two positions where they are at  
right angles4 ,in consequence of this   
varying leverage1 by which the force    
with which the connecting rod is driven 
by the steam is transmitted to the axle 
on which the crank revolves1 a          
corresponding variation of speed would  
necessarily be produced in the motion   

imparted to the crank4 ,the speed at the
 dead points would be least1 being due  
altogether to the momentum already      
imparted to the revolving mass of the   
crank and axle2 and it would gradually  
increase and be greatest at the points  
where the effect of the crank on the    
connecting rod is greatest4 ,although   
this change of speed would not affect   
the actual mechanical efficacy of the   
machine1 and although the same quantity 
of steam would perform the same work at 
the varying velocity as it would do if  
the velocity were regulated1 yet this   
variation of speed would be incompatible
 with the purposes to which it was now  
proposed that the steam engine should be
 applied in manufactures4 ,in these a   
regular uniform motion should be        
imparted to the main axle4   7#abc47    
,one of the expedients which ,watt      
proposed for the attainment of this end 
was1 by placing two cranks on the same  
axle1 in different positions1 to be     
worked by different cylinders1 so that  

while one crank should be at its dead   
points1 the other should be in the      
attitude most favourable for its action4
 ,this expedient has since1 as we shall 
see1 been carried into effect in steam  
vessels2 but one more simple and        
efficient presented itself in the use of
 a fly-wheel4  ,on the main axle driven 
by the crank ,watt placed a large wheel 
of metal1 as represented in fig4 #dc41  
called a fly-wheel4 ,this wheel being   
well constructed1 and nicely balanced on
 its ,pg#bjf axle1 was subject to very  
little resistance from friction2 any    
moving force which it would receive it  
would therefore retain1 and would be    
ready to impart such moving force to the
 main axle whenever that axle ceased to 
be driven by the power4 ,when the crank1
 therefore1 is in those positions in    
which the action of the power upon it is
 most efficient1 a portion of the energy
 of the power is expended in increasing 
the velocity of the mass of matter      
composing the fly-wheel4 ,as the crank  

approaches the dead points1 the effect  
of the moving power upon the axle and   
upon the crank is gradually enfeebled1  
and at these points vanishes altogether4
 ,the momentum which has been imparted  
to the fly-wheel then comes into play1  
and carries forward the axle and crank  
out of the dead points with a velocity  
very little less than that which it had 
when the crank was in the most          
favourable position for receiving the   
action of the moving power4  ,by this   
expedient1 the motion of revolution     
received by the axle from the steam     
piston is subject to no other variation 
than just the amount of change of       
momentum in the great mass of the       
fly-wheel1 which is sufficient to       
extricate the crank twice in every      
revolution from the mechanical dilemma  
to which its peculiar form exposes it2  
and this change of velocity may be      
reduced to as small an amount as can be 
requisite by giving the necessary weight
 and magnitude to the fly-wheel4        

7#abd47 ,by such arrangements the motion
 imparted to the main axle ,k would be  
uniform1 provided that the moving power 
of the engine be always proportionate to
 the load which it drives4 ,but in the  
general application of the steam engine 
to manufactures it was evident that the 
amount of the resistance to which any   
given machine would be subject must be  
liable to variation4 ,if1 for example1  
the engine drive a cotton-mill1 it will 
have to impart motion to all the        
spinning frames in that mill4 ,the      
operation of one or more of these may   
from time to time be suspended1 and the 
moving power would be relieved from a   
corresponding amount of resistance4 ,if1
 under such circumstances1 the energy of
 the moving power remained the same1 the
 velocity with which the machines would 
be driven would be subject to variation1
 being increased whenever the operation 
of any portion of the machines usually  
,pg#bjg driven by it is suspended2 and1 
on the other hand1 diminished when any  

increased number of machines are brought
 into operation4 ,in fine1 the speed    
would vary nearly in the inverse        
proportion of the load driven1          
increasing as the load is diminished1   
and vice vers4  ,on the other hand1     
supposing that no change took place in  
the amount of the load driven by the    
engine1 and that the same number of     
machines of whatever kind would have to 
be continually driven1 the motion       
imparted to the main axle would still be
 subject to variation by the changes    
inevitable to the moving power4 ,the    
piston of the engine being subject to an
 unvaried resistance1 a uniform motion  
could only be imparted to it1 by        
maintaining a corresponding uniformity  
in the impelling power4 ,this would     
require a uniform supply of steam from  
the boiler1 which would further imply a 
uniform rate of evaporation in the      
boiler1 unless means were provided in   
the admission of steam from the boiler  
to the cylinder to prevent any excess of

 steam which might be produced in the   
boiler from reaching the cylinder4      
,illustration3 ,fig4 #ci4               
,illustration3 ,fig4 #dj4  ,this end was
 attained by a contrivance afterwards   
called the throttle-valve4 ,an axis ,a  
,b 7figs4 #ci1 #dj47 was placed across  
the steam pipe in a ring of cast-iron ,d
 ,e1 of proper thickness4 ,on this axis 
was fastened a thin circular plate ,t1  
of nearly the same diameter as the steam
 pipe4 ,on the outer end ,b of this axle
 was placed a short lever or handle ,b  
,c1 by which it could be turned4 ,when  
the circular plate ,t was turned into   
such a position as to be at right angles
 to the length of the tube1 it stopped  
the passage within the tube altogether1 
so that no steam could pass from the    
boiler to the engine4 ,on the other     
hand1 when the handle was turned through
 a fourth of a revolution from this     
position1 then the circular plate ,t had
 its plane in the direction of the      
length of the tube1 so that its edge    

would be presented towards the current  
of steam flowing from the boiler to the 
cylinder4 ,in that position the passage 
within the tube ,pg#bjh would be        
necessarily unobstructed by the         
throttle-valve4 ,in intermediate        
positions of the valve1 as that         
represented in figs4 #ci1 #dj41 the     
passage might be left more or less      
opened1 so that steam from the boiler   
might be admitted to the cylinder in any
 regulated quantity according to the    
position given to the lever ,b ,c4  ,a  
view of the throttle-valve taken by a   
section across the steam pipe is        
exhibited in fig4 #dj41 and a section of
 it through the axis of the steam pipe  
is represented in fig4 #ci4 ,the form of
 the valve is such1 that1 if accurately 
constructed1 the steam in passing from  
the boiler would have no effect by its  
pressure to alter any position which    
might be given to the valve2 and any    
slight inaccuracy of form which might   
give a tendency to the steam to alter   

the position would be easily            
counteracted by the friction of the     
valve upon its axle4 ,the latter might  
be regulated at pleasure4  ,by this     
expedient1 however the evaporation of   
water in the boiler might vary within   
practical limits1 the supply of steam to
 the cylinder would be rendered regular 
and uniform4 ,if the boiler became too  
active1 and produced more steam than was
 necessary to move the engine with its  
load at the requisite speed1 then the   
throttle-valve was shifted so as to     
contract the passage and limit the      
supply of steam4 ,if1 on the other hand1
 the process of evaporation in the      
boiler was relaxed1 then the            
throttle-valve was placed with its edge 
more directed towards the steam4        
,independently of the boiler1 if the    
load on the engine was lightened1 then  
the same supply of steam to the cylinder
 would unduly accelerate the motion4 ,in
 this case1 likewise1 the partial       
closing of the throttle-valve would     

limit the supply of steam and regulate  
the motion2 and if1 on the other hand1  
the increase of load upon the engine    
rendered necessary an increased supply  
of steam1 then the opening of the       
throttle-valve would accomplish the     
purpose4 ,by these means1 therefore1 a  
uniform motion might be maintained1     
provided the vigilance of the engine-man
 was sufficient for the due management  
of the lever ,b ,c1 and provided that   
the furnace under the boiler was kept in
 sufficient activity to supply the      
greatest amount of steam which would be 
necessary ,pg#bji for the maintenance of
 a uniform motion with the              
throttle-valve fully opened4   7#abe47  
,watt1 however1 soon perceived that the 
proper manipulation of the lever ,b ,c  
would be impracticable with any degree  
of vigilance and skill which could be   
obtained from the persons employed to   
attend the engine4 ,he1 therefore1      
adapted to this purpose a beautiful     
application of a piece of mechanism1    

which had been previously used in the   
regulation of mill-work1 and which has  
since been well known by the name of the
 ,governor1 and has always been         
deservedly a subject of much admiration4
  ,the governor is an apparatus by which
 the axle of the fly-wheel is made to   
regulate the throttle-valve1 so that the
 moment that the axle begins to increase
 its velocity1 it shifts the position of
 the throttle-valve1 so as to limit the 
supply of steam from the boiler1 and    
thereby to check the increase of speed4 
,and on the other hand1 whenever the    
velocity of the axle is diminished1 the 
lever ,b ,c is moved in the contrary    
direction1 so as to open more fully the 
passage for the steam1 and accelerate   
the motion of the engine4  ,a small     
grooved wheel ,a ,b 7fig4 #da47 is      
attached to a vertical spindle supported
 in pivots or sockets ,c and ,d1 in     
which it is capable of revolving4 ,an   
endless cord works in the groove ,a ,b1 
and is carried over proper pulleys to   

the axle of the fly-wheel1 where it     
likewise works in a groove4 ,when this  
cord is properly tightened the motion of
 the fly-wheel will give motion to the  
wheel ,a ,b1 so that the velocity of the
 one will be subject to all the changes 
incidental to the velocity of the other4
 ,by this means the speed of the grooved
 wheel ,a ,b may be considered as       
representing the speed of the fly-wheel1
 and of the machinery which the axle of 
the fly-wheel drives4  ,illustration3   
,fig4 #da4  ,it is evident that the same
 end might be attained by substituting  
for the grooved wheel ,a ,b a toothed   
wheel1 which might be connected by other
 toothed wheels1 and proper shafts1 and 
axles with the axle of the fly-wheel4   
,a ring or collar ,e is placed on the   
upright spindle1 so as to be capable of 
moving freely upwards and downwards4 ,to
 this ring are attached by pivots two   
short levers1 ,e ,f1 the ,pg#baj pivots 
or joints at ,e allowing these levers to
 play upon them4 ,at ,f these levers are

 joined by pivots to other levers ,f ,g1
 which cross each other at ,h1 where an 
axle or pin passes through them1 and    
attaches them to the upright spindle ,c 
,d4 ,these intersecting levers are      
capable1 however1 of playing on this    
axle or pin ,h4 ,to the ends ,g of these
 levers are attached two heavy balls of 
metal ,i4 ,the levers ,f ,g pass through
 slits in a metallic arch attached to   
the upright spindle1 so as to be capable
 of revolving upon it4 ,if the balls ,i 
are drawn outwards from the vertical    
axis1 it is evident that the ends ,f of 
the levers will be drawn down1 and      
therefore the pivots ,e likewise drawn  
down4 ,in fact1 the angles ,e ,f ,h will
 become more acute1 and the angle ,f ,e 
,f more obtuse4 ,by these means the     
sliding ring ,e will be drawn down4 ,to 
this sliding ring ,e1 and immediately   
above it1 is attached a grooved collar1 
which slides on the vertical spindle    
upwards and downwards with the ring ,e4 
,in the grooved collar are inserted the 

prongs of a fork ,k1 formed at the end  
of the lever ,k ,l1 the fulcrum or pivot
 of the lever being at ,l4 ,by this     
arrangement1 when the divergence of the 
balls ,i causes the collar ,e to be     
drawn down1 the fork ,k1 whose prongs   
are inserted in the groove of that      
collar1 is likewise drawn down2 and1 on 
the other hand1 when1 by reason of the  
balls ,i falling towards the ,pg#baa    
vertical spindle1 the collar ,e is      
raised1 the fork ,k is likewise raised4 
,the ascent and descent of the fork ,k  
necessarily produce a contrary motion in
 the other end ,n of the lever4 ,this   
end is connected by a rod1 or system of 
rods1 with the end ,m of the short lever
 which works the throttle-valve ,t4 ,by 
such means the motion of the balls ,i1  
towards or from the vertical spindle1   
produces in the throttle-valve a        
corresponding motion2 and they are so   
connected that the divergence of the    
balls ,i will cause the throttle-valve  
to close1 while their descent towards   

the vertical spindle will cause it to   
open4  ,these arrangements being        
comprehended1 let us suppose that1      
either by reason of a diminished load   
upon the engine or an increased activity
 of the boiler1 the speed has a tendency
 to increase4 ,this would impart        
increased velocity to the grooved wheel 
,a ,b1 which would cause the balls ,i to
 revolve with an accelerated speed4 ,the
 centrifugal force which attends their  
motion would therefore give them a      
tendency to move from the axle1 or to   
diverge4 ,this would cause1 by the means
 already explained1 the throttle-valve  
,t to be partially closed1 by which the 
supply of steam from the boiler to the  
cylinder would be diminished1 and the   
energy of the moving power1 therefore1  
mitigated4 ,the undue increase of speed 
would thereby be prevented4  ,if1 on the
 other hand1 either by an increase of   
the load1 or a diminished activity in   
the boiler1 the speed of the machine was
 lessened1 a corresponding diminution of

 velocity would take place in the       
grooved wheel ,a ,b4 ,this would cause  
the balls ,i to revolve with less speed1
 and the centrifugal force produced by  
their circular motion would be          
diminished4 ,this force being thus no   
longer able fully to counteract their   
gravity1 they would fall towards the    
spindle1 which would cause1 as already  
explained1 the throttle-valve to be more
 fully opened4 ,this would produce a    
more ample supply of steam to the       
cylinder1 by which the velocity of the  
machine would be restored to its proper 
amount4  ,illustration3 ,fig4 #db4      
7#abf47 ,the principle which renders the
 governor so perfect a regulator of the 
velocity of the machine is difficult to 
be ,pg#bab explained without having     
recourse to the aid of the technical    
language of mathematical physics4 ,as1  
however1 this instrument is of such     
great practical importance1 and has     
attracted such general admiration1 it   
may be worth while here to attempt to   

render intelligible the mechanical      
principles which govern its operation4  
,let ,s 7fig4 #db47 be the point of     
suspension of a common pendulum ,s ,p1  
and let ,p ,o ,p be the arch of its     
vibration1 so that the ball ,p shall    
swing or vibrate alternately to the east
 and to the west of the lowest point ,o1
 through the arches ,o ,p and ,o ,p4 ,it
 is a property of such an instrument    
that1 provided the arch in which it     
vibrates be not considerable in         
magnitude1 the time of its vibration    
will be the same whether the arch be    
long or short4 ,thus1 for example1 if   
the pendulum1 instead of vibrating in   
the arch ,p ,p1 vibrated in the arch p  
p1 the time which it would take to      
perform its vibrations would be the     
same4 ,if1 however1 the magnitude of the
 arch of vibration be increased1 then a 
variation will take place in the time of
 vibration2 but unless the arch of      
vibration be considerably increased1    
this variation will not be great4  ,now 

let it be supposed that while the       
pendulum ,p ,p continues to vibrate east
 and west through the arch ,p ,p1 it    
shall receive such an impulse from north
 and south as would1 if it were not in a
 state of previous vibration1 cause it  
to vibrate between north and south1 in  
an arch similar to the arch ,p ,p4 ,this
 second vibration between north and     
south ,pg#bac would not prevent the     
continuance of the other vibration      
between east and west2 but the ball ,p  
would be at the same time affected by   
both vibrations4 ,while1 in virtue of   
the vibration from east to west1 the    
ball would swing from ,p to ,p1 it      
would1 in virtue of the other vibration1
 extend its motion towards the north to 
a distance from the line ,w ,e equal to 
half a vibration1 and will return from  
that distance again to the position ,p4 
,while returning from ,p to ,p1 its     
second vibration will carry it towards  
the south to an equal distance on the   
southern side of ,w ,e1 and it will     

return again to the position ,p4 ,if the
 combination of these two motions or    
vibrations be attentively considered1 it
 will be perceived that the effect on   
the ball will be a circular motion1     
precisely similar to the circular motion
 of the balls of the governor already   
described4  ,now the time of vibration  
of the pendulum ,s ,p between east and  
west will not in any way be affected by 
the second vibration1 which it is       
supposed to receive between north and   
south1 and therefore the time the       
pendulum takes in moving from ,p to ,p  
and back again from ,p to ,p will be the
 same whether it shall have             
simultaneously or not the other         
vibration between north and south4      
,hence it follows that the time of      
revolution of the circular pendulum will
 be equal to the time of similar        
vibrations of the same pendulum1 if1    
instead of having a circular motion1 it 
were allowed to vibrate in the manner of
 a common pendulum4  ,if this point be  

understood1 and if it also be remembered
 that the time of vibration of a common 
pendulum is necessarily the same whether
 the arch of vibration be small or      
great1 it will be easily perceived that 
the revolving pendulum or governor will 
have nearly the same time of revolution 
whether it revolve in a large circle or 
a small one3 in other words1 whether the
 balls revolve at a greater or a less   
distance from the central spindle or    
axis4 ,this1 however1 is to be          
understood only approximately4 ,when the
 angle of divergence of the balls is as 
considerable as it usually is in        
governors1 the time of revolution at    
different distances from the axis will  
therefore be subject to some variation1 
but to a very small one4 ,pg#bad  ,the  
centrifugal force 7which is the name    
given in mechanics to that influence    
which makes a body revolving in a circle
 fly from the centre7 depends conjointly
 on the velocity of revolution1 and on  
the distance of the revolving body from 

the centre of the circle4 ,if the       
velocity of revolution be the same1 then
 the centrifugal force will increase in 
the same proportion as the distance of  
the revolving body from the centre4 ,if1
 on the other hand1 the distance of the 
revolving body from the centre remain   
the same1 the centrifugal force will    
increase in the same proportion as the  
square of the time of vibration         
diminishes1 or1 in other words1 it will 
increase in the same proportion as the  
square of the number of revolutions per 
minute4 ,it follows from this1          
therefore1 that the greater is the      
divergence of the balls of the governor1
 and the more rapidly they revolve1 the 
greater will be their centrifugal force4
 ,now this centrifugal force1 if it were
 not counterbalanced1 would give the    
balls a constant tendency to recede from
 the centre2 but from the construction  
of the apparatus1 the further they are  
removed from the centre the greater will
 be the effect of their gravitation in  

resisting the centrifugal force4  ,it is
 evident that the ball at ,p will have a
 greater tendency to fall by gravitation
 towards ,o than it would have at p1    
because the acclivity of the arch       
descending towards ,o at ,p is greater  
than its acclivity at p4 ,the           
gravitation1 therefore1 or tendency of  
the ball to fall towards the central    
axis being greater at ,p than at p it   
will be able to resist a greater        
centrifugal force4 ,this increased      
centrifugal force1 which the ball would 
have revolving at the distance ,p above 
what it would have at the distance p1 is
 produced partly by the greater distance
 of the ball from the central axis1 and 
partly by the greater velocity of its   
motion4 ,but it will be evident that the
 time of its revolution may nevertheless
 be the same1 or nearly the same1 at    
both distances4 ,if it should appear    
that the actual velocity of its motion  
of revolution at ,p be greater than its 
velocity at p1 in the same proportion as

 the circles in which they revolve1 then
 it is evident that the time of         
revolution would be as much increased by
 the greater space which ,p will have to
 travel over1 as it will have to be     
,pg#bae diminished by the greater speed 
with which that space is traversed4 ,the
 time of revolution1 therefore1 may be  
the same1 or nearly the same1 in both   
cases4  ,if this explanation be         
comprehended1 it will not be difficult  
to apply it to the actual case of the   
governor4 ,if a sudden increase of the  
energy of the moving power1 or a        
diminution of the load1 should give the 
machine an increased velocity1 then the 
increased speed of the balls of the     
governor will give them an increased    
centrifugal force1 which for the moment 
will be greater than the tendency of    
their gravitation to make them fall     
towards the vertical axis4 ,this        
centrifugal force1 therefore1           
prevailing1 the balls will recede from  
the axis2 but as they recede1 their     

gravitation towards the vertical axis   
will1 as has been already explained1 be 
increased1 and will become equal to the 
centrifugal force produced by the       
increased velocity1 provided that       
velocity do not exceed a certain limit4 
,when the balls1 by diverging1 get such 
increased gravitation as to balance the 
centrifugal force1 then they will       
continue to revolve at a fixed distance 
from the vertical axis4 ,when this      
happens1 the time of the revolution must
 be nearly the same as it was before    
their increased divergence2 in other    
words1 the proportion of the moving     
power to the load will be so restored by
 the action of the levers of the        
governor on the throttle-valve that the 
machine will move at its former         
velocity1 or nearly so4  ,the principle 
on which the governor acts1 as just     
explained1 necessarily supposes         
temporary disarrangements of the speed4 
,in fact1 the governor1 strictly        
speaking1 does not maintain a uniform   

velocity1 but restores it after it has  
been disturbed4 ,when a sudden change of
 motion of the engine takes place1 the  
governor being immediately affected will
 cause a corresponding alteration in the
 throttle-valve2 and this will not      
merely correct the change of motion1 but
 it will1 as it were1 overdo it1 and    
will cause a derangement of speed of the
 opposite kind4 ,thus if the speed be   
suddenly increased to an undue amount1  
then the governor being affected will   
first close the throttle-valve too much1
 so as to reduce the speed below the    
proper limit4 ,this second error will   
again affect the governor in the        
contrary way1 and the speed ,pg#baf will
 again be increased rather too much4 ,in
 this way a succession of alterations of
 effect will ensue until the governor   
settles down into that position in which
 it will maintain the engine at the     
proper speed4  ,to prevent the          
inconvenience which would attend any    
excess of such variations1 the governor 

is made to act with great delicacy on   
the throttle-valve1 so that even a      
considerable change in the divergence of
 the balls shall not produce too much   
alteration in the opening of that valve3
 the steam in the boiler should have at 
least #b lbs4 per square inch pressure  
more than is generally required in the  
cylinder4 ,this excess is necessary to  
afford scope for that extent of         
variation of the power which it is the  
duty of the throttle-valve to regulate4 
,the governor is usually so adjusted as 
to make thirty-six revolutions per      
minute1 when in uniform motion2 but if  
the motion is increased to the rate of  
thirty-nine revolutions1 the balls will 
fly to the utmost extent allowed them1  
being the limitation of the grooves in  
which their rods move2 and if1 on the   
other hand1 the speed be diminished to  
thirty-four revolutions per minute1 they
 will collapse to the lowest extent of  
their play4 ,the duty of the governor1  
therefore1 is to correct smaller casual 

derangements of the velocity2 but if any
 permanent change to a considerable     
extent be made either in the load driven
 by the machine or in the moving power  
supplied to it from the boiler1 then a  
permanent change is necessary to be made
 in the connection between the governor 
and the throttle-valve1 so as to render 
the governor capable of regulating those
 smaller changes to which the speed of  
the machine is liable4   7#abg47 ,having
 thus explained the principal mechanical
 contrivances provided by ,watt for the 
maintenance and regulation of the       
rotatory motion to be produced by his   
double-acting steam engine1 let us now  
consider the machine as a whole1 and    
investigate the process of its          
operation4 ,a section of this engine is 
represented in fig4 #dc4  ,illustration3
 ,fig4 #dc4  ,steam is supplied from the
 boiler to the cylinder by the steam    
pipe ,s4 ,the throttle-valve ,t in that 
pipe1 near the cylinder1 is regulated by
 a system of levers connected with      

,pg#bag the governor4 ,the piston ,p is 
accurately fitted in the steam cylinder 
,c by packing1 as already described in  
the single-acting engine4 ,this piston1 
as it moves1 divides the cylinder into  
two compartments1 between which there is
 no communication by which steam or any 
other elastic fluid can pass4 ,the upper
 steam box ,b is divided into three     
compartments by the two valves4 ,above  
the upper steam valve ,v is a           
compartment communicating with the steam
 pipe2 below the upper exhausting valve 
,e is another compartment communicating 
with the eduction pipe which leads to   
the condenser4 ,by the valves ,v and ,e 
a communication may be opened or closed 
between the boiler on the one hand1 or  
the condenser on the other1 and the top 
of the cylinder4 ,the continuation ,s of
 the steam pipe leads to the lower box  
,b1 which1 like the upper1 is divided   
into three compartments by two valves ,v
 and ,e4 ,the upper compartment         
communicates with the steam pipe1 and   

thereby with the boiler2 and the lower  
compartment communicates with the       
eduction pipe1 and thereby with the     
condenser4 ,by means of the two valves  
,v and ,e1 a communication may be opened
 or closed between the steam pipe on the
 one hand1 or the exhausting pipe on the
 other1 and the lower part of the       
cylinder4 ,the four valves ,v1 ,e1 ,v1  
and ,e are connected by a system of     
levers with a handle or spanner m1      
which1 being driven downwards or        
upwards1 is capable of opening or       
closing the valves in pairs1 in the     
manner already described 7#aaf474 ,the  
condensers1 the air-pump1 and the       
hot-water pump1 are in all respects     
similar to those already described in   
the single-acting engine1 except that   
the condensing jet is governed by a     
lever ,i1 by which it is allowed to play
 continually in the condenser1 and by   
which the quantity of water admitted    
through it is regulated4 ,the cold-water
 pump ,n is worked by the engine as     

already described in the single-acting  
engine1 and supplies the cistern in     
which the air-pump and condenser are    
submerged1 so as to keep down its       
temperature to the proper limit4 ,on the
 air-pump rod ,r are two pins properly  
placed1 so as to strike the spanner m1  
upwards and downwards1 at the proper    
times1 when the piston approaches the   
termination of the stroke at the top or 
bottom of the cylinder4 ,the pump ,l    
,pg#bah conducts the warm water drawn by
 the air-pump from the condenser to a   
proper reservoir for feeding the boiler4
 ,the vertical motion of the piston-rod 
in a straight line is rendered          
compatible with the circular motion of  
the end of the beam by the parallel     
motion already described4 ,the point b1 
on the beam1 moves upwards and downwards
 in a circular arch1 of which the axis  
of the beam is the centre4 ,in like     
manner the point d of the rod d c moves 
upwards and downwards1 in a similar arch
 of which the fixed pivot c is the      

centre4 ,the joint or bar d b1 which    
joins these two pivots1 will be moved so
 that its middle point e will ascend and
 descend nearly in a straight line1 as  
has been already explained 7#abj472     
,pg#bai opposite this point e is        
attached the piston-rod of the air-pump1
 which is accordingly guided upwards and
 downwards by this means4 ,the jointed  
parallelogram b d g f is attached to the
 beam by pivots2 and1 as has been       
explained 7#abj471 the point g will be  
moved upwards and downwards in a        
straight line1 through twice the space  
through which the point e is moved4 ,to 
the point g the rod of the steam piston 
is attached4 ,thus1 the rods of the     
steam piston and air-pump are moved by  
the same system of jointed bars1 and    
moved through spaces which are in the   
proportion of two to one4  ,although    
this system of jointed rods forming the 
parallel motion1 appears in the figure  
to consist only of one parallelogram b d
 g f1 and one rod c d1 called the radius

 rod1 it is1 in fact1 double1 a similar 
parallelogram and radius rod being      
attached to corresponding points1 and in
 the same manner on the other side of   
the beam2 but from the view given in the
 cut1 the one set of rods hides the     
other4 ,the two systems of rods thus    
attached to opposite sides of the beam  
at several inches asunder1 are connected
 by cross rods1 the ends of which form  
the pivots or joints1 and extend between
 the parallelograms4 ,the ends of these 
rods are only visible in the figure4 ,it
 is to the middle of one of these rods1 
the end of which is represented at e1   
that the air-pump piston-rod is         
attached2 and it is to the middle of    
another1 the end of which is represented
 at g1 that the steam piston-rod is     
attached4 ,these two piston-rods1       
therefore1 are driven1 not immediately  
by either of the parallelograms forming 
the parallel motion1 but by the bars    
extending between them4  ,to the working
 end of the beam ,h is attached a rod of

 cast-iron ,o1 called the connecting    
rod1 the lower end of which is attached 
to the crank by a pivot4 ,the weight of 
the connecting rod is so made1 that it  
shall balance the weight of the         
piston-rods of the air-pump and cylinder
 on the other side of the beam2 and the 
weight of the piston-rod of the         
cold-water pump ,n nearly balances the  
weight of the piston-rod of the         
hot-water pump ,l4 ,thus1 so far as the 
weights of the machinery are concerned1 
the engine is in equilibrium1 and the   
piston would rest in any position       
indifferently in the cylinder4  ,the    
axis of the fly-wheel on which the crank
 is formed is ,pg#bbj square in the     
middle part1 where the fly-wheel is     
attached to it1 but has cylindrical     
necks at each end1 which rest in sockets
 or bearings supported by the framing of
 the machine1 in which sockets the axis 
revolves freely4 ,on the axle of the    
crank is placed the fly-wheel1 and      
connected with its axle is the governor 

,q1 which regulates the throttle-valve  
,t in the manner already described4     
,let us now suppose the engine to be in 
full operation4 ,the piston being at the
 top of the cylinder1 the spanner m will
 be raised by the lower pin on the      
air-pump rod1 and the upper steam valve 
,v1 and the lower exhausting valve ,e1  
will be opened1 while the upper         
exhausting valve ,e and the lower steam 
valve ,v are closed4 ,steam will1       
therefore1 be admitted above the piston1
 and the steam which filled the cylinder
 below it will be drawn off to the      
condenser1 where it will be converted   
into water4 ,the piston will1 therefore1
 be urged by the pressure of the steam  
above it to the bottom of the cylinder4 
,as it approaches that limit1 the       
spanner m will be struck downwards by   
the upper pin on the air-pump rod1 and  
the valves ,v and ,e will be closed1 and
 at the same time the lower steam valve 
,v and the upper exhausting valve ,e    
will be opened4 ,steam will1 therefore1 

be admitted below the piston1 while the 
steam above it will be drawn off into   
the condenser1 and converted into water4
 ,the pressure of the steam1 therefore1 
below the piston will urge it upwards1  
and in the same manner the motion will  
be continued4  ,while this process is   
going on in the cylinder and the        
condenser1 the water formed in the      
condenser will be gradually drawn off by
 the operation of the air-pump piston1  
in the same manner as explained in the  
single-acting engine2 and at the same   
time the hot water thrown into the hot  
well by the air-pump piston will be     
carried off by the hot-water pump ,l4   
,such are the chief circumstances       
attending the continuance of the        
operation of the double-acting engine4  
,it is only necessary here to recall    
what has been already explained         
respecting the operation of the         
fly-wheel4 ,the commencement of the     
motion of the piston from the top and   
bottom of the cylinder is produced1 not 

by the pressure of the steam upon it    
upwards or downwards1 which must1 for   
the reasons ,pg#bba already explained1  
be entirely inefficient2 but by the     
momentum of the fly-wheel1 which        
extricates the crank from those         
positions in which the moving power     
cannot affect it4  ,the manner in which 
the motion of the crank affects the     
connecting rod at the dead points       
produces an effect of great importance  
in the operation of the engine4 ,when   
the crank-pin is approaching the lowest 
point of its play1 and therefore the    
piston approaching the top of the       
cylinder1 the motion of the crank-pin   
becomes nearly horizontal1 and          
consequently its effect in drawing the  
connecting rod and the working end of   
the beam downwards and the piston       
upwards1 is extremely small4 ,the       
consequence of this is1 that as the     
piston approaches the top of the        
cylinder1 its motion becomes very       
rapidly retarded2 and as the motion of  

the crank-pin at its lowest point is    
actually horizontal1 the piston is      
brought to a state of rest by this      
gradually retarded motion at the top of 
the cylinder4 ,in like manner1 when the 
crank-pin moves from its dead point     
upwards1 its motion at first is very    
nearly horizontal1 and consequently its 
effect in driving the working end of the
 beam upwards1 and the piston downwards1
 is at first very small1 but gradually  
accelerated4 ,the effect of this upon   
the piston is1 that it arrives at and   
departs from the top of the stroke with 
a very slow motion1 being absolutely    
brought to rest at that point4  ,the    
same effect is produced when the piston 
arrives at the bottom of the cylinder4  
,this retardation and suspension of the 
motion of the piston at the termination 
of the stroke affords time for the      
process of condensation to be effected1 
so that when the moving power of the    
steam upon the piston can come into     
action1 the condensation shall be       

sufficiently complete4 ,as the piston   
approaches the top of the cylinder1 and 
its motion becomes slow1 the working    
gear is made to open the lower          
exhausting valve2 the steam enclosed in 
the cylinder below the piston1 and which
 has just driven the piston upwards1    
presses with an elastic force of #ag    
lbs4 per square inch on every part of   
the interior of the cylinder1 while the 
uncondensed vapour in the condenser     
presses with a force of about #b lbs4   
per square inch4 ,the steam1 therefore1 
will have a tendency to rush from the   
cylinder to the ,pg#bbb condenser       
through the open exhausting valve1 with 
an excess of pressure amounting to #ae  
lbs4 per square inch1 while the piston  
pauses at the top of the cylinder4 ,this
 process goes on1 and when the piston   
has descended by the motion of the      
fly-wheel1 a sufficient distance from   
the top of the cylinder to call the     
moving force of the steam into action1  
the exhaustion will be complete1 and the

 pressure of the uncondensed vapour in  
the cylinder will become the same as in 
the condenser4  ,the pressure of steam  
in the cylinder1 and of uncondensed     
vapour in the condenser1 varies1 within 
certain limits1 in different engines1   
and therefore the amount here assigned  
to them must be taken merely as an      
example4  ,the size of the valves by    
which the steam is allowed to pass from 
the cylinder to the condenser should be 
such as to cause the condensation to    
take place in a sufficiently short time1
 to be completed when the steam         
impelling the piston is called into     
action4  ,watt1 in the construction of  
his engines1 made the exhaustion-valves 
with a diameter which was one fifth of  
the diameter of the cylinder1 and       
therefore the actual magnitude of the   
aperture for the escape of the steam was
 one twenty-fifth of the magnitude of   
the cylinder2 but the spindle of the    
valve diminished this so that the       
available space for the escape of steam 

did not exceed one twenty-seventh of the
 magnitude of the cylinder4 ,this was   
found to produce a sufficiently rapid   
condensation4  ,it was usual to make the
 steam valves of the same magnitude as  
the exhausting valves1 but the flow of  
steam through the former was resisted by
 the throttle-valve1 while no           
obstruction was opposed to its passage  
through the latter4  ,the rapidity with 
which the cylinder must be exhausted by 
the condenser will1 however1 depend upon
 the velocity with which the piston is  
moved in it4 ,the magnitude1 therefore1 
of the exhausting valves which would be 
sufficient for an engine which acts with
 a slow motion would be too small where 
a rapid motion is required4  ,in the    
single-acting steam engine1 where the   
moving force always acted downwards on  
the piston1 the pressure upon ,pg#bbc   
all the joints of the machinery by which
 the force of the piston was conveyed to
 the working parts1 always took place in
 the same direction1 and consequently   

whatever might be the mechanical        
connection by which the several joints  
were formed1 the pins by which they were
 connected1 must always come to a       
bearing in their respective sockets1    
however loosely they may have been      
fitted4 ,for the same reason1 however1  
that the arch head and chain were       
abandoned as a means of connecting the  
steam piston with the beam1 and the     
parallel motion substituted1 it was also
 necessary in the double-acting engine1 
where all joints whatever were driven   
alternately in opposite directions1 to  
fit the connecting pins with the        
greatest accuracy in their sockets1 and 
to abandon all connection of the parts  
by chains4 ,if any sensible looseness   
was left in the joints1 a violent jerk  
would be produced every time the motion 
of the piston was reversed4 ,any        
looseness either in the pivots or joints
 of the parallel motion of the working  
beam1 the connecting rod1 or crank1     
would1 at every change of stroke1 be so 

accumulated as to produce upon the      
machinery the effects of percussion1 and
 would consequently be attended with the
 danger of straining and breaking the   
moveable parts of the mechanism4  ,to   
secure1 therefore1 the necessary        
accuracy of the joints1 ,watt contrived 
that every joint in the engine should   
admit of the size of the socket being   
exactly adapted to the size of the pin1 
so as always to make a good fitting by  
closing the socket upon the pin1 when   
any looseness would be produced by wear4
 ,with this view1 all the joints were   
fitted with sockets made of brass or    
gun-metal1 capable of adjustment4 ,each 
socket was composed of two pieces1      
accurately fitted into a cell or groove1
 in which one of the brasses can be     
moved towards the other by means of a   
wedge or screw4 ,each brass has in it a 
semi-cylindrical cavity1 and the two    
cavities being opposed to each other1   
form a socket for the joint-pin4 ,one of
 the two brasses can always be tightened

 round that pin1 so as to enclose it    
tight between the two semi-cylindrical  
cavities1 and to prevent any looseness  
taking place4 ,the brasses1 and other   
parts of such a joint1 are represented  
,pg#bbd in fig4 #dd4 ,these joints still
 continue to be used in the engines as  
now constructed4  ,illustration3 ,fig4  
#dd4  ,the motion of the working beam1  
and the pump-rods which it drives1 and  
of the connecting rod1 ought1 if the    
whole were constructed with perfect     
precision1 to take place in the same or 
parallel vertical planes2 but this      
supposes a perfection of execution which
 could hardly have been expected in the 
early manufacture of such engines1      
whatever may have been attained by      
improvements which have been since made4
 ,in the details of construction1 ,watt 
saw that there would be a liability to  
lateral strain1 owing to the planes of  
the different motions not being truly   
vertical and truly parallel1 and that if
 a provision were not made for such     

lateral motion1 the machinery would be  
subject to constant strain in its joints
 and rapid wear4 ,he provided against   
this by constructing the main joints by 
which the great working lever was       
connected with the pistons and          
connecting rod1 so as to form universal 
joints1 giving freedom of motion        
laterally as well as vertically4  ,the  
great lever1 or working beam1 was so    
called from being originally made from a
 beam of oak4 ,it is now1 however1      
universally constructed of cast-iron4   
,the connecting rod is also made of     
cast-iron1 and attached to the beam and 
to the crank by axles or pivots4  ,the  
mechanism by which the four valves are  
opened and closed1 is subject to        
considerable variation in different     
engines4 ,they have been described above
 as being opened and closed             
simultaneously by a single lever4       
,sometimes1 however1 they are opened    
alternately in pairs by two distinct    
levers driven by two pins attached to   

the air-pump rod4 ,one pin strikes the  
lever1 which opens and closes the upper 
steam valve1 and lower exhausting valve2
 the other strikes that which opens and 
closes the lower steam valve and upper  
exhausting valve4  ,since the date of   
the earlier double-acting engines1      
constructed by ,boulton and ,watt1 a    
great variety of mechanical expedients  
have been practised for working the     
valves1 by which the steam is admitted  
to and withdrawn from the ,pg#bbe       
cylinder4 ,we shall here describe a few 
of these methods3--   7#abh47 ,the      
method of working the valves by pins on 
the air-pump rod driving levers         
connected with the valves has been1 in  
almost all modern double-acting         
machines1 superseded by an apparatus    
called an eccentric1 by which the motion
 of the axle of the fly-wheel is made to
 open and close the valves at the proper
 times4  ,illustration3 ,fig4 #de4  ,an 
eccentric is a metallic circle attached 
to a revolving axle1 so that the centre 

of the circle shall not coincide with   
the centre round which the axle         
revolves4 ,let us suppose that ,g 7fig4 
#de471 is a square revolving shaft4 ,let
 a circular plate of metal ,b ,d1 having
 its centre at ,c1 have a square hole   
cut in it1 corresponding to the shaft   
,g1 and let the shaft ,g pass through   
this square aperture1 so that the       
circular plate ,b ,d shall be fastened  
upon the shaft1 and capable of revolving
 with it as the shaft revolves4 ,the    
centre ,c of the circular plate ,b ,d   
will be carried round the centre ,g of  
the revolving shaft1 and will describe  
round it a circle1 the radius of which  
will be the distance of the centre ,c of
 the circular plate from the centre of  
the shaft4 ,such circular plate so      
placed upon a shaft1 and revolving with 
it1 is an eccentric4  ,let ,e ,f be a   
metallic ring1 formed of two semicircles
 of metal screwed together at ,h1 so as 
to be capable1 by the adjustment of the 
screws1 of having the circular aperture 

formed by the ring enlarged and         
diminished within certain ,pg#bbf small 
limits4 ,let this circular aperture be  
supposed to be equal to the magnitude of
 the eccentric ,b ,d4 ,to the circular  
ring ,e ,f let an arm ,l ,m be attached4
 ,if the ring ,e ,f be placed around the
 eccentric ,b ,d1 and that the screws ,h
 be so adjusted as to allow the         
eccentric ,b ,d to revolve within the   
ring ,e ,f1 then while the eccentric    
revolves1 the ring not partaking of its 
revolution1 the arm ,l ,m will be       
alternately driven to the right and to  
the left1 by the motion of the centre ,c
 of the eccentric as it revolves round  
the centre ,g of the axle4 ,when the    
centre ,c of the eccentric is in the    
same horizontal line with the centre ,g1
 and to the left of it1 then the        
position of ,l ,m will be that which is 
represented in fig4 #de42 but when1     
after half a revolution of the main     
axle1 the centre ,c of the eccentric is 
thrown on the other side of the centre  

,g1 then the point ,m will be           
transferred to the right1 to a distance 
equal to twice the distance ,c ,g4 ,thus
 as the eccentric ,b ,d revolves within 
the ring ,e ,f1 that ring1 together with
 the arm ,l ,m1 will be alternately     
driven1 right and left1 through a space 
equal to twice the distance between the 
centre of the eccentric and the centre  
of the revolving shaft4  ,if we suppose 
a notch formed at the extremity of the  
arm ,l ,m1 which is capable of embracing
 a lever ,n ,m1 moveable on a pivot at  
,n1 the motion of the eccentric would   
give to such a lever an alternate motion
 from right to left1 and vice vers4 ,if 
we suppose another lever ,n ,o connected
 with ,n ,m1 and at right angles to it1 
forming what is called a bell-crank1    
then the alternate motion received by   
,m1 from right to left1 would give a    
corresponding motion to the extremity ,o
 of the lever ,n ,o1 upwards and        
downwards4 ,if this last point ,o were  
attached to a vertical arm or shaft1 it 

would impart to such arm or shaft an    
alternate motion upwards and downwards1 
the extent of which would be regulated  
by the length of the levers             
respectively4  ,by such a contrivance   
the revolution of the fly-wheel shaft is
 made to give an alternate vertical     
motion of any required extent to a      
vertical shaft placed near the cylinder1
 which may be so connected with the     
valves as to open and close them4 ,since
 the upward and downward motion of this 
vertical shaft is governed by the       
alternate motion of the centre ,pg#bbg  
,c to the right and to the left of the  
centre ,g1 it is evident that by the    
adjustment of the eccentric upon the    
fly-wheel shaft1 the valves may be      
opened and closed at any required       
position of the fly-wheel and crank1 and
 therefore at any required position of  
the piston in the cylinder4  ,such is   
the contrivance by which the valves1    
whatever form may be given to them1 are 
now almost universally worked in        

double-acting steam engines4         99 
99       99       99       99  ,having  
described the general structure and     
operation of the steam engine as        
improved by ,watt1 we shall now explain1
 in a more detailed manner1 some parts  
of its machinery which have been        
variously constructed1 and in which more
 or less improvements have been made4   
,,of ,,the ,,cocks ,,and ,,valves4      
7#abi47 ,in the steam engine1 as well as
 in every other machine in which fluids 
act1 it is necessary to open or close1  
occasionally1 the tubes or passages     
through which these fluids move4 ,the   
instruments by which this is            
accomplished are called cocks or valves4
  ,cocks or valves may be classified by 
the manner in which they are opened3    
#ast1 they may be opened by a motion    
similar to the lid of a box upon its    
hinges2 #b;d1 they may be opened by     
being raised directly upwards1 in the   
same manner as the lid of a pot or      
kettle2 #c;d1 they may be opened by a   

sliding motion1 like that of the sash of
 a window or the lid of a box which     
slides in grooves2 #dth1 they may be    
opened by a motion of revolution1 in the
 same manner as the cock of a           
beer-barrel is opened or closed4 ,the   
term valve is more properly applied to  
the first and second of these classes2  
the third class are usually called      
slides1 and the fourth cocks4   7#acj47 
,the single clack valve is the most     
simple example of the first class4 ,it  
is usually constructed by attaching to a
 plate of metal larger than the aperture
 which the valve is intended to stop1 a 
piece of leather1 and to the under side 
of this leather another piece of metal  
smaller than the aperture4 ,the leather 
,pg#bbh extending on one side beyond the
 larger metallic plate1 and being       
flexible1 forms the hinge on which the  
valve plays4 ,such a valve is usually   
closed by its own weight1 and opened by 
the pressure of the fluid which passes  
through it4 ,it is also held closed more

 firmly by the pressure of the fluid    
whose return it is intended to obstruct4
 ,an example of this valve occurs in the
 steam engine1 in the passage between   
the condenser and the air-pump4 ,the    
aperture which it stops is there a seat 
inclined at an angle whose inclination  
is such as to render the weight of the  
valve sufficient to close it4 ,in cases 
where the valve is exposed to heat1 as  
in the example just mentioned1 where it 
is continually in contact with the hot  
water flowing from the condenser to the 
air-pump1 the use of leather is         
inadmissible1 and in that case the      
metallic surface of the valve is ground 
smooth to fit its seat4  ,the extent to 
which such a valve should be capable of 
opening1 ought to be such that the      
aperture produced by it shall be equal  
to the aperture which it stops4 ,this   
will be effected if the angle through   
which it rises be about #cj4            
,illustration3 ,fig4 #df4  ,the valve by
 which the air and water collected in   

the bottom of the air-pump are admitted 
to pass through the air-pump piston is a
 double clack1 consisting of two        
semicircular plates1 having the hinges  
on the diameters of these semicircles1  
as represented in fig4 #df4   7#aca47   
,of the valves which are opened by a    
motion perpendicular to their seat1 the 
most simple is a flat metallic plate1   
made larger than the orifice which it is
 intended to stop1 and ground so as to  
rest in steam-tight contact with the    
surface surrounding the aperture4 ,such 
a valve is usually guided in its        
perpendicular motion by a spindle       
passing through its centre1 and sliding 
in holes made in cross bars extending   
above and below the seat of the valve4  
,the conical steam-valves1 which have   
been already described 7#aaf471 usually 
called spindle-valves1 are the most     
common of this class4 ,the best angle to
 be given to the conical seat is found  
in practice to be #de4 ,with a less     
inclination the valve has a tendency to 

be fastened in its seat1 and a greater  
inclination would cause the top of the  
valve to occupy ,pg#bbi unnecessary     
space in the valve-box4 ,the area1 or   
transverse section of the valve-box1    
should be rather more than double the   
magnitude of the upper surface of the   
valve1 in order to allow a sufficiently 
free passage for the steam1 and the play
 of the valve should be such as to allow
 it to rise from its seat to a height   
not less than one fourth of the diameter
 of its upper surface4  ,the valves     
coming under this class are sometimes   
formed as spheres or hemispheres resting
 in a conical seat1 and in such cases   
they are generally closed by their own  
weight1 and opened by the pressure of   
the fluid which passes through them4    
7#acb47 ,one of the advantages attending
 the use of slides1 compared with the   
other form of valves1 is the simplicity 
with which the same slide may be made to
 govern several passages1 so that a     
single motion with a slide may perform  

the office of two or more motions       
imparted to independent valves4  ,in    
most modern engines the passage of the  
steam to and from the cylinder is       
governed by slides of various forms1    
some of which we shall now explain4     
,illustration3 ,fig4 #dg4   7#acc47 ,in 
figs4 #dg4 and #dh4 is represented a    
slide-valve contrived by ,mr4 ,murray of
 ,leeds4 ,a ,b is a steam-tight case    
attached to the side of the cylinder2 ,e
 ,f is a rod1 which receives an         
alternate motion1 upwards and downwards1
 from the eccentric1 or from whatever   
other part of the engine is intended to 
move the slide4 ,this rod1 passing      
through a stuffing-box1 moves the slide 
,g upwards and downwards4 ,s is the     
mouth of the steam pipe coming from the 
boiler2 ,t is the mouth of a tube or    
pipe leading to the condenser2 ,h is a  
passage leading to the top1 and ,i to   
the bottom1 of the cylinder4 ,in the    
position of the slide represented in    
fig4 #dg41 the steam coming from the    

boiler through ,s passes through the    
space ,h to the top of the cylinder1    
while the steam from the bottom of the  
cylinder passes through the space ,i    
into the tube ,t1 and goes to the       
condenser4 ,when the rod ,pg#bcj ,e ,f  
is raised to the position represented in
 fig4 #dh41 then the passage ,h is      
thrown into communication with the tube 
,t1 while the passage ,i is made to     
communicate with the tube ,s4 ,steam1   
therefore1 passes from the boiler       
through ,i below the piston1 while the  
steam which was above the piston1       
passing through ,h into ,t1 goes to the 
condenser4 ,thus the single slide ,g    
performs the office of the four valves  
described in 7#aaf474  ,illustration3   
,fig4 #dh4   7#acd47 ,the slide ,g has  
always steam of a full pressure behind  
it1 while the steam in front of it      
escaping to the condenser1 exerts but   
little pressure upon it4 ,it is         
therefore always forcibly pressed       
against the surfaces in contact with    

which it moves1 and is thereby          
maintained steam-tight4 ,indeed this    
pressure would rapidly wear the rubbing 
surfaces1 unless they were made         
sufficiently extensive1 and hardened so 
as to resist the effects of the         
friction4 ,where fresh water is used1 as
 in land boilers1 the slide may be made 
of hardened steel2 and in the case of   
marine boilers1 it may be constructed of
 gun-metal4 ,in this and all other      
contrivances in which the apertures by  
which the steam is admitted to and      
withdrawn from the piston are removed to
 any considerable distance from the top 
and bottom of the cylinder1 there is a  
waste of steam1 for the steam consumed  
at each stroke of the piston is not only
 that which would fill the capacity of  
the cylinder1 but also the steam which  
fills the passage between the slide ,g  
and the top or bottom of the cylinder4  
,any arrangement which would throw the  
passages ,h and ,i on the other side of 
the slide ,g1 that is1 between ,s and   

,g1 instead of being1 as they are1      
between ,g and the top and bottom of the
 cylinder1 would remove this defect4    
,this is accomplished by a slide1 which 
is usually called the ,d valve1 because1
 being semi-cylindrical in its form1 and
 hollow1 its cross section resembles the
 letter ,d4 ,this slide1 which is that  
which at present is in most general use1
 is represented in figs4 #di1 #ej42 ,e  
is the rod by which the slide is moved1 
passing ,pg#bca through a stuffing-box  
,f2 ,g ,g is the slide represented by a 
vertical section1 a a being a passage in
 it extending from the top to the       
bottom2 ,s is the mouth of the great    
steam pipe coming from the boiler2 ,p is
 the pipe leading to the condenser2 ,t  
,h is a hollow space formed in the slide
 always in communication with the steam 
pipe ,s1 and consequently always filled 
with steam from the boiler4 ,a          
transverse section of the slide and     
cylinder is represented in fig4 #ea41   
where a represents the top of the       

passage marked a in fig4 #di4 ,in the   
position of the slide represented in    
fig4 #di41 the steam filling the space  
,t ,h has access to the top of the      
cylinder1 but is excluded from the      
bottom4 ,the steam which was below the  
piston1 passing up the passage a1       
escapes through the tube ,p to the      
condenser4 ,when the piston has         
descended1 the rod ,e moves the slide   
downwards1 so as to give it the position
 represented in ,,fig4 #ej4 ,the steam  
in ,t ,h has now access to the bottom of
 the cylinder1 while the steam above the
 piston passing through ,p escapes to   
the condenser4 ,in this way the         
operation of the piston is continued and
 the steam consumed at each stroke only 
exceeds the capacity of the cylinder by 
what is necessary to fill the passages  
between the slide and the cylinder4     
,illustration3 ,fig4 #di4               
,illustration3 ,fig4 #ej4               
,illustration3 ,fig4 #ea4  ,in a slide  
constructed in this manner1 the steam   

filling the space ,t ,h has a tendency  
to press the slide back1 so as to break 
the contact of the rubbing surfaces1 and
 thereby to cause the steam to leak from
 the space ,t ,h to the back of the     
slide4 ,this is counteracted by the     
packing x1 at the back of the slide4    
,in engines of very long stroke1 the    
extent of the rubbing surfaces of slides
 of this kind renders it difficult to   
keep ,pg#bcb them in steam-tight contact
 and to insure their uniform wear4 ,in  
such cases1 therefore1 separate slides1 
upon the same principle1 are provided at
 the top and bottom of the cylinder1    
moved1 however1 by a single rod of      
communication4   7#ace47 ,in slides1 as 
we have here described them1 the same   
motion which admits steam to either end 
of the cylinder1 withdraws it from the  
other end4 ,such an arrangement is only 
compatible with the operation of a      
cylinder which works without expansion2 
for in such a cylinder the full flow of 
steam to the piston is only interrupted 

for a moment during the change of       
position of the slide4 ,but if the steam
 act expansively1 it would be necessary 
to move the slide1 so as to stop its    
flow to one end of the cylinder1 without
 at the same time obstructing the escape
 of steam from the other end to the     
condenser4 ,it would therefore be       
necessary that the slide should close   
the passage leading to the cylinder at  
one end1 without at the same time       
obstructing the communication between   
the passage from the cylinder to the    
condenser at the other end4 ,on the     
arrival of the piston1 however1 at the  
bottom of the cylinder1 it would be     
necessary immediately to put the lower  
passage to the cylinder in communication
 with the steam pipe1 and the upper     
passage in communication with the       
condenser4 ,this would necessarily      
suppose two motions of the slide as well
 as some modifications in its length4   
,let the length of the slide be such    
that when the passage to the top of the 

cylinder is stopped1 the lower part of  
the slide shall not reach the passage to
 the lower part of the cylinder2 and let
 such a provision be made in the        
mechanism by which the rod ,e governing 
the slide is driven that it shall       
receive two motions during the descent  
of the piston1 the first to be imparted 
to it at the moment the steam is to be  
cut off1 and the second just before the 
termination of the stroke4 ,let the     
position of the slide1 at the           
commencement of the stroke1 be          
represented in fig4 #eb41 and let it be 
required that the steam shall be cut off
 at one half of the stroke4 ,when the   
piston has made half the stroke1 the rod
 governing the slide is moved downwards1
 so as to throw the slide into the      
position represented in fig4 #ec4 ,the  
passage between the steam pipe and the  
cylinder is ,pg#bcc now stopped at both 
ends2 but the passage from the bottom of
 the cylinder to the condenser remains  
open4 ,during the remainder of the      

stroke1 therefore1 the steam in the     
cylinder works expansively4 ,as the     
piston approaches the bottom of the     
cylinder1 another motion is imparted to 
the rod governing the slide1 by which   
the latter is thrown into the position  
represented in fig4 #ed4 ,steam now     
flows below the piston while the steam  
above it passes to the condenser4 ,in a 
similar manner1 by two motions          
successively imparted to the slide      
during the ascent of the piston1 the    
steam may be cut off at half stroke2 and
 it is evident that by regulating the   
time at which these motions are given to
 the slide1 the steam may be worked     
expansively1 to any required extent4    
,illustration3 ,fig4 #eb4               
,illustration3 ,fig4 #ec4               
,illustration3 ,fig4 #ed4  ,it is easy  
to conceive various mechanical means by 
which1 in the same engine1 the point at 
which the steam is cut off may be       
regulated at pleasure4  ,in cases where 
the motion of the piston is very rapid1 

as in locomotive engines1 it is         
desirable that the passages to and from 
the cylinder should be opened very      
suddenly4 ,this is difficult to be      
accomplished with any form of slide     
consisting of a single aperture2 but if1
 instead of admitting the steam to the  
cylinder by a single aperture1 the same 
magnitude of opening were divided among 
several apertures1 then a proportionally
 less extent of motion in the slide     
would clear the passage for the steam1  
and consequently greater suddenness of  
opening would be effected4 ,pg#bcd  ,the
 great advantages in the economy of fuel
 resulting from the application of the  
expansive principle have1 of late years 
forced themselves on the attention of   
engineers1 and considerable improvements
 have been made in its application1     
especially in the case of marine engines
 used for long voyages1 in which the    
economy of fuel has become an object of 
the last importance4 ,the mechanism by  
which expansive slides are moved1 is    

made capable of adjustment1 so that the 
part of the stroke at which the steam is
 cut off1 can be altered at pleasure4   
,the working power of the engine1       
therefore1 instead of being controlled  
by the throttle-valve1 is regulated by  
the greater or less extent to which the 
expansive principle is applied4 ,steam  
of the same pressure is admitted to the 
cylinder in all cases2 but it is cut off
 at a greater or less portion of the    
stroke1 according to the power which the
 engine is required to exert4  ,the last
 degree of perfection has been conferred
 on this principle by connecting the    
governor with the mechanism by which the
 slide is moved1 so that the governor   
instead of acting on the throttle-valve1
 is made to act upon the slide4 ,by this
 means when1 by reason of any diminution
 of the resistance1 the motion of the   
engine is accelerated1 the balls of the 
governor diverging shift the cam or     
lever which governs the slide1 so that  
the steam is cut off after a shorter    

portion of the stroke1 the expansive    
principle is brought into greater play1 
and the quantity of steam admitted to   
the cylinder at each stroke is          
diminished4 ,if1 on the other hand1 the 
resistance to the machine be increased1 
so as to diminish the velocity of the   
engine1 then the balls collapsing the   
levers of the governor shift the cam    
which moves the slides1 so as to        
increase the portion of the stroke made 
by the piston before the steam is cut   
off1 and thereby to increase the amount 
of mechanical power developed in the    
cylinder at each stroke4 ,the extent to 
which the expansive principle is capable
 of being applied1 more especially in   
marine engines1 has been hitherto       
limited by the necessity of using steam 
of very high pressure1 whenever the     
steam is cut off after the piston has   
performed only a small part of the      
stroke4 ,a method1 however1 is now      
7,march1 #ahdj7 under experimental      
trial1 by ,pg#bce ,messrs4 ,maudsley and

 ,field1 by which the expansive         
principle may be applied to any required
 extent without raising the steam in the
 boiler above the usual pressure of from
 three to five pounds per square inch4  
,this method consists in the use of a   
piston of great magnitude4 ,the force   
urging the piston is thus obtained not  
by an excessive pressure on a limited   
surface1 but by a moderate pressure     
diffused over a large surface4 ,the     
entire moving force acting on the piston
 before the steam is cut off1 is        
considerably greater than the           
resistance2 but during the remainder of 
the stroke this force is gradually      
enfeebled until the piston is brought to
 the extremity of its play4             
,illustration3 ,fig4 #ee4   7#acf47 ,mr4
 ,samuel ,seaward1 of the firm of       
,messrs4 ,seawards1 engineers1 has      
contrived an improved system of slides1 
for which he has obtained a patent4 ,a  
section of ,seaward's slides is         
represented in fig4 #ee4 ,the steam pipe

 proceeding from the boiler to the      
cylinder is represented at ,a ,a1 and it
 communicates with passages ,s and ,s   
leading to the top and bottom of the    
cylinder4 ,these passages are formed in 
nozzles of iron or other hard metal cast
 upon the side of the cylinder4 ,these  
nozzles present a smooth face outwards1 
upon which the slides ,b ,b1 also formed
 with smooth faces1 play4 ,the slides ,b
 ,b are attached by knuckle-joints to   
rods ,e ,e1 which move through          
stuffing-boxes1 and the ,pg#bcf         
connection of these rods with the slides
 is such that the slides have play so as
 to detach their surfaces easily from   
the smooth surfaces of the nozzles when 
not pressed against these surfaces4 ,the
 steam in the steam pipe ,a ,a will     
press against the backs of the slides ,b
 ,b1 and keep their faces in steam-tight
 contact with the smooth surfaces of the
 nozzles4 ,these slides may be opened or
 closed by proper mechanism at any point
 of the stroke4 ,when steam is to be    

admitted to the top of the cylinder1 the
 upper slide is raised and the passage  
,s opened2 and when it is to be admitted
 to the bottom of the cylinder1 the     
lower slide is raised and the passage ,s
 opened2 and its communication to the   
top or bottom of the cylinder is stopped
 by the lowering of these slides        
respectively4 ,on the other side of the 
cylinder are provided two passages ,c ,c
 leading to a pipe ,g1 which is         
continued to the condenser4 ,on this    
pipe are cast nozzles of iron or other  
metal presenting smooth faces towards   
the cylinder1 and having passages ,d ,d 
communicating between the top and bottom
 of the cylinder respectively and the   
pipe ,g ,g leading to the condenser4    
,two slides b b'1 having smooth faces   
turned from the cylinder1 and pressing  
upon the faces of the nozzles ,d ,d1 are
 governed by rods playing through       
stuffing-boxes1 in the same manner as   
already described4 ,the faces of these  
slides being turned from the cylinder1  

the steam in the cylinder having free   
communication with them1 has a tendency 
to keep them by its pressure in         
steam-tight contact with the surfaces in
 which the apertures leading to the     
condenser are formed4 ,these two slides 
may be opened or closed whenever it is  
necessary4  ,when the piston commences  
its descent1 the upper steam slide is   
raised1 so as to open the passage ,s1   
and admit steam above the piston2 and   
the lower exhausting slide b is also    
raised1 so as to allow the steam below  
the piston to escape through ,g to the  
condenser1 the other two passages ,s and
 ,c being closed by their respective    
slides4 ,the slide which governs ,s is  
lowered at that part of the stroke at   
which the steam is intended to be cut   
off1 the other slides remaining         
unchanged2 and when the piston has      
reached the bottom of the cylinder1 the 
lower steam slide opens the passage ,s1 
and ,pg#bcg the upper exhausting slide  
opens the passage ,c2 and at the same   

time the lower exhausting slide closes  
the passage ,c4 ,steam being admitted   
below the piston through ,s1 and at the 
same time the steam above it being drawn
 away to the condenser through the open 
passage ,c and the tube ,g1 the piston  
ascends4 ,when it has reached that point
 at which the steam is intended to be   
cut off1 the slide which governs ,s is  
lowered1 the other slides remaining     
unaltered1 and the upward stroke is     
completed in the same manner as the     
downward4  ,these four slides may be    
governed by a single lever1 or they may 
be moved by separate means4 ,from the   
small spaces between the several slides 
and the body of the cylinder1 it will be
 evident that the waste of steam by this
 contrivance will be very small4  ,in   
the slide valves commonly used1 the     
packing of hemp at the back of the      
slide1 by which the pressure necessary  
to keep the slide in steam-tight contact
 is obtained1 requires constant         
attention from the engine-man while the 

engine is at work4 ,any neglect of this 
will produce a corresponding loss in the
 power of the engine2 and accordingly it
 is found that in many cases where      
engines work inefficiently1 the defect  
is owing either to ignorance or want of 
attention on the part of the engine-man 
in the packing of the slides4 ,in       
,seaward's slides no hemp packing is    
used1 nor is any attention on the part  
of the engine-man required after the    
slides are first adjusted4 ,the slides  
receive the pressure necessary to keep  
them in steam-tight contact with the    
surfaces of the nozzles from the steam  
itself1 which acts behind them4  ,the   
eduction and steam slides being         
independent of each other1 they may be  
adjusted so that the engine shall work  
expansively in any required degree2 and 
this may be accomplished either by      
working the slides by separate          
mechanism1 or by a single eccentric4    
,one of the advantages claimed by the   
patentees for these slides is1 that the 

engines are secured from the accidents  
which arise from the accumulation of    
water within the steam cylinder4 ,if    
such a circumstance should occur1 the   
action of the piston will press the     
water against the faces of the steam    
,pg#bch slides1 and the play allowed to 
them by their connection with the rods  
which move them permits their faces to  
be raised from the surfaces of the      
nozzles1 so that the water collected in 
the cylinder shall be driven into the   
steam pipe1 and sent back from thence to
 the boiler4  ,illustration3 ,fig4 #ef4 
,illustration3 ,fig4 #eg4               
,illustration3 ,fig4 #eh4   7#acg47 ,of 
the cocks or valves which are opened and
 closed by the motion of an axis passing
 through their centre1 the              
throttle-valve1 whether worked by hand  
or by the governor1 is an example4 ,but 
the most common form for cocks is that  
of a cylindrical or slightly conical    
plug 7fig4 #ef471 inserted in an        
aperture of corresponding magnitude     

passing across the pipe or passage which
 the cock is intended to open or close4 
,one or more holes are pierced          
transversely in the cock1 and when the  
cock is turned so that these holes run  
in the direction of the tube1 the       
passage through the tube is opened2 but 
when the passage through the cock is    
placed at right angles to the tube1 then
 the sides of the tube stop the ends of 
the passage in the cock1 and the passage
 through the tube is obstructed4 ,the   
simple cock is designed to open or close
 the passage through a single tube4     
,when the cock is turned1 as in fig4    
#eg41 so that the passage through the   
cock shall be at right angles to the    
length of the tube1 then the passage    
through the tube is stopped2 but when   
the cock is turned from that position   
through a quarter of a revolution1 as in
 fig4 #eh41 then the passage through the
 cock takes the direction of the passage
 through the tube1 and the cock is      
opened1 and the passage through the tube

 unobstructed4 ,in such a cock the      
passage may be more or less throttled by
 ,pg#bci adjusting the position of the  
cock1 so that a part of the opening in  
it shall be covered by the side of the  
tube4   7#ach47 ,it is sometimes        
required to put one tube or passage     
alternately in communication with two   
others4 ,this is accomplished by a      
two-way cock4 ,in this cock the passage 
is curved1 opening usually at points on 
the surface of the cock1 at right angles
 to each other4 ,such a cock has already
 been described1 and its use illustrated
 in the description of the ,marquis of  
,worcester's engine 7#ag472 the two-way 
cock1 as represented at ,k and ,r 7fig4 
#d471 being the means by which steam and
 water are alternately supplied to the  
two forcing vessels4  ,illustration3    
,fig4 #ei4  ,illustration3 ,fig4 #fj4   
7#aci47 ,when it is required to put four
 passages alternately in communication  
by pairs1 a four-way cock is used4 ,such
 a cock has two curved passages 7fig4   

#ei471 each similar to the curved       
passage in the two-way cock4 ,let ,s ,c 
,b ,t be the four tubes which it is     
required to throw alternately into      
communication by pairs4 ,when the cock  
is in the position fig4 #ei41 the tube  
,s communicates with ,t1 and the tube ,c
 with ,b4 ,by turning the cock through a
 quarter of a revolution1 as in fig4    
#fj41 the tube ,s is made to communicate
 with ,b1 and the tube ,c with ,t2 and  
if the cock continue to be turned at    
intervals through a quarter of a        
revolution1 these changes of            
communication will continue to be       
alternately made4 ,it is evident that   
this may be accomplished by turning the 
cock continually in the same direction4 
,the four-way cock is sometimes used as 
a substitute for the valves or slides in
 a double-acting steam engine to conduct
 the steam to and from the cylinder4 ,if
 ,s represent a pipe conducting steam   
from the boiler1 ,c that which leads to 
the condenser1 ,t the tube which leads  

to the top of the cylinder1 and ,b that 
which leads to the bottom1 then when the
 cock is in the position 7fig4 #ei471   
steam would flow from the boiler to     
,pg#bdj the top of the piston1 while the
 steam below it would be drawn off to   
the condenser2 and in the position 7fig4
 #fj471 steam would flow from the boiler
 to the bottom of the piston1 while the 
steam above it would be drawn off to the
 condenser4 ,thus by turning the cock   
through a quarter of a revolution       
towards the termination of each stroke1 
the operation of the machine would be   
continued4  ,one of the disadvantages   
which is inseparable from the use of a  
four-way cock for this purpose is the   
loss of the steam at each stroke1 which 
fills the tubes between the cock and the
 ends of the cylinder4 ,this            
disadvantage could only be avoided by   
the substitution of two two-way cocks   
7#ach47 instead of a four-way cock4 ,a  
two-way cock at the top of the cylinder 
would open an alternate communication   

between the cylinder and steam pipe1 and
 the cylinder and condenser1 while a    
similar office would be performed by    
another two-way cock at the other end4  
,the friction on cocks of this          
description is more than on other       
valves2 but this is in some degree      
compensated by the great simplicity of  
the instrument4 ,when the cock is truly 
ground into its seat1 being slightly    
conical in its form1 the pressure of the
 steam has a tendency to keep the       
surfaces in contact2 but this pressure  
also increases the friction1 and has a  
tendency to wear the seat of the cock   
into an elliptical shape4 ,consequently1
 such cocks require to be occasionally  
ground and refitted4   7#adj47 ,the     
four-way cock1 as above described1      
admits the steam to one end of the      
piston at the same moment that it stops 
it at the other end4 ,it would therefore
 be inapplicable where steam is worked  
expansively4 ,a slight modification1    
however1 analogous to that already      

described in the slides1 will adapt it  
to expansive action4 ,this will be      
accomplished by giving to one of the    
passages through the cock one aperture  
larger than the other1 and working the  
cock so that this passage shall always  
be used to conduct steam to the         
cylinder2 also by enlarging both        
apertures of the other passage1 and     
using it always to conduct steam from   
the cylinder4 ,the effect of such an    
arrangement will be readily understood4 
,illustration3 ,fig4 #fa4               
,illustration3 ,fig4 #fb4               
,illustration3 ,fig4 #fc4               
,illustration3 ,fig4 #fd4  ,let the     
position of the cock at the commencement
 of the ,pg#bda descending stroke be    
represented in fig4 #fa4 ,steam flows   
from ,s through ,t to the top of the    
cylinder1 while it escapes from ,b      
through ,c from the bottom of the       
cylinder4 ,when the piston has arrived  
at that point at which the steam is to  
be cut off1 let the cock be shifted to  

the position represented in fig4 #fb4   
,the passage of steam from the boiler is
 now stopped1 but the escape of steam   
from the bottom of the cylinder through 
,c continues1 and the cock is maintained
 in this position until the piston      
approaches the bottom of the cylinder1  
when it is further shifted to the       
position represented in fig4 #fc4 ,steam
 now flows from ,s through ,b to the    
bottom of the cylinder1 while the steam 
from the top of the cylinder escapes    
through ,c to the condenser4 ,when the  
piston has arrived at that point where  
the steam is to be cut off1 the cock is 
shifted to the position represented in  
fig4 #fd4 ,the communication between the
 steam and the bottom of the piston is  
now stopped1 while the communication    
between the top of the cylinder and the 
condenser is still open4 ,during the    
next double stroke of the piston the    
position of the cock is similarly       
changed1 but in the contrary direction1 
and in the same way the motion is       

continued4 ,under these circumstances   
the cock1 instead ,pg#bdb of being moved
 constantly in the same direction1 as in
 the case of the common four-way cock1  
will require to be moved alternately in 
opposite directions4   ,,pistons4       
7#ada47 ,the office of a piston being to
 divide a cylinder into two compartments
 by a movable partition which shall     
obstruct the passage of any fluid from  
one compartment to the other1 it is     
evident that the two conditions which   
such an instrument ought to fulfil are1 
first1 that the contact of its sides    
with the surface of the cylinder shall  
be so close and tight throughout its    
entire play that no steam or other fluid
 can pass between them2 secondly1 that  
it shall be so free from friction1      
notwithstanding this necessary          
tightness1 that it shall not absorb any 
injurious quantity of the moving power4 
,since1 however accurately the surfaces 
of the piston and cylinder may be       
constructed1 there will always be in    

practice more or less imperfection of   
form1 it is evident that the contact of 
the surface of the piston with the      
cylinder throughout the stroke can only 
be maintained by giving to the          
circumference of the piston sufficient  
elasticity to accommodate itself to such
 inequalities of form4 ,the substance1  
whatever it may be1 used for this       
purpose1 and by which the piston is     
surrounded1 is called packing4  ,in     
steam pistons the material used for     
packing must be such as is capable of   
resisting the united effects of heat and
 moisture4 ,hence leather and other     
animal substances are inapplicable4     
,the packing used for steam pistons is  
therefore of two kinds1 vegetable       
packing1 usually hemp1 or metallic      
packing4  ,the common hemp-packed piston
 has been already in part described     
7#gi474 ,the bottom of the piston is a  
circular plate just so much less in     
diameter than the cylinder as is        
sufficient to allow its free motion in  

ascending and descending4 ,a little     
above its lowest point this plate begins
 gradually to diminish in thickness1    
until its diameter is reduced to from   
one to two inches less than that of the 
cylinder1 leaving therefore around      
,pg#bdc it a hollow space1 as           
represented in fig4 #fe4 ,the cover of  
the piston is a plate similarly formed1 
being in like manner gradually reduced  
in thickness downwards1 so as to        
correspond with the lower plate4 ,in the
 hollow space which thus surrounds the  
piston a packing of unspun hemp or soft 
rope1 called gasket1 is introduced by   
winding it round the piston so as to    
render it an even and compact mass4     
,when the space is thus filled up1 the  
top of the piston is attached to the    
bottom by screws4 ,the curved form of   
the space within which the hempen       
packing is confined is such that when   
the screws are tightened1 that part of  
the packing which is nearest to the top 
and bottom of the piston is forced      

against the cylinder1 so as to produce  
upon the two parallel rings as much     
pressure as is necessary to render it   
steam-tight4 ,when by use the packing is
 worn down so as to produce leakage1 the
 cover of the cylinder must be removed1 
and the screws connecting the top and   
bottom of the piston tightened3 this    
will force out the packing and render   
the piston steam-tight4 ,this packing is
 lubricated by melted tallow let down   
upon the piston from the funnel inserted
 in the top of the cylinder1 furnished  
with a stop-cock to prevent the escape  
of steam4 ,the lower end of the         
piston-rod is formed slightly conical1  
the thickest part of the cone being     
downward4 ,it is passed up through the  
piston1 and a nut or wedge between the  
top and bottom is inserted so as to     
secure the piston in its position upon  
the rod4  ,illustration3 ,fig4 #fe4     
,the process of removing the top of the 
cylinder for the purpose of tightening  
the screws in the piston is one of so   

laborious a nature1 that the men        
entrusted with the superintendence of   
these machines are tempted to allow the 
engine to work notwithstanding injurious
 leakage at the piston1 rather than     
incur the labour of tightening the      
screws as often as it is necessary to do
 so4  ,to avoid this inconvenience1 the 
following method of ,pg#bdd tightening  
the packing of the piston without       
removing the lid of the cylinder1 was   
contrived by ,woolf4 ,the head of each  
of the screws was formed into a toothed 
pinion1 and as these screws were placed 
at equal distances from the centre of   
the piston1 these several pinions were  
driven by a large toothed wheel1        
revolving on the piston-rod as an axis4 
,by such an arrangement it is evident   
that if any one of the screws be turned1
 a like motion will be imparted to all  
the others through the medium of the    
large central wheel4 ,woolf accordingly 
formed1 on the head of one of the       
screws1 a square end4 ,when the piston  

was brought to the top of the cylinder1 
this square end entered an aperture made
 in the under side of the cover of the  
cylinder4 ,this aperture was covered by 
a small circular piece screwed into the 
top of the cylinder1 which was capable  
of being removed so as to render the    
square head of the screw accessible4    
,when this was done1 a proper key being 
applied to the square head of the screw1
 it was turned2 and by being turned1 all
 the other screws were in like manner   
moved4 ,in this way1 instead of having  
to remove the cover of the cylinder1    
which in large cylinders was attended   
with great labour and loss of time1 the 
packing was tightened by merely         
unscrewing a piece in the top of the    
cylinder not much greater in magnitude  
than the head of one of the screws4     
,this method was further simplified by  
causing the great circular wheel already
 described to move upon the piston-rod1 
not as an axis1 but as a screw1 the     
thread being cut upon a part of the     

piston-rod which worked in a            
corresponding female screw cut upon the 
central plate4 ,by such means1 the screw
 whose head was let into the cover of   
the cylinder which turned1 would cause  
this circular plate to be pressed       
downwards by the force of the screw     
constructed on the piston-rod4 ,this    
circular plate thus pressed downwards1  
acted upon pins or plugs which pressed  
together the top and bottom of the      
cylinder in the same manner as they were
 pressed together by the screws         
connecting them as already described4   
,,metallic ,,pistons4   7#adb47 ,the    
notion of constructing a piston so as to
 move steam-tight in the cylinder       
without the use of packing of vegetable 
,pg#bde matter was first suggested by   
the ,rev4 ,mr4 ,cartwright1 a gentleman 
well known for other mechanical         
inventions4 ,a patent was granted in    
#agig for a new form of steam engine1 in
 which he proposed to use the vapour of 
alcohol to work the piston instead of   

the steam of water3 and since the       
principle of the engine excluded the use
 of lubrication by oil or tallow1 he    
substituted a piston formed of metallic 
rings pressed against the surface of the
 cylinder by springs1 so as to be       
maintained in steam-tight contact with  
it1 independently either of packing or  
lubrication4 ,although the engine for   
which this form of piston was intended  
never came into practical use1 yet it is
 so simple and elegant in its structure1
 and forms a link so interesting in the 
history of the steam engine1 that some  
explanation of it ought not to be       
omitted in this work4  ,the steam-pipe  
from the boiler is represented cut off  
at ,b 7fig4 #ff472 ,t is a              
spindle-valve1 for admitting steam above
 the piston1 and ,r is a spindle-valve  
in the piston2 ,d is a curved pipe      
forming a communication between the     
cylinder and the condenser1 which is of 
very peculiar construction4 ,cartwright 
proposed effecting a condensation       

without a jet1 by exposing the steam to 
contact with a very large quantity of   
cold surface4 ,for this purpose1 he     
formed his condenser by placing two     
cylinders nearly equal in size1 one     
within the other1 allowing the water of 
the cold cistern in which they were     
placed to flow through the inner        
cylinder1 and to surround the outer one4
 ,thus1 the thin space between the two  
cylinders formed the condenser4         
,illustration3 ,fig4 #ff4  ,the air-pump
 is placed immediately under the        
cylinder1 and the continuation of the   
piston-rod works its piston1 which is   
solid and without a valve4 ,f is the    
pipe from the condenser to the air-pump1
 through which the condensed steam is   
drawn off through the valve ,g on the   
ascent of the piston1 and on the descent
 this is forced through a tube into a   
hot well ,h1 for the purpose of feeding 
the boiler through the feed-pipe ,i4 ,in
 the top of the hot well ,h is a valve  
which opens inwards1 and is kept closed 

by a ball floating on the surface of the
 liquid4 ,the pressure of the condensed 
air above the surface of the liquid in  
,h forces it through ,i into the boiler4
 ,when the air accumulates in too great 
a degree ,pg#bdf in ,h1 the surface of  
the liquid is pressed so low that the   
ball falls and opens the valve1 and     
allows it to escape4 ,the air in ,h is  
that which is pumped from the condenser 
with the liquid1 and from which it was  
disengaged4  ,let us suppose the piston 
at the top of the cylinder3 it strikes  
the tail of the valve ,t1 and raises it1
 while the stem of the piston-valve ,r  
strikes the top of the cylinder1 and is 
pressed into its seat4 ,a free          
communication is at the same time open  
between the cylinder1 below the piston  
and the condenser1 through the tube ,d4 
,the pressure of the steam ,pg#bdg thus 
admitted above the piston acting against
 the vacuum below it1 will cause its    
descent4 ,on arriving at the bottom of  
the cylinder1 the tail of the           

piston-valve ,r will strike the bottom1 
and it will be lifted from its seat1 so 
that a communication will be opened     
through it with the condenser4 ,at the  
same moment1 a projecting spring ,k1    
attached to the piston-rod1 strikes the 
stem of the steam-valve ,t1 and presses 
it into its seat4 ,thus while the       
further admission of steam is cut off1  
the steam above the piston flows into   
the condenser1 and the piston being     
relieved from all pressure1 is drawn up 
by the momentum of the fly-wheel1 which 
continues the motion it received from   
the descending force4 ,on the arrival of
 the piston again at the top of the     
cylinder1 the valve ,t is opened and ,r 
closed1 and the piston descends as      
before1 and so the process is continued4
  ,the mechanism by which motion is     
communicated from the piston to the     
fly-wheel is peculiarly elegant4 ,on the
 axis of the fly-wheel is a small wheel 
with teeth1 which work in the teeth of  
another larger wheel ,l4 ,this wheel is 

turned by a crank1 which is worked by a 
cross-piece attached to the end of the  
piston-rod4 ,another equal-toothed wheel
 ,m is turned by a crank1 which is      
worked by the other end of the cross-arm
 attached to the piston-rod4  ,one of   
the peculiarities of this engine is1    
that the liquid which is used for the   
production of steam in the boiler       
circulates through the machine without  
either diminution or admixture with any 
other fluid1 so that the boiler never   
wants more feeding than what can be     
supplied from the hot well ,h4 ,this    
circumstance forms an important feature 
in the machine1 as it allows of ardent  
spirits being used in the boiler instead
 of water1 which1 since they boil at low
 heats1 promised a saving of fuel4 ,the 
inventor proposed that the engine should
 be used as a still1 as well as a       
mechanical power1 in which case the     
whole of the fuel would be saved4       
,illustration3 ,fig4 #fg4               
,illustration3 ,fig4 #fh4   7#adc47     

,that part of ,cartwright's piston which
 in the common piston is occupied by the
 packing of gasket1 already explained   
7#ada471 was filled by a number of      
rings1 one placed within and above      
another1 and divided into three or four 
,pg#bdh segments4 ,two rings of brass   
were made of the full size of the       
cylinder1 and so ground as to fit the   
cylinder nearly steam-tight4 ,these were
 cut into several segments ,a ,a ,a     
7fig4 #fg471 and were placed one above  
the other1 so as to fill the space      
between the top and bottom plates of the
 piston4 ,the divisions of the segments 
of the one ring were made to fit between
 the divisions of the other4 ,within    
these another series of rings1 ,b ,b ,b1
 were placed1 similarly constructed1 so 
as to fit within the first series in the
 same manner as the first series were   
made to fit within the cylinder4 ,the   
joints of the upper series of each set  
of rings are exhibited in the plan 7fig4
 #fg472 the places of the joints of the 

lower series are shown by dotted lines2 
the position of the rings of each series
 one above the other is shown in the    
section 7fig4 #fh474 ,the joints of the 
inner series of rings are so placed as  
to lie between those of the outer       
series1 to prevent the escape of steam  
which would take place by one continued 
joint from top to bottom of the packing4
 ,the segments into which the rings are 
divided are pressed outwards by steel   
springs in the form of the letter ,v1   
the springs which act upon the outer    
series of segments abutting upon the    
inner series1 and those which act on the
 inner series abutting upon the solid   
centre of the piston3 these springs are 
represented in fig4 #fg4  ,illustration3
 ,fig4 #fi4  ,illustration3 ,fig4 #gj4  
7#add47 ,an improved form was given to  
the metallic piston by ,barton4         
,barton's piston consists of a solid    
cylinder of cast iron1 represented at ,a
 in section in fig4 #fi41 and in plan in
 ,pg#bdi fig4 #gj4 ,in the centre of    

this is a conical hole1 increasing in   
magnitude downwards1 to receive the     
piston-rod1 in which the latter is      
secured by a cross-pin ,b4 ,a deep      
groove1 square in its section1 is formed
 around the piston1 so that while the   
top and bottom of the piston form       
circles equal in magnitude to the       
section of the cylinder1 the            
intermediate part of the body of the    
piston forms a circle less than the     
former by the depth of the groove4 ,let 
a ring of brass1 cast iron1 or cast     
steel1 be made to correspond in         
magnitude and form with this groove1 and
 let it be divided as represented in    
fig4 #gj41 into four segments ,c ,c ,c  
,c1 and four corresponding angular      
pieces ,d ,d ,d ,d4 ,let the groove     
which surrounds the piston be filled by 
the four segments with the four         
wedge-like angular pieces within them1  
and let the latter be urged against the 
former by eight spiral springs1 as      
represented in fig4 #fi4 and fig4 #gj4  

,these springs will abut against the    
solid centre by the piston1 and will    
urge the segments ,c against the        
cylinder4 ,the spiral springs which urge
 the wedges are confined in their action
 by steel pins which pass through their 
centre1 and by being ,pg#bej confined in
 cylindrical cavities worked into the   
wedges and into corresponding parts of  
the solid centre of the piston1 as the  
segments ,c wear1 the springs urge the  
wedges outwards1 and the points of the  
latter protruding1 are gradually worn   
down so as to fill up the spaces left   
between the segments1 and thus to       
complete the outer surface of the       
piston4  ,various other forms of        
metallic pistons have been proposed1 but
 as they do not differ materially in    
principle from those we have just       
described1 it will not be necessary here
 to describe them4  ,illustration3      
,,engine ,,at ,,the ,,city ,,saw        
,,mills4  ,pg#bea     ,illustration3    
,,furnace ,,at ,,the ,,city ,,saw       

,,mills4  ,,chap4 ,,ix4                 
,,constituents ,,of ,,coal4 -- ,,process
 ,,of ,,combustion4 -- ,,heat ,,evolved 
,,in ,,it4 -- ,,form ,,and ,,structure  
,,of ,,boiler4 -- ,,waggon ,,boiler4 -- 
,,furnace4 -- ,,method ,,of ,,feeding   
,,it4 -- ,,combustion ,,of ,,gas ,,in   
,,flues4     -- ,,construction ,,of     
,,grate ,,and ,,ash-,,pit4 --           
,,magnitude ,,of ,,heating     ,,surface
 ,,of ,,boiler4 -- ,,steam-,,space ,,and
 ,,water-,,space ,,in ,,boiler4 --      
,,position ,,of ,,flues4 -- ,,method    
,,of ,,feeding ,,boiler4 -- ,,level     
,,gauges4     -- ,,self-,,regulating    
,,feeders4 -- ,,steam-,,gauge4 --       
,,barometer-,,gauge4 --     ,,indicator4
 -- ,,counter4 -- ,,safety-,,valve4 --  
,,fusible ,,plugs4 --                   
,,self-,,regulating ,,damper4 --        
,,self-,,regulating ,,furnace4 --       
,,power ,,and     ,,duty ,,of ,,engines4
 -- ,,horse-,,power ,,of ,,steam        
,,engines4 -- ,,evaporation             
,,proportional ,,to ,,horse-,,power4 -- 

,,sources ,,of ,,loss ,,of ,,power4 --  
,,absence ,,of ,,good ,,practical       
,,rules ,,for ,,power4 -- ,,common      
,,rules     ,,followed ,,by ,,engine    
,,makers4 -- ,,duty ,,distinguished     
,,from ,,power4 --     ,,duty ,,of      
,,boilers4 -- ,,proportion ,,of ,,stroke
 ,,to ,,diameter ,,of     ,,cylinder4 --
 ,,duty ,,of ,,engines4 -- ,,cornish    
,,system ,,of ,,inspection4 --     ,,its
 ,,good ,,effects4 -- ,,historical      
,,detail ,,of ,,the ,,duty ,,of         
,,cornish     ,,engines4   7#ade47 ,the 
machinery which has been explained in   
the preceding chapters1 consisting of   
the cylinder with its passages and      
valves1 the piston-rod1 parallel motion1
 beam1 connecting-rod and crank1        
together with the condenser1 air-pump1  
and other appendages1 having no source  
of moving power in themselves1 must be  
regarded as mere instruments by which   
the mechanical effect developed by the  
furnace and the boiler is transmitted to
 the working point and so ,pg#beb       

modified as to be adapted to the uses to
 which the machine is applied4 ,the     
boiler is at once a magazine in which   
the moving power is stored in sufficient
 quantity to supply the demands of the  
engine and an apparatus in which that   
power is fabricated4 ,the mechanical    
effect evolved in the conversion of     
water into steam by heat1 is the process
 by which the power of the steam-engine 
is produced1 and space is provided in   
the boiler1 capacious enough to contain 
as much steam as is necessary for the   
engine1 besides a sufficient quantity of
 water to continue that supply          
undiminished1 notwithstanding the       
constant drafts made upon it by the     
cylinder3 even the water itself1 from   
the evaporation of which the mechanical 
power is produced1 ought to be regarded 
as an instrument by which the effect of 
the heat of the combustible is rendered 
mechanically efficient1 inasmuch as the 
same heat1 applied not only to other    
liquids but even to solids1 would       

likewise be productive of mechanical    
effects4 ,the boiler and its furnace are
 therefore parts of the steam-engine1   
the construction and operation of which 
are entitled to especial attention4     
7#adf47 ,,coal1 the combustible almost  
universally used in steam-engines1 is a 
substance1 the principal constituents of
 which are carbon and hydrogen1         
occasionally mixed with sulphur in a    
small proportion1 and earthy            
incombustible matter4 ,in different     
sorts of coal the proportions of these  
constituents vary1 but in coal of good  
quality about three quarters of the     
whole weight of the combustible is      
carbon4  ,when carbon is heated to a    
temperature of about #gjj in an         
atmosphere of pure oxygen1 it will      
combine chemically with that gas1 and   
the product will be the gas called      
carbonic acid4 ,the volume of carbonic  
acid produced by this combination1 will 
be exactly equal to that of the oxygen  
combined with the carbon1 and therefore 

the weight of a given volume of the gas 
will be increased by the weight of      
carbon which enters the combination4 ,it
 is found that two parts by weight of   
oxygen combined with three of carbon1   
form carbonic acid4 ,the weight of the  
carbonic acid1 therefore1 produced in   
the combustion1 will be greater than the
 weight of the oxygen1 bulk for bulk1 in
 the proportion of five to two1 the     
volume being the same and the gases     
being ,pg#bec compared at the same      
temperatures and under equal pressures4 
,in this combination heat is evolved in 
very large quantities4 ,this effect     
arises from the heat previously latent  
in the carbon and oxygen being rendered 
sensible in the process of combustion4  
,the carbonic acid proceeding from the  
combustion is by such means raised to a 
very high temperature1 and the carbon   
during the process acquires a heat so   
intense as to become luminous2 no flame1
 however1 is produced4  ,hydrogen1      
heated to a temperature of about #ajjj1 

in contact with oxygen will combine with
 the latter1 and a great evolution of   
heat will attend the process2 the gases 
will be rendered luminous1 and flame    
will be produced4 ,the product of this  
process will be water1 which being      
exposed to the intense heat of          
combustion1 will be immediately         
converted into steam4 ,hydrogen combines
 with eight times its own weight of     
oxygen1 producing nine times its own    
weight of water4  ,hydrogen gas is1     
however1 not usually disengaged from    
coal in a simple form1 but combined     
chemically with a certain portion of    
carbon1 the combination being called    
carburetted hydrogen4 ,pure hydrogen    
burns with a very faintly luminous blue 
flame1 but carburetted hydrogen gives   
that bright flame occasionally having an
 orange or reddish tinge1 which is seen 
to issue from burning coals3 this is the
 gas used for illumination1 being       
expelled from the coal by the process of
 coking1 and conducted to the various   

burners through proper pipes4  ,the     
sulphur1 which in a very small          
proportion is contained in coals1 is    
also combustible1 and combines in the   
process of combustion with oxygen1      
forming sulphurous acid3 it is also     
sometimes evolved in combination with   
hydrogen1 forming sulphuretted hydrogen4
  ,atmospheric air consists of two      
gases1 azote and oxygen1 mixed together 
in the proportion of four to one2 five  
cubic feet of atmospheric air consisting
 of four cubic feet of azote and one of 
oxygen4 ,any combustible will combine   
with the oxygen contained in atmospheric
 air1 if raised to a temperature        
somewhat higher than that which is      
necessary to cause its combustion in an 
atmosphere of pure oxygen4  ,if coals1  
therefore1 or other fuel exposed to     
atmospheric ,pg#bed air1 be raised to a 
sufficiently high temperature1 their    
combustible constituents will combine   
with the oxygen of the atmospheric air1 
and all the phenomena of combustion will

 ensue4 ,in order1 however1 that the    
combustion should be continued1 and     
should be carried on with quickness and 
activity1 it is necessary that the      
carbonic acid1 and other products1      
should be removed from the combustible  
as they are produced1 and fresh portions
 of atmospheric air brought into contact
 with it2 otherwise the combustible     
would soon be surrounded by an          
atmosphere composed chiefly of carbonic 
acid to the exclusion of atmospheric    
air1 and therefore of uncombined oxygen1
 and consequently the combustion would  
cease1 and the fuel be extinguished4 ,to
 maintain the combustion1 therefore1 a  
current of atmospheric air must be      
constantly carried through the fuel3 the
 quantity and force of this current must
 depend on the quantity and quality of  
the fuel to be consumed4 ,it must be    
such that it shall supply sufficient    
oxygen to the fuel to maintain the      
combustion1 and not more than           
sufficient1 since any excess would be   

attended with the effect of absorbing   
the heat of combustion1 without         
contributing to the maintenance of that 
effect4  ,heat is communicated from body
 to body in two ways1 by radiation and  
by contact4  ,rays of heat issue from a 
heated body1 and are dispersed through  
the surrounding space in a manner1 and  
according to laws1 similar to those     
which govern the radiation of light4    
,the heat thus radiated meeting other   
bodies is imparted to them1 and         
penetrates them with more or less       
facility according to their physical    
qualities4  ,a heated body also brought 
into contact with another body of lower 
temperature1 communicates heat to that  
other body1 and will continue to do so  
until the temperature of the two bodies 
in contact shall be equalised4 ,heat    
proceeds from fuel in a state of        
combustion in both these ways3 the      
heated fuel radiates heat in all        
directions around it1 and the heat thus 
radiated will be imparted to all parts  

of the furnace which are exposed to the 
fuel4  ,the gases1 which are the        
products of the combustion1 escape from 
the fuel at a very high temperature1 and
 consequently1 in acquiring that        
temperature they absorb a considerable  
,pg#bee quantity of the heat of         
combustion4 ,but besides the gases      
actually formed in the process of       
combustion1 the azote forming four      
fifths of the air carried through the   
fuel to support the combustion1 absorbs 
heat from the combustible1 and rises    
into the upper part of the furnace at a 
high temperature4 ,these various gases1 
if conducted directly to the chimney1   
would carry off with them a considerable
 quantity of the heat4 ,provision should
 therefore be made to keep them in      
contact with the boiler such a length of
 time as will enable them to impart such
 a portion of the heat which they have  
absorbed from the fuel1 as will still   
leave them at a temperature sufficient1 
and not more than sufficient1 to produce

 the necessary draft in the chimney4    
7#adg47 ,the forms of boiler which have 
been proposed as the most convenient for
 the attainment of all these requisite  
purposes have been very various4 ,if    
strength alone were considered1 the     
spherical form would be the best2 and   
the early boilers were very nearly      
hemispheres1 placed on a slightly       
concave base4 ,the form adopted by      
,watt1 called the waggon boiler1        
consists of a semi-cylindrical top1 flat
 perpendicular sides1 flat ends1 and a  
slightly concave bottom4 ,the steam     
intended to be used in boilers of this  
description did not exceed the pressure 
of the external atmosphere by more than 
from #c to #e lbs4 per square inch2 and 
the flat sides and ends1 though         
unfavourable to strength1 could be      
constructed sufficiently strong for this
 purpose4 ,in a boiler of this sort1 the
 air and smoke passing through the flues
 that are carried round it1 are in      
contact at one side only with the       

boiler4 ,the brickwork1 or other        
materials forming the flue1 must        
therefore be non-conductors of heat1    
that they may not absorb any            
considerable portion of heat from the   
air passing in contact with them4 ,a    
boiler of this form is represented in   
fig4 #ga4  ,the grate and a part of the 
flues are rendered visible by the       
removal of a portion of the surrounding 
masonry in which the boiler is set4 ,the
 interior of the boiler is also shown by
 cutting off one half of the            
semi-cylindrical roof4 ,a longitudinal  
vertical section is shown in fig4 #gb41 
and a cross section in fig4 #gc4 ,a     
horizontal section taken above the level
 of the grate1 and below the level of   
the water in the boiler1 showing ,pg#bef
 the course of the flues1 is given in   
fig4 #gd4 ,the corresponding parts in   
all the figures are marked by the same  
letters4  ,illustration3 ,fig4 #ga4     
,the door by which fuel is introduced   
upon the grate is represented at ,a1 and

 the door leading to the ash-pit at ,b4 
,the fire bars at ,c slope downwards    
from the front at an angle of about #be1
 giving a tendency to the fuel to move  
from the front towards the back of the  
grate4 ,the ash-pit ,d is constructed of
 such a magnitude1 form1 and depth1 as  
to admit a current of atmospheric air to
 the grate-bars1 sufficient to sustain  
the combustion4 ,the form of the ash-pit
 is usually wide below1 contracting     
towards the top4  ,illustration3 ,fig4  
#gb4  ,the fuel when introduced at the  
fire-door ,a1 should be laid on that    
part of the grate nearest to the        
fire-door1 called the dead plates3 there
 it is submitted to the process of      
coking1 by which the gases and volatile 
matter which it contains are expelled1  
and being carried by a current of air1  
admitted ,pg#beg through small apertures
 in the fire-door over the burning fuel 
in the hinder part of the grate1 they   
are burnt4 ,when the fuel in front of   
the grate has been thus coked1 it is    

pushed back1 and a fresh feed introduced
 in front4 ,the coal thus pushed back   
soon becomes vividly ignited1 and by    
continuing this process1 the fuel spread
 over the grate is maintained in the    
most active state of combustion at the  
hinder part of the grate4 ,by such an   
arrangement1 the smoke produced by the  
combustion of the fuel may be burnt     
before it enters the flues4 ,the flame  
and heated air proceeding from the      
burning fuel arising from the grate1 and
 rushing towards the back of the        
furnace1 passes over the fire-bridge ,e1
 and is carried through the flue ,f     
which passes under the boiler4 ,this    
flue 7the cross section of which is     
shown in fig4 #gc41 by the dark shade   
put under the boiler7 is very nearly    
equal in width to the bottom of the     
boiler1 the space at the bottom of the  
boiler1 near the corners1 being only    
what is sufficient to give the weight of
 the boiler support on the masonry      
forming the ,pg#beh sides of the flue4  

,the bottom of the boiler being concave1
 the flame and heated air as they pass  
along the flue rise to the upper part by
 the effects of their high temperature1 
and lick the bottom of the boiler from  
the fire-bridge at ,e to the further end
 ,g4  ,illustration3 ,fig4 #gc4         
,illustration3 ,fig4 #gd4  ,at ,g the   
flue rises to ,h1 and turning to the    
side of the boiler at ,i ,i1 conducts   
the flame in contact with the side from 
the back to the front2 it then passes   
through the flue ,k across the front1   
and returns to the back by the other    
side ,pg#bei flue ,l4 ,the side flue is 
represented1 stripped of the masonry1 in
 fig4 #ga41 and also appears in the plan
 in fig4 #gd41 and in the cross section 
in fig4 #gc4 ,the course of the air is  
represented in fig4 #gd4 by the arrows4 
,from the flue ,l the air is conducted  
into the chimney at ,m4  ,by such an    
arrangement1 the flame and heated air   
proceeding from the grate are made to   
circulate round the boiler1 and the     

length and magnitude of the flues       
through which it is conducted should be 
such1 that when it shall arrive at the  
chimney its temperature shall be        
reduced1 as nearly as is consistent with
 the maintenance of draught in the      
chimney1 to the temperature of the water
 with which it is in contact4  ,the     
method of feeding the furnace1 which has
 been described above1 is one which1 if 
conducted with skill and care1 would    
produce a much more perfect combustion  
of the fuel than would attend the common
 method of filling the grate from the   
back to the front with fresh fuel1      
whenever the furnace is fed4 ,this      
method1 however1 is rarely observed in  
the management of the furnace4 ,it      
requires the constant attention of the  
stokers 7such is the name given to those
 who feed the furnaces74 ,the fuel must 
be supplied1 not in large quantities1   
and at distant intervals1 but in small  
quantities and more frequently4 ,on the 
other hand1 the more common practice is 

to allow the fuel on the grate to be in 
a great degree burned away1 and then to 
heap on a large quantity of fresh fuel1 
covering over with it the burning fuel  
from the back to the front of the grate4
 ,when this is done1 the heat of the    
ignited coal acting upon the fresh fuel 
introduced1 expels the gases combined   
with it and1 mixed with these1 a        
quantity of carbon1 in a state of minute
 division1 forming an opaque black      
smoke4 ,this is carried through the     
flues and drawn up the chimney4 ,the    
consequence is1 that not only a quantity
 of solid fuel is sent out of the       
chimney unconsumed1 but the hydrogen and
 other gases also escape unburned1 and a
 proportional waste of the combustible  
is produced2 besides which1 the nuisance
 of an atmosphere filled with smoke     
ensues4 ,such effects are visible to all
 who observe the chimneys of            
steam-vessels1 while the engine is in   
operation4 ,when the furnaces are thus  
filled with fresh fuel1 a large volume  

of ,pg#bfj dense black smoke is observed
 to issue from the chimney4 ,this       
gradually subsides as the fuel on the   
grate is ignited1 and does not reappear 
until a fresh feed is introduced4  ,this
 method of feeding1 by which the furnace
 would be made to consume its own smoke1
 and the combustion of the fuel be      
rendered complete1 is not however free  
from counteracting effects4 ,in ordinary
 furnaces the feed can only be          
introduced by opening the fire-doors1   
and during the time the fire-doors are  
opened a volume of cold air rushes in1  
which passing through the furnace is    
carried through the flues to the        
chimney4 ,such is the effect of this in 
lowering the temperature of the flues1  
that in many cases the loss of heat     
occasioned is greater than any economy  
of fuel obtained by the complete        
consumption of smoke4 ,various methods1 
however1 may be adopted by which fuel   
may be supplied to the grate without    
opening the fire-doors1 and without     

disturbing the supply of air to the     
fire4 ,a hopper built into the front of 
the furnace1 with a moveable bottom or  
valve1 by which coals may be allowed to 
drop in from time to time upon the front
 of the grate1 would accomplish this4   
7#adh47 ,in order to secure the         
combustion of the gases evolved from the
 coals placed in the front of the grate1
 it is necessary that a supply of       
atmospheric air should be admitted with 
them over the burning fuel4 ,this is    
effected by small apertures or          
regulators1 provided in the fire-doors1 
governed by sliding-plates1 by which    
they may be opened or closed to any     
required extent4  ,a patent has recently
 been granted to ,mr4 ,williams1 one of 
the directors of the ,city of ,dublin   
,steam ,navigation ,company1 for a      
method of consuming the unburned gases  
which escape from the grate1 and are    
carried through the flues4 ,this method 
consists in introducing into the flue   
tubes placed in a vertical position1 the

 lower ends of which being inserted in  
the bottom of the flue are made to      
communicate with the ash-pit1 and the   
upper ends of which are closed4 ,the    
sides and tops of these tubes are       
pierced with small holes1 through which 
atmospheric air drawn from the ash-pit  
issues in jets4 ,the oxygen supplied by 
this air immediately combines with the  
carburetted hydrogen1 which ,pg#bfa     
having escaped from the furnace unburned
 is carried through the flues at a      
sufficient temperature to enter into    
combination with the oxygen admitted    
through holes in the tubes4 ,a number of
 jets of flame thus proceed from these  
holes1 having an appearance similar to  
the flame of a gas-lamp4  ,it is evident
 that such tubes must be inefficient    
unless they are placed in the flues so  
near the furnace1 that the temperature  
of the unburned gases shall be          
sufficiently high to produce their      
combustion4   7#adi47 ,the magnitude of 
the grate and ash-pit must be determined

 by the rate at which the evaporation is
 required to be conducted in the boiler 
and the quality of the fuel4 ,it must be
 a matter of regret1 that the           
proportions of the various parts of     
steam-engines1 with their boilers and   
furnaces1 have not been determined by   
any exact or satisfactory experiments2  
and those who project and manufacture   
the engines themselves1 are not less in 
ignorance on those points than others4  
,with coals of the common quality a     
certain average proportion must exist   
between the necessary magnitude of the  
grate-surface and the quantity of water 
to be evaporated in a given time in the 
boiler4 ,but what that proportion is for
 any given quality of fuel1 is at       
present unascertained4 ,each            
engine-maker follows his own rule1 and  
the rule thus followed is in most cases 
a matter of bare conjecture1 unsupported
 by any experimental evidence4 ,some    
engine-makers will allow a square foot  
of grate-surface for every cubic foot of

 water per hour1 which is expected to be
 evaporated in the boiler2 others allow 
only half a square foot3 and practice   
varies between these limits4 ,bituminous
 coals which melt and cake1 and which   
burn with much flame and smoke1 must be 
spread more thinly on the grate than    
other descriptions of fuel1 otherwise a 
considerable quantity of combustible    
gases would be dismissed into the flues 
unburnt4 ,such coals therefore1 other   
circumstances being the same1 require a 
larger portion of grate-surface2 and the
 same may be said of coals which produce
 clinkers in their combustion1 and form 
lumps of vitrified matter on the grate1 
by which the spaces between the         
grate-bars are speedily closed up4 ,when
 such fuel is used1 the grate-bars      
require to be frequently raked ,pg#bfb  
out1 otherwise the spaces between them  
being obstructed1 the draught would     
become insufficient for the due         
combustion of the fuel4  ,to facilitate 
the raking out of the grate1 the bars   

are placed with their ends towards the  
fire-door3 they are usually made of     
cast-iron1 from two to two inches and a 
half wide on the upper surface1 with    
intervals of nearly half an inch between
 them4 ,the bars taper downwards1 their 
under surfaces being much narrower than 
their upper1 the spaces between them    
thus widening1 to facilitate the fall of
 the ashes between them4 ,the grate-bars
 slope downwards from the front to the  
back4 ,the height of the centre of the  
bottom of the boiler1 above the front of
 the grate1 is usually about two feet1  
and about three feet above the back of  
it4 ,the concave bottom of the boiler1  
however1 brings its surfaces at the     
slide closer to the grate4   7#aej47    
,between the evaporating power of the   
boiler1 and the magnitude of surface it 
exposes to the action of the furnace1   
there is a relation which1 like that of 
the grate surface1 has never been       
ascertained by any certain or           
satisfactory experimental investigation2

 much less have the different degrees of
 efficiency attending different parts of
 the boiler-surface been determined4    
,that part of the surface of the boiler 
immediately over and around the grate1  
is exposed to the immediate radiation of
 the burning fuel1 and is therefore     
probably the most efficient in the      
production of steam4 ,the tendency of   
flame and heated air to rise1 would     
naturally bring them in the flues into  
closer contact with those parts of the  
boiler-surface which are horizontal in  
their position1 and which form the tops 
of the flues1 than with those which are 
lateral or vertical in their position1  
and which form the sides of the flues4  
,in a boiler constructed like that      
already described1 the flue-surface     
therefore1 which would be most          
efficient1 would be the concave bottom  
of the boiler extending from the        
fire-bridge to its remote end4 ,in some 
boilers1 especially those in which steam
 of high pressure is produced1 the form 

is cylindrical1 the middle flue being   
formed into an elliptical tube the      
greater axis of which is horizontal from
 end to end of the boiler4 ,it seems    
doubtful1 however1 ,pg#bfc whether in   
such a boiler the heat produces any     
useful effect on the water below the    
flue1 the water above being always at a 
higher temperature1 and therefore       
lighter than that below1 and            
consequently no currents being          
established between the upper and lower 
strata of the water4  ,it was considered
 by ,mr4 ,watt1 but we are not aware on 
what experimental grounds1 that from    
eight to ten square feet of heating     
surface were sufficient to produce the  
evaporation of one cubic foot of water  
per hour4 ,the practice of engine-makers
 since that time has been to increase   
the allowance of heating surface for the
 same rate of evaporation4              
,engine-builders have varied very much  
in this respect1 some allowing twelve1  
fifteen1 and even eighteen square feet  

of surface for the same rate of         
evaporation4 ,it must1 however1 still be
 borne in mind1 that whether this       
increased allowance did or did not      
produce the actual evaporation imputed  
to it1 has not been1 as far as we are   
informed1 ever accurately ascertained4  
,the production of a given rate of      
evaporation by a moderate heat diffused 
over a larger surface1 rather than by a 
fiercer temperature confined to a       
smaller surface1 is attended with many  
practical advantages4 ,the plates of the
 boiler acted upon by the fire are less 
exposed to oxydisation1 and the boiler  
will be proportionally more durable4    
7#aea47 ,besides presenting to the      
action of the fire a sufficient surface 
to produce steam at the required rate1  
the capacity of the boiler must be      
proportioned to the quantity of water to
 be evaporated4 ,the space within the   
boiler is appropriated to a twofold     
purpose3 #ast1 ,to contain the water to 
be evaporated2 #b;dly1 ,to contain a    

quantity of ready made steam for the    
supply of the cylinder4 ,if the space   
appropriated to the steam did not bear a
 considerable proportion to the         
magnitude of the cylinder1 the momentary
 expansion of the steam passing to the  
cylinder from the boiler at each stroke 
would reduce the pressure of the steam  
in a great proportion1 and unless the   
pressure in the boiler were considerably
 greater than that which the steam is   
intended to have in the cylinder1 the   
pressure in the latter would be reduced 
below the proper amount4 ,the proportion
 of the ,pg#bfd steam space in the      
boiler to the magnitude of the cylinder 
has been very variously estimated1 nor  
can it be said that any practical rule  
of a general kind has been adopted4 ,it 
is held by some that the steam-space    
will be sufficient if it contain five   
times the quantity of steam consumed at 
each stroke1 while others maintain that 
it should contain at least ten times    
that quantity1 and opinions vary between

 these limits4   7#aeb47 ,the proportion
 of water-space in the boiler to its    
evaporating power should also be        
regulated1 so that the introduction of  
the feed at a comparatively low         
temperature may not unduly chill the    
water in the boiler4 ,supposing the feed
 to be introduced in a low pressure     
boiler at the temperature of #ajj1 and  
that the necessary temperature within   
the boiler be #bbe1 the quantity of     
water it contains should be about five  
times the quantity evaporated1 and      
therefore also five times the quantity  
introduced through the feed per hour4   
,for every cubic foot of water per hour 
therefore1 intended to be evaporated by 
the boiler1 water-space for five cubic  
feet should be provided4 ,it is1        
however1 right to repeat that this 7like
 almost every other so called rule7 is  
the result not of any exact general     
calculation1 but one deduced from the   
custom which has obtained among the     
manufacturers of steam-engines4         

7#aec47 ,the surface of the water in the
 boiler should always be above the range
 of the flues4 ,when the heated air in  
the flues acts upon a part of the boiler
 within which water is contained1 the   
water within receiving an increased     
temperature becomes1 bulk for bulk1     
lighter than the strata of water above  
it1 and ascends4 ,it is replaced by the 
descending strata1 which1 in their turn 
receiving increased temperature1 rise to
 the surface2 or if the action of the   
heat convert the water into steam1 the  
bubbles of steam rise to the surface1   
fresh portions of water continually     
coming into contact with the            
boiler-plates on which the heated air or
 flame acts4 ,by this process the       
boiler-plates are continually cooled1   
either by being successively washed by  
water at a lower temperature1 or by the 
heat taken from them becoming latent in 
the steam bubbles formed in contact with
 them4 ,but if the heat act ,pg#bfe upon
 a part of the boiler containing steam  

within it1 which steam being a slow     
recipient of heat1 and no currents being
 established1 nor any phenomenon        
produced in which heat is rendered      
latent1 the heat of the fire            
communicated to the boiler-plates       
accumulates in them1 and raises their   
temperature to an injurious degree4 ,the
 plates may by this means be softened1  
so as to cause the boiler to burst1 or  
the difference between the expansion of 
the highly heated plates thus exposed to
 fire in contact with steam and that of 
the plates which are cooled by contact  
with water1 may cause the joinings of   
the boiler-plates to open1 and the      
boiler to leak4 ,by whatever means1     
therefore1 the boiler be fed1 care      
should be taken that the evaporation    
should not be allowed to reduce the     
level of the water in it below the      
highest flue4   7#aed47 ,as the water by
 which the boiler is fed must always    
have a much lower temperature than that 
at which the boiler is maintained1 the  

supply of the feed will have a constant 
tendency to lower the temperature of the
 water1 and this tendency will be       
determined by the proportion between the
 magnitude of the feed and the quantity 
of water in the boiler4  ,since it is   
requisite that the level of the water in
 the boiler shall not suffer any        
considerable change1 it is evident that 
the magnitude of the feed must be equal 
to the quantity of water evaporated4 ,if
 it were less1 the level of the water   
would continually fall by reason of the 
excess of the evaporation over the feed2
 and if it were greater1 the level would
 rise by the accumulation of water in   
the boiler4 ,if therefore the quantity  
of water-space allowed in the boiler be 
five times the volume of water          
evaporated per hour1 the quantity       
introduced by the feed per hour1 whether
 continuously or at intervals1 must be  
of the same amount4 ,since the process  
of evaporation is continuous1 the       
variation of level of water in the      

boiler will be entirely dependent on the
 intervals between the successive feeds4
 ,if the feed be continuous1 and always 
equal to the evaporation1 then the level
 of the water in the boiler will undergo
 no change2 but if while the evaporation
 is continuous the feed be made at      
intervals1 then the change of level of  
water in the boiler as ,pg#bff well as  
its change of temperature1 will be      
subject to a variation proportional to  
the intervals between the successive    
feeds4 ,it is manifest1 therefore1 that 
the feed should either be uninterrupted 
or be supplied at short intervals1 so   
that the change of level and temperature
 of the water in the boiler should not  
be considerable4   7#aee47 ,different   
methods have been1 from time to time1   
suggested for indicating the level of   
the water in the boiler4 ,we have       
already mentioned the two gauge-pipes   
used in the earlier steam-engines       
7#ca471 and which are still generally   
continued4 ,there are1 however1 some    

other methods which merit our attention4
  ,illustration3 ,fig4 #ge4  ,a weight  
,f 7fig4 #ge471 half immersed in the    
water in the boiler1 is supported by a  
wire1 which1 passing steam-tight through
 a small hole in the top1 is connected  
by a flexible string1 or chain1 passing 
over a wheel ,w1 with a counterpoise ,a1
 which is just sufficient to balance ,f 
when half immersed4 ,if ,f be raised    
above the water1 ,a being lighter will  
no longer balance it1 and ,f will       
descend pulling up ,a1 and turning the  
wheel ,w4 ,if1 on the other hand1 ,f be 
plunged deeper in the water1 ,a will    
more than balance it1 and will pull it  
up1 so that the only position in which  
,f and ,a will balance each other is1   
when ,f is half immersed4 ,the wheel ,w 
is so adjusted1 that when two pins      
placed on its rim are in the horizontal 
position1 the water is at its proper    
level4 ,consequently it follows1 that if
 the water rise above this level1 the   
weight ,f is lifted and ,a falls1 so    

that the pins come into another         
position4 ,if1 on the other hand1 the   
level of the water fall1 ,f falls and ,a
 rises1 so that the pins assume a       
different position4 ,thus1 in general1  
the position of the pins becomes an     
indication of the quantity of water in  
the boiler4   7#aef47 ,another method is
 to place a glass tube 7fig4 #gf471 with
 one end ,t entering the boiler above   
the proper level1 and the other end ,t  
entering it below the proper level4 ,it 
must ,pg#bfg be evident that the water  
in the tube will always stand at the    
same level as the water in the boiler1  
since the lower part has a free         
communication with that water1 while the
 surface is submitted to the pressure of
 the same steam as the water in the     
boiler4 ,this and the last-mentioned    
gauge have the advantage of addressing  
the eye of the engineer at once1 without
 any adjustment2 whereas the gauge-cocks
 must be both opened1 whenever the depth
 is to be ascertained4  ,illustration3  

,fig4 #gf4  ,these gauges1 however1     
require the frequent attention of the   
engine-man2 and it becomes desirable    
either to find some more effectual means
 of awakening that attention1 or to     
render the supply of the boiler         
independent of any attention4 ,in order 
to enforce the attention of the         
engine-man to replenish the boiler when 
partially exhausted by evaporation1 a   
tube was sometimes inserted at the      
lowest level to which it was intended   
that the water should be permitted to   
fall4 ,this tube was conducted from the 
boiler into the engine-house1 where it  
terminated in a mouth-piece or whistle1 
so that whenever the water fell below   
the level at which this tube was        
inserted in the boiler1 the steam would 
rush through it1 and issuing with great 
velocity at the mouth-piece1 would      
summon the engineer to his duty with a  
call that would rouse him even from     
sleep4  ,illustration3 ,fig4 #gg4       
7#aeg47 ,in the most effectual of these 

methods1 the task of replenishing the   
boiler should still be executed by the  
engineer2 and the utmost that the boiler
 itself was made to do1 was to give due 
notice of the necessity for the supply  
of water4 ,the consequence was1 among   
other inconveniences1 that the level of 
the water was subject to constant       
variation4  ,to remedy this a method has
 been invented1 by which ,pg#bfh the    
engine is made to feed its own boiler4  
,the pipe ,g 7fig4 #gg471 which leads   
from the hot water pump1 terminates in a
 small cistern ,c in which the water is 
received4 ,in the bottom of this        
cistern1 a valve ,v is placed1 which    
opens upwards1 and communicates with a  
feed-pipe1 which descends into the      
boiler below the level of the water in  
it4 ,the stem of the valve ,v is        
connected with a lever turning on the   
centre ,d1 and loaded with a weight ,f  
dipped in the water in the boiler in a  
manner similar to that described in fig4
 #ge41 and balanced by a counterpoise ,a

 in exactly the same way4 ,when the     
level of the water in the boiler falls1 
the float ,f falls with it1 and pulling 
down the arm of the lever raises the    
valve ,v1 and lets the water descend    
into the boiler from the cistern ,c4    
,when the boiler has thus been          
replenished1 and the level raised to its
 former place1 ,f will again be raised1 
and the valve ,v closed by the weight   
,a4 ,in practice1 however1 the valve ,v 
adjusts itself by means of the effect of
 the water on the weight ,f1 so as to   
permit the water from the               
feeding-cistern ,c to flow in a         
continued stream1 just sufficient in    
quantity to supply the consumption from 
evaporation1 and to maintain the level  
of the water in the boiler constantly   
the same4  ,by this arrangement the     
boiler is made to replenish itself1 or1 
more properly speaking1 it is made to   
receive such a supply1 as that it never 
wants replenishing1 an effect which no  
effort of attention on the part of an   

engine-man could produce4 ,but this is  
not the only good effect produced by    
this contrivance4 ,a part of the steam  
which originally left the boiler1 and   
having discharged its duty in moving the
 piston1 was condensed and reconverted  
into water1 and lodged by the air-pump  
in the hot well 7fig4 #gg471 is here    
again restored to the source from which 
it came1 bringing back all the          
unconsumed portion of its heat          
preparatory to being once more put in   
circulation through the machine4  ,the  
entire quantity of hot water pumped into
 the cistern ,c1 is not always necessary
 for the boiler4 ,a waste-pipe may be   
provided for carrying off the surplus1  
which may be turned to any purpose for  
which it may be required2 or it may be  
discharged into a cistern to cool1      
preparatory to ,pg#bfi being restored to
 the cold cistern1 in case water for the
 supply of that cistern be not          
sufficiently abundant4  ,illustration3  
,fig4 #gh4   7#aeh47 ,another method of 

arranging a self-regulating feeder is   
shown in fig4 #gh4 ,a is a hollow ball  
of metal attached to the end of a lever1
 whose fulcrum is at ,b4 ,the other arm 
of the lever ,c is connected with the   
stem of a spindle-valve1 communicating  
with a tube which receives water from   
the feeding-cistern4 ,thus1 when the    
level of the water in the boiler        
subsides1 the ball ,a preponderating    
over the weight of the opposite arm1 the
 lever falls1 the arm ,c rises and opens
 the valve1 and admits the feeding      
water4 ,this apparatus will evidently   
act in the same manner and on the same  
principles as that already described4   
,pg#bgj  ,the mouth of the tube by which
 the feed is introduced should be placed
 at that part of the boiler which is    
nearest the end of the flues which issue
 into the chimney4 ,by such means the   
temperature of the water in contact with
 those flues will be lowest at the place
 where the temperature of the heated air
 intended to act upon it is also lowest4

 ,the difference of the temperatures    
will therefore be greater than it would 
be if the point of the boiler containing
 water of a higher temperature was left 
in contact with this part of the flue4  
,illustration3 ,fig4 #gi4   7#aei47 ,it 
is necessary to have a ready method of  
ascertaining at all times the pressure  
of the steam which is used in working   
the engine4 ,for this purpose a bent    
tube containing mercury is inserted into
 some part of the apparatus1 which has  
free communication with the steam4 ,let 
,a ,b ,c 7fig4 #gi47 be such a tube4    
,the pressure of the steam forces the   
mercury down in the leg ,a ,b1 and up in
 the leg ,b ,c4 ,if the mercury in both 
legs be at exactly the same level1 the  
pressure of the steam must be exactly   
equal to that of the atmosphere2 because
 the steam pressure on the mercury in ,a
 ,b balances the atmospheric pressure on
 the mercury in ,b ,c4 ,if1 however1 the
 level of the mercury in ,b ,c be above 
the level of the mercury in ,b ,a1 the  

pressure of the steam will exceed that  
of the atmosphere4 ,the excess of its   
pressure above that of the atmosphere   
may be found by observing the difference
 of the level of the mercury in the     
tubes ,b ,c and ,b ,a1 allowing a       
pressure of one pound on each square    
inch for every two inches in the        
difference of the levels4  ,if1 on the  
contrary1 the level of the mercury in ,b
 ,c should fall below its level in ,a   
,b1 the atmospheric pressure will       
,pg#bga exceed that of the steam1 and   
the quantity of the excess may be       
ascertained exactly in the same way4    
,if the tube be glass1 the difference of
 levels of the mercury would be visible2
 but it is most commonly made of iron2  
and in order to ascertain the level1 a  
thin wooden rod with a float is inserted
 in the open end of ,b ,c1 so that the  
portion of the stick within the tube    
indicates the distance of the level of  
the mercury from its mouth4 ,a bulb or  
cistern of mercury might be substituted 

for the leg ,a ,b1 as in the common     
barometer4 ,this instrument is called   
the steam-gauge4  ,if the steam-gauge be
 used as a measure of the strength of   
the steam which presses on the piston1  
it ought to be on the same side of the  
throttle-valve 7which is regulated by   
the governor7 as the cylinder2 for if it
 were on the same side of the           
throttle-valve with the boiler1 it would
 not be affected by the changes which   
the steam may undergo in passing through
 the throttle-valve1 when partially     
closed by the agency of the governor4   
,for boilers in which steam of very high
 pressure is used1 as in those of       
locomotive engines1 a steam-gauge1      
constructed on the above principle1     
would have inconvenient or impracticable
 length4 ,in such boilers the pressure  
of the steam is equal to four or five   
times that of the atmosphere1 to        
indicate which the column of mercury in 
the steam-gauge would be four or five   
feet in height4 ,in such cases a        

thermometer-gauge may be used with      
advantage4 ,the principle of this gauge 
is founded on the fact1 that between the
 pressure and temperature of steam      
produced in contact with water there is 
a fixed relation1 the same temperature  
always corresponding to the same        
pressure4 ,if1 therefore1 a thermometer 
be immersed in the boiler which shall   
show the temperature of the steam1 a    
scale may be attached to it1 on which   
shall be engraved the corresponding     
pressures4 ,such gauges are now very    
generally used on locomotive engines4   
,illustration3 ,fig4 #hj4   7#afj47 ,the
 force with which the piston is pressed 
depends on two things1 #ast1 the actual 
strength of the steam which presses on  
it2 and1 #b;dly1 on the actual strength 
of the vapour which resists it4 ,for    
although the vacuum produced by the     
method of separate condensation be much 
more perfect than ,pg#bgb what had been 
produced in the atmospheric engines1 yet
 still some vapour of a small degree of 

elasticity is found to be raised from   
the hot water in the bottom of the      
condenser before it can be extracted by 
the air-pump4 ,one of these pressures is
 indicated by the steam-gauge already   
described2 but still1 before we can     
estimate the force with which the piston
 descends1 it is necessary to ascertain 
the force of the vapour which remains   
uncondensed1 and resists the motion of  
the piston4 ,another gauge1 called the  
barometer-gauge1 is provided for this   
purpose4 ,a glass tube ,a ,b 7fig4      
#hj471 more than thirty inches long and 
open at both ends1 is placed in an      
upright or vertical position1 having the
 lower end ,b immersed in a cistern of  
mercury ,c4 ,to the upper end is        
attached a metal tube1 which            
communicates with the condenser1 in     
which a constant vacuum1 or rather high 
degree of rarefaction1 is sustained4    
,the same vacuum must therefore exist in
 the tube ,a ,b1 above the level of the 
mercury1 and the atmospheric pressure on

 the surface of the mercury in the      
cistern ,c will force the mercury up in 
the tube ,a ,b1 until the column which  
is suspended in it is equal to the      
difference between the atmospheric      
pressure and the pressure of the        
uncondensed steam4 ,the difference      
between the column of mercury sustained 
in this instrument and in the common    
barometer1 will determine the strength  
of the uncondensed steam1 allowing a    
force proportional to one pound per     
square inch for every two inches of     
mercury in the difference of the two    
columns4 ,in a well-constructed engine  
which is in good order1 there is very   
little difference between the altitude  
in the barometer-gauge and the common   
barometer4  ,to compute the force with  
which the piston descends1 thus becomes 
a very simple arithmetical process4     
,first1 ascertain the difference of the 
levels of the mercury in the            
steam-gauge2 this gives the excess of   
the steam pressure above the atmospheric

 pressure4 ,then find the height of the 
mercury in the barometer-gauge2 this    
gives the excess of the atmospheric     
pressure above the uncondensed steam4   
,hence1 if these two heights be added   
together1 we shall obtain the ,pg#bgc   
excess of the impelling force of the    
steam from the boiler1 on the one side  
of the piston1 above the resistance of  
the uncondensed steam on the other side3
 this will give the effective impelling 
force4 ,now1 if one pound be allowed for
 every two inches of mercury in the two 
columns just mentioned1 we shall have   
the number of pounds of impelling       
pressure on every square inch of the    
piston4 ,then1 if the number of square  
inches in the section of the piston be  
found1 and multiplied by the number of  
pounds on each square inch1 the force   
with which it moves will be obtained4   
,from what we have stated it appears    
that1 in order to estimate the force    
with which the piston is urged1 it is   
necessary to refer to both the barometer

 and the steam-gauge4 ,this double      
computation may be obviated by making   
one gauge serve both purposes4 ,if the  
end ,c of the steam-gauge 7fig4 #gi471  
instead of communicating with the       
atmosphere were continued to the        
condenser1 we should have the pressure  
of the steam acting upon the mercury in 
the tube ,b ,a1 and the pressure of the 
uncondensed vapour which resists the    
piston acting on the mercury in the tube
 ,b ,c4 ,hence the difference of the    
levels of the mercury in the tubes would
 at once indicate the difference between
 the force of the steam and that of the 
uncondensed vapour1 which is the        
effective force with which the piston is
 urged4   7#afa47 ,but these methods of 
determining the effective force by which
 the piston is urged1 can only be       
regarded as approximations1 and not very
 perfect ones4 ,if the condensation of  
steam on one side of the piston were    
instantaneously effected1 or the        
uncondensed vapour were of the same     

tension during the whole stroke2 and if1
 besides this1 the pressure of steam on 
the piston were of uniform intensity    
from the beginning to the end of the    
stroke1 then the steam and barometer    
gauges taken together would become an   
accurate index of the effective force of
 steam on the piston3 but such is not   
the case4 ,when the steam is first      
admitted through the steam-valve it acts
 on the piston with a pressure which is 
first slightly diminished1 and          
afterwards a little increased1 until it 
arrives at that part of the stroke at   
which the steam-valve is closed1 after  
which the pressure is diminished4 ,the  
,pg#bgd pressure1 therefore1 urging the 
piston is subject to variation2 but the 
pressure of the uncondensed vapour on   
the other side of the piston is subject 
to still greater change4 ,at the moment 
the exhausting-valve is opened1 the     
piston is relieved from the pressure    
upon it by the commencement of the      
condensation2 but this process during   

the descent of the piston is gradual1   
and the vacuum is rendered more and more
 perfect1 until the piston has nearly   
attained the limit of its play4 ,these  
variations1 both as well of the force   
urging the piston as of the force       
resisting it1 are such as not to be     
capable of being accurately measured by 
a mercurial column1 since they would    
produce oscillations in such a column1  
which would render any observations of  
its mean height impracticable4  ,to     
measure the mean efficient force of the 
piston1 taking into account these       
circumstances1 ,mr4 ,watt invented an   
instrument1 which1 like all his         
mechanical inventions1 has answered its 
purpose perfectly1 and is still in      
general use4 ,this instrument1 called an
 indicator1 consists of a cylinder of   
about #a-c_/d inch in diameter1 and #h  
inches in length4 ,it is bored with     
great accuracy1 and fitted with a solid 
piston moving steam-tight in it with    
very little friction4 ,the rod of this  

piston is guided in the direction of the
 axis of the cylinder through a collar  
in the top1 so as not to be subject to  
friction in any part of its play4 ,at   
the bottom of the cylinder is a pipe    
governed by a stop-cock and turned in a 
screw1 by which the instrument may be   
screwed on the top of the steam-cylinder
 of the engine4 ,in this position1 if   
the stop-cock of the indicator be       
opened1 a free communication will be    
made between the cylinder of the        
indicator and that of the engine4 ,the  
piston-rod of the indicator is attached 
to a spiral spring1 which is capable of 
extension and compression1 and which by 
its elasticity is capable of measuring  
the force which extends or compresses it
 in the same manner as a spring         
steel-yard or balance4 ,if a scale be   
attached to the instrument at any point 
on the piston-rod to which an index     
might be attached1 then the position of 
that index upon the scale would be      
governed by the position of the         

indicator-piston in its cylinder4 ,if   
any force pressed the indicator-piston  
upwards1 so as to compress the spring1  
,pg#bge the index would rise upon the   
scale2 and if1 on the other hand1 a     
force pressed the indicator-piston      
downwards1 then the spiral spring would 
be extended1 and the index on the       
piston-rod descend upon the scale4 ,in  
each case the force of the spring1      
whether compressed or extended1 would be
 equal to the force urging the          
indicator-piston1 and the scale might be
 so divided as to show the amount of    
this force4  ,now1 let the instrument be
 supposed to be screwed upon the top of 
the cylinder of a steam-engine1 and the 
stop-cock opened so as to leave a free  
communication between the cylinder of   
the indicator below its piston and the  
cylinder of the steam-engine above the  
steam-piston4 ,at the moment the upper  
steam-valve is opened1 the steam rushing
 in upon the steam-piston will also pass
 into the indicator1 and press the      

indicator-piston upwards3 the index upon
 its piston-rod will point upon the     
scale to the amount of pressure thus    
exerted4 ,as the steam-piston descends1 
the indicator-piston will vary its      
position with the varying pressure of   
the steam in the cylinder1 and the index
 on the piston-rod will play upon the   
scale1 so as to show the pressure of the
 steam at each point during the descent 
of the piston4  ,if it were possible to 
observe and record the varying position 
of the index on the piston-rod of the   
indicator1 and to refer each of these   
varying positions to the corresponding  
point of the descending stroke1 we      
should then be able to declare the      
actual pressure of the steam at every   
point of the stroke4 ,but it is evident 
that such an observation would not be   
practicable4 ,a method1 however1 was    
contrived by ,mr4 ,southern1 an         
assistant of ,messrs4 ,boulton and      
,watt1 by which this is perfectly       
effected4 ,a square piece of paper1 or  

card1 is stretched upon a board1 which  
slides in grooves formed in a frame4    
,this frame is placed in a vertical     
position near the indicator1 so that the
 paper may be moved in a horizontal     
direction backwards and forwards1       
through a space of fourteen or fifteen  
inches4 ,instead of an index a pencil is
 attached to the indicator of the       
piston-rod3 this pencil is lightly      
pressed by a spring against the paper   
above mentioned1 and as the paper is    
moved in a horizontal direction ,pg#bgf 
under the pencil1 would trace upon the  
paper a line4 ,if the pencil were       
stationary this line would be straight  
and horizontal1 but if the pencil were  
subject to a vertical motion1 the line  
traced on the paper moved under the     
pencil horizontally would be a curve1   
the form of which would depend on the   
vertical motion of the pencil4 ,the     
board thus supporting the paper is put  
into connexion by a light cord carried  
over pulleys with some part of the      

parallel motion1 by which it is         
alternately moved to the right and to   
the left4 ,as the piston ascends or     
descends1 the whole play of the board in
 the horizontal direction will therefore
 represent the length of the stroke1 and
 every fractional part of that play will
 correspond to a proportional part of   
the stroke of the steam-piston4         
,illustration3 ,fig4 #ha4  ,the         
apparatus being thus arranged1 let us   
suppose the steam-piston at the top of  
the cylinder commencing its descent4 ,as
 it descends1 the pencil attached to the
 indicator piston-rod varies its height 
according to the varying pressure of the
 steam in the cylinder4 ,at the same    
time the paper is moved uniformly under 
the pencil1 and a curved line is traced 
upon it from right to left4 ,when the   
piston has reached the bottom of the    
cylinder1 the upper exhausting-valve is 
opened1 and the steam drawn off to the  
condenser4 ,the indicator-piston being  
immediately relieved from a part of the 

pressure acting upon it descends1 and   
with it the pencil also descends2 but at
 the same time the steam-piston has     
begun to ascend1 and the paper to return
 from left to right under the pencil4   
,while the steam-piston continues to    
ascend1 the condensation becomes more   
and more perfect1 and the vacuum in the 
cylinder1 and therefore also in the     
indicator1 being gradually increased in 
power1 the atmospheric pressure above   
the indicator-piston presses it         
downwards and stretches the spring4 ,the
 pencil meanwhile1 with the paper moving
 under it from right to left1 traces a  
second curve4 ,as the former curve      
showed the actual pressure of the steam 
impelling the piston in its descent1    
this latter will show the pressure of   
the uncondensed steam raising the piston
 in its ascent1 and a comparison of the 
two will exhibit the effective force on 
the piston4 ,fig4 #ha4 represents such a
 diagram as would be ,pg#bgg produced by
 this instrument4 ,a ,b ,c is the curve 

traced by the pencil during the descent 
of the piston1 and ,c ,d ,e that during 
its ascent4 ,a is the position of the   
pencil at the moment the piston         
commences its descent1 ,b is its        
position at the middle of the stroke1   
and ,c at the termination of the stroke4
 ,on closing the upper steam-valve and  
closing the exhausting-valve1 the       
indicator-piston being gradually        
relieved from the pressure of the steam 
the pencil descends1 and at the same    
time the paper moving from left to      
right1 the pencil traces the curve ,c ,d
 ,e1 the gradual descent of this curve  
showing the progressive increase of the 
vacuum4 ,as the atmospheric pressure    
constantly acts above the piston of the 
indicator1 its position will be         
determined by the difference between the
 atmospheric pressure and the pressure  
of the steam below it2 and therefore the
 difference between the heights of the  
pencil at corresponding points in the   
ascending and descending stroke1 will   

express the difference between the      
pressure of the steam impelling the     
piston in the ascent and resisting it in
 the descent at these points4 ,thus at  
the middle of the stroke1 the line ,b ,d
 will express the extent to which the   
spring governing the indicator-piston   
would be stretched by the difference    
between the force of steam impelling the
 piston at the middle of the descending 
stroke1 and the force of steam resisting
 it at the middle of the ascending      
stroke4 ,the force therefore measured by
 the line ,b ,d will be the effective   
force on the piston at that point2 and  
the same may be said of every part of   
the diagram produced by the indicator4  
,the whole mechanical effect produced by
 the stroke of the piston being composed
 of the aggregate of all its varying    
effects throughout the stroke1 the      
determination of its amount ,pg#bgh is a
 matter of easy calculation by the      
measurement of the diagram supplied by  
the indicator4 ,let the horizontal play 

of the pencil from ,a to ,c be divided  
into any proposed number of equal parts1
 say ten3 at the middle of the stroke1  
,b ,d expresses the effective force on  
the piston1 and if this be considered to
 be uniform through the tenth part of   
the stroke1 as from f to g1 then the    
number of pounds expressed by ,b ,d     
multiplied by the tenth part of the     
stroke expressed in parts of a foot1    
will be the mechanical effect through   
that part of the stroke expressed in    
pounds' weight raised one foot4 ,in like
 manner m n will express the effective  
force on the piston after three fourths 
of the stroke have been performed1 and  
if this be multiplied by a tenth part of
 the stroke as before1 the mechanical   
effect similarly expressed will be      
obtained2 and the same process being    
applied to any successive tenth part of 
the stroke1 and the numerical results   
thus obtained being added together1 the 
whole effect of the stroke will be      
obtained1 expressed in pounds' weight   

raised one foot4   7#afb47 ,by means of 
the indicator1 the actual mechanical    
effect produced by each stroke of the   
engine can be obtained1 and if the      
actual number of strokes made in any    
given time be known1 the whole effect of
 the moving power would be determined4  
,an instrument called a counter was also
 contrived by ,watt1 to be attached     
either to the working beam or to any    
other reciprocating part of the engine4 
,this instrument consisted of a train of
 wheel-work with governing hands or     
indices moved upon divided dials1 like  
the hand of a clock4 ,a record of the   
strokes was preserved by means precisely
 similar to those by which the hands of 
a clock or time-piece indicated and     
recorded the number of vibrations of the
 pendulum or balance-wheel4   7#afc47   
,to secure the boiler from accidents    
arising from the steam contained in it  
acquiring an undue pressure1 a          
safety-valve is used1 similar in        
principle to those adopted in the early 

engines4 ,this valve is represented in  
fig4 #ga4 at ,n4 ,it is a conical valve1
 kept down by a weight sliding on a rod 
upon it4 ,when the pressure of the steam
 overcomes the force of this weight1 it 
raises the valve and escapes1 being     
carried off through the tube4 ,pg#bgi   
,with a view to the economy of heat1    
this waste steam tube is sometimes      
conducted into the feeding cistern1     
where the steam carried off by it is    
condensed1 and heats the feeding water4 
,the magnitude of the safety-valve      
should be such that1 when open1 steam   
should be capable of passing through it 
as rapidly as it is generated in the    
boiler4 ,the superficial magnitude1     
therefore1 of such valves must be       
proportional to the evaporating power of
 the boiler4 ,in low pressure boilers   
the steam is generally limited to five  
or six pounds' pressure per square inch1
 and consequently the load over the     
safety-valve in pounds would be found by
 multiplying the superficial magnitude  

of its smallest part by these numbers4  
,in boilers in which the steam is       
maintained at a higher pressure1 it     
would be inconvenient to place upon the 
safety-valve the necessary weight4 ,in  
such cases a lever is used1 the shorter 
arm of which presses down the valve1 and
 the longer arm is held down by a weight
 capable of adjustment1 so that the     
pressure on the valve may be regulated  
at discretion4 ,two safety-valves should
 be provided on all boilers1 one of     
which should be locked up1 so that the  
persons in care of the engine should    
have no power to increase the load upon 
it4 ,in such case1 however1 it is       
necessary that a handle connected with  
the valve should project outside the box
 containing it1 so that it may always be
 possible for the engineer to ascertain 
that the valve is not locked in its     
seat1 a circumstance which is liable to 
happen4  ,sometimes also two            
safety-valves are provided1 one loaded a
 little heavier than the other4 ,the    

escape of steam from the lighter valve  
in this case gives notice to the        
engine-man of the growing increase of   
pressure1 and warns him to check the    
production of steam4 ,the lever by which
 the safety-valve is held down is       
sometimes acted on by a spiral spring1  
capable of being so adjusted as to      
produce any required pressure on the    
valve4 ,this arrangement is adopted in  
locomotive engines1 where steam of very 
high pressure is used2 and in such cases
 also there are always provided two such
 valves1 one of which cannot be         
increased in its pressure4  ,the pipe by
 which the boiler is fed with water will
 ,pg#bhj necessarily act as a           
safety-valve1 for when the pressure of  
the steam increases in an undue degree1 
it will press the water in the boiler up
 through the feed-pipe1 so as to        
discharge it into the feed-cistern1 a   
circumstance which would immediately    
give notice of the internal state of the
 boiler4 ,the steam-gauge1 already      

described 7fig4 #gi471 would also act as
 a safety-valve2 for if the pressure of 
steam in the boiler should be so        
augmented as to blow the mercury out of 
the steam-gauge1 the steam would then   
issue through the gauge1 and the        
pressure of the boiler be reduced1      
provided that the magnitude of the tube 
forming the steam-gauge were sufficient 
for this purpose4   7#afd47 ,in high    
pressure boilers which are exposed to   
extreme temperatures and pressures1 and 
which are therefore subject to danger of
 explosion1 a plug of metal is sometimes
 inserted1 which is capable of being    
fused at a temperature above which the  
boiler should not be permitted to be    
raised4 ,if the pressure of steam       
increase beyond the proper limit1 the   
temperature of the water and steam will 
undergo a corresponding increase2 and if
 the metal of the plug be capable of    
being fused at such a temperature1 the  
plug will fall out of the boiler1 and   
the steam and water will issue from it4 

,various alloys of metal are fusible at 
temperatures sufficiently low for this  
purpose4 ,an alloy composed of one part 
of lead1 three of tin1 and five of      
bismuth1 will fuse at the common        
temperature of boiling water2 and alloys
 of the same metals1 in various         
proportions1 will fuse at different     
temperatures from #bjj to #djj4         
,although fusible plugs may be used1 in 
addition to other means of insuring     
safety1 they ought not to be exclusively
 relied on at the ordinary working      
pressure of the boiler4 ,the fusible    
plug ought to be capable of more than   
resisting the pressure2 but if it be so1
 its point of fusion would be one at    
which the steam would have a pressure of
 at least two atmospheres above its     
working pressure4 ,the plug would       
therefore be capable of being fused only
 as soon as the steam would acquire a   
pressure of #cj lbs4 per inch above its 
regular working pressure4  ,when a      
boiler ceases to be worked1 and the     

furnace has been extinguished1 the space
 within it appropriated to steam ,pg#bha
 will be left a vacuum by the           
condensation of the steam with which it 
was previously filled4 ,the external    
pressure of the atmosphere acting on the
 boiler would1 under such circumstances1
 have a tendency to crush it inwards4   
,to prevent this1 a safety-valve is     
provided1 opening inwards1 and balanced 
by a weight sufficient to keep it closed
 until it be relieved from the pressure 
of the steam below4  ,a large aperture  
closed by a flange secured with screws1 
represented at ,o in fig4 #ga41 called  
the man-hole1 is provided to admit      
persons into the boiler for the purpose 
of cleaning or repairing its interior4  
7#afe47 ,the manner in which the        
governor regulates the supply of steam  
from the boiler to the cylinder1        
proportioning the quantity to the work  
to be done1 and thereby sustaining a    
uniform motion1 has been already        
explained 7p4 #abe474 ,since then the   

consumption of steam in the engine is   
subject to variation1 owing to the      
various quantities of work it may have  
to perform1 it is evident that the      
production of steam in the boiler should
 be subject to a proportional variation4
 ,for otherwise1 one of two effects     
would ensue3 the boiler would either    
fail to supply the engine with steam1 or
 steam would accumulate in the boiler   
from being produced in too great        
abundance1 and would escape at the      
safety-valve1 and thus be wasted4  ,in  
order to vary the production of steam in
 proportion to the demands of the       
engine1 it is necessary to stimulate or 
mitigate the furnace1 as the evaporation
 is to be augmented or diminished4  ,the
 activity of the furnace must depend on 
the current of air which is drawn       
through the grate-bars1 and this will   
depend on the magnitude of the space    
afforded for the passage of that current
 through the flues4 ,a plate called a   
damper is accordingly placed with its   

plane at right angles to the flue1 so   
that by raising and lowering it in the  
same manner as the sash of a window is  
raised or lowered1 the space allowed for
 the passage of air through the flue may
 be regulated4 ,this plate might be     
regulated by the hand1 so that by       
raising or lowering it the draught might
 be increased or diminished1 and a      
corresponding effect produced on the    
,pg#bhb evaporation in the boiler3 but  
the force of the fire is rendered       
uniformly proportional to the rate of   
evaporation by the following            
arrangement1 without the intervention of
 the engineer4 ,the column of water     
sustained in the feed-pipe 7figs4 #ga1  
#gb47 represents by its weight the      
difference between the pressure of steam
 within the boiler and that of the      
atmosphere4 ,if the engine consumes     
steam faster than the boiler produces   
it1 the steam contained in the boiler   
acquires a diminished pressure1 and     
consequently the column of water in the 

feed-pipe will fall4 ,if1 on the other  
hand1 the boiler produce steam faster   
than the engine consumes it1 the        
accumulation of steam in the boiler will
 cause an increased pressure on the     
water it contains1 and thereby increase 
the height of the column of water       
sustained in the feed-pipe4 ,this column
 therefore necessarily rises and falls  
with every variation in the rate of     
evaporation in the boiler4 ,a hollow    
float ,p is placed upon the surface of  
the water of this column2 a chain       
connected with this float is carried    
upwards1 and passed over two pulleys1   
after which it is carried downwards     
through an aperture leading to the flue 
which passes beside the boiler3 to this 
chain is attached the damper4 ,by such  
an arrangement it is evident that the   
damper will rise when the float ,p      
falls1 and will fall when the float ,p  
rises1 since the weight of the damper is
 so adjusted1 that it will only balance 
the float ,p when the latter rests on   

the surface of the water4  ,whenever the
 evaporation of the boiler is           
insufficient1 it is evident from what   
has been stated1 that the float ,p will 
fall and the damper will rise1 and will 
afford a greater passage for air through
 the flue4 ,this will stimulate the     
furnace1 will augment its heating power1
 and will therefore increase the rate of
 evaporation in the boiler4 ,if1 on the 
other hand1 the production of steam in  
the boiler be more than is requisite for
 the supply of the engine1 the float    
will be raised and the damper let down1 
so as to contract the flue1 to diminish 
the draught1 to mitigate the fire1 and  
therefore to check the evaporation4 ,in 
this way the excess1 or defect1 of      
evaporation in the boiler is made to act
 upon the fire1 so as to render the heat
 proceeding from the combustion as      
nearly as possible proportional to the  
wants of the engine4 ,pg#bhc   7#aff47  
,the method of feeding the furnace by   
hand through the fire-door being subject

 to the double objection of admitting   
more cold air over the fuel than is     
necessary for its combustion1 and the   
impracticability of insuring that       
regular attendance on the part of the   
stokers1 directed the attention of      
engineers to the construction of        
self-regulating furnaces4 ,the most     
effectual of these1 and that which has  
come into most general use1 was invented
 by ,mr4 ,william ,brunton of           
,birmingham4  ,the advantages proposed  
to be attained by him were those        
expressed in his patent3--  ,first1 ,i  
put the coal upon the grate by small    
quantities1 and at very short intervals1
 say every two or three seconds4 #b;dly1
 ,i so dispose of the coals upon the    
grate1 that the smoke evolved must pass 
over that part of the grate upon which  
the coal is in full combustion1 and is  
thereby consumed4 #c;dly1 ,as the       
introduction of coal is uniform in short
 spaces of time1 the introduction of air
 is also uniform1 and requires no       

attention from the fireman4  ,as it     
respects economy3 #ast1 ,the coal is put
 upon the fire by an apparatus driven by
 the engine1 and so contrived that the  
quantity of coal is proportioned to the 
quantity of work which the engine is    
performing2 and the quantity of air     
admitted to consume the smoke is        
regulated in the same manner4 #b;dly1   
,the fire-door is never opened1         
excepting to clean the fire2 the boiler1
 of course1 is not exposed to that      
continual irregularity of temperature   
which is unavoidable in the common      
furnace1 and which is found exceedingly 
injurious to boilers4 #c;dly1 ,the only 
attention required is to fill the       
coal-receiver every two or three hours1 
and clean the fire when necessary4      
#dthly1 ,the coal is more completely    
consumed than by the common furnace1 as 
all the effect of what is termed        
stirring up the fire 7by which no       
inconsiderable quantity of coal is      
passed into the ash-pit71 is attained   

without moving the coal upon the grate4 
,a circular grate is placed on a        
vertical revolving shaft2 on the lower  
part of this shaft1 under the ash-pit1  
is placed a toothed wheel driven by a   
pinion4 ,this pinion is placed on       
another vertical shaft1 which ascends   
above the boiler2 and ,pg#bhd on the    
other end of this is placed a bevelled  
wheel driven by a pinion4 ,this pinion  
is attached to a shaft1 which takes its 
motion from the axis of the fly-wheel1  
or any other revolving shaft connected  
with the engine4 ,a constant motion of  
revolution is therefore imparted to the 
circular grate1 and its velocity being  
proportional to that of the engine1 will
 necessarily be also proportional to the
 quantity of fuel which ought to be     
consumed4 ,through that part of the     
boiler which is over the fire-grate a   
vertical tube or opening is made        
directly over that part of the furnace  
which is most distant from the flues4   
,over this opening a hopper is placed1  

which contains the fuel by which the    
boiler is to be fed2 and in the bottom  
of this hopper is a sliding valve1      
capable of being opened or closed1 so as
 to regulate the quantity of fuel       
supplied to the fire-grate4 ,the fuel   
dropping in in small quantities through 
this open valve falls on the grate1 and 
is carried round by it1 so as to leave a
 fresh portion of the grate to receive  
succeeding feeds4 ,the coals admitted   
through the hopper are previously broken
 to a proper size2 and in some forms of 
this apparatus there are two rollers1 at
 a regulated distance asunder1 the      
surfaces of which are formed into blunt 
angular points1 and which are kept in   
slow revolution by the engine4 ,between 
these rollers the coals must pass before
 they reach the valve through which the 
furnace is fed1 and they are thus broken
 and reduced to a regulated size4 ,the  
valve which regulates the opening       
through which the feed is admitted1 is  
connected by chains and pulleys with the

 self-regulating damper already         
described1 so that in proportion as the 
damper is raised1 the valve governing   
the feed may be opened4 ,thus1 while the
 quantity of air admitted by the damper 
is increased according to the demands of
 the engine1 the quantity of fuel       
admitted for the feed is increased by   
opening the valve in the bottom of the  
hopper in the same proportion4          
,apertures are also provided in the     
front of the grate1 governed by         
regulators1 by which the quantity of air
 necessary and sufficient to produce the
 combustion of the gas evolved from the 
fuel is admitted1 these openings being  
also connected with the self-regulating 
damper4  ,a considerable portion of the 
heat imparted to the water ,pg#bhe in   
the boiler escapes by radiation from the
 surface of the boiler1 steam-pipes1 and
 other parts of the machinery in contact
 with the steam and hot water4 ,the     
effects of this are rendered very       
apparent in marine engines1 where a     

large quantity of water is found to be  
condensed in the great steam-pipes      
leading from the boiler to the cylinder4
 ,in stationary land boilers this loss  
of heat is usually diminished1 and in   
some cases in a great degree removed1 by
 surrounding the boiler with            
non-conducting substances4 ,in some     
cases the boiler is built round in brick
 work4 ,in ,cornwall1 where the economy 
is regarded perhaps to a greater extent 
than elsewhere1 the boiler and          
steam-pipes are surrounded with a       
packing of sawdust1 which being almost a
 non-conductor of heat1 is impervious to
 the heat proceeding from the surfaces  
with which it is in contact1 and        
consequently confines all the heat      
within the boiler4 ,in marine boilers it
 has been the practice recently to      
clothe the boiler and steam-pipes with a
 coating of felt1 which is attended with
 a similar effect4 ,when these remedies 
are properly applied1 the loss of heat  
proceeding from the radiation of the    

boiler is reduced to an extremely small 
amount4 ,the engine-houses of some of   
the ,cornish engines1 where the boiler  
generates steam at a very high          
temperature1 are nevertheless frequently
 maintained at a lower temperature than 
the external air1 and on entering them  
they have in a great degree the effect  
of a cave4   7#afg47 ,all mechanical    
action is measured by the amount of     
force exercised1 or resistance overcome1
 and the space through which that force 
has acted1 or through which the         
resistance has been moved4  ,the gross  
amount of mechanical action developed by
 the moving power of an engine1 is      
expended partly on moving the engine    
itself1 and partly on overcoming the    
resistance on which the engine is       
intended to act4 ,that part of the      
mechanical energy of the moving power   
which is expended on the resistance or  
load which the engine moves exclusively1
 and of the power expended on moving the
 engine itself1 is called the useful    

effect of the machine4  ,the gross      
effect1 therefore1 exceeds the useful   
effect by the ,pg#bhf amount of power   
spent in moving the engine1 or which may
 be wasted or destroyed in any way by   
the engine4  ,it is usual to express and
 estimate all mechanical effect whatever
 by nature of the resistance overcome1  
by an equivalent weight raised a certain
 height4 ,thus1 if an engine exerts a   
certain power in driving a mill1 in     
drawing a carriage on a road1 or in     
propelling a vessel on water1 the       
resistance against which it has to act  
must be equal to a definite amount of   
weight4 ,if a carriage be drawn1 the    
traces are stretched by the tractive    
power1 by the same tension that would be
 given to them if a certain weight were 
appended to them4 ,if the paddle-wheels 
of a boat are made to revolve1 the water
 opposes to them a resistance equal to  
that which would be produced1 if instead
 of moving the water the wheel had to   
raise some certain weight4 ,in any case1

 therefore1 weight becomes the exponent 
of the energy of the resistance against 
which the moving power acts4  ,but the  
amount of mechanical effect depends     
conjointly on the amount of resistance1 
and the space through which that        
resistance is moved4 ,the quantity of   
this effect1 therefore1 will be         
increased in the same proportion1       
whether the quantity of resistance or   
the space through which that resistance 
is moved be augmented4 ,thus1 a         
resistance of one hundred pounds1 moved 
through two feet1 is mechanically       
equivalent to a resistance of two       
hundred pounds moved through one foot1  
or of four hundred pounds moved through 
six inches4 ,to simplify1 therefore1 the
 expression of mechanical effect1 it is 
usual to reduce it invariably to a      
certain weight raised one foot4 ,if the 
resistance under consideration be       
equivalent to a certain weight raised   
through ten feet1 it is always expressed
 by ten times the amount of that weight 

raised through one foot4  ,it has also  
been usual in the expression of         
mechanical effect1 to take the pound    
weight as the unit of weight1 and the   
foot as the unit of length1 so that all 
mechanical effect whatsoever is         
expressed by a certain number of pounds 
raised one foot4   7#afh47 ,the gross   
effect of the moving power in a         
steam-engine1 is the whole mechanical   
force developed by the evaporation      
,pg#bhg of water in the boiler4 ,a part 
of this effect is lost by the partial   
condensation of the steam before it acts
 upon the piston1 and by the imperfect  
condensation of it subsequently3 another
 portion is expended on overcoming the  
friction of the different moving parts1 
and in acting against the resistance    
which the air opposes to the machine4   
,if the motion be subject to sudden     
shocks1 a portion of the power is then  
lost by the destruction of momentum     
which such shocks produce4 ,but if those
 parts of the machine which have a      

reciprocating motion be1 as they ought  
to be1 brought gradually to rest at each
 change of direction1 then no power is  
absorbed in this way4   7#afi47 ,the    
useful effect of an engine is variously 
denominated according to the relation   
under which it is considered4 ,if it be 
referred to the time during which it is 
produced1 it is called ,,power4         
7#agj47 ,if it be referred to the fuel1 
by the combustion of which the          
evaporation has been effected1 it is    
called ,,duty4   7#aga47 ,when          
steam-engines were first brought into   
use1 they were commonly applied to work 
pumps for mills which had been          
previously worked or driven by horses4  
,in forming their contracts1 the first  
steam-engine builders found themselves  
called upon to supply engines capable of
 executing the same work as was         
previously executed by some certain     
number of horses4 ,it was therefore     
convenient1 and indeed necessary1 to be 
able to express the performance of these

 machines by comparison with the animal 
power to which manufacturers1 miners1   
and others1 had been so long accustomed4
 ,when an engine1 therefore1 was capable
 of performing the same work in a given 
time as any given number of horses of   
average strength usually performed1 it  
was said to be an engine of so many     
horses' power4 ,steam-engines had been  
in use for a considerable time before   
this term had acquired any settled or   
uniform meaning1 and the nominal power  
of engines was accordingly very         
arbitrary4 ,at length1 however1 the use 
of steam-engines became more extended1  
and the confusion and inconvenience     
arising out of all questions respecting 
the performance of engines1 rendered it 
necessary that some fixed ,pg#bhh and   
definite meaning should be assigned to  
the terms by which the powers of this   
machine were expressed4 ,to have        
abandoned the term horse-power1 which   
had been so long in use1 would have been
 obviously inconvenient2 nor could there

 be any objection to its continuance1   
provided all engine-makers1 and all     
those who used engines1 could be brought
 to agree upon some standard by which   
the unit of horse-power might be        
defined4 ,the performance of a horse of 
average strength working for eight hours
 a day was therefore selected as a      
standard1 or unit1 of steam-engine      
power4 ,smeaton estimated that such an  
animal1 so working1 was capable of      
performing a quantity of work equal in  
its mechanical effect to #bb1iaf lbs4   
raised one foot per minute1 while       
,desaguliers estimated the same power at
 #bg1ejj lbs4 raised through the same   
height in the same time4 ,the           
discrepancy between these estimates     
probably arose from their being made    
from the performances of different      
classes of horses4 ,messrs4 ,boulton and
 ,watt caused experiments to be made    
with the strong horses used in the      
breweries in ,london1 and from the      
result of these trials they assigned    

#cc1jjj lbs4 raised one foot per minute1
 as the value of a horse's power4 ,this 
is the unit of engine-power now         
universally adopted2 and when an engine 
is said to be of so many horses' power1 
what is meant is1 that that engine1 in  
good working order and properly managed1
 is capable of moving a resistance equal
 to #cc1jjj lbs4 through one foot per   
minute4 ,thus an engine of ten          
horse-power is one that would raise     
#ccj1jjj lbs4 weight one foot per       
minute4  ,whether this estimate of an   
average horse's power be correct or not1
 in reference to the actual work which  
the animal is capable of executing1 is a
 matter of no present importance in its 
application to steam-power4 ,the        
steam-engine is no longer used to       
replace the power of horses1 and        
therefore no contracts are based upon   
such a comparison4 ,the term            
horse-power1 therefore1 as applied to   
steam-engines1 must be understood to    
have no reference whatever to the actual

 animal power1 but must be taken as a   
term having no other meaning than the   
expression of the ability of the ,pg#bhi
 machine to move the amount of          
resistance above mentioned through one  
foot per minute4   7#agb47 ,it has been 
already explained 7#fg47 that the       
conversion of a given volume of water   
into steam is productive of a certain   
definite amount of mechanical force1    
this amount depending on the pressure   
under which the water is evaporated1 and
 the extent to which the expansive      
principle is used in working the steam4 
,it is evident that this amount of      
mechanical effect is a major limit1     
which cannot be exceeded by the power of
 the engine4  ,if the steam be not      
worked expansively1 then the whole power
 of the water1 transmitted in the form  
of steam from the boiler to the working 
machinery1 will be a matter of easy     
calculation1 when the pressure at which 
the steam is worked is known4 ,a table1 
exhibiting the mechanical power of a    

cubic foot of water converted into steam
 at various pressures1 expressed in an  
equivalent number of pounds' weight     
raised one foot high1 is given in the   
,appendix to this volume4 ,where much   
accuracy is sought for1 the pressure at 
which the steam is used must be taken   
into account2 but by reference to the   
table it will be seen1 that when steam  
is worked without expansion1 its        
mechanical effect varies very little    
with the pressure4 ,it may therefore be 
assumed1 as has been already stated1    
that for every cubic inch of water      
transmitted in the form of steam to the 
cylinders1 a force is produced1         
represented by a ton weight raised a    
foot high4 ,now1 as #cc1jjj lbs4 is very
 nearly #ae tons1 it follows that #ae   
cubic inches of water converted into    
steam per minute1 or #ijj cubic inches  
per hour1 will produce a mechanical     
force equal to one horse4 ,if1          
therefore1 to #ijj cubic inches be added
 the quantity of water per hour         

necessary to move the engine itself1    
independently of its load1 we shall     
obtain the quantity of water per hour   
which must be supplied by the boiler to 
the engine for each horse-power1 and    
this will be the same whatever may be   
the magnitude or proportions of the     
cylinder4   7#agc47 ,the quantity of    
power expended in working the engine    
itself1 independently of that required  
to move its load1 will be less in       
proportion to the degree of perfection  
which ,pg#bij may be attained in the    
construction of the engine1 and to the  
order in which it is kept while working4
 ,engines vary one from another so much 
in these respects1 that it is scarcely  
possible to lay down any general rules  
for the quantity of power to be allowed 
over and above what is necessary to move
 the load4 ,the means whereby mechanical
 power is expended in working the engine
 may be enumerated as follows3--        
,first4 ,steam in passing from the      
boiler to the cylinder is liable to lose

 its temperature by the radiation of the
 steam-pipes and other passages through 
which it is conducted4 ,since the steam 
produced in the boiler is in contact    
with water1 it will be common steam     
7#id471 and consequently the least loss 
of heat will cause a partial            
condensation4 ,to whatever extent this  
condensation may be carried1 a          
proportional loss of power1 in reference
 to the heat obtained from the fuel1    
will be entailed upon the engine4  ,it  
has been said that the force necessary  
to move the steam from the boiler to the
 cylinder through passages more or less 
contracted1 subject to the friction of  
the pipes and tubes through which it    
moves1 should be taken into account in  
estimating the power1 and a             
corresponding deduction made4 ,this1    
however1 is not the case3 the steam     
having passed into the cylinder remains 
common steam1 its pressure being        
diminished by reason of the force       
expended in thus moving it from the     

boiler to the cylinder4 ,but its        
mechanical efficacy at the reduced      
pressure is not sensibly different from 
the efficacy which it had in the boiler4
 ,if at the reduced pressure its volume 
were the same1 then a loss of effect    
would be sustained equivalent to the    
difference of the pressures2 but its    
volume being augmented in very nearly   
the same proportion as its pressure is  
diminished1 the mechanical efficacy of a
 given weight of steam in the cylinder  
will be sensibly the same as in the     
boiler4  ,second4 ,the radiation of heat
 from the cylinder and its appendages1  
will cause a partial condensation of    
steam1 and thereby produce a diminished 
mechanical effect4  ,third4 ,the steam1 
which at each stroke of the piston fills
 the passages between the steam-valves  
and the piston1 at the ,pg#bia moment   
the latter commences the stroke will be 
inefficient4 ,if it were possible for   
the piston to come into steam-tight     
contact with each end of the cylinder1  

and that the steam-valve should be in   
immediate contact with the side or top  
of the piston1 then the whole of the    
steam which would pass through the      
steam-valve would be efficient2 but as  
some space1 however small1 must remain  
between the piston and the ends of the  
cylinder1 and between the side of the   
cylinder and the steam-valve1 there will
 always be a volume of steam bearing a  
sensible proportion to the magnitude of 
the cylinder1 which at each stroke of   
the piston will be inefficient4 ,this   
volume of steam is called the clearance4
  ,fourth4 ,since the piston must move  
in steam-tight contact with the         
cylinder1 it must have a definite amount
 of friction with the sides of the      
cylinder by whatever means it may be    
packed4 ,this friction will produce a   
corresponding resistance to the moving  
power4  ,fifth4 ,the various joints of  
the machinery where steam is contained  
are subject to leakage1 and whatever    
amount of steam shall thus escape must  

be placed to the account of power lost4 
,sixth4 ,when the eduction-valve is     
opened to admit the steam to the        
condenser1 a certain force is required  
to expel the steam from the cylinder4   
,this force reacts upon the piston1 and 
counteracts to a proportional extent the
 moving power of the steam on the other 
side4 ,besides this the water in the    
condenser cannot be conveniently reduced
 below the temperature of about #ajj1   
and at this temperature steam has a     
pressure of about #a lb4 per square     
inch4 ,this vapour will continue to fill
 the cylinder1 and will resist the      
moving power which impels the piston4   
,seventh4 ,power must be provided for   
opening and closing the valves or       
slides1 for working the air-pump1       
hot-water pump1 and cold-water pump1 and
 finally to overcome the friction on the
 journals and centres of the parts of   
the parallel motion1 the main axle of   
the beam1 the connecting rod1 crank1 and
 fly-wheel axle4  ,it will be apparent  

how very much these sources of          
resistances must vary in different      
engines1 and how rough ,pg#bib an       
approximation any general estimate must 
be of their gross amount4   7#agd47     
,there are many circumstances which     
obstruct the practical application of   
any standard of engine-power3 the       
magnitude of furnace1 and the extent of 
heating surface necessary to produce any
 required rate of evaporation in the    
boiler1 are unascertained2 each         
engine-maker has his own rule in these  
matters1 and all the rules are equally  
unsupported by any experimental test    
entitled to respect4 ,thus the          
circumstances that govern the rate of   
evaporation in the boiler may be        
regarded as almost wholly unknown4 ,but 
supposing the rate of evaporation to be 
ascertained1 the amount of power        
absorbed by the condensation of steam on
 its passage to the cylinder1 the       
imperfect condensation of the same steam
 after it has worked the piston1 the    

friction of the various moving parts of 
the machinery1 and1 above all1 the      
difference of effect of these losses of 
power in engines constructed on         
different scales of magnitude1 are      
absolutely unknown4 ,we are1 therefore1 
not placed in a condition to assign any 
thing more than a general account of    
what has been the practice of           
engine-makers in constructing engines   
which are nominally of a certain power4 
,in common low-pressure engines of the  
larger kind1 to which class alone we at 
present refer1 it has been usual1 with  
the same fuel and under like            
circumstances1 to allow from #aj to #ah 
square feet of heating surface in the   
boiler for every nominal horse-power of 
the engine4 ,within these wide limits   
the practice of engine-makers has       
varied4 ,it is not1 however1 to be      
supposed1 that the boiler with #ah      
square feet of surface per horse-power  
has the same evaporating power as that  
which has but #aj4 ,this difference1    

therefore1 amounts to nothing more than 
different manufacturers of steam-engines
 putting into circulation boilers having
 powers really different while they are 
nominally the same4 ,the magnitude of   
the cylinder is regulated by the nominal
 power of the engine1 and it is usual so
 to regulate the evaporating power of   
the boiler1 that the piston shall move  
at the average rate of #bjj feet per    
minute4 ,this being assumed1 it is      
customary to allow about #bb square     
inches of piston ,pg#bic surface for    
every nominal horse-power of the engine4
 ,if this power were in conformity to   
the standard already defined1 this      
amount of surface moved at #bjj feet per
 minute would be impelled by a pressure 
amounting to #g-a_/b lbs4 per square    
inch4 ,the safety-valve of the boiler of
 such engines is usually loaded at from 
#d to #e lbs4 per square inch1 and      
consequently the steam in the boiler    
will have a pressure of from #ai to #bj 
lbs4 per square inch4 ,if1 therefore1   

the effective pressure on the piston be 
really only #g-a_/b lbs4 per square     
inch1 the pressure expended in          
overcoming the friction of the engine1  
and the loss consequent on the partial  
condensation of steam on one side and   
its imperfect condensation on the other1
 would amount to from #ab to #ac lbs4   
per square inch1 or nearly double the   
assumed useful effect of the engine4    
,messrs4 ,maudslay and ,field are       
accustomed to allow an evaporation of   
ten gallons1 or #af cubic feet of water 
per hour1 for each nominal horse-power  
of the engine4 ,they also allow about   
#bb square inches of piston surface per 
nominal horse-power1 the piston being   
supposed to move at the rate of #bjj    
feet per second4#bd  ,the quantity of   
grate surface necessary in proportion to
 the power of the engine1 has been      
equally unascertained1 and engine-makers
 vary in their practice from half a     
square foot to one square foot per      
nominal horse-power4  ,the proportion   

which the magnitude of the heating      
surface of the boiler1 and the fire     
surface of the grate bears to the       
evaporating power of the boiler1 has not
 been determined by experiment1 nor1 so 
far as we are informed1 by any          
well-ascertained practical results4     
,the estimates or rather conjectures of 
engine-makers1 of the evaporation       
necessary to produce one horse-power1   
vary from one to two cubic feet of water
 per hour4 ,it has been ,pg#bid already 
shown that the evaporation of #ijj cubic
 inches1 or little more than half a     
cubic foot per hour1 evolves a gross    
mechanical effect representing one      
horse-power2 from which it appears1 that
 if the evaporation of the boilers of   
steam engines were what engineers       
suppose them to be1 the gross mechanical
 power produced in them for every       
nominal horse-power of the engine varies
 in actual amount from the power of two 
to that of four horses4  ,the above     
estimates must be understood as         

referring to double-acting steam engines
 above thirty-horse power4 ,the         
circumstances attending the performance 
of single-acting engines applied to the 
drainage of mines1 have been ascertained
 with much greater precision4 ,this has 
been mainly owing to a spirited system  
of general inspection1 which has been   
established in ,cornwall1 to which we   
shall hereafter more particularly       
advert4   7#age47 ,in expressing the    
duty of engines1 it would have been     
desirable that the duty of the boiler   
should have been separated from that of 
the engine4  ,the duty of a boiler is   
estimated by the volume of water        
evaporated by a given quantity of fuel1 
independently of the time which such    
evaporation may take4 ,the duty1        
therefore1 will be expressed by the     
number of cubic feet of water           
evaporated1 divided by the number of    
bushels of coal necessary for that      
evaporation1 supposing the bushel of    
coal to be the unit of fuel4 ,it will be

 observed that the duty of an engine or 
boiler is entirely distinct from1 and   
independent of1 its power4 ,one boiler  
may be greater than another in power to 
any extent1 while it may be equal to or 
less than it in duty4 ,a bushel of coals
 may evaporate the same number of cubic 
feet of water under two boilers1 but may
 take twice as great a time to produce  
such evaporation under one than under   
the other4 ,in such a case the power of 
one boiler will be double that of the   
other1 while their duty will be the     
same4  ,in like manner1 a bushel of     
coals consumed in working two engines   
may produce the same useful effect1 but 
it may produce that useful effect in the
 one in half the time it takes to       
produce it in the other4 ,in that case  
the duty of the engines will be the     
same1 but the power of the one will be  
double that of the other4 ,pg#bie  ,in  
fine1 power has reference to            
time1--duty1 to fuel4 ,the more rapidly 
the engine produces its mechanical      

effect1 the greater its power will be1  
whatever may be the fuel consumed in    
working it4 ,and1 on the other hand1 the
 greater the useful effect produced by a
 given weight of fuel1 the greater will 
be the duty1 however long the time may  
be which the fuel may take to produce   
the useful effect4   7#agf47 ,the       
proportion of the stroke to the diameter
 of the cylinder must be determined by  
the velocity intended to be given to the
 piston4 ,with the same capacity of     
cylinder1 and the same evaporation in   
the boiler1 the velocity of the piston  
will augment as the magnitude of its    
diameter is diminished4  ,the proportion
 of the diameter to the stroke of the   
cylinder is very various4 ,in engines   
used for steam-vessels the length of the
 cylinder very little exceeds its       
diameter4 ,in land engines1 however1 the
 proportion of the length to the        
diameter is greater4 ,it is maintained  
by some that the proportion of the      
diameter and length of the cylinder     

should be such as to render its surface 
exposed to the cooling of the external  
air1 the smallest possible4 ,tredgold   
has maintained that since1 during the   
stroke1 the steam is gradually exposed  
to contact with the surface of the      
cylinder from the top to the bottom1 the
 mean surface exposed in contact with   
steam being half that of the entire     
cylinder1 the proportion of the diameter
 to the stroke should be such that the  
surface of half the length of the       
cylinder1 added to the magnitude of the 
top and bottom1 shall be a minimum4 ,if 
this principle be admitted1 then the    
best proportion of the diameter to the  
stroke would be that of one to two1 the 
length of the stroke being twice the    
diameter of the cylinder2 but since the 
whole surface of the cylinder is        
constantly exposed to the cooling       
effects of the air1 and since in the    
intervals of the stroke there is no     
sensible change of the temperature of   
the surface1 the loss of heat by cooling

 will in effect be the same1 especially 
in double-acting engines1 as if the     
cylinder were constantly filled with    
steam4 ,if this be admitted1 then the   
object should be to give the cylinder   
such a proportion1 that its entire      
surface1 including the top and bottom1  
shall be a minimum4 ,pg#bif ,the        
proportion given by this condition would
 be very nearly that which is observed  
in the cylinders of marine engines1 viz4
 that the length of the cylinder should 
be equal to its diameter4  ,if in a     
low-pressure engine the pressure of     
steam in the cylinder be taken at #ag   
lbs4 per square inch1 then the volume of
 steam will be about fifteen hundred    
times that of the water which produces  
it4 ,for every cubic foot of water1     
therefore1 in the effective evaporation 
of the boiler1 #aejj cubic feet of steam
 will be passed through the cylinder4   
,if it be intended that the motion of   
the piston shall be at the rate of #be  
strokes per minute1 or #aejj strokes per

 hour1 then the capacity of that portion
 of the cylinder between the steam-valve
 and the piston at the end of the       
stroke1 must consist of half as many    
cubic feet as there are cubic feet per  
hour evaporated in the boiler4 ,if the  
steam1 therefore1 be cut off at half    
stroke1 the number of cubic feet of     
space in the cylinder will be equal to  
the number of cubic feet of water       
effectively evaporated by the boiler2   
and if a cubic foot of water effectively
 evaporated be taken as the measure of a
 horse-power1 then there would be as    
many cubic feet in the capacity of the  
cylinder as is equal to the nominal     
power of the engine4   7#agg47 ,the duty
 of engines varies according to their   
form and magnitude1 the circumstances   
under which they are worked1 and the    
purposes to which they are applied4 ,in 
double-acting engines working without   
expansion1 the coal consumed per nominal
 horse-power per hour varies from #g to 
#ab lbs4 ,an examination of the         

steam-logs of several government        
steamers made by me a few years since1  
gave1 as the average of consumption of  
fuel at that time of the best class of  
marine engines1 about #h lbs4 per       
nominal horse-power per hour4 ,since1   
however1 no account could be obtained of
 the actual evaporation of water in the 
boiler1 nor1 with the necessary degree  
of precision1 of the quantity and       
pressure of the steam which passed      
through the cylinders1 this estimate    
must be regarded as an approximation    
subject to several causes of error4 ,the
 question of the duty of boilers and    
engines applied to the ,pg#big general  
purposes of manufactures and navigation1
 is one which has not yet been          
satisfactorily investigated2 and it were
 much to be desired that the proprietors
 of such engines should combine to      
establish a strict analysis of their    
performance in reference to their       
consumption of fuel1 their evaporation  
of water1 and their useful effects4 ,the

 results of such an investigation1 if   
properly conducted1 would perhaps tend  
more to the improvement of the steam    
engine than any discoveries in science1 
or inventions in mechanical detail      
likely to be made in the present stage  
of the progress of that machine4        
7#agh47 ,a strict investigation of this 
kind has been for many years carried on 
respecting the performance of the steam 
engines used for the drainage of the    
mines in ,cornwall2 and it has been     
attended with effects the most          
beneficial to the interests of those    
concerned in them4 ,the engines to which
 this important inquiry has been applied
 being used for the purpose of pumping1 
are generally single-acting engines1 in 
which steam is used expansively to a    
great extent4 ,the steam is produced    
under a very high pressure in the       
boiler1 and being admitted to the       
cylinder is cut off after a small       
portion of the entire stroke has been   
made1 the remainder of the stroke being 

produced by the expansion of the steam4 
,about the year #ahaa1 a number of the  
proprietors of the principal ,cornish   
mines agreed to establish this system of
 inspection1 under the management and   
direction of ,captain ,joel ,lean1 and  
to publish monthly reports4 ,in these   
reports were stated the following       
particulars3--#a4 ,the load per square  
inch on the piston2 #b4 ,the consumption
 of coal in bushels2 #c4 ,the number of 
strokes made by the engine2 #d4 ,the    
length of the strokes in the pumps2 #e4 
,the load in pounds2 #f4 ,the duty of   
the engine1 expressed by the number of  
pounds raised one foot high by the      
consumption of a bushel of coals2 #g4   
,the number of strokes per minute2 #h4  
,the diameter and stroke of the         
cylinder1 and a general description of  
the engine4 ,when these reports were    
commenced1 the number of engines brought
 under inspection was twenty-one4 ,in   
the year #ahac it increased to          
twenty-nine2 in #ahad to thirty-two2 in 

#ahbj the number reported upon increased
 ,pg#bih to forty2 in #ahbh the number  
was fifty-seven2 and in #ahcf it was    
sixty-one4 ,this gradual increase in the
 number of engines brought under this   
system of inspection1 was produced by   
the good effects which attended it4     
,these beneficial consequences were     
manifested1 not only in the improved    
performance of the same engines1 but in 
the gradually improved efficiency of    
those which were afterwards constructed4
  ,the following table taken from the   
statement of the duty of ,cornish       
engines by ,thomas ,lean and brother1   
lately published by the ,british        
,association1 will show in a striking   
manner the improvement of the ,cornish  
engines1 from the commencement of this  
system of inspection to the present     
time4 ,the duty is expressed by the     
number of pounds raised one foot high by
 the consumption of a bushel of coals4  
----------------------------------------
----------------------------------------

----------------------------------------
------          ,no4 of  ,average ,duty 
of the  ,average ,duty of the best      
,years4,engines4      ,whole4           
,engine4                                
----------------------------------------
----------------------------------------
--------------------------------------  
#ahab    #ba         #ai1cjj1jjj        
#ahac    #bi         #ai1ejj1jjj        
#bf1djj1jjj    #ahad    #cb             
#bj1fjj1jjj           #cb1jjj1jjj       
#ahae    #ce         #bj1ejj1jjj        
#bh1gjj1jjj    #ahaf    #ce             
#bc1jjj1jjj           #cb1djj1jjj       
#ahag    #ce         #bf1ejj1jjj        
#da1fjj1jjj    #ahah    #cf             
#be1djj1jjj           #ci1cjj1jjj       
#ahai    #dj         #bf1cjj1jjj        
#dj1jjj1jjj    #ahbj    #df             
#bh1gjj1jjj           #da1cjj1jjj       
#ahba    #de         #bh1bjj1jjj        
#db1hjj1jjj    #ahbb    #eb             
#bh1ijj1jjj           #db1ejj1jjj       
#ahbc    #eb         #bh1bjj1jjj        

#db1ajj1jjj    #ahbd    #di             
#bh1cjj1jjj           #dc1ejj1jjj       
#ahbe    #ef         #cb1jjj1jjj        
#de1djj1jjj    #ahbf    #ea             
#cj1ejj1jjj           #de1bjj1jjj       
#ahbg    #ea         #cb1ajj1jjj        
#ei1gjj1jjj    #ahbh    #eg             
#cg1ajj1jjj           #gf1hjj1jjj       
#ahbi    #ec         #da1gjj1jjj        
#gg1jjj1jjj    #ahcj    #ef             
#dc1cjj1jjj           #gh1jjj1jjj       
#ahca    #eh         #dc1djj1jjj        
#ga1ajj1jjj    #ahcb    #ei             
#de1jjj1jjj           #he1jjj1jjj       
#ahcc    #ef         #df1fjj1jjj        
#hd1cjj1jjj    #ahcd    #eb             
#dg1hjj1jjj           #ij1ijj1jjj       
#ahce    #ea         #dg1hjj1jjj        
#ia1gjj1jjj    #ahcf    #fa             
#df1fjj1jjj           #he1djj1jjj       
#ahcg    #eh         #dg1jjj1jjj        
#hg1bjj1jjj    #ahch    #fa             
#dh1gjj1jjj           #hd1bjj1jjj       
----------------------------------------
----------------------------------------

--------------------------------------  
,pg#bii ,as an example of the beneficial
 effects produced upon the efficiency of
 an individual engine by the first      
application of this system of           
inspection1 the case of the ,stray ,park
 engine may be mentioned4 ,this engine1 
constructed by ,boulton and ,watt1 had a
 sixty inch cylinder1 and when first    
reported in #ahaa1 its duty amounted to 
#af1jjj1jjj pounds4 ,after having been  
reported on for three years1 its duty   
was found to have increased to          
#cb1jjj1jjj2 this estimate being taken  
from the average result of twelve       
months' performance4 ,its duty was      
doubled in less than three years4  ,it  
will appear1 by inspection of the duties
 registered in the preceding table1 that
 the augmentation of the efficiency of  
the engines has not been the effect of  
any great or sudden improvement1 but has
 rather resulted from the combination of
 a great number of small improvements in
 the details of the operation of these  

machines4 ,in these improvements more is
 due to the successful application of   
practical experience than to any new    
principles developed by scientific      
research4 ,mr4 ,john ,taylor1 in his    
,records of ,mining1 has traced the     
successive improvements on which the    
increased duty of engines depends1 and  
has connected these improvements with   
their causes in the order of their      
dates4 ,the following results1 abridged 
from his estimates1 may not be          
uninteresting3--  ,in #agfi1 soon after 
the date of the earliest discoveries of 
,mr4 ,watt1 but before they had come    
into practical application1 ,smeaton    
computed that the average duty of       
fifteen atmospheric engines1 working at 
,newcastle-on-,tyne1 was #e1eij1jjj4    
,the duty of the best of these engines  
was #g1ddj1jjj1 and that of the worst   
#c1bbj1jjj4  ,in #aggb1 ,smeaton        
commenced his improvements on the       
atmospheric engine1 and raised the duty 
to #i1dej1jjj4  ,in #aggf1 ,watt        

obtained a duty of #ba1fjj1jjj4  ,at    
this time ,smeaton acknowledged that    
,watt's engines gave a duty amounting to
 double that of his own4  ,in #aggh-gi1 
,watt reported a duty of #bc1djj1jjj4   
,from #aggi to #aghh1 ,watt introduced  
the application of expansion1 and raised
 the duty to #bf1fjj1jjj4 ,pg#cjj  ,in  
#agih1 an engine by ,boulton and ,watt1 
erected at ,herland1 was reported as    
giving a duty of #bg1jjj1jjj4  ,this    
engine1 which was probably the best     
which at that time had ever been        
erected1 attracted the particular       
attention of ,mr4 ,watt1 who1 on        
visiting ,cornwall1 went to see it1 and 
had many experiments tried with it4 ,it 
was under the care of ,mr4 ,murdock1 the
 agent of ,messrs4 ,boulton and ,watt in
 ,cornwall4 ,when ,mr4 ,watt inspected  
it he pronounced it perfect1 and that   
further improvement could not be        
expected4 ,how singular an instance this
 of the impossibility1 even of the most 
sagacious1 to foresee the results of    

mechanical improvement6 ,in twenty years
 afterwards the average duty of the best
 engine was nearly #dj1jjj1jjj1 and in  
forty years it was above #hd1jjj1jjj4   
,illustration3 ,,boiler ,,manufactory4  
,,footnotes3    #bd ,if #bb square      
inches of piston surface be allowed to  
represent a horse-power1 the power of an
 engine may always be   computed by     
dividing the square of the diameter of  
the piston   expressed in inches by #bh4
 ,and1 on the other hand1 to find the   
diameter of piston which would          
correspond to any given power1          
multiply the number of horses' power by 
#bh1 and take the   square root of the  
product4 ,these rules1 however1 cannot  
be   applied if the piston be supposed  
to move with any other   velocity2      
since1 in that case1 the same amount of 
piston   surface would cease to         
represent a horse-power1 unless the     
effective pressure on the piston were at
 the same time   changed4  ,pg#cja      
,illustration3 ,,watt',s ,,chapel ,,in  

,,handsworth ,,church4  ,,chap4 ,x4     
,,notice ,,of ,,the ,,life ,,of ,,mr4   
,,watt4 -- ,,his ,,friends ,,and        
,,associates     ,,at ,,birmingham4 --  
,,invention ,,of ,,the ,,copying        
,,press4 -- ,,heating ,,by     ,,steam4 
-- ,,drying ,,linen ,,by ,,steam4 --    
,,theory ,,of ,,the ,,composition ,,of  
,,water4 -- ,,first ,,marriage ,,of     
,,watt4 -- ,,death ,,of ,,his ,,first   
,,wife4 --     ,,his ,,second           
,,marriage4 -- ,,death ,,of ,,his       
,,younger ,,son4 -- ,,extracts          
,,from ,,his ,,letters4 -- ,,character  
,,of ,,watt ,,by ,,lord ,,brougham4 --  
,,by     ,,sir ,,walter ,,scott4 -- ,,by
 ,,lord ,,jeffrey4 -- ,,occupation ,,of 
,,his ,,old     ,,age4 -- ,,invention   
,,of ,,machine ,,for ,,copying          
,,sculpture4 -- ,,his ,,last     ,,days4
 -- ,,monuments4   7#agi47 ,having      
brought this historical analysis of the 
invention and application of the steam  
engine to the date of the decease of the
 illustrious man1 to the powers of whose

 mind the world stands indebted for the 
benefits conferred upon ,pg#cjb mankind 
by that machine1 it will perhaps not be 
deemed an improper digression in this   
work1 to devote some pages to a notice  
of the principal labours of the same    
mind in other departments of art and    
science1 and to circumstances connected 
with his personal history and the close 
of his life1 which cannot fail to       
possess general interest4  ,at the      
period when ,watt1 having connected     
himself in partnership with ,boulton1   
went to reside at ,soho1 near           
,birmingham1 a number of persons1 some  
of whom have since attained great       
celebrity by their discoveries and their
 works1 and all of whom were devoted to 
inquiries connected with the arts and   
sciences1 resided in that neighbourhood4
 ,among these may be mentioned          
,,priestley1 whose discoveries in       
physical science have rendered his name 
immortal2 ,,darwin1 the philosopher and 
poet2 ,,withering1 a distinguished      

physician and botanist2 ,,keir1 a       
chemist1 who published a translation of 
,macquer1 with annotations2 ,,galton1   
the ornithologist2 and ,,edgeworth1     
whose investigations respecting wheeled 
carriages and other subjects1 have      
rendered him well known4 ,a society was 
formed by these and other individuals1  
of which ,boulton and ,watt were leading
 members1 the meetings of which were    
held monthly on the evening of full     
moon1 and which was thence called the   
,lunar ,society4 ,at the meetings of    
this society1 subjects connected with   
the arts and sciences were discussed1   
and out of those discussions            
occasionally arose suggestions not      
unattended with important and           
advantageous consequences4 ,at one of   
these meetings1 ,darwin stated that he  
had discovered a pen formed with two    
quills1 by means of which1 at a single  
operation1 an original and a copy of a  
letter might be produced4 ,watt almost  
instantly observed that he thought he   

could find a better expedient1 and that 
he would turn it in his mind that night4
 ,by the next morning the ,,copying     
,,press was invented1 for which he      
afterwards obtained a patent4  ,this    
machine1 which is now so generally used 
in counting-houses1 consists of a       
rolling-press1 by which a leaf of thin  
paper1 previously damped1 is pressed    
upon the letter to be copied4 ,the      
writing1 of which the ink is not yet    
quite dry1 leaves its impression upon   
the thin paper thus pressed upon ,pg#cjc
 it1 and the copy taken in this manner  
is read through the semi-transparent    
paper4 ,if a letter be written with ink 
suitable for this purpose1 a copy may be
 taken at any time within several hours 
after the letter is written4  ,the      
method of heating apartments and        
buildings by steam1 which has since been
 improved and brought into extensive    
use1 was likewise brought forward by    
,watt4 ,although this contrivance had   
been previously pointed out by ,sir     

,hugh ,platt about the middle of the    
seventeenth century1 and by ,colonel    
,cooke in #agde1 yet these suggestions  
remained barren4 ,mr4 ,watt gave        
detailed methods of heating buildings by
 steam#be2 and also invented a machine  
for drying linen by steam1 a description
 of which he communicated to ,dr4       
,brewster1 which was read in ,december1 
#ahbd1 before the ,society for promoting
 ,useful ,arts in ,scotland4#bf  ,but   
the circumstance1 exclusive of those    
connected with the invention of the     
steam engine1 which is by far the most  
memorable in the career of ,watt1 is the
 share which he had in the discovery of 
the composition of water4 ,as this      
circumstance has recently excited much  
interest1 and led to some controversy1  
we shall here state1 as distinctly as   
possible1 the leading facts connected   
with it4  ,water1 which was so long held
 to be a simple element1 has1 in modern 
times1 been proved to be a substance    
consisting of two aeriform bodies or    

gases chemically combined4 ,these two   
gases are those called in chemistry     
oxygen and hydrogen4 ,if eight grains   
weight of oxygen be mixed with one grain
 weight of hydrogen1 and the mixture be 
submitted to such effects as would cause
 the chemical combination of these two  
airs1 it would be converted into nine   
grains weight of pure water4  ,if1 on   
the other hand1 nine grains weight of   
pure water be submitted to any          
conditions which would separate its     
constituent parts1 the result would be  
eight grains weight of oxygen gas1 and  
one grain weight of hydrogen gas4 ,there
 are a variety of methods in physics by 
which these effects would be ,pg#cjd    
produced4 ,it will be sufficient here to
 state one method of producing each of  
the above changes4  ,if eight grains    
weight of oxygen be inclosed in a strong
 vessel with one grain weight of        
hydrogen1 all other substances being    
excluded1 and the mixture be inflamed1  
an explosion will take place1 the gases 

will disappear1 and a small quantity of 
water will be the only substance        
remaining in the vessel4 ,if this water 
be weighed1 it will be found to weigh   
exactly nine grains4  ,it is known that 
the metals have a strong attraction for 
oxygen gas1 and this attraction is      
promoted by elevating their temperature4
 ,if a glass tube be filled with iron   
wire heated to redness1 and to one end  
of this tube a small vessel of boiling  
water be attached1 the steam evolved    
from the water will force its way       
through the spaces between the red-hot  
wires in the tube1 and would be expected
 to issue from the remote end2 but if   
the substance issuing from the remote   
end of the tube be examined1 it will be 
found to be not steam1 but hydrogen gas4
 ,if the quantity of this gas be        
ascertained by weight1 and also the     
quantity of weight lost by the vessel of
 water at the other end of the tube1 it 
will be found that the loss of weight of
 the water by evaporation will be nine  

times the weight of the hydrogen which  
has issued from the remote end of the   
tube4 ,if the weight of the tube with   
the wire contained in it be next        
ascertained1 it will be found to be     
increased by eight times the weight of  
the hydrogen which has issued from its  
remote end4 ,from this it follows that  
the weight of the hydrogen which has    
escaped from the tube1 added to the     
increase of weight which has been given 
to the wire in the tube1 makes up the   
whole weight of the water evaporated4   
,if the wire in the tube be next        
examined1 it will be found that it has  
suffered oxydation1 or1 in other words1 
that a new substance has been formed in 
it called the oxyde of iron1--such      
substance being a chemical compound     
formed of oxygen gas and iron4  ,it     
follows1 therefore1 that in this process
 the vapour of the water1 in passing    
through the tube1 has been decomposed1  
and that1 having given up to the iron   
its oxygen1 the hydrogen ,pg#cje alone  

escaped from the other end2 and for     
every nine grains weight of steam which 
passed through the tube1 eight grains of
 oxygen have been combined with the     
iron1 and one grain of hydrogen has     
escaped from the end of the tube4  ,such
 are the class of effects on which the  
modern discovery of the composition of  
water has been based4 ,the merit of that
 discovery has been shared between the  
celebrated ,english chemist1            
,,cavendish1 and the not less celebrated
 ,french chemist1 ,,lavoisier1 the chief
 merit1 however1 being ascribed to the  
former4  ,we shall now briefly state the
 facts which led to this discovery1 with
 their dates1 which will necessarily    
show the share which ,watt had in it4   
,when pure hydrogen gas is burned in an 
atmosphere of common air1 the process   
which takes place is now known to be    
nothing more than the chemical          
combination of the hydrogen with eight  
times its own weight of oxygen taken    
from the atmosphere1 and the product of 

the combustion is a quantity of water   
nine times the weight of the hydrogen   
consumed4 ,in the year #aggf1 ,macquer1 
a well-known chemist of that day1 having
 held a saucer of white porcelain over a
 flame of hydrogen which was burning at 
the mouth of a bottle1 observed that no 
smoke was produced and no soot deposited
 on the saucer4 ,on the other hand1 he  
found that after the lapse of some time 
drops of a clear pellucid liquid were   
perceptible on the saucer3 this liquid  
he submitted to analysis1 and found it  
to be pure water4 ,macquer mentioned    
this fact without comment or inference4 
,it did not occur to him that the water 
thus produced upon the saucer was a     
substance which contained the hydrogen1 
which disappeared upon combustion from  
the bottle4  ,on the #ahth of ,april1   
#agha1 ,mr4 ,warltire addressed a letter
 to ,dr4 ,priestley1 dated ,birmingham1 
which letter is published in ,dr4       
,priestley's ,experiments on ,air1      
printed at ,birmingham in #agha1 in     

which ,warltire informs ,priestley that 
he had fired a mixture of hydrogen and  
common air in close glass vessels1 and  
that1 although previously to firing the 
mixture the vessels were clean and dry1 
a dewy deposit was ,pg#cjf observed     
afterwards on their sides4 ,in fact1    
water was present which was not present 
before4  ,the mixture was in this case  
fired by passing an electric spark      
through the vessel2 and it is now known 
that the effect produced was the        
combination of the hydrogen1 which      
formed part of the mixture of airs in   
the vessel with the oxygen1 which also  
formed part of the same mixture4  ,it   
appears1 from expressions in ,warltire's
 letter1 that the same experiment had   
been previously made by ,priestley1 and 
the same result observed by him4  ,the  
inference deduced from this by          
,warltire1 and apparently acquiesced in 
by ,priestley1 was1 that whenever       
hydrogen was fired in atmospheric air1  
the moisture1 which is always more or   

less sustained in the latter1 was       
deposited2 but neither of these chemists
 perceived the real cause of the        
production of the water4  ,in the       
beginning of #aghc1 and not later than  
the #bast of ,april1 this experiment of 
,warltire and ,priestley was repeated by
 ,cavendish1 with this difference1 that1
 instead of exploding the mixture of    
hydrogen and common air1 ,cavendish     
exploded a mixture of hydrogen and      
oxygen4 ,he observed that water was     
present after the explosion1 but        
inferred nothing4  ,in a published paper
 dated ,april1 #aghc1 ,priestley        
announced a further and most important  
result of his experiments4 ,this was1   
that in examining the weight of water   
produced by the explosion of a mixture  
of oxygen and hydrogen1 that weight was 
found to be precisely equal to the sum  
of the weights of the two gases1 which  
disappeared in the process4             
,immediately on observing this1         
,priestley1 being then1 as has been     

already stated1 ,watt's near neighbour1 
communicated to the latter what he had  
observed2 upon which ,watt immediately1 
viz4 by a letter dated the #bfth of the 
same month1 declared that the inevitable
 consequence which followed from        
,priestley's observations was1 that     
water was a substance compounded of     
oxygen and hydrogen deprived of ,pg#cjg 
a quantity of heat which was previously 
latent in them4#bg ,the letter          
containing this inference was           
communicated immediately by ,priestley  
to ,sir ,joseph ,banks1 then ,president 
of the ,royal ,society1 to be laid      
before that body2 and it is accordingly 
printed with its proper date in the     
#gdth volume of the ,philosophical      
,transactions4  ,about two months after 
the date of ,mr4 ,watt's letter just    
quoted1 ,lavoisier made experiments on  
the combustion of oxygen and hydrogen1  
and read a memoir before the ,academy of
 ,sciences in ,paris1 in which his views
 of the formation of water by the       

combination of these gases were         
developed4 ,this paper1 by ,lavoisier1  
was afterwards printed in the ,memoirs  
of the ,academy in the year #aghd4 ,the 
experiments are there stated to have    
been made in the month of ,june1 #aghc2 
and it is stated that ,sir ,charles     
,blagden1 who was present at the        
experiments1 told ,lavoisier that ,mr4  
,cavendish had already burned the same  
gases in close vessels1 and obtained a  
very sensible quantity of water4  ,on   
the #aeth of ,january1 #aghd1 the       
celebrated paper by ,cavendish1 entitled
 ,experiments on ,air1 was read before  
the ,royal ,society1 and in this paper  
the composition of water by the union of
 oxygen and hydrogen is explained4  ,in 
a controversy which afterwards ensued on
 the respective ,pg#cjh claims of       
,cavendish and ,lavoisier to credit for 
the discovery of the composition of     
water1 ,sir ,charles ,blagden stated    
that he had told ,lavoisier1 in ,june1  
#aghc1 more than ,lavoisier             

acknowledged1 that he had not only told 
him that water was produced by the      
combustion of the gases1 but that his   
information embraced the whole theory of
 the composition of water4 ,this        
declaration of ,blagden was subsequent  
in date to ,january1 #aghd1 and there is
 no evidence of any explanation of this 
theory1 verbal or otherwise1 having been
 given by ,cavendish1 or any other      
person1 antecedent to ,april1 #aghc4    
,from this brief statement of the facts 
and dates it will appear that the merit 
of the discovery of the ,,fact1 that the
 weight of water resulting from the     
combustion of oxygen and hydrogen1 is   
equal to the sum of the weights of the  
oxygen and hydrogen which disappear in  
the combustion1 is due to ,priestley2   
and that the merit of the ,,inference   
from that fact1 that water is a compound
 body1 whose constituents are oxygen and
 hydrogen1 is due to ,watt4#bh ,whether 
those who subsequently deduced the same 
inference1 and promulgated the same     

theory1 were or were not informed of    
,mr4 ,watt's solution of the phenomenon1
 or what credit may be due to any       
person1 however eminent1 who at any time
 posterior to ,mr4 ,watt's letter to    
,priestley1 asserted that they had1 at a
 time antecedently to that1 made the    
same inference without having published 
it1 or communicated it in such a manner 
as to establish their claim upon        
rational and credible evidence1 are     
questions which we shall not here       
discuss1 being contented with           
establishing the right of ,mr4 ,watt to 
the merit of the discovery of the       
,,theory which explained the ,,fact     
discovered by ,priestley4  ,even in his 
declining years1 after he had withdrawn 
from the active pursuits of his         
business1 the least excitement was      
sufficient to call into play the        
slumbering powers of his inventive      
genius4 ,no object could present itself 
to his notice ,pg#cji without receiving 
from that genius adaptation in form and 

construction to useful purposes4 ,as an 
example of this restless activity of    
mind the following anecdote may be      
mentioned3--  ,a company at ,glasgow had
 erected on the right bank of the ,clyde
 extensive buildings and powerful       
engines for supplying water to the town4
 ,after this expense it was found that a
 source of water1 of very superior      
quality1 existed on the left bank of the
 river4 ,to change the site of the      
establishment1 after the expense which  
had been incurred in its erection could 
not be contemplated1 and they therefore 
proposed to carry across the bottom of  
the river a flexible suction pipe1 the  
mouth of which should terminate in the  
source from which the pure water was to 
be derived4 ,this pipe was to be        
supported by a flooring constructed upon
 the bed of the river2 but it was soon  
apparent that the construction of such a
 flooring on a shifting and muddy       
bottom1 full of inequalities1 and under 
several feet depth of water would       

require a greater expenditure of capital
 than could with propriety be afforded4 
,in this difficulty the aged            
mechanician1 for whom ,glasgow itself   
had been the earliest stage of          
professional labour1 was applied to1 and
 instantly solved the problem4 ,his     
attention is said to have been attracted
 by a lobster which had been served at  
table3 he set himself about to contrive 
how1 by mechanism1 he could make an     
apparatus of iron with joints which     
should have all the flexibility of the  
tail of the lobster4 ,he therefore      
proposed that an articulated            
suction-pipe1 capable of accommodating  
itself to all the inequalities and to   
the possible changes of the bed of the  
river1 should be carried across it2 that
 this flexible pipe should be two feet  
in diameter1 and one thousand feet in   
length4 ,this project the company       
accordingly caused to be executed after 
the plans and drawings of ,watt with the
 most complete success4#bi  ,pg#caj     

,among the less prominent1 though not   
less useful services rendered by ,watt  
to his country1 may be mentioned the    
introduction of the use of chlorine in  
bleaching4 ,that invention of           
,berthollet was introduced into ,england
 by ,watt after his visit to ,paris at  
the close of the year #aghf4 ,he        
constructed all the necessary apparatus 
for it1 directed its erection1 and      
superintended its first performances4   
,he then left it to his wife's father1  
,mr4 ,macgregor1 to carry on the        
processes4  ,when the properties of the 
gases began to occupy the attention of  
chemists1 attempts were made to apply   
them as a means of curing diseases of   
the lungs4 ,dr4 ,beddoes pursued this   
inquiry with great activity1 and        
established1 through the means of       
private subscription1 at ,clifton1 an   
institution in which this method of cure
 was carefully investigated4 ,the       
,pneumatic ,institution 7for so it was  
called7 has been rendered celebrated for

 having at its head ,humphry ,davy1 just
 then commencing his scientific career4 
,among its founders was also numbered   
,james ,watt4 ,not content1 however1    
with affording the institution the      
sanction of his name1 he designed and   
caused to be constructed1 at ,soho1 the 
apparatus used for making the gases and 
administering them to the patients4  ,as
 the exalted powers of the mind of      
,watt1 unfolded in his numerous         
mechanical and philosophical inventions 
and discoveries1 have commanded the     
admiration and respect of his species1  
the affection and love of his fellow men
 would not have been less conciliated1  
had the qualities of his heart1 as      
developed in his private and personal   
relations1 been as well known as the    
products of his genius4  ,in the year   
#agfd1 ,watt being then in the          
twenty-ninth year of his age1 married   
his cousin1 ,miss ,miller4 ,at this time
 he had fallen into a state of          
despondency from his disappointments1   

which produced a serious attack of      
nervous illness4 ,the accomplishments   
and superior understanding1 the mildness
 of temper and goodness of disposition  
of his wife1 soon restored him to       
health4 ,of this marriage four children1
 two sons and two daughters1 were the   
issue4 ,two of these children died in   
infancy2 another1 a daughter1 was       
married to ,mr4 ,miller of ,glasgow2 and
 the fourth is the ,pg#caa present ,mr4 
,james ,watt4 ,in ,september1 #aggc1    
while her husband was engaged in the    
design of the ,caledonian canal in the  
,north of ,scotland1 ,mrs4 ,watt died in
 child-bed of a fifth child1 who was    
still-born3 ,would that ,i might here   
transcribe1 says ,m4 ,arago1 in all     
their simple beauty1 some lines of the  
journal in which he daily recorded his  
inmost thoughts1 his fears1 his hopes6  
,would that you could see him1 after    
this heavy affliction1 pausing on the   
threshold of that home1 where ',,his    
,,kind ,,welcomer' awaited him no more2 

unable to summon courage to enter those 
rooms where he was never more to meet   
',,the ,,comfort ,,of ,,his ,,life6'    
,possibly1 so faithful a picture of a   
very deep sorrow might at last put to   
silence those obstinate theorists1 who1 
without being struck by the thousands of
 instances to the contrary1 do yet      
refuse qualities of the heart to every  
man whose intellect has been fostered by
 the fertile1 sublime1 and imperishable 
truths of the exact sciences6  ,after   
the lapse of some years ,watt married   
,miss ,macgregor1 a person who is       
represented to have possessed qualities 
of mind which rendered her a companion  
every way suitable to her husband4 ,this
 lady survived ,watt1 and died in #ahcb 
at an advanced age4 ,two children were  
the issue of this second marriage4  ,in 
the year #ahjj the extended patent      
right1 which had been granted to        
,boulton and ,watt for their improved   
engine1 expired1 and at this time ,mr4  
,watt retired altogether from business4 

,he was succeeded by his two sons1 the  
present ,mr4 ,james ,watt1 and ,gregory1
 one of the children of his second      
marriage4 ,the works at ,soho continued 
to be conducted by the present ,mr4     
,boulton1 the son of the partner of ,mr4
 ,watt1 and the two ,messrs4 ,watt4 ,in 
#ahjd ,gregory ,watt died at the age of 
twenty-seven1 of a disease of the chest4
 ,this afflicting event was deeply felt 
by ,mr4 ,watt2 but he did not sink under
 it into that state of despondency in   
which he has been represented to have   
fallen by ,m4 ,arago4 ,on the contrary1 
he continued to show the same activity  
of mind which had characterised his     
whole ,pg#cab life2 nor did he lose that
 interest which he always took in the   
pursuit of literature and in society4   
,the state of his feelings under this   
affliction is shown by the following    
extracts from letters written by him at 
that time1 which have been published by 
,mr4 ,muirhead4     ,heathfield1        
,january #bfth1 #ahje4      99 99 ,i1   

perhaps1 have said too much to you and  
,mrs4 ,campbell   on the state of my    
mind4 ,i1 therefore1 think it necessary 
to   say that ,i am not low spirited2   
and were you here1 you would   find me  
as cheerful in the company of my friends
 as usual2 my   feelings for the loss of
 poor ,gregory are not passion1 but a   
deep regret that such was his and my    
lot4      ,i know that all men must die1
 and ,i submit to the decrees   of      
nature1 ,i hope with due reverence to   
the ,disposer of   ,events4 ,yet one    
stimulus to exertion is taken away1 and1
   somehow or other1 ,i have lost my    
relish for my usual avocations4         
,perhaps time may remedy that in some   
measure2 meanwhile1   ,i do not neglect 
the means of amusement which are in my  
power4    ,heathfield1 ,april #hth1     
#ahje4      99 99 ,it is rather         
mortifying to see how easily the want of
   even the best of us is dispensed with
 in the world2 but it is   very well it 
should be so4 ,we here1 however1 cannot 

help   feeling a terrible blank in our  
family4 ,when ,i look at my   son's     
books1 his writings and drawings1 ,i    
always say to   myself1 where are the   
mind that conceived these things1 and   
the hands that executed them8 ,in the   
course of nature1 he   should have said 
so of mine2 but it was otherwise        
ordered1 and   our sorrow is unavailing4
 ,as ,catullus says3--    ---- ',nunc   
it1 per iter tenebricosum1   ,illuc1    
unde negant redire quemquam4   ,at vobis
 male sit1 mal tenebr   ,orci1 qu omnia 
bella devoratis6'      ,but ,catullus   
was a heathen2 let us hope that he 7,g47
 is now   rejoicing in another and a    
better world1 free from our cares1      
griefs1 and infirmities4 ,some one has  
said1 ,i shall not wholly   die2 and    
,gregory's name1 his merits and virtues1
 will live at   least as long as those  
do who knew him4 ,you are not1 from     
this1 to conceive that we give way to   
grief2 on the contrary1   you will find 
us as cheerful as we ought to be1 and as

 much   disposed to enjoy the friends we
 have left as ever2 but we   should     
approach to brutes if we had no regrets4
  ,mr4 ,watt1 at the date of these      
letters1 had entered on his seventieth  
year1 a period after which great mental 
exertions are rarely made4 ,pg#cac  ,in 
the summer of #ahai1 symptoms of        
indisposition manifested themselves     
which soon rendered ,watt aware of his  
approaching dissolution4 ,i am very     
sensible1 said he to his afflicted      
friends1 of the attachment you show me1 
and ,i hasten to thank you for it1 as ,i
 am now come to my last illness4 ,he    
died on the #beth of ,august1 #ahai4    
,his remains were deposited in the      
church of ,handsworth1 near his estate  
of ,heathfield4 ,his son has raised over
 his grave a ,gothic chapel1 in the     
centre of which is placed a statue by   
,chantrey4  ,the personal character of  
,watt could not fail to excite the      
admiration and the love of those        
distinguished persons1 whose pride and  

happiness it was to be admitted to a    
share in the friendship of the great    
engineer4 ,among these were reckoned    
some of the men who will leave upon the 
present age the deepest and most lasting
 impressions of their genius1 and such  
persons have bequeathed to posterity the
 sentiments with which he inspired them4
 ,we cannot here do more justice to the 
personal character of the subject of    
this notice than by repeating the       
portraiture of it which has been given  
by three of the most distinguished of   
his friends1 and of the most illustrious
 men of the present age4  ,at a meeting 
convened in #ahbd1 for erecting a       
monument to ,watt1 ,lord ,brougham      
pronounced a speech1 from which we      
extract the following observations3--   
,i had the happiness of knowing ,mr4    
,watt1 for many years1 in the           
intercourse of private life2 and ,i will
 take upon me to bear a   testimony in  
which all who had that gratification ,i 
am sure will   join1 that they who only 

knew his public merit1 prodigious as    
that was1 knew but half his worth4      
,those who were admitted to   his       
society will readily allow that anything
 more pure1 more   candid1 more simple1 
more scrupulously loving of justice1    
than   the whole habits of his life and 
conversation1 proved him to be1   was   
never known in society4 ,one of the most
 astonishing   circumstances in this    
truly great man1 was the versatility of 
his talents4 ,his accomplishments were  
so various1 the powers of   his mind    
were so vast1 and yet of such universal 
application1   that it was hard to say  
whether we should most admire the       
extraordinary grasp of his              
understanding1 or the accuracy of   nice
 research with which he could bring it  
to bear upon the most   minute objects  
of investigation4 ,i forget of whom it  
was said1   that his mind resembled the 
trunk of an elephant1 which can pick    
up ,pg#cad straws1 and tear up trees by 
the roots4 ,mr4 ,watt1 in   some sort1  

resembled the greatest and most         
celebrated of his own   inventions1 of  
which we are at a loss whether most to  
wonder at   the power of grappling with 
the mightiest objects1 or of   handling 
the most minute2 so that1 while nothing 
seems too large   for its grasp1 nothing
 seems too small for the delicacy of its
   touch1 which can cleave rocks1 and   
pour forth rivers from the   bowels of  
the earth1 and1 with perfect exactness1 
though not   with greater ease1 fashion 
the head of a pin1 or strike the        
impress of some curious die4 ,now1 those
 who knew ,mr4 ,watt1 had   to          
contemplate a man whose genius could    
create such an engine1   and indulge in 
the most abstruse speculations of       
philosophy1 and   could at once pass    
from the most sublime researches of     
geology   and physical astronomy1 the   
formation of our globe1 and the         
structure of the universe1 to the       
manufacture of a needle or a   nail2 who
 could discuss1 in the same             

conversation1 and with   equal accuracy1
 if not with the same consummate skill1 
the most   forbidding details of art and
 the elegances of classical             
literature1 the most abstruse branches  
of science and the   niceties of verbal 
criticism4    ,there was one quality in 
,mr4 ,watt which most honourably        
distinguished him from too many         
inventors1 and was worthy of   all      
imitation--he was not only entirely free
 from jealousy1   but he exercised a    
careful and scrupulous self-denial1 and 
was   anxious not to appear1 even by    
accident1 as appropriating to   himself 
that which he thought belonged to       
others4 ,i have heard   him refuse the  
honour universally ascribed to him1 of  
being   the inventor of the steam       
engine1 and call himself simply its     
improver2 though1 in my mind1 to doubt  
his right to that   honour1 would be as 
inaccurate as to question ,sir ,isaac   
,newton's claim to his greatest         
discoveries1 because ,descartes   in    

mathematics1 and ,galileo in astronomy  
and mechanics1 had   preceded him2 or to
 deny the merits of his illustrious     
successor1 because galvanism was not his
 discovery1 though1   before his time1  
it had remained as useless to science as
 the   instrument called a steam engine 
was to the arts before ,mr4   ,watt4    
,the only jealousy ,i have known him to 
betray1 was with   respect to others1 in
 the nice adjustment he was fond of     
giving to the claims of inventors4      
,justly prizing scientific   discovery  
above all other possessions1 he deemed  
the title to   it so sacred1 that you   
might hear him arguing by the hour to   
settle disputed rights2 and if you ever 
perceived his temper   ruffled1 it was  
when one man's invention was claimed by1
 or   given to another2 or when a clumsy
 adulation pressed upon   himself that  
which he knew to be not his own4  ,in   
the preface to the ,monastery ,sir      
,walter ,scott speaks of ,watt in the   
following terms3--    ,there were       

assembled about half a score of our     
northern   lights4 99 99 ,amidst this   
company stood ,mr4 ,watt1 the man whose 
genius discovered the means of          
multiplying our national   resources to 
a degree1 perhaps1 even beyond his own  
stupendous   powers of calculation and  
combination2 bringing the treasures   of
 the abyss to the summit of the         
earth--giving the feeble arm   of man   
the momentum of an ,afrite--commanding  
manufactures to   arise as the rod of   
the prophet produced water in the       
desert--affording the means of          
dispensing with that time and   tide    
which wait for no man--and of sailing   
without that wind   which defied the    
command and threats of ,xerxes himself4 
,this   potent commander of the         
elements--this abridger of time and     
space--this magician1 whose cloudy      
,pg#cae machinery has   produced a      
change on the world1 the effects of     
which1   extraordinary as they are1 are1
 perhaps1 only now beginning to   be    

felt--was not only the most profound man
 of science--the   most successful      
combiner of powers1 and calculator of   
numbers1   as adapted to practical      
purposes--was not only one of the most  
generally well informed1 but one of the 
best and kindest of   human beings4     
,there he stood1 surrounded by the      
little band ,i have   mentioned of      
northern literati1 men not less         
tenacious1   generally speaking1 of     
their own fame and their own opinions1  
than the national regiments are supposed
 to be jealous of the   high character  
which they have won upon service4       
,methinks ,i   yet see and hear what ,i 
shall never see or hear again4 ,in his  
eighty-second year1 the alert1 kind1    
benevolent old man1 had   his attention 
alive to every one's question1 his      
information   at every one's command4   
,his talents and fancy overflowed on    
every subject4 ,one gentleman   was a   
deep philologist--he talked with him on 
the origin of the   alphabet1 as if he  

had been coeval with ,cadmus2 another a 
celebrated critic--you would have said  
the old man had studied   political     
economy and belles lettres all his life4
 ,of science it is   unnecessary to     
speak--it was his own distinguished     
walk4 ,and yet1   ,captain ,clutterbuck1
 when he spoke with your countryman1    
,jedediah   ,cleishbotham1 you would    
have sworn he had been coeval with      
,claverse   and ,burley1 with the       
persecutors and persecuted1 and could   
number   every shot the dragoons had    
fired at the fugitive ,covenanters4 ,in 
fact1 we discovered that no novel of the
 least celebrity escaped   his perusal1 
and that the gifted man of science was  
as much   addicted to the productions of
 your native country1 in other words1   
as shameless and obstinate a peruser of 
novels1 as if he had been a   very      
milliner's apprentice of eighteen4  ,in 
the ,edinburgh newspaper1 called the    
,scotsman1 of the #dth ,september1      
#ahai1 immediately after the decease of 

,watt1 the following sketch was         
published from the pen of ,lord         
,jeffrey3--    ,this name fortunately   
needs no commemoration of ours2 for he  
that bore it survived to see it crowned 
with undisputed and   unenvied honours2 
and many generations will probably pass 
away   before it shall have gathered    
'all its fame4' ,we have said   that    
,mr4 ,watt was the great improver of the
 steam engine2   but1 in truth1 as to   
all that is admirable in its structure1 
or vast in its utility1 he should rather
 be described as its   inventor4 ,it was
 by his inventions1 that its action was 
so   regulated as to make it capable of 
being applied to the finest   and most  
delicate manufactures1 and its power so 
increased1 as   to set weight and       
solidity at defiance4 ,by his admirable 
contrivance1 it has become a thing      
stupendous alike for its   force and its
 flexibility--for the prodigious power  
which it   can exert1 and the ease1 and 
precision1 and ductility with   which it

 can be varied1 distributed1 and        
applied4 ,the trunk of   an elephant1   
that can pick up a pin or rend an oak1  
is as   nothing to it4 ,it can engrave a
 seal1 and crush masses of   obdurate   
metal before it--draw out1 without      
breaking1 a thread   as fine as         
gossamer1 and lift a ship of war like a 
bauble in   the air4 ,it can embroider  
muslin1 and forge anchors--cut steel    
into ribands1 and impel loaded vessels  
against the fury of the   winds and     
waves4 ,pg#caf    ,it would be difficult
 to estimate the value of the benefits  
which these inventions have conferred   
upon this country4 ,there   is no branch
 of industry that has not been indebted 
to them2   and1 in all the most         
material1 they have not only widened    
most   magnificently the field of its   
exertions1 but multiplied a   thousand  
fold the amount of its productions4 ,it 
is our   improved steam engine that has 
fought the battles of ,europe1   and    
exalted and sustained1 through the late 

tremendous   contest1 the political     
greatness of our land4 ,it is the same  
great power which now enables us to pay 
the interest of our   debt1 and to      
maintain the arduous struggle in which  
we are   still engaged 7#ahai71 with the
 skill and capital of countries   less  
oppressed with taxation4 ,but these are 
poor and narrow   views of its          
importance4 ,it has increased           
indefinitely the   mass of human        
comforts and enjoyments1 and rendered   
cheap and   accessible all over the     
world the materials of wealth and       
prosperity4 ,it has armed the feeble    
hand of man1 in short1   with a power to
 which no limits can be assigned2       
completed the   dominion of mind over   
the most refractory qualities of matter2
   and laid a sure foundation for all   
those future miracles of   mechanic     
power which are to aid and reward the   
labours of   after generations4 ,it is  
to the genius of one man1 too1 that     
all this is mainly owing2 and certainly 

no man ever bestowed   such a gift on   
his kind4 ,the blessing is not only     
universal1   but unbounded2 and the     
fabled inventors of the plough and the  
loom1 who were deified by the erring    
gratitude of their rude                 
contemporaries1 conferred less important
 benefits on mankind   than the inventor
 of our present steam engine4    ,this  
will be the fame of ,watt with future   
generations2 and it is   sufficient for 
his race and his country4 ,but to those 
to whom he   more immediately belonged1 
who lived in his society and enjoyed his
   conversation1 it is not1 perhaps1 the
 character in which he will be   most   
frequently recalled--most deeply        
lamented--or even most highly   admired4
 ,independently of his great attainments
 in mechanics1 ,mr4   ,watt was an      
extraordinary1 and in many respects a   
wonderful man4   ,perhaps no individual 
in his age possessed so much and such   
varied   and exact information--had read
 so much1 or remembered what he had     

read so accurately and well4 ,he had    
infinite quickness of   apprehension1 a 
prodigious memory1 and a certain        
rectifying and   methodising power of   
understanding1 which extracted something
   precious out of all that was         
presented to it4 ,his stores of         
miscellaneous knowledge were immense2   
and yet less astonishing than   the     
command he had at all times over them4  
,it seemed as if every   subject that   
was casually started in conversation    
with him1 had   been that which he had  
been last occupied in studying and      
exhausting2--such was the copiousness1  
the precision1 and the   admirable      
clearness of the information which he   
poured out upon it   without effort or  
hesitation4 ,nor was this promptitude   
and compass   of knowledge confined in  
any degree to the studies connected with
   his ordinary pursuits4 ,that he      
should have been minutely and           
extensively skilled in chemistry and the
 arts1 and in most of the   branches of 

physical science1 might perhaps have    
been conjectured2   but it could not    
have been inferred from his usual       
occupations1 and   probably is not      
generally known1 that he was curiously  
learned in   many branches of antiquity1
 metaphysics1 medicine1 and etymology2  
and perfectly at home in all the details
 of architecture1 music1   and law4 ,he 
was well acquainted1 too1 with most of  
the modern   languages1 and familiar    
with their most recent literature4 ,nor 
was   it at all extraordinary to hear   
the great mechanician and engineer      
detailing and expounding1 for hours     
together1 ,pg#cag the   metaphysical    
theories of the ,german logicians1 or   
criticising the   measures or the matter
 of the ,german poetry4    ,his         
astonishing memory was aided1 no doubt1 
in a great measure1   by a still higher 
and rarer faculty--by his power of      
digesting1   and arranging in its proper
 place1 all the information he          
received2 and of casting aside and      

rejecting1 as it were   instinctively1  
whatever was worthless or immaterial4   
,every   conception that was suggested  
to his mind seemed instantly to   take  
its place among its other rich          
furniture1 and to be   condensed into   
the smallest and most convenient form4  
,he never   appeared1 therefore1 to be  
at all incumbered or perplexed with     
the verbiage of the dull books he       
perused1 or to the idle talk   to which 
he listened2 but to have at once        
extracted1 by a kind   of intellectual  
alchemy1 all that was worthy of         
attention1 and   to have reduced it1 for
 his own use1 to its true value and to  
its simplest form4 ,and thus it often   
happened1 that a great deal   more was  
learned from his brief and vigorous     
account of the   theories and arguments 
of tedious writers1 than an ordinary    
student could ever have derived from the
 most painful study of   the originals2 
and that errors and absurdities became  
manifest   from the mere clearness and  

plainness of his statement of them1     
which might have deluded and perplexed  
most of his hearers   without that      
invaluable assistance4    ,it is        
needless to say that1 with those vast   
resources1 his   conversation was at all
 times rich and instructive in no       
ordinary   degree3 but it was1 if       
possible1 still more pleasing than wise2
 and   had all the charms of familiarity
 with all the substantial   treasures of
 knowledge4 ,no man could be more social
 in his spirit1   less assuming or      
fastidious in his manners1 or more kind 
and   indulgent toward all who          
approached him4 ,he rather liked to     
talk1--at least in his latter years2 but
 though he took a   considerable share  
of the conversation1 he rarely suggested
 the   topics on which it was to turn1  
but readily and quietly took up         
whatever was presented by those around  
him1 and astonished the idle   and      
barren propounders of an ordinary theme 
by the treasures which   he drew from   

the mine they had unconsciously opened4 
,he generally   seemed1 indeed1 to have 
no choice or predilection for one       
subject   of discourse rather than      
another2 but allowed his mind1 like a   
great cyclopdia1 to be opened at any    
letter his associates might   choose to 
turn up1 and only endeavoured to select 
from his   inexhaustible stores1 what   
might be best adapted to the taste of   
his present hearers4 ,as to their       
capacity he gave himself no   trouble2  
and indeed such was his singular talent 
for making all   things plain1 clear1   
and intelligible1 that scarcely any one 
could   be aware of such a deficiency in
 his presence4 ,his talk1 too1   though 
overflowing with information1 had no    
resemblance to   lecturing or solemn    
discoursing1 but1 on the contrary1 was  
full of   colloquial spirit and         
pleasantry4 ,he had a certain quiet and 
grave   humour which ran through most of
 his conversation2 and a vein of        
temperate jocularity1 which gave        

infinite zest and effect to the         
condensed and inexhaustible information 
which formed its main   staple and      
characteristic4 ,there was a little air 
of affected   testiness1 and a tone of  
pretended rebuke and contradiction1 with
   which he used to address his younger 
friends1 that was always felt   by them 
as an endearing mark of his kindness and
 familiarity2 and   prized1 accordingly1
 far beyond all the solemn compliments  
that   ever proceeded from the lips of  
authority4 ,his voice was deep and      
powerful1 though he commonly spoke in a 
low and somewhat monotonous   tone1     
which harmonised admirably with the     
weight and brevity of his               
observations1 and set off to the        
greatest advantage the pleasant         
,pg#cah anecdotes1 which he delivered   
with the same grave brow1 and   the same
 calm smile playing soberly on his lips4
 ,there was nothing   of effort1 indeed1
 or impatience1 any more than of pride  
or levity1   in his demeanour2 and there

 was a finer expression of reposing     
strength1 and mild self-possession in   
his manner1 than we ever   recollect to 
have met with in any other person4 ,he  
had in his   character the utmost       
abhorrence for all sorts of forwardness1
   parade1 and pretensions2 and1 indeed1
 never failed to put all such           
impostures out of countenance1 by the   
manly plainness and honest   intrepidity
 of his language and deportment4    ,in 
his temper and dispositions1 he was not 
only kind and   affectionate1 but       
generous1 and considerate of the        
feelings of   all around him2 and gave  
the most liberal assistance and         
encouragement to all young persons who  
showed any indications of   talent1 or  
applied to him for patronage or advice4 
,his health1   which was delicate from  
his youth upwards1 seemed to become     
firmer as he advanced in years2 and he  
preserved1 up almost to   the last      
moment of his existence1 not only the   
full command of   his extraordinary     

intellect1 but all the alacrity of      
spirit and   the social gaiety which had
 illumined his happiest days4 ,his      
friends in this part of the country     
never saw him more full of              
intellectual vigour and colloquial      
animation--never more   delightful or   
more instructive--than in his last visit
 to   ,scotland in autumn #ahag4        
,indeed1 it was after that time that he 
applied himself1 with all the ardour of 
early life1 to the   invention of a     
machine for mechanically copying all    
sorts of   sculpture and statuary2 and  
distributed among his friends some   of 
its earliest performances1 as the       
productions of a young   artist just    
entering on his eighty-third year4      
,this happy and useful life came1 at    
last1 to a gentle close4   ,he had      
suffered some inconvenience through the 
summer2 but was   not seriously         
indisposed till within a few weeks of   
his death4   ,he then became perfectly  
aware of the event which was            

approaching2 and with his usual         
tranquillity and benevolence   of       
nature1 seemed only anxious to point out
 to the friends   around him1 the many  
sources of consolation which were       
afforded by the circumstances under     
which it was about to take   place4 ,he 
expressed his sincere gratitude to      
,providence for   the length of days    
with which he had been blessed1 and his 
exemption from most of the infirmities  
of age2 as well as for   the calm and   
cheerful evening of life that he had    
been   permitted to enjoy1 after the    
honourable labours of the day   had been
 concluded4 ,and thus1 full of years and
 honours1 in   all calmness and         
tranquillity1 he yielded up his soul    
without   pang or struggle2 and passed  
from the bosom of his family to   that  
of his ,god4  ,the ,english nation has  
ever shown itself insensible to the     
claims of genius and high intellectual  
endowments1 except where the results    
have been brought directly to bear in   

statesmanship or war4 ,of this inability
 to appreciate the highest order of     
intellectual excellence ,watt affords a 
striking example4 ,when it was suggested
 to the ,british government by those    
better capable than that government was 
of appreciating the genius of this great
 man1 that the nation would do itself   
honour by erecting a splendid monument  
at his own ,pg#cai cost to him to whom  
it was so deeply indebted for the       
extension of its resources and the      
augmentation of its power1 the reply was
 that such a measure could not be       
adopted as it might be drawn into a     
precedent in like cases thereafter6 ,a  
precedent in like cases66 ,when will the
 time arrive when the world will produce
 a like case8 ,the monument which has   
been erected in ,westminster ,abbey was 
in fact raised by private subscription1 
the nation having thus stigmatised      
itself through the act of its government
 with the everlasting disgrace of       
refusing the honour proposed to it4 ,the

 other statues and monuments which have 
been erected to this great man1 have    
been for the most part raised by the    
filial piety and the never-dying        
affection and veneration of the present 
,mr4 ,james ,watt4 ,a statue has been   
presented by him to the ,university of  
,glasgow1 and placed in one of the halls
 of that college4 ,the inhabitants of   
,greenock have also erected a marble    
statue of ,watt1 for which1 and for a   
library1 a building has been erected at 
the expense of about #c1ejjl4 which has 
been defrayed by ,mr4 ,james ,watt4 ,a  
colossal bronze statue has been erected 
on a handsome granite pedestal1 standing
 at one of the corners of ,george       
,square1 ,glasgow4 ,the monument in     
,westminster ,abbey1 erected by the     
subscription raised at the public       
meeting already alluded to1 is a        
colossal statue of ,carrara marble1 by  
,chantrey4  ,watt was elected a fellow  
of the ,royal ,society of ,edinburgh in 
#aghd2 of the ,royal ,society of ,london

 in #aghe2 a member of the ,batavian    
,society in #aghg2 and a corresponding  
member of the ,institut of ,france in   
#ahjh4 ,the degree of ,doctor of ,laws  
was conferred upon him by the           
,university of ,glasgow1 in #ahjf2 and  
in #ahad1 the highest scientific honour 
which can be attained by a philosopher1 
was conferred on him by the ,academy of 
,sciences of the ,institut of ,france1  
who nominated him one of its eight      
foreign associates4  ,on the pedestal of
 the monument in ,westminster ,abbey is 
engraved the following inscription from 
the pen of ,lord ,brougham3-- ,pg#cbj   
,,not ,,to ,,perpetuate ,a ,,name       
,,which ,,must ,,endure ,,while ,,the   
,,peaceful   ,,arts ,,flourish1 ,,but   
,,to ,,show ,,that ,,mankind ,,have     
,,learned ,,to ,,honour   ,,those ,,who 
,,best ,,deserve ,,their ,,gratitude1   
,,the ,,king ,,his ,,ministers1   ,,and 
,,many ,,of ,,the ,,nobles ,,and        
,,commoners ,,of ,,the ,,realm ,,raised 
,,this   ,,monument ,,to    ,,james     

,,watt1    ,,who ,,directing ,,the      
,,force ,,of ,,an ,,original ,,genius1  
,,early ,,exercised   ,,in ,,philosophic
 ,,research ,,to ,,the ,,improvement    
,,of ,,the ,,steam   ,,engine1          
,,enlarged ,,the ,,resources ,,of ,,his 
,,country1 ,,increased ,,the   ,,power  
,,of ,,man1 ,,and ,,rose ,,to ,,an      
,,eminent ,,place ,,among ,,the ,,most  
,,illustrious ,,followers ,,of ,,science
 ,,and ,,the ,,real ,,benefactors ,,of  
,,the ,,world4 ,,born ,,at ,,greenock   
,,mdccxxxvi4 ,,died ,,at ,,heathfield   
,,in   ,,staffordshire ,,mdcccxix4      
,illustration3 ,,watt',s ,,chapel ,,in  
,,handsworth ,,church4    ,,footnotes3  
#be ,see ,buchanan on the ,economy of   
,fuel and ,management of   ,heat1       
especially as it relates to heating and 
drying by means   of ,steam4    #bf ,see
 ,brewster's ,edinburgh ,encyclopdia1   
article   ,,steam-,,drying ,,machine4   
#bg ,the following are the words in     
which ,watt makes this   remarkable     
announcement to ,priestley3--    ,let us

 now consider what obviously happens in 
the deflagration   of the inflammable   
7hydrogen7 and dephlogisticated air     
7oxygen74   ,these two kinds of air     
unite with violence2 they become red    
hot1   and upon cooling1 totally        
disappear4 ,when the vessel is cooled1  
a quantity of water is found in it equal
 to the weight of the   air employed4   
,this water is then the only remaining  
product of   the process2 and water1    
light1 and heat are all the products4   
,are we not then authorised to conclude1
 that water is composed   of            
dephlogisticated air 7oxygen7 and       
phlogiston 7hydrogen71   deprived of    
part of their latent or elementary heat2
 that   dephlogisticated or pure air    
7oxygen7 is composed of water   deprived
 of its phlogiston 7hydrogen71 and      
united to elementary   heat and light2  
and that the latter are contained in it 
in a   latent state1 so as not to be    
sensible to the thermometer or to   the 
eye2 and if light be only a modification

 of heat1 or a   circumstance attending 
it1 or a component part of the          
inflammable air 7hydrogen71 then pure or
 dephlogisticated air   7oxygen7 is     
composed of water deprived of its       
phlogiston   7hydrogen71 and united to  
elementary heat4    #bh ,those who      
desire to investigate this controversy  
more in   detail will find very full    
information on the subject in the       
,translation of ,arago's ,eloge1 with   
notes and appendix by ,j4 ,p4           
,muirhead1 ,esq4 ,murray1 ,london1      
#ahci4    #bi ,an account of this       
remarkable apparatus1 accompanied by an 
engraving made from a drawing supplied  
by ,watt1 was communicated   by ,sir    
,john ,robison to the ,edinburgh        
,philosophical ,journal in   #ahbj4 ,see
 vol4 iii1 p4 #fj4  ,pg#cba             
,illustration  ,,chap4 ,,xi4            
,,locomotive ,,engines ,,on ,,railways4 
,,non-,,condensing ,,engines4 --        
,,leupold',s ,,engine4-,,trevethick     
,,and     ,,vivian4 -- ,,effects ,,of   

,,railway ,,transport4 -- ,,history ,,of
 ,,the     ,,locomotive ,,engine4 --    
,,blenkinsop4 -- ,,messrs4 ,,chapman4 --
 ,,walking     ,,engine4 -- ,,mr4       
,,stephenson',s ,,engines ,,at          
,,killingworth4 --     ,,liverpool ,,and
 ,,manchester ,,railway4 --             
,,experimental ,,trial4 -- ,,the        
,,rocket4 -- ,,the ,,sanspareil4 --     
,,the ,,novelty4 -- ,,subsequent        
,,improvements ,,in ,,the ,,locomotive  
,,engine4 -- ,,lardner',s ,,experiments 
,,in #ahcb4 -- ,,adoption ,,of ,,brass  
,,tubes4 -- ,,mr4 ,,booth',s ,,report4  
--     ,,detailed ,,description ,,of    
,,the ,,most ,,improved ,,locomotive    
,,engines4     -- ,,power ,,of          
,,locomotive ,,engines4 -- ,,evaporation
 ,,of ,,boilers4 --     ,,lardner',s    
,,experiments ,,in #ahch4 --            
,,resistance ,,to ,,railway ,,trains4   
-- ,,restrictions ,,on ,,gradients4 --  
,,compensating ,,effect ,,of            
,,gradients4 -- ,,experiment ,,with     
,,the ,,hecla4 -- ,,methods ,,of        

,,surmounting ,,steep ,,inclinations4   
7#ahj47 ,in the various modifications of
 the steam engine which we have hitherto
 considered1 the pressure introduced on 
one side of the piston derives its      
efficacy either wholly or partially from
 the vacuum produced by condensation on 
the other side4 ,this always requires a 
condensing apparatus1 and a constant and
 abundant supply of cold water4 ,an     
engine of this kind must therefore      
necessarily have considerable dimensions
 and weight1 and is inapplicable to uses
 in which a small and light machine only
 is admissible4 ,if the condensing      
apparatus be dispensed with1 the piston 
will always be resisted by a force equal
 to the atmospheric ,pg#cbb pressure1   
and the only part of the steam pressure 
which will be available as a moving     
power1 is that part by which it exceeds 
the pressure of the atmosphere4 ,hence1 
in engines which do not work by         
condensation1 steam of a much higher    
pressure than that of the atmosphere is 

indispensably necessary1 and such       
engines are therefore called            
high-pressure engines4  ,we are not1    
however1 to understand that every       
engine1 in which steam is used of a     
pressure exceeding that of the          
atmosphere1 is what is meant by an      
high-pressure engine2 for in the        
ordinary engines in common use1         
constructed on ,watt's principle1 the   
safety-valve is loaded with from #c to  
#e lbs4 on the square inch2 and in      
,woolf's engines1 the steam is produced 
under a pressure of #dj lbs4 on the     
square inch4 ,these would therefore be  
more properly called condensing engines 
than low-pressure engines2 a term quite 
inapplicable to those of ,woolf4 ,in    
fact1 by high-pressure engines is meant 
engines in which no vacuum is produced1 
and1 therefore1 in which the piston     
works against a pressure equal to that  
of the atmosphere4  ,in these engines   
the whole of the condensing apparatus1  
viz4 the cold-water cistern1 condenser1 

air-pump1 cold-water pump1 c41 are      
dispensed with1 and nothing is retained 
except the boiler1 cylinder1 piston1 and
 valves4 ,consequently1 such an engine  
is small1 light1 and cheap4 ,it is      
portable also1 and may be moved1 if     
necessary1 along with its load1 and is  
therefore well adapted to locomotive    
purposes4   7#aha47 ,high-pressure      
engines were one of the earliest forms  
of the steam engine4 ,the contrivance1  
which is obscurely described in the     
article already quoted 7#g471 from the  
,century of ,inventions1 is a           
high-pressure engine2 for the power     
there alluded to is the elastic force of
 steam working against the atmospheric  
pressure4 ,newcomen1 in #agje1 applied  
the working-beam1 cylinder1 and piston  
to the atmospheric engine2 and ,leupold1
 about #agbj1 combined the working-beam 
and cylinder with the high-pressure     
principle1 and produced the earliest    
high-pressure engine worked by a        
cylinder and piston4 ,the following is a

 description of ,leupold's engine3--    
,pg#cbc  ,illustration3 ,fig4 #hb4  ,a  
7fig4 #hb47 is the boiler1 with the     
furnace beneath it2 ,c ,c are two       
cylinders with solid pistons ,p ,p1     
connected with the working-beams ,b ,b1 
to which are attached the pump-rods ,r  
,r1 of two forcing pumps ,f ,f1 which   
communicate with a great force-pipe ,s2 
,g is a four-way cock 7#ff47 already    
described4 ,in the position in which it 
stands in the figure1 the steam issues  
from below the piston ,p into the       
atmosphere1 and the piston is descending
 by its own weight2 steam from the      
boiler is at the same time pressing up  
the piston ,p1 with a force equal to the
 difference between the pressure of the 
steam and that of the atmosphere4 ,thus 
the piston ,r of the forcing-pump is    
being drawn up1 and the piston ,p is    
forcing the piston ,r down1 and thereby 
driving water into the force-pipe       
,pg#cbd ,s4 ,on the arrival of the      
piston ,p at the bottom of the cylinder 

,c1 and ,p at the top of the cylinder   
,c1 the position of the cock is changed 
as represented in fig4 #hc4 ,the steam1 
which has just pressed up the piston ,p1
 is allowed to escape into the          
atmosphere1 while the steam1 passing    
from the boiler below the piston ,p1    
presses it up1 and thus ,p ascends by   
the steam pressure1 and ,p descends by  
its own weight4 ,by these means the     
piston ,r is forced down1 driving before
 it the water in the pump-cylinder into 
the force-pipe ,s1 and the piston ,r is 
drawn up to allow the other             
pump-cylinder to be re-filled2 and so   
the process is continued4               
,illustration3 ,fig4 #hc4  ,a valve is  
placed in the bottom of the force-pipes1
 to prevent the water which has been    
driven into it from returning4 ,this    
valve opens upwards2 and1 consequently1 
the weight of the water pressing upon it
 only keeps it more effectually closed4 
,on each descent of the piston1 the     
pressure transmitted to the valve acting

 upwards being greater than the weight  
of the water resting upon it1 forces it 
open1 and an increased quantity of water
 is introduced4   7#ahb47 ,from the date
 of the improvement of ,watt until the  
commencement of the present century1    
non-condensing engines were altogether  
neglected in these countries4 ,in the   
year #ahjb1 ,messrs4 ,trevethick and    
,vivian constructed the first           
non-condensing engine of this kind which
 was ever brought into extensive        
practical use in this kingdom4 ,a       
section of this machine1 made by a      
vertical plane1 is represented in fig4  
#hd4  ,the boiler ,a ,b is a cylinder   
with flat circular ends4 ,the fire-place
 is constructed in the following        
manner3--,a tube enters the cylindrical 
boiler at one end2 and1 proceeding      
onwards near the other extremity1 is    
turned and recurved1 so as to be carried
 back parallel to the direction in which
 it entered4 ,it is thus conducted out  
of the boiler1 at another part of the   

same end at which it entered4 ,one of   
the ends of this tube communicates with 
the chimney ,e1 which is carried upwards
 as represented in the figure4 ,the     
other mouth is furnished ,pg#cbe with a 
door2 and in it is placed the grate1    
which is formed of horizontal bars1     
dividing the tube into two parts2 the   
upper part forming the fire-place1 and  
the lower the ash-pit4 ,the fuel is     
maintained in a state of combustion1 on 
the bars1 in that part of the tube      
represented at ,c ,d2 and the flame is  
carried by the draught of the chimney   
round the curved flue1 and issues at ,e 
into the chimney4 ,the flame is thus    
conducted through the water1 so as to   
expose the latter to as much heat as    
possible4  ,illustration3 ,fig4 #hd4  ,a
 section of the cylinder is represented 
at ,f1 immersed in the boiler1 except a 
few inches of the upper end1 where the  
four-way cock ,g is placed for          
regulating the admission of the steam4  
,a tube is represented at ,h1 which     

leads from this four-way cock into the  
chimney2 so that the waste steam1 after 
working the piston1 is carried off      
through this tube1 and passes into the  
chimney4 ,the upper end of the          
piston-rod is furnished with a          
cross-bar1 which is placed in a         
direction at right angles to the length 
of the boiler1 and also to the ,pg#cbf  
piston-rod4 ,this bar is guided in its  
motion by sliding on two iron           
perpendicular rods fixed to the sides of
 the boiler1 and parallel to each other4
 ,to the ends of this cross-bar are     
joined two connecting rods1 the lower   
ends of which work two cranks fixed on  
an axis extending across and beneath the
 boiler1 and immediately under the      
centre of the cylinder4 ,this axis is   
sustained in bearings formed in the legs
 which support the boiler1 and upon its 
extremity is fixed the fly-wheel as     
represented at ,b4 ,a large-toothed     
wheel is placed on this axis2 which1    
being turned with the cranked axle1     

communicates motion to other wheels2 and
 through them1 to any machinery which   
the engine may be applied to move4      
,illustration3 ,fig4 #he4  ,as the      
four-way cock is represented in the     
figure1 the steam passes from the boiler
 through the curved passage ,g above the
 piston1 while the steam below the      
piston is carried off through a tube    
which does not appear in the figure1 by 
which it is conducted to the tube ,h1   
and thence to the chimney4 ,the steam1  
therefore1 which passes above the piston
 presses it downwards2 while the        
pressure upwards does not exceed that of
 the atmosphere4 ,the piston will       
therefore descend with a force depending
 on the excess of the pressure of the   
steam produced in the boiler above the  
atmospheric pressure4 ,when the piston  
has arrived at the bottom of the        
cylinder1 the cock is made to assume the
 position represented in fig4 #he4 ,this
 effect is produced by the motion of the
 piston-rod4 ,the steam now passes from 

above the piston1 through the tube ,h1  
into the chimney1 while the steam from  
the boiler is conducted through another 
tube below the piston4 ,the pressure    
above the piston1 in this case1 does not
 exceed that of the atmosphere2 while   
the pressure below it will be that of   
the steam in the boiler4 ,the piston    
will therefore ascend with the          
difference of these pressures4 ,on the  
arrival of the piston at the top of the 
cylinder1 the four-way cock is again    
turned to the position represented in   
fig4 #he41 and the piston again         
descends2 and in the same manner the    
process is continued4 ,a safety-valve is
 placed on the boiler at ,v1 loaded with
 a weight ,w1 proportionate ,pg#cbg to  
the strength of the steam with which it 
is proposed to work4  ,in the engines   
now described1 this valve was frequently
 loaded at the rate of from #fj to #hj  
lbs4 on the square inch4 ,as the boilers
 of high-pressure engines were          
considered more liable to accidents from

 bursting than those in which steam of a
 lower pressure was used1 greater       
precautions were taken against such     
effects4 ,a second safety-valve was     
provided1 which was not left in the     
power of the engine-man4 ,by this means 
he had a power to diminish the pressure 
of the steam1 but could not increase it 
beyond the limit determined by the valve
 which was removed from his             
interference4 ,the greatest cause of    
danger1 however1 arose from the water in
 the boiler being consumed by           
evaporation faster than it was supplied2
 and therefore falling below the level  
of the tube containing the furnace4 ,to 
guard against accidents arising from    
this circumstance1 a hole was bored in  
the boiler1 at a certain depth1 below   
which the water should not be allowed to
 fall2 and in this hole a plug of metal 
was soldered with lead1 or with some    
other metal1 which would fuse at that   
temperature which would expose the      
boiler to danger4 ,thus1 in the event of

 the water being exhausted1 so that its 
level would fall below the plug1 the    
heat of the furnace would immediately   
melt the solder1 and the plug would fall
 out1 affording a vent for the steam1   
without allowing the boiler to burst4   
,the mercurial steam-gauge1 already     
described1 was also used as an          
additional security4 ,when the force of 
the steam exceeded the length of the    
column of mercury which the tube would  
contain1 the mercury would be blown out1
 and the tube would give vent to the    
steam4 ,the water by which the boiler   
was replenished was forced into it by a 
pump worked by the engine4 ,in order to 
economise the heat1 this water was      
contained in a tube ,t1 which surrounded
 the pipe ,h4 ,as the waste steam1 after
 working the piston1 passed off through 
,h1 it imparted a portion of its heat to
 the water contained in the tube ,t1    
which was thus warmed to a certain      
temperature before it was forced into   
the boiler by the pump4 ,thus a part of 

the heat1 which was originally ,pg#cbh  
carried from the boiler in the form of  
steam1 was returned again to the boiler 
with the water with which it was fed4   
,it is evident that engines constructed 
in this manner may be applied to all the
 purposes to which the condensing       
engines are applicable4   7#ahc47 ,two  
years after the date of the patent of   
this engine1 its inventor constructed a 
machine of the same kind for the purpose
 of moving carriages on railroads2 and  
applied it successfully1 in the year    
#ahjd1 on the railroad at ,merthyr      
,tydvil1 in ,south ,wales4 ,it was in   
principle the same as that already      
described4 ,the cylinder however was in 
a horizontal position1 the piston-rod   
working in the direction of the line of 
road3 the extremity of the piston-rod1  
by means of a connecting rod1 worked    
cranks placed on the axletree1 on which 
were fixed two cogged wheels3 these     
worked in others1 by which their motion 
was communicated finally to cogged      

wheels fixed on the axle of the hind    
wheels of the carriage1 by which this   
axle was kept in a state of revolution4 
,the hind wheels being fixed on the     
axletree1 and turning with it1 were     
caused likewise to revolve2 and so long 
as the weight of the carriage did not   
exceed that which the friction of the   
road was capable of propelling1 the     
carriage would thus be moved forwards4  
,on this axle was placed a fly-wheel to 
continue the rotatory motion at the     
termination of each stroke4 ,the fore   
wheels are described as being capable of
 turning like the fore wheels of a      
carriage1 so as to guide the vehicle4   
,the projectors appear to have          
contemplated1 in the first instance1 the
 use of this carriage on common roads2  
but that notion seems to have been      
abandoned1 and its use was only adopted 
on the railroad before mentioned4 ,on   
the occasion of its first trial1 it drew
 after it as many carriages as contained
 ten tons of iron a distance of nine    

miles2 which stage it performed without 
any fresh supply of water1 and travelled
 at the rate of five miles an hour4     
7#ahd47 ,capital and skill have of late 
years been directed with extraordinary  
energy to the improvement of inland     
transport2 and this important instrument
 of national wealth and civilisation has
 received a proportionate impulse4      
,effects are now witnessed1 which1 had  
they been narrated a few years ,pg#cbi  
since1 could only have been admitted    
into the pages of fiction or volumes of 
romance4 ,who could have credited the   
possibility of a ponderous engine of    
iron1 loaded with some hundred          
passengers1 in a train of carriages of  
corresponding magnitude1 and a large    
quantity of water and coal1 taking      
flight from ,manchester and arriving at 
,liverpool1 a distance of above thirty  
miles1 in little more than an hour8 ,and
 yet this is a matter of daily and      
almost hourly occurrence4 ,the rapidity 
of transport thus attained is not less  

wonderful than the weights transported4 
,its capabilities in this respect far   
transcend the exigencies even of the two
 greatest commercial marts in ,great    
,britain4 ,loads1 varying from fifty to 
one hundred and fifty tons1 are         
transported at the average rate of      
fifteen miles an hour2 and in one       
instance we have seen a load--we should 
rather say a cargo--of waggons1         
conveying merchandise to the amount of  
two hundred and thirty tons gross1      
transported from ,liverpool to          
,manchester at the average rate of      
twelve miles an hour4  ,the astonishment
 with which such performances must be   
viewed1 might be qualified1 if the art  
of transport by steam on railways had   
been matured1 and had attained that full
 state of perfection which such an art  
is always capable of receiving from long
 experience1 aided by great scientific  
knowledge1 and the unbounded application
 of capital4 ,but such is not the       
present case4 ,the art of constructing  

locomotive engines1 so far from having  
attained a state of maturity1 has not   
even emerged from its infancy4 ,so      
complete was the ignorance of its powers
 which prevailed1 even among engineers1 
previous to the opening of the          
,liverpool railway1 that the transport  
of heavy goods was regarded as the chief
 object of the undertaking1 and its     
principal source of revenue4 ,the       
incredible speed of transport1 effected 
even in the very first experiments in   
#ahcj1 burst upon the public1 and on the
 scientific world1 with all the effect  
of a new and unlooked-for phenomenon4   
,on the unfortunate occasion which      
deprived this country of ,mr4           
,huskisson1 the wounded body of that    
statesman was transported a distance of 
about fifteen miles in twenty-five      
minutes1 being at the rate of thirty-six
 miles an hour4 ,the revenue of the road
 arising from passengers since its      
opening1 ,pg#ccj has1 contrary to all   
that was foreseen1 been nearly double   

that which has been derived from        
merchandise4 ,so great was the want of  
experience in the construction of       
engines1 that the company was at first  
ignorant whether they should adopt large
 steam engines fixed at different       
stations on the line1 to pull the       
carriages from station to station1 or   
travelling engines to drag the loads the
 entire distance4 ,having decided on the
 latter1 they have1 even to the present 
moment1 laboured under the disadvantage 
of the want of that knowledge which     
experience alone can give4 ,the engines 
have been constantly varied in their    
weight and proportions1 in their        
magnitude and form1 as the experience of
 each successive month has indicated4   
,as defects became manifest they were   
remedied2 improvements suggested were   
adopted2 and each year produced engines 
of such increased power and efficiency1 
that their predecessors were abandoned1 
not because they were worn out1 but     
because they had been outstripped in the

 rapid march of improvement4 ,add to    
this1 that only one species of          
travelling engine has been effectively  
tried2 the capabilities of others remain
 still to be developed2 and even that   
form of engine which has received the   
advantage of a course of experiments on 
so grand a scale to carry it towards    
perfection1 is far short of this point1 
and still has defects1 many of which1 it
 is obvious1 time and experience will   
remove4  ,if1 then1 the locomotive      
engine1 subject thus to all the         
imperfections inseparable from a novel  
contrivance--with the restrictions on   
the free application of skill and       
capital1 arising from the nature of the 
monopolies granted to railway           
companies--with the disadvantage of very
 limited experience1 the great parent of
 practical improvement1 having been     
submitted to experiments hitherto only  
on a limited scale1 and confined almost 
to one form of machine2--if1 under such 
disadvantages1 such effects have been   

produced as are now daily witnessed by  
the public1 what may not be looked for  
from this extraordinary power when the  
enterprise of the country shall be more 
unfettered--when greater fields of      
experience are opened--when time1       
ingenuity1 and capital have removed or  
diminished existing imperfections1 and  
have brought to light new and more      
powerful principles8 ,this is not mere  
speculation ,pg#cca on abstract         
possibilities1 but refers to what is in 
actual progress4 ,the points of greatest
 wealth and population--the centres of  
largest capital and most active industry
 throughout the country--will soon be   
connected by lines of railway2 and      
various experiments are proposed1 with  
more or less prospect of success1 for   
the application of steam engines on     
stone roads where the intercourse is not
 sufficient to render railways          
profitable4  ,the important commercial  
and political effects attending such    
increased facility and speed in the     

transport of persons and goods1 are too 
obvious to require any very extended    
notice here4 ,a part of the price 7and  
in many cases a considerable part7 of   
every article of necessity or luxury1   
consists of the cost of transporting it 
from the producer to the consumer2 and  
consequently every abatement or saving  
in this cost must produce a             
corresponding reduction in the price of 
every article transported2 that is to   
say1 of every thing which is necessary  
for the subsistence of the poor1 or for 
the enjoyment of the rich--of every     
comfort1 and of every luxury of life4   
,the benefit of this will extend1 not to
 the consumer only1 but to the producer3
 by lowering the expense of transport of
 the produce1 whether of the soil or of 
the loom1 a less quantity of that       
produce will be spent in bringing the   
remainder to market1 and consequently a 
greater surplus will reward the labour  
of the producer4 ,the benefit of this   
will be felt even more by the           

agriculturist than by the manufacturer2 
because the proportional cost of        
transport of the produce of the soil is 
greater than that of manufactures4 ,if  
two hundred quarters of corn be         
necessary to raise four hundred1 and one
 hundred more be required to bring the  
four hundred to market1 then the net    
surplus will be one hundred4 ,but if by 
the use of steam carriages the same     
quantity can be brought to market with  
an expenditure of fifty quarters1 then  
the net surplus will be increased from  
one hundred to one hundred and fifty    
quarters2 and either the profit of the  
farmer1 or the rent of the landlord1    
must be increased by the same amount4   
,but the agriculturist would not merely 
be benefited by an increased return from
 the soil already under cultivation4    
,any ,pg#ccb reduction in the cost of   
transporting the produce to market would
 call into cultivation tracts of        
inferior fertility1 the returns from    
which would not at present repay the    

cost of cultivation and transport4 ,thus
 land would become productive which is  
now waste1 and an effect would be       
produced equivalent to adding so much   
fertile soil to the present extent of   
the country4 ,it is well known1 that    
land of a given degree of fertility will
 yield increased produce by the         
increased application of capital and    
labour4 ,by a reduction in the cost of  
transport1 a saving will be made which  
may enable the agriculturist to apply to
 tracts already under cultivation the   
capital thus saved1 and thereby increase
 their actual production4 ,not only1    
therefore1 would such an effect be      
attended with an increased extent of    
cultivated land1 but also with an       
increased degree of cultivation in that 
which is already productive4  ,it has   
been said1 that in ,great ,britain there
 are above a million of horses engaged  
in various ways in the transport of     
passengers and goods1 and that to       
transport each horse requires as much   

land as would1 upon an average1 support 
eight men4 ,if this quantity of animal  
power were displaced by steam engines1  
and the means of transport drawn from   
the bowels of the earth1 instead of     
being raised upon its surface1 then1    
supposing the above calculation correct1
 as much land would become available for
 the support of human beings as would   
suffice for an additional population of 
eight millions2 or1 what amounts to the 
same1 would increase the means of       
support of the present population by    
about one third of the present available
 means4 ,the land which now supports    
horses for transport would then support 
men1 or produce corn for food4  ,the    
objection that a quantity of land exists
 in the country capable of supporting   
horses alone1 and that such land would  
be thrown out of cultivation1 scarcely  
deserves notice here4 ,the existence of 
any considerable quantity of such land  
is extremely doubtful4 ,what is the soil
 which will feed a horse and not feed   

oxen or sheep1 or produce food for man8 
,but even if it be admitted that there  
exists in the country a small portion of
 such land1 that portion cannot exceed1 
nor indeed equal1 what would be         
sufficient for the number of horses     
,pg#ccc which must after all continue to
 be employed for the purposes of        
pleasure1 and in a variety of cases     
where steam must necessarily be         
inapplicable4 ,it is to be remembered1  
also1 that the displacing of horses in  
one extensive occupation1 by diminishing
 their price must necessarily increase  
the demand for them in others4  ,the    
reduction in the cost of transport of   
manufactured articles1 by lowering their
 price in the market1 will stimulate    
their consumption4 ,this observation    
applies of course not only to home but  
to foreign markets4 ,in the latter we   
already in many branches of manufactures
 command a monopoly4 ,the reduced price 
which we shall attain by cheapness and  
facility of transport will still further

 extend and increase our advantages4    
,the necessary consequence will be1 an  
increased demand for manufacturing      
population2 and this increased          
population again reacting on the        
agricultural interests1 will form an    
increased market for that species of    
produce4 ,so interwoven and complicated 
are the fibres which form the texture of
 the highly civilised and artificial    
community in which we live1 that an     
effect produced on any one point is     
instantly transmitted to the most remote
 and apparently unconnected parts of the
 system4  ,the two advantages of        
increased cheapness and speed1 besides  
extending the amount of existing        
traffic1 call into existence new objects
 of commercial intercourse4 ,for the    
same reason that the reduced cost of    
transport1 as we have shown1 calls new  
soils into cultivation1 it also calls   
into existence new markets for          
manufactured and agricultural produce4  
,the great speed of transit which has   

been proved to be practicable1 must open
 a commerce between distant points in   
various articles1 the nature of which   
does not permit them to be preserved so 
as to be fit for use beyond a certain   
time4 ,such are1 for example1 many      
species of vegetable and animal food1   
which at present are confined to markets
 at a very limited distance from the    
grower or feeder4 ,the truth of this    
observation is manifested by the effects
 which have followed the intercourse by 
steam on the ,irish ,channel4 ,the      
western towns of ,england have become   
markets for a prodigious quantity of    
,irish produce1 which it had been       
previously ,pg#ccd impossible to export4
 ,if animal food be transported alive   
from the grower to the consumer1 the    
distance of the market is limited by the
 power of the animal to travel1 and the 
cost of its support on the road4 ,it is 
only particular species of cattle which 
bear to be carried to market on common  
roads and by horse carriages4 ,but the  

peculiar nature of a railway1 the       
magnitude and weight of the loads which 
may be transported on it1 and the       
prodigious speed which may be attained1 
render the transport of cattle1 of every
 species1 to almost any distance1 both  
easy and cheap4 ,in process of time1    
when the railway system becomes         
extended1 the metropolis and populous   
towns will therefore become markets1 not
 as at present to districts within      
limited distances of them1 but to the   
whole country4  ,the moral and political
 consequences of so great a change in   
the powers of transition of persons and 
intelligence from place to place are not
 easily calculated4 ,the concentration  
of mind and exertion which a great      
metropolis always exhibits1 will be     
extended in a considerable degree to the
 whole realm4 ,the same effect will be  
produced as if all distances were       
lessened in the proportion in which the 
speed and cheapness of transit are      
increased4 ,towns at present removed    

some stages from the metropolis1 will   
become its suburbs2 others1 now at a    
day's journey1 will be removed to its   
immediate vicinity2 business will be    
carried on with as much ease between    
them and the metropolis1 as it is now   
between distant points of the metropolis
 itself4 ,let those who discard         
speculations like these as wild and     
improbable1 recur to the state of public
 opinion1 at no very remote period1 on  
the subject of steam navigation4 ,within
 the memory of persons who have not yet 
passed the meridian of life1 the        
possibility of traversing by the steam  
engine the channels and seas that       
surround and intersect these islands1   
was regarded as the dream of            
enthusiasts4 ,nautical men and men of   
science rejected such speculations with 
equal incredulity1 and with little less 
than scorn for the understanding of     
those who could for a moment entertain  
them4 ,yet we have witnessed steam      
engines traversing not these channels   

and seas alone1 but sweeping the face of
 the waters round every coast in        
,europe4 ,the ,pg#cce seas which        
interpose between our ,asiatic dominions
 and ,egypt1 and those which separate   
our own shores from our ,west ,indian   
possessions1 have offered an equally    
ineffectual barrier to its powers1 and  
the establishment of a regular steam    
communication between the capitals of   
the ,old and ,new ,world has ceased to  
be a question of practicability1 having 
become merely one of commercial profit4 
,if steam be not used as the only means 
of connecting the most distant points of
 our planet1 it is not because it is    
inadequate to the accomplishment of that
 end1 but because the supply of the     
material1 from which at the present     
moment it derives its powers1 is        
restricted by local and accidental      
circumstances4#cj  ,we propose in the   
present chapter to lay before our       
readers some account of the means       
whereby the effects above referred to   

have been produced2 of the manner and   
degree in which the public have availed 
themselves of these means2 and of the   
improvements of which they seem to us to
 be susceptible4   7#ahe47 ,it is a     
singular fact1 that in the history of   
this invention considerable time and    
great ingenuity were vainly expended in 
attempting to overcome a difficulty1    
which in the end turned out to be purely
 imaginary4 ,to comprehend distinctly   
the manner in which a wheel carriage is 
propelled by steam1 suppose that a pin  
or handle is attached to the spoke of   
the wheel at some distance from its     
centre1 and that a force is applied to  
this pin in such a manner as to make the
 wheel revolve4 ,if the tire of the     
wheel and the surface of the road were  
absolutely smooth and free from         
friction1 so that the face of the tire  
would slide without resistance upon the 
road1 then the effect of the force thus 
applied would be merely to cause the    
wheel to turn round1 the carriage being 

stationary1 the surface of the tire     
slipping or sliding upon the road as the
 wheel is made to revolve4 ,but if1 on  
the other hand1 the pressure of the face
 of the tire upon the road is such as to
 produce between them such a degree of  
adhesion as will render it impossible   
for the wheel to slide or slip upon the 
road by ,pg#ccf the force which is      
applied to it1 the consequence will be1 
that the wheel can only turn round in   
obedience to the force which moves it by
 causing the carriage to advance1 so    
that the wheel will roll upon the road1 
and the carriage will be moved forward1 
through a distance equal to the         
circumference of the wheel1 each time it
 performs a complete revolution4  ,it is
 obvious that both of these effects may 
be partially produced2 the adhesion of  
the wheel to the road may be            
insufficient to prevent slipping        
altogether1 and yet it may be sufficient
 to prevent the wheel from slipping as  
fast as it revolves4 ,under such        

circumstances the carriage would advance
 and the wheel would slip4 ,the         
progressive motion of the carriage      
during one complete revolution of the   
wheel would be equal to the difference  
between the complete circumference of   
the wheel and the portion through which 
in one revolution it has slipped4  ,when
 the construction of travelling steam   
engines first engaged the attention of  
engineers1 and for a considerable period
 afterwards1 a notion was impressed upon
 their minds that the adhesion between  
the face of the wheel and the surface of
 the road must necessarily be of very   
small amount1 and that in every         
practical case the wheels thus driven   
would either slip altogether1 and       
produce no advance of the carriage1 or  
that a considerable portion of the      
impelling power would be lost by the    
partial slipping or sliding of the      
wheels4 ,it is singular that it should  
never have occurred to the many         
ingenious persons who for several years 

were engaged in such experiments and    
speculations1 to ascertain by experiment
 the actual amount of adhesion in any   
particular case between the wheels and  
the road4 ,had they done so1 we should  
probably now have found locomotive      
engines in a more advanced state than   
that to which they have attained4  ,to  
remedy this imaginary difficulty1       
,messrs4 ,trevethick and ,vivian        
proposed to make the external rims of   
the wheels rough and uneven1 by         
surrounding them with projecting heads  
of nails or bolts1 or by cutting        
transverse grooves on them4 ,they       
proposed1 in cases where considerable   
elevations were to be ascended1 to cause
 claws or nails to project from the     
surface during the ascent1 so as to take
 hold of the road4 ,pg#ccg  ,in seven   
years after the construction of the     
first locomotive engine by these        
engineers1 another locomotive engine was
 constructed by ,mr4 ,blinkensop1 of    
,middleton ,colliery1 near ,leeds4 ,he  

obtained a patent1 in #ahaa1 for the    
application of a rack-rail4 ,the        
railroad thus1 instead of being composed
 of smooth bars of iron1 presented a    
line of projecting teeth1 like those of 
a cog-wheel1 which stretched along the  
entire distance to be travelled4 ,the   
wheels on which the engine rolled were  
furnished with corresponding teeth1     
which worked in the teeth of the        
railroad1 and1 in this way1 produced a  
progressive motion in the carriage4     
,the next contrivance for overcoming    
this fictitious difficulty1 was that of 
,messrs4 ,chapman1 who1 in the year     
#ahab1 obtained a patent for working a  
locomotive engine by a chain extending  
along the middle of the line of         
railroad1 from the one end to the other4
 ,this chain was passed once round a    
grooved wheel under the centre of the   
carriage2 so that1 when this grooved    
wheel was turned by the engine1 the     
chain being incapable of slipping upon  
it1 the carriage was consequently       

advanced on the road4 ,in order to      
prevent the strain from acting on the   
whole length of the chain1 its links    
were made to fall upon upright forks    
placed at certain intervals1 which      
between those intervals sustained the   
tension of the chain produced by the    
engine4 ,friction-rollers were used to  
press the chain into the groove of the  
wheel1 so as to prevent it from         
slipping4 ,this contrivance was soon    
abandoned1 for the very obvious reason  
that a prodigious loss of force was     
incurred by the friction of the chain4  
,the following year1 #ahac1 produced a  
contrivance of singular ingenuity1 for  
overcoming the supposed difficulty      
arising from the want of adhesion       
between the wheels and the road4 ,this  
was no other than a pair of mechanical  
legs and feet1 which were made to walk  
and propel in a manner somewhat         
resembling the feet of an animal4       
,illustration3 ,fig4 #hf4  ,a sketch of 
these propellers is given in fig4 #hf4  

,a is the carriage moving on the        
railroad1 ,l and ,l are the legs1 ,f and
 ,f the feet4 ,the foot ,f has a joint  
at ,o1 which corresponds to the ankle2  
another joint is placed at ,k1 which    
corresponds to the knee2 and a third is 
placed at ,l1 which corresponds to      
,pg#cch the hip4 ,similar joints are    
placed at the corresponding letters in  
the other leg4 ,the knee-joint ,k is    
attached to the end of the piston of the
 cylinder4 ,when the piston1 which is   
horizontal1 is pressed outwards1 the leg
 ,l presses the foot ,f against the     
ground1 and the resistance forces the   
carriage ,a onwards4 ,as the carriage   
proceeds1 the angle ,k at the knee      
becomes larger1 so that the leg and     
thigh take a straighter position2 and   
this continues until the piston has     
reached the end of its stroke4 ,at the  
hip ,l there is a short lever ,l ,m1 the
 extremity of which is connected by a   
cord or chain with a point ,s1 placed   
near the shin of the leg4 ,when the     

piston is pressed into the cylinder1 the
 knee ,k is drawn towards the engine1   
and the cord ,m ,s is made to lift the  
foot ,f from the ground2 to which it    
does not return until the piston has    
arrived at the extremity of the         
cylinder4 ,on the piston being again    
driven out of the cylinder1 the foot ,f1
 being placed on the road1 is pressed   
backwards by the force of the piston-rod
 at ,k2 but the friction of the ground  
preventing its backward motion1 the     
re-action causes the engine to advance3 
and in the same manner this process is  
continued4  ,attached to the thigh at   
,n1 above the knee1 by a joint1 is a    
horizontal rod ,n ,r1 which works a rack
 ,r4 ,this rack has beneath it a        
cog-wheel4 ,this cog-wheel acts in      
another rack below it4 ,by these means1 
when the knee ,k is driven from the     
engine1 the rack ,r is moved backwards2 
but the cog-wheel acting on the other   
rack beneath it1 will move the latter in
 the contrary direction4 ,the rack ,r   

being then moved in the ,pg#cci same    
direction with the knee ,k1 it follows  
that the other rack will always be moved
 in a contrary direction4 ,the lower    
rack is connected by another horizontal 
rod with the thigh of the leg ,l ,f1    
immediately above the knee at ,n4 ,when 
the piston is forced inwards1 the knee  
,k will thus be forced backwards2 and   
when the piston is forced outwards1 the 
knee ,k will be drawn forwards4 ,it     
therefore follows1 that the two knees ,k
 and ,k are pressed alternately         
backwards and forwards4 ,the foot ,f1   
when the knee ,k is drawn forward1 is   
lifted by the means already described   
for the foot ,f4  ,it will be apparent1 
from this description1 that the piece of
 mechanism here exhibited is a          
contrivance derived from the motion of  
the legs of an animal1 and resembling in
 all respects the fore legs of a horse4 
,it is however to be regarded rather as 
a specimen of great ingenuity than as a 
contrivance of practical utility4       

7#ahf47 ,it was about this period that  
the important fact was first ascertained
 that the adhesion or friction of the   
wheels with the rails on which they     
moved was amply sufficient to propel the
 engine1 even when dragging after it a  
load of great weight2 and that in such  
case1 the progressive motion would be   
effected without any slipping of the    
wheels4 ,the consequence of this fact   
rendered totally useless all the        
contrivances for giving wheels a        
purchase on the road1 such as racks1    
chains1 feet1 c4 ,the experiment by     
which this was determined appears to    
have been first tried on the ,wylam     
railroad2 where it was proved1 that when
 the road was level1 and the rails      
clean1 the adhesion of the wheels was   
sufficient1 in all kinds of weather1 to 
propel considerable loads4 ,by manual   
labour it was first ascertained how much
 weight the wheels of a common carriage 
would overcome without slipping round on
 the rail1 and having found the         

proportion which that bore to the       
weight1 they then ascertained that the  
weight of the engine would produce      
sufficient adhesion to drag after it on 
the railroad the requisite number of    
waggons4#ca  ,in #ahad1 an engine was   
constructed at ,killingworth1 by ,mr4   
,stephenson1 having two cylinders with a
 cylindrical ,pg#cdj boiler1 and working
 two pair of wheels1 by cranks placed at
 right angles2 so that when the one was 
in full operation1 the other was at its 
dead points4 ,by these means the        
propelling power was always in action4  
,the cranks were maintained in this     
position by an endless chain1 which     
passed round two cogged wheels placed   
under the engine1 and which were fixed  
on the same axles on which the wheels   
were placed4 ,the wheels in this case   
were fixed on the axles1 and turned with
 them4  ,illustration3 ,fig4 #hg4  ,this
 engine is represented in fig4 #hg41 the
 sides being open1 to render the        
interior mechanism visible4 ,a ,b is the

 cylindrical boiler2 ,c ,c are the      
working cylinders2 ,d ,e are the cogged 
wheels fixed on the axle of the wheels  
of the engine1 and surrounded by the    
endless chain4 ,these wheels being equal
 in magnitude1 perform their revolutions
 in the same time2 so that1 when the    
crank ,f descends to the lowest point1  
the crank ,g rises from the lowest point
 to the horizontal position ,d2 and1    
again1 when the crank ,f rises from the 
lowest point to the horizontal position 
,e1 the other crank rises to the highest
 point2 and so on4 ,a very beautiful    
contrivance was adopted in this engine1 
by which it was suspended on springs of 
steam4 ,small cylinders1 represented at 
,h1 are screwed by flanges to one side  
of the boiler1 and project within it a  
few inches2 they have free communication
 at the top with the water or steam of  
the boiler4 ,solid pistons are          
represented at ,i1 which move           
steam-tight in these ,pg#cda cylinders2 
the cylinders are open at the bottom1   

and the piston-rods are screwed on the  
carriage of the engine1 over the axle of
 each pair of wheels1 the pistons being 
presented upwards4 ,as the engine is    
represented in the figure1 it is        
supported on four pistons1 two at each  
side4 ,the pistons are pressed upon by  
the water or steam which occupies the   
upper chamber of the cylinder2 and the  
latter being elastic in a high degree1  
the engine has all the advantage of     
spring suspension4 ,the defect of this  
method of supporting the engine is1 that
 when the steam loses that amount of    
elasticity necessary for the support of 
the machine1 the pistons are forced into
 the cylinders1 and the bottoms of the  
cylinders bear upon them4 ,all spring   
suspension is then lost4 ,this mode of  
suspension has consequently since been  
laid aside4  ,in an engine subsequently 
constructed by ,mr4 ,stephenson1 for the
 ,killingworth railroad1 the mode       
adopted of connecting the wheels by an  
endless chain and cog-wheels was        

abandoned2 and the same effect was      
produced by connecting the two cranks by
 a straight rod4 ,all such contrivances1
 however1 have this great defect1 that1 
if the fore and hind wheels be not      
constructed with dimensions accurately  
equal1 there must necessarily be a      
slipping or dragging on the road4 ,the  
nature of the machinery requires that   
each wheel should perform its revolution
 exactly in the same time2 and          
consequently1 in doing so1 must pass    
over exactly equal lengths of the road4 
,if1 therefore1 the circumference of the
 wheels be not accurately equal1 that   
wheel which has the lesser circumference
 must be dragged along so much of the   
road as that by which it falls short of 
the circumference of the greater wheel2 
or1 on the other hand1 the greater wheel
 must be dragged in the opposite        
direction1 to compensate for the same   
difference4 ,as no mechanism can        
accomplish a perfect equality in four1  
much less in six1 wheels1 it may be     

assumed that a great portion of that    
dragging effect is a necessary          
consequence of the principle of this    
machine2 and even were the wheels1 in   
the first instance1 accurately          
constructed1 it is not possible that    
their wear could be so exactly uniform  
as to continue equal4   7#ahg47 ,the    
next stimulus which the progress of this
 ,pg#cdb invention received1 proceeded  
from the great national work undertaken 
at ,liverpool1 by which that town and   
the extensive commercial mart of        
,manchester were connected by a double  
line of railway4 ,when this project was 
undertaken1 it was not decided what     
moving power it might be most expedient 
to adopt as a means of transport on the 
proposed road3 the choice lay between   
horse power1 fixed steam engines1 and   
locomotive engines2 but the first1 for  
many obvious reasons1 was at once       
rejected in favour of one or other of   
the last two4  ,the steam engine may be 
applied1 by two distinct methods1 to    

move waggons either on a turnpike road  
or on a railway4 ,by the one method the 
steam engine is fixed1 and draws the    
carriage or train of carriages towards  
it by a chain extending the whole length
 of road on which the engine works4 ,by 
this method the line of road over which 
the transport is conducted is divided   
into a number of short intervals1 at the
 extremity of each of which an engine is
 placed4 ,the waggons or carriages1 when
 drawn by any engine to its own station1
 are detached1 and connected with the   
extremity of the chain worked by the    
next stationary engine2 and thus the    
journey is performed1 from station to   
station1 by separate engines4 ,by the   
other method the same engine draws the  
load the whole journey1 travelling with 
it4  ,the ,directors of the ,liverpool  
and ,manchester railroad1 when that work
 was advanced towards its completion1   
employed1 in the spring of the year     
#ahbi1 ,messrs4 ,stephenson and ,lock1  
and ,messrs4 ,walker and ,rastrick1     

experienced engineers1 to visit the     
different railways1 where practical     
information respecting the comparative  
effects of stationary and locomotive    
engines was likely to be obtained2 and  
from these gentlemen they received      
reports on the relative merits1         
according to their judgment of the two  
methods4 ,the particulars of their      
calculations are given at large in the  
valuable work of ,mr4 ,nicholas ,wood on
 railways2 to which we refer the reader1
 not only on this1 but on many other    
subjects connected with the locomotive  
steam engine1 into which it would be    
foreign to our object to enter4 ,the    
result of the comparison of the two     
systems was1 that the capital ,pg#cdc   
necessary to be advanced to establish a 
line of stationary engines was          
considerably greater than that which was
 necessary to establish an equivalent   
power in locomotive engines2 that the   
annual expense by the stationary engines
 was likewise greater2 and that1        

consequently1 the expense of transport  
by the latter was greater1 in a like    
proportion4 ,the subjoined table        
exhibits the results numerically3--     
----------------------------------------
----------------------------------------
----------------------------------------
----------                              
,expense of                             
taking a                                
,annual       ,ton of ,goods            
,capital4      ,expense4        a ,mile4
                                        
----------------------------------------
----------------------------------------
----------------------------------------
-                              s4  d4   
s4  d4   ,locomotive engines   #eh1jjj  
#j  #j  #be1eag   #h  #b   #jafd penny  
,stationary engines  #aba1dif  #g  #j   
#db1jca  #af  #e   #jbfi                
----------------------------------------
----------------------------------------
----   ,locomotive system               
less      #fc1dif  #g  #j  #af1ead   #h 

#c   #jaje                              
----------------------------------------
----------------------------------------
----------------------------------------
-  ,on the score of economy1 therefore1 
the system of locomotive engines was    
entitled to a preference2 but there were
 other considerations which conspired   
with this to decide the choice of the   
,directors in its favour4 ,an accident  
occurring in any part of a road worked  
by stationary engines must necessarily  
produce a total suspension of work along
 the entire line4 ,the most vigilant and
 active attention on the part of every  
workman1 however employed1 in every part
 of the line1 would therefore be        
necessary2 but1 independently of this1  
accidents arising from the fracture or  
derangement of any of the chains1 or    
from the suspension of the working of   
any of the fixed engines1 would be      
equally injurious1 and would effectually
 stop the intercourse along the line4   
,on the other hand1 in locomotive       

engines an accident could only affect   
the particular train of carriages drawn 
by the engine to which the accident     
might occur2 and even then the          
difficulty could be remedied by having a
 supply of spare engines at convenient  
stations along the line4 ,it is true    
that the probability of accident is1    
perhaps1 less in the stationary than in 
the locomotive system2 but the injurious
 consequences1 when accident does       
happen1 are prodigiously greater in the 
former4 ,the one system1 says ,mr4      
,walker1 is like a chain extending from 
,liverpool to ,manchester1 the failure  
,pg#cdd of a single link of which would 
destroy the whole2 while the other is   
like a number of short and unconnected  
chains1 the destruction of any one of   
which does not interfere with the effect
 of the others1 and the loss of which   
may be supplied with facility4  ,the    
decision of the ,directors was1         
therefore1 in favour of locomotive      
engines2 and their next measure was to  

devise some means by which the inventive
 genius of the country might be         
stimulated to supply them with the best 
possible form of engines for this       
purpose4 ,with this view1 it was        
proposed and carried into effect to     
offer a prize for the best locomotive   
engine which might be produced under    
certain proposed conditions1 and to     
appoint a time for a public trial of the
 claims of the candidates4 ,a premium of
 five hundred pounds was accordingly    
offered for the best locomotive engine  
to run on the ,liverpool and ,manchester
 railway2 under the condition that it   
should produce no smoke2 that the       
pressure of the steam should be limited 
to fifty pounds on the inch2 and that it
 should draw at least three times its   
own weight1 at the rate of not less than
 ten miles an hour2 that the engine     
should be supported on springs1 and     
should not exceed fifteen feet in       
height4 ,precautions were also proposed 
against the consequences of the boiler  

bursting2 and other matters not         
necessary to mention more particularly  
here4 ,this proposal was announced in   
the spring of #ahbi1 and the time of    
trial was appointed in the following    
,october4 ,the engines which underwent  
the trial were1 the ,rocket1 constructed
 by ,mr4 ,stephenson2 the ,sanspareil1  
by ,hackworth2 and the ,novelty1 by     
,messrs4 ,braithwaite and ,ericson4 ,of 
these1 the ,rocket obtained the premium4
 ,a line of railway was selected for the
 trial1 on a level piece of road about  
two miles in length1 near a place called
 ,rainhill1 between ,liverpool and      
,manchester2 the distance between the   
two stations was a mile and a half1 and 
the engine had to travel this distance  
backwards and forwards ten times1 which 
made altogether a journey of thirty     
miles4 ,the ,rocket performed this      
journey twice3 the first time in #b     
hours #ad minutes and #h seconds2 and   
the second time in #b hours #f minutes  
and #di seconds4 ,its speed at different

 parts of the journey varied3 its       
greatest rate of motion was ,pg#cde     
rather above #bi miles an hour2 and its 
least1 about #aa-a_/b miles an hour4    
,the average rate of the one journey was
 #ac-d_/aj miles an hour2 and of the    
other1 #ad-b_/bj miles4 ,this was the   
only engine which performed the complete
 journey proposed1 the others having    
been stopped from accidents which       
occurred to them in the experiment4 ,the
 ,sanspareil performed the distance     
between the stations eight times1       
travelling #bb-a_/b miles in #a hour #cg
 minutes and #af seconds4 ,the greatest 
velocity to which this engine attained  
was something less than #bc miles per   
hour4 ,the ,novelty had only passed     
twice between the stations when the     
joints of the boiler gave way1 and put  
an end to the experiment4   7#ahh47 ,the
 great object to be attained in the     
construction of these engines was1 to   
combine with sufficient lightness the   
greatest possible heating power4 ,the   

fire necessarily acts on the water in   
two ways3 first1 by its radiant heat2   
and second1 by the current of heated air
 which is carried by the draught through
 the flues1 and finally passes into the 
chimney4 ,to accomplish this object1    
therefore1 it is necessary to expose to 
both these sources of heat the greatest 
possible quantity of surface in contact 
with the water4 ,these ends were        
attained by the following admirable     
arrangement in the ,rocket3--           
,illustration3 ,fig4 #hh4               
,illustration3 ,fig4 #hi4  ,this engine 
is represented in fig4 #hh4 ,it is      
supported on four wheels2 the principal 
part of the weight being thrown on one  
pair1 which are worked by the engine4   
,the boiler consists of a cylinder six  
feet in length1 with flat ends2 the     
chimney issues from one end1 and to the 
other end is attached a square box ,b1  
the bottom of which is furnished with   
the grate on which the fuel is placed4  
,this box is composed of two casings of 

iron1 one contained within the other1   
having between them a space about three 
inches in breadth2 the magnitude of the 
box being three feet in length1 two feet
 in width1 and three feet in depth4 ,the
 casing which surrounds the box         
communicates with the lower part of the 
boiler by a pipe marked ,c2 and the same
 casing at the top of the box           
communicates with the upper part of the 
boiler by another pipe marked ,d4 ,when 
water is admitted into the boiler1      
therefore1 it flows freely1 through the 
pipe ,c1 into the casing which ,pg#cdf  
surrounds the furnace or fire-box1 and  
fills this casing to the same level as  
that which it has in the boiler4 ,when  
the engine is at work1 the boiler is    
kept about half filled with water2 and1 
consequently1 the casing surrounding the
 furnace is completely filled4 ,the     
steam which is generated in the water   
contained in the casing finds its exit  
through the pipe ,d1 and escapes into   
the upper part of the boiler4 ,a section

 of the engine1 taken at right angles to
 its length1 is represented at fig4 #hi4
 ,through the lower part of the boiler  
pass a number of copper tubes of small  
size1 which communicate at one end with 
the fire-box1 and at the other with the 
chimney1 and form a passage for the     
heated air from the furnace to the      
chimney4 ,the ignited fuel spread on the
 grate at the bottom of the fire-box    
disperses its heat by radiation1 and    
acts in this manner on the whole surface
 of the casing surrounding the fire-box2
 and thus raises the temperature of the 
thin shell of water contained in that   
casing4 ,the chief ,pg#cdg part of the  
water in the casing1 being lower in its 
position than the water in the boiler1  
acquires a tendency to ascend when      
heated1 and passes into the boiler2 so  
that a constant circulation of the      
heated water is maintained1 and the     
water in the boiler must necessarily be 
kept at nearly the same temperature as  
the water in the casing4 ,the air which 

passes through the burning fuel1 and    
which fills the fire-box1 is carried by 
the draught through the tubes which     
extend through the lower part of the    
boiler2 and as these tubes are          
surrounded on every side with the water 
contained in the boiler1 this air       
transmits its heat through these tubes  
to the water4 ,it finally issues into   
the chimney1 and rises by the draught4  
,the power of this furnace must         
necessarily depend on the power of      
draught in the chimney2 and to increase 
this1 and at the same time to dispose of
 the waste steam after it has worked the
 piston1 this steam is carried off by a 
pipe ,l1 which passes from the cylinder 
to the chimney1 and escapes there in a  
jet which is turned upwards4 ,by the    
velocity with which it issues from this 
jet1 and by its great comparative       
levity1 it produces a strong current    
upwards in the chimney1 and thus gives  
force to the draught of the furnace4 ,in
 fig4 #hi4 the grate-bars are           

represented at the bottom of the        
fire-box at ,f4 ,there are two          
cylinders1 one of which works each      
wheel2 one only appearing in the drawing
 fig4 #hh41 the other being concealed by
 the engine4 ,the spokes which these    
cylinders work are placed at right      
angles on the wheels2 the wheels being  
fixed on a common axle1 with which they 
turn4  ,in this engine1 the surface of  
water surrounding the fire-box1 exposed 
to the action of radiant heat1 amounted 
to twenty square feet1 which received   
heat from the surface of six square feet
 of burning fuel on the bars4 ,the      
surface exposed to the action of the    
heated air amounted to #aah square feet4
 ,the engine drew after it another      
carriage1 containing fuel and water2 the
 fuel used was coke1 for the purpose of 
avoiding the production of smoke4       
7#ahi47 ,the ,sanspareil of ,mr4        
,hackworth is represented in fig4 #ij42 
the horizontal section being exhibited  
in fig4 #ia4  ,illustration3 ,fig4 #ij4 

,illustration3 ,fig4 #ia4  ,the draught 
of the furnace is produced in the same  
manner as in the ,rocket1 by ejecting   
the waste steam coming from ,pg#cdh the 
cylinder into the chimney2 the boiler1  
however1 differs considerably from that 
of the ,rocket4 ,a recurved tube passes 
through the boiler1 somewhat similar to 
that already described in the early     
engine of ,messrs4 ,trevethick and      
,vivian4 ,in the horizontal section     
7fig4 #ia471 ,d expresses the opening of
 the furnace at the end of the boiler1  
beside the chimney4 ,the grate-bars     
appear at ,a1 supporting the burning    
fuel2 and a curved tube passing through 
the boiler1 and terminating in the      
chimney1 is expressed at ,b1 the        
direction ,pg#cdi of the draught being  
indicated by the arrow2 ,c is a section 
of the chimney4 ,the cylinders are      
placed1 as in the ,rocket1 on each side 
of the boiler2 each working a separate  
wheel1 but acting on spokes placed at   
right angles to each other4 ,the tube in

 which the grate and flue are placed    
diminishes in diameter as it approaches 
the chimney4 ,at the mouth where the    
grate was placed1 its diameter was two  
feet2 and it was gradually reduced1 so  
that1 at the chimney1 its diameter was  
only fifteen inches4 ,the grate-bars    
extended five feet into the tube4 ,the  
surface of water exposed to the radiant 
heat of the fire was sixteen square     
feet2 and that exposed to the action of 
the heated air and flame was about      
seventy-five square feet4 ,the magnitude
 of the grate1 or sheet of burning fuel 
which radiated heat1 was ten square     
feet4   7#aij47 ,the ,novelty1 of       
,messrs4 ,braithwaite and ,ericson1 is  
represented in fig4 #ib42 and a section 
of the generator and boiler is exhibited
 in fig4 #ic42 the corresponding parts  
in the two figures are marked by the    
same letters4  ,illustration3 ,fig4 #ib4
  ,a is the generator or receiver       
containing the steam which works the    
engine2 this communicates with a lower  

generator ,b1 which extends in a        
horizontal direction the entire length  
of the carriage4 ,within the generator  
,a is contained the furnace ,f1 which   
communicates in a tube ,c1 carried up   
through the generator1 and terminated at
 the top by sliding shutters1 which     
exclude the air1 and which are only     
opened to supply fuel to the grate ,f4  
,below the grate the furnace is not     
open1 as usual1 to the atmosphere1 but  
communicates1 ,pg#cej by a tube ,e1 with
 a bellows ,d2 which is worked by the   
engine1 and which forces a constant     
stream of air1 by the tube ,e1 through  
the fuel on ,f1 so as to keep that fuel 
in vivid combustion4 ,the heated air    
contained in the furnace ,f is driven   
on1 by the same force1 through a small  
curved tube marked e1 which circulates  
like a worm 7as represented in fig4     
#ic47 through the horizontal generator  
or receiver2 and1 tapering gradually1   
until reduced to very small dimensions1 
it finally issues into the chimney ,g4  

,the air in passing along this tube1    
imparts its heat to the water by which  
the tube is surrounded1 and is brought  
to a considerably reduced temperature   
when discharged into the chimney4 ,the  
cylinder1 which is represented at ,k1   
works one pair of wheels1 by means of a 
bell-crank1 the other pair1 when        
necessary1 being connected with them4   
,illustration3 ,fig4 #ic4  ,in this     
engine1 the magnitude of the surface of 
burning fuel on the grate-bars is less  
than two square feet2 the surface       
exposed to radiant heat is nine and a   
half square feet2 and the surface of    
water exposed to heated air is about    
thirty-three square feet4  ,the         
superiority of the ,rocket may be       
attributed chiefly to the greater       
quantity of surface of the water which  
is exposed to the action of the fire4   
,with a less extent of grate-bars than  
the ,sanspareil1 in the proportion of   
three to five1 it exposes a greater     
surface of water to radiant heat1 in the

 proportion of four to three2 and a     
greater surface of water to heated air1 
in the proportion of more than three to 
two4 ,it was found that the ,rocket1    
compared with the ,sanspareil1 consumed 
fuel1 in the evaporation of a given     
quantity of water1 ,pg#cea in the       
proportion of eleven to twenty-eight4   
,the suggestion of using the tubes to   
conduct through the water the heated air
 to the chimney is due to ,mr4 ,booth1  
treasurer of the ,liverpool and         
,manchester ,railway ,company4   7#aia47
 ,the object to be effected in the      
boilers of these engines is1 to keep a  
small quantity of water at an excessive 
temperature1 by means of a small        
quantity of fuel kept in the most active
 state of combustion4 ,to accomplish    
this1 it is necessary1 first1 so to     
shape the boiler1 furnace1 and flues1   
that the water shall be in contact with 
as extensive a surface as possible1     
every part of which is acted on1 either 
immediately1 by the heat radiating from 

the fire1 or mediately1 by the air which
 has passed through the fire1 and which 
finally rushes into the chimney3 and1   
secondly1 that such a forcible draught  
should be maintained in the furnace1    
that a quantity of heat shall be        
extricated from the fuel1 by combustion1
 sufficient to maintain the water at the
 necessary temperature1 and to produce  
the steam with sufficient rapidity4 ,to 
accomplish these objects1 therefore1 the
 chamber containing the grate should be 
completely surrounded by water1 and     
should be below the level of the water  
in the boiler4 ,the magnitude of the    
surface exposed to radiation should be  
as great as is consistent with the whole
 magnitude of the machine4 ,the         
comparative advantage which the ,rocket 
possessed in these respects over the    
other engines will be evident on        
inspection4 ,in the next place1 it is   
necessary that the heat1 which is       
absorbed by the air passing through the 
fuel1 and keeping it in a state of      

combustion1 should be transferred to the
 water before the air escapes into the  
chimney4 ,air being a bad conductor of  
heat1 to accomplish this it is necessary
 that the air in the flues should be    
exposed to as great an extent of surface
 in contact with the water as possible4 
,no contrivance can be less adapted for 
the attainment of this end than one or  
two large tubes traversing the boiler1  
as in the earliest locomotive engines3  
the body of air which passed through the
 centre of these tubes had no contact   
with their surface1 and1 consequently1  
passed into the chimney at nearly the   
same temperature as that which it had   
when it quitted the fire4 ,the only     
portion of air which imparted its heat  
to the water ,pg#ceb was that portion   
which passed next to the surface of the 
tube4  ,several methods suggest         
themselves to increase the surface of   
water in contact with a given quantity  
of air passing through it4 ,this would  
be accomplished by causing the air to   

pass between plates placed near each    
other1 so as to divide the current into 
thin strata1 having between them strata 
of water1 or it might be made to pass   
between tubes differing slightly in     
diameter1 the water passing through an  
inner tube1 and being also in contact   
with the external surface of the outer  
tube4 ,such a method would be similar in
 principle to the steam-jacket used in  
,watt's steam engines1 or to the        
condenser of ,cartwright's engine       
already described4 ,but1 considering the
 facility of constructing small tubes1  
and of placing them in the boiler1 that 
method1 perhaps1 is1 on the whole1 the  
best in practice2 although the shape of 
a tube1 geometrically considered1 is    
most unfavourable for the exposure of a 
fluid contained in it to its surface4   
,the air which passes from the          
fire-chamber1 being subdivided as it    
passes through the boiler by a great    
number of very small tubes1 may be made 
to impart all its excess of heat to the 

water before it issues into the chimney4
 ,this is all which the most refined    
contrivance can effect4 ,the ,rocket    
engine was traversed by twenty-five     
tubes1 each three inches in diameter2   
and the principle has since been carried
 to a much greater extent4  ,the        
abstraction of a great quantity of heat 
from the air before it reaches the      
chimney is attended with one            
consequence1 which1 at first view1 would
 present a difficulty apparently        
insurmountable2 the chimney would1 in   
fact1 lose its power of draught4 ,this  
difficulty1 however1 was removed by     
using the waste steam1 which had passed 
from the cylinder after working the     
engine1 for the purpose of producing a  
draught4 ,this steam was urged through a
 jet presented upwards in the chimney1  
and driven out with such force in that  
direction as to create a sufficient     
draught to work the furnace4  ,it will  
be observed that the principle of       
draught in the ,novelty is totally      

distinct from this3 in that engine the  
draught is produced by a bellows worked 
by the engine4 ,the question1 as far as 
relates to these two methods1 is1       
whether more power ,pg#cec is lost in   
supplying the steam through the jet1 as 
in the ,rocket1 or in working the       
bellows1 as in the ,novelty4 ,the force 
requisite to impel the steam through the
 jet must be exerted by the returning   
stroke of the piston1 and1 consequently1
 must rob the working effect to an      
equivalent amount4 ,on the other hand1  
the power requisite to work the bellows 
in the ,novelty must be subducted from  
the available power of the engine4 ,the 
former method has been hitherto found to
 be the more effectual and economical4  
,the importance of these details will be
 understood1 when it is considered that 
the only limit to the attainment of     
speed by locomotive engines is the power
 to produce1 in a given time1 a certain 
quantity of steam4 ,each stroke of the  
piston causes one revolution of the     

wheels1 and consumes four cylinders full
 of steam3 consequently1 a cylinder of  
steam corresponds to a certain number of
 feet of road travelled over3 hence it  
is that the production of a rapid and   
abundant supply of heat1 and the        
imparting of that heat quickly and      
effectually to the water1 is the key to 
the solution of the problem to construct
 an engine capable of rapid motion4     
,the method of subdividing the flue into
 tubes was carried much further by ,mr4 
,stephenson after the construction of   
the ,rocket2 and1 indeed1 the principle 
was so obvious1 it is only surprising   
that1 in the first instance1 tubes of   
smaller diameter than three inches were 
not used4 ,in engines since constructed1
 the number of tubes vary from ninety to
 one hundred and twenty1 the diameter   
being reduced to two inches or less2 and
 in some instances tubes have been      
introduced1 even to the number of one   
hundred and fifty1 of one and a half    
inch diameter4 ,in the ,meteor1 twenty  

square feet are exposed to radiation1   
and one hundred and thirty-nine to the  
contact of heated air2 in the ,arrow1   
twenty square feet to radiation1 and one
 hundred and forty-five to the contact  
of heated air4 ,the superior economy of 
fuel gained by this means will be       
apparent by inspecting the following    
table1 which exhibits the consumption of
 fuel which was requisite to convey a   
ton weight a mile in each of four       
engines1 expressing also the rate of the
 motion3-- ,pg#ced                      
----------------------------------------
----------------------------------------
----------------------------------------
                       ,average ,rate of
    ,consumption of ,coke               
,engines4     ,speed in ,miles per   in 
,pounds per ,ton                        
,hour4               per ,mile4         
----------------------------------------
----------------------------------------
----------------------------------------
   ,no4 #a4 ,rocket             #ad     

#bda       #b4 ,sanspareil         #ae  
#bdg       #c4 ,phnix             #ab   
#adb       #d4 ,arrow              #ab  
#abe                                    
----------------------------------------
----------------------------------------
----------------------------------------
  7#aib47 ,since the period at which    
this railway was opened for the actual  
purposes of transport1 the locomotive   
engines have been in a state of         
progressive improvement4 ,scarcely a    
month has passed without suggesting some
 change in the details1 by which fuel   
might be economised1 the production of  
steam rendered more rapid1 the wear of  
the engine rendered slower1 the         
proportionate strength of the different 
parts improved1 or some other desirable 
end obtained4  ,engines constructed in  
the form of the ,rocket1 were subject to
 two principal defects4 ,the cylinders1 
being placed outside the engine1 were   
exposed to the cold of the atmosphere1  
which produced a waste of heat more or  

less considerable by condensation4 ,the 
points at which the power of the steam  
to turn the wheels was applied1 being at
 the extremities of the axle and on the 
exterior of the wheel1 a considerable   
strain was produced1 owing to the       
distance of the point of application of 
the power from the centre of resistance4
 ,if it were possible that the impelling
 power could act in drawing the train at
 all times with equal energy on both    
sides of the engine1 then no injurious  
strain would be produced2 but from the  
relative position of the points on the  
opposite wheels to which it was         
necessary to attach the connecting rods1
 it was inevitable that1 at the moment  
when one of the pistons exerts its full 
power in driving the wheel1 the other   
piston must be altogether inactive4 ,the
 impelling power1 therefore1 at         
alternate moments of time1 acted on     
opposite wheels1 and on each of them at 
the greatest possible distance from the 
centre of the axle4  ,illustration3     

,fig4 #id4   7#aic47 ,the next step in  
the improvement of the machine was made 
with a view to remove these two defects4
 ,the cylinders were transferred from   
the exterior of the engine to the       
,pg#cee interior of the casing called   
the smoke-box1 ,b1 fig4 #id41 which     
supports the chimney1 and which receives
 the heated air issuing from the tubes  
which traverse the boiler4 ,thus placed1
 the cylinders are always maintained as 
hot as the air which issues from the    
flues1 and all condensation of steam by 
their exposure is prevented4 ,the       
piston-rods are likewise brought closer 
together1 and nearer the centre of the  
engine3 the connecting rods1 no longer  
attached to the wheels1 are made to act 
upon two cranks constructed upon the    
axle of the wheels1 and placed at right 
angles to each other4 ,from the position
 of these cranks1 one would always be at
 its dead point when the other is in    
full action4 ,the action of the steam   
upon them would1 therefore1 be generally

 unequal2 but this would not produce the
 same strain as when the connecting rods
 are attached to points upon the        
exterior of the wheels1 owing to the    
cranks being constructed on the axle at 
points so much nearer its centre4 ,by   
this means it was found that the working
 of the machine was more even1 and      
productive of much less strain1 than in 
the arrangement adopted in the ,rocket1 
and the earlier engines4 ,on the other  
hand1 a serious disadvantage was        
incurred by a double-cranked axle4 ,the 
weakness necessarily arising from such a
 form of axle could only be removed by  
great thickness ,pg#cef and weight of   
metal2 and even this precaution1 at     
first1 did not prevent their occasional 
fracture4 ,the forging of them was1     
however1 subsequently much improved3 the
 cranks1 instead of being formed by     
bending the metal when softened by heat1
 were made by cutting the square of the 
crank out of the solid metal2 and now it
 rarely happens that one of these axles 

fails4  ,the adoption of smaller tubes1 
and a greater number of them1 with a    
view more perfectly to extract the heat 
from the air in passing to the chimney1 
rendered a more forcible draft          
necessary4 ,this was accomplished by the
 adoption of a more contracted          
blast-pipe leading from the             
eduction-pipes of the cylinders and     
presented up the chimney4 ,a            
representation of such a blast-pipe1    
with the two tubes leading from the     
cylinders and uniting together near the 
point1 which is presented up the        
chimney1 is given at p p in fig4 #ajd4  
,the engine thus improved is represented
 in fig4 #id4  ,a represents the        
cylindrical boiler1 the lower half of   
which is traversed by tubes1 as         
described in the ,rocket4 ,they are     
usually from eighty to one hundred in   
number1 and about an inch and a half in 
diameter2 the boiler is about seven feet
 in length2 the fire-chamber is attached
 to one end of it1 at ,f1 as in the     

,rocket1 and similar in construction3   
the cylinders are inserted in a chamber 
at the other end1 immediately under the 
chimney4 ,the piston-rods are supported 
in the horizontal position by guides2   
and connecting rods extend from them1   
under the engine1 to the two cranks     
placed on the axle of the large wheels4 
,the effects of an inequality in the    
road are counteracted by springs1 on    
which the engine rests2 the springs     
being below the axle of the great       
wheels1 and above that of the less4 ,the
 steam is supplied to the cylinders1 and
 withdrawn1 by means of the common      
sliding valves1 which are worked by an  
eccentric wheel placed on the axle of   
the large wheels of the carriage4 ,the  
motion is communicated from this        
eccentric wheel to the valve by sliding 
rods4 ,the stand is placed for the      
attendant at the end of the engine1 next
 the fire-place ,f2 and two levers ,l   
project from the end which communicate  
with the valves by means of rods1 by    

which the engine is governed so as to   
reverse the motion4 ,pg#ceg  ,the wheels
 of these engines have been commonly    
constructed of wood with strong iron    
ties1 furnished with flanges adapted to 
the rails4 ,but ,mr4 ,stephenson        
afterward substituted1 in some          
instances1 wheels of iron with hollow   
spokes4 ,the engine draws after it a    
tender carriage containing the fuel and 
water2 and1 when carrying a light load1 
is capable of performing the whole      
journey from ,liverpool to ,manchester  
without a fresh supply of water4 ,when a
 heavy load of merchandise is drawn1 it 
is usual to take in water at the middle 
of the trip4   7#aid47 ,in reviewing all
 that has been stated1 it will be       
perceived that the efficiency of the    
locomotive engines used on this railway 
is mainly owing to three circumstances3 
#ast1 ,the unlimited power of draft in  
the furnace1 by projecting the waste    
steam into the chimney2 #b;d1 ,the      
almost unlimited abstraction of heat    

from the air passing from the furnace1  
by arrangement of tubes traversing the  
boiler2 and1 #c;d1 ,keeping the         
cylinders warm1 by immersing them in the
 chamber under the chimney4 ,there are  
many minor details which might be       
noticed with approbation1 but these     
constitute the main features of the     
improvements4  ,the successive          
introduction of improvements in the     
engines1 some of which we have          
mentioned1 was accompanied by           
corresponding accessions to their       
practical power1 and to the economy of  
fuel4 ,in the spring of the year #ahcb1 
,i made several experiments on the      
,manchester ,railway1 with a view to    
determine1 in the actual state of the   
locomotive engines at that time1 their  
powers with respect to the amount of    
load and the economy of fuel1 from which
 ,i select the following as examples3-- 
,i4    ,on ,saturday1 the #eth of ,may1 
the engine called the ,victory   took   
#bj waggons of merchandise1 weighing    

gross #ib tons #ai cwt4   #a qr41       
together with the tender containing fuel
 and water1 of   the weight of which ,i 
have no account1 from ,liverpool to     
,manchester 7#cj miles71 in #a h4 #cd   
min4 #de sec4 ,the train   stopped to   
take in water half-way1 for #aj minutes1
 ,pg#ceh   not included in the          
above-mentioned time4 ,on the inclined  
plane rising #a in #if1 and extending   
#a-a_/b mile1 the engine was   assisted 
by another engine called the ,samson1   
and the ascent   was performed in #i    
minutes4 ,at starting1 the fire-place   
was   well filled with coke1 and the    
coke supplied to the tender   accurately
 weighed4 ,on arriving at ,manchester1  
the fire-place   was again filled1 and  
the coke remaining in the tender        
weighed4 ,the consumption was found to  
amount to #ibi pounds net   weight1     
being at the rate of one third of a     
pound per ton per   mile4    ,speed on  
the level was #ah miles an hour2 on a   
fall of #d feet   in a mile1 #ba-a_/b   

miles an hour2 fall of #f feet in a     
mile1   #be-a_/b miles an hour2 on the  
rise over ,chatmoss1 #h feet in a       
mile1 #ag-e_/h miles an hour2 on level  
ground sheltered from the   wind1 #bj   
miles an hour4 ,the wind was moderate1  
but direct   ahead4 ,the working wheels 
slipped three times on ,chatmoss1 and   
the train was retarded from #b to #c    
minutes4    ,the engine1 on this        
occasion1 was not examined before or    
after   the journey1 but was presumed to
 be in good working order4     ,,ii4    
,on ,tuesday1 the #hth of ,may1 the same
 engine performed the same   journey1   
with #bj waggons1 weighing gross #ij    
tons #g cwt4 #b   qrs41 exclusive of the
 unascertained weight of the tender4    
,the   time of the journey was #a h4 #da
 min4 ,the consumption of coke   #ajdj  
lbs4 net weight1 estimated as before4   
,rate of speed3--    ,level             
#ag-e_/h miles per hour4   ,fall of #d  
feet in a mile    #bb   ----      #f    
#bb-a_/b   ,rise of #h                  

#ae    ,on this occasion there was a    
high wind ahead on the quarter1   and   
the connecting rod worked hot1 owing to 
having been keyed   too tight4 ,on      
arriving at ,manchester1 ,i caused the  
cylinders   to be opened1 and found that
 the pistons were ,pg#cei so   loose1   
that the steam blew through the         
cylinders with great   violence4 ,by    
this cause1 therefore1 the machine was  
robbed of   a part of its power during  
the journey2 and this circumstance   may
 explain the slight decrease in speed1  
and increase in the   consumption of    
fuel1 with a lighter load1 in this      
journey1   compared with that performed 
on the #eth of ,may4    ,the ,victory   
weighs #h tons #b cwt41 of which #e tons
 #d cwt4 rest   on the drawing wheels4  
,the cylinders are #aa inches diameter1 
and #af inches stroke1 and the diameter 
of the drawing wheels   is #e feet4     
,,iii4    ,on the #bith of ,may1 the    
engine called the ,samson 7weighing     
#aj tons #b cwt41 with #ad-;inch        

cylinders1 and #af-;inch stroke2        
wheels #d feet #f inches diameter1 both 
pairs being worked by   the engine2     
steam #ej lbs4 pressure1 #acj tubes7 was
 attached to   #ej waggons1 laden with  
merchandise2 net weight about #aej tons2
   gross weight1 including waggons1 #bbc
 tons #f cwt4 ,the tender   weighed #g  
tons1 making a gross load 7including the
 engine7 of   #bdj tons #h cwt4 ,the    
engine with this load travelled from    
,liverpool to ,manchester 7#cj miles7 in
 #b hours and #dj min41   exclusive of  
delays upon the road for watering1 c42  
being at   the rate of nearly #ab miles 
an hour4 ,the speed varied   according  
to the inclinations of the road4 ,upon a
 level1 it   was #ab miles an hour2 upon
 a descent of #f feet in a mile1 it     
was #af miles an hour2 upon a rise of #h
 feet in a mile1 it was   about #i miles
 an hour4 ,the weather was calm1 the    
rails very   wet2 but the wheels did not
 slip1 even in the slowest speed1       
except at starting1 the rails being at  

that place soiled and   greasy with the 
slime and dirt to which they are always 
exposed at the stations4 ,the coke      
consumed in this journey1   exclusive of
 what was raised in getting up the      
steam1 was #agfb   lbs41 being at the   
rate of a quarter of a pound per ton per
   mile4   7#aie47 ,the great original  
cost1 and the heavy expense of keeping  
the engines used on the railway in      
repair1 have pressed severely on the    
resources of the undertaking4 ,one of   
the best ,pg#cfj constructed of the     
later engines costs originally #aejjl4  
and sometimes more4 ,the original cost1 
however1 is far from being the principal
 source of expense3 the wear and tear of
 these machines1 and the occasional     
fracture of those parts on which the    
greatest strain has been laid1 have     
greatly exceeded what the directors had 
anticipated4 ,although this source of   
expense must be in part attributed to   
the engines not having yet attained that
 state of perfection1 in the proportion 

and adjustment of their parts1 of which 
they are susceptible1 and to which      
experience alone can lead1 yet there are
 some obvious defects which demand      
attention4  ,the heads of the boilers   
are flat1 and formed of iron1 similar to
 the material of the boilers themselves4
 ,the tubes which traverse the boiler   
were1 until recently1 copper1 and so    
inserted into the flat head or end as to
 be water-tight4 ,when the boiler was   
heated1 the tubes were found to expand  
in a greater degree than the other parts
 of the boiler2 which frequently caused 
them either to be loosened at the       
extremities1 so as to cause leakage1 or 
to bend from want of room for expansion4
 ,the necessity of removing and         
refastening the tubes caused1 therefore1
 a constant expense4  ,it will be       
recollected that the fire-place is      
situated at one end of the boiler1      
immediately below the mouths of the     
tubes3 a powerful draft of air1 passing 
through the fire1 carries with it ashes 

and cinders1 which are driven violently 
through the tubes1 and especially the   
lower ones1 situated near the fuel4     
,these tubes are1 by this means1 subject
 to rapid wear1 the cinders continually 
acting upon their interior surface4     
,after a short time it becomes necessary
 to replace single tubes1 according as  
they are found to be worn1 by new ones2 
and it not unfrequently happens1 when   
this is neglected1 that tubes burst4    
,after a certain length of time the     
engines require new tubing4 ,this wear  
of the tubes might possibly be avoided  
by constructing the fire-place in a     
lower position1 so as to be more removed
 from their mouths2 or1 still more      
effectually1 by interposing a casing of 
metal1 which might be filled with water1
 between the fire-place and those tubes 
which are the most exposed to the       
cinders and ashes4 ,the unequal         
expansion of the tubes ,pg#cfa and      
boilers appears to be an incurable      
defect1 if the present form of the      

engine be retained4 ,if the fire-place  
and chimney could be placed at the same 
end of the boiler1 so that the tubes    
might be recurved1 the unequal expansion
 would then produce no injurious effect2
 but it would be difficult to clean the 
tubes1 if they were exposed1 as they are
 at present1 to the cinders4 ,the next  
source of expense arises from the wear  
of the boiler-heads1 which are exposed  
to the action of the fire4  ,a          
considerable improvement was            
subsequently introduced into the method 
of tubing1 by substituting brass for    
copper tubes4 ,i am not aware that the  
cause of this improvement has been      
discovered2 but it is certain1 whatever 
be the cause1 that brass tubes are      
subject to considerably slower wear than
 copper ones4   7#aif47 ,the expense of 
locomotive power having so far exceeded 
what was anticipated at the commencement
 of the undertaking1 it was thought     
advisable1 about the beginning of the   
year #ahcd1 to institute an inquiry into

 the causes which produced the          
discrepancy between the estimated and   
actual expenses1 with a view to the     
discovery of some practical means by    
which they could be reduced4 ,the       
directors of the company1 for this      
purpose1 appointed a sub-committee of   
their own body1 assisted by ,mr4 ,booth1
 their treasurer1 to inquire and report 
respecting the causes of the amount of  
this item of their expenditure1 and to  
ascertain whether any and what measures 
could be devised for the attainment of  
greater economy4 ,a very able and       
satisfactory report was made by this    
committee1 or1 to speak more correctly1 
by ,mr4 ,booth4  ,it appears that1      
previous to the establishment of the    
railway1 ,messrs4 ,walker and ,rastrick1
 engineers1 were employed by the company
 to visit various places where steam    
power was applied on railways1 for the  
purpose of forming an estimate of the   
probable comparative expense of working 
the railway by locomotive and by fixed  

power4 ,these engineers recommended the 
adoption of locomotive power2 and their 
estimate was1 that the transport might  
be effected at the rate of #bgh of a    
penny1 or very little more than a       
farthing per ton per mile4 ,in the year 
,pg#cfb #ahcc1 five years after this    
investigation took place1 it was found  
that the actual cost was #fbe of a      
penny1 or something more than a         
halfpenny1 per ton per mile1 being      
considerably above double the estimated 
rate4 ,mr4 ,booth very properly directed
 his inquiries to ascertain the cause of
 this discrepancy1 by comparing the     
various circumstances assumed by        
,messrs4 ,walker and ,rastrick1 in      
making their estimate1 with those under 
which the transport was actually        
effected4 ,the first point of difference
 which he observed was the speed of     
transport3 the estimate was founded on  
an assumed speed of ten miles an hour1  
and it was stated that a four-fold speed
 would require an addition of #ej per   

cent4 to the power1 without taking into 
account wear and tear4 ,now1 the actual 
speed of transport being double the     
speed assumed in the statement1 ,mr4    
,booth holds it to be necessary to add  
#be per cent4 on that score4  ,the next 
point of difference is in the amount of 
the loads3 the estimate is founded upon 
the assumption1 that every engine shall 
start with its full complement of load1 
and that with this it shall go the whole
 distance4 ,the facts1 however1 are1    
says ,mr4 ,booth1 that1 instead of a    
full load of profitable carriage from   
,manchester1 about half the waggons come
 back empty2 and1 instead of the tonnage
 being conveyed the whole way1 many     
thousand tons are conveyed only half the
 way2 also1 instead of the daily work   
being uniform1 it is extremely          
fluctuating4 ,it is further remarked1   
that in order to accomplish the         
transport of goods from the branches and
 from intermediate places1 engines are  
despatched several times a-day1 from    

both ends of the line1 to clear the     
road2 the object of this arrangement    
being rather to lay the foundation of a 
beneficial intercourse in future1 than  
with a view to any immediate profit4    
,mr4 ,booth makes a rough estimate of   
the disadvantages arising from these    
circumstances1 by stating them at #cc   
per cent4 in addition to the original   
estimate4  ,the next point of difference
 is the fuel4 ,in the original estimate1
 coal is assumed as the fuel1 and it is 
taken at the price of five shillings and
 ten-pence per ton3 now the act of      
parliament forbids the use of coal which
 would produce smoke2 the company have1 
therefore1 been obliged to use coke1 at 
,pg#cfc seventeen shillings and sixpence
 a ton4#cb ,taking coke1 then1 to be    
equivalent to coal1 ton for ton1 this   
would add #afb to the original estimate4
  ,these several discrepancies being    
allowed for1 and a proportional amount  
being added to the original estimate1   
the amount would be raised to #fja of a 

penny per ton per mile1 which is within 
one fortieth of a penny of the actual   
cost4 ,this difference is considered to 
be sufficiently accounted for by the    
wear and tear produced by the very rapid
 motion1 more especially when it is     
considered that many of the engines were
 constructed before the engineer was    
aware of the great speed that would be  
required4  ,what1 then1 says ,mr4       
,booth1 in the ,report already alluded  
to1 is the result of these opposite and 
mutually counteracting circumstances8   
and what is the present position of the 
company in respect of their moving      
power8 ,simply1 that they are still in a
 course of experiment1 to ascertain     
practically the best construction1 and  
the most durable materials1 for engines 
required to transport greater weights1  
and at greater velocities1 than had1    
till very recently1 been considered     
possible2 and which1 a few years ago1 it
 had not entered into the imagination of
 the most daring and sanguine inventor  

to conceive3 and farther1 that these    
experiments have necessarily been made1 
not with the calm deliberation and quiet
 pace which a salutary caution          
recommends1--making good each step in   
the progress of discovery before        
advancing another stage1--but amidst the
 bustle and responsibilities of a large 
and increasing traffic2 the directors   
being altogether ignorant of the time   
each engine would last before it would  
be laid up as inefficient1 but compelled
 to have engines1 whether good or bad2  
being aware of various defects and      
imperfections1 which it was impossible  
at the time to remedy1 yet obliged to   
keep the machines in motion1 under all  
the disadvantages of heavy repairs1     
constantly going on during the night1 in
 order that the requisite number of     
engines might be ready for the morning's
 work4 ,neither is this great experiment
 yet complete2 it is still going        
forward4 ,but the most prominent        
difficulties have been in a great       

measure surmounted1 ,pg#cfd and your    
committee conceive that they are        
warranted in expecting1 that the        
expenditure in this department will1 ere
 long1 be materially reduced1--more     
especially when they consider the       
relative performances of the engines at 
the present time1 compared with what it 
was two years ago4  ,in the half year   
ending #cast ,december1 #ahca1 the six  
best engines performed as follows3--    
,miles4   ,planet           #i1ihf      
,mercury         #aa1jdj   ,jupiter     
#aa1fah   ,saturn          #aa1ghf      
,venus           #ab1hej   ,etna        
#h1gfd                   ------------   
,making in all   #ff1jdd                
------------  ,in the half year ending  
#cast ,december1 #ahcc1 the six best    
engines performed as follows3--         
,miles4   ,jupiter          #af1egb     
,saturn           #ah1fgh   ,sun        
#ad1eeb   ,etna             #ag1gfc     
,ajax             #aa1fgh   ,firefly    
#ae1fjh                    ------------ 

,making in all    #ie1hea               
------------   7#aig47 ,since the date  
to which the preceding observations     
refer1 the locomotive engine has        
undergone several improvements in detail
 of considerable importance2 among      
which1 the addition of a third pair of  
wheels deserves to be particularly      
mentioned4 ,an engine supported on three
 pair of wheels has great security in   
the event of the fracture of any one of 
the axles1--the remaining axles and     
wheels being sufficient for the support 
of the machine4 ,connected with this    
change is another1 recommended by ,mr4  
,robert ,stephenson1 by which the       
flanges are removed from the driving    
wheels1 those upon the remaining pairs  
of wheels being sufficient to keep the  
engine in its position upon the rails4  
,we shall now describe a locomotive     
engine similar in construction to those 
almost ,pg#cfe universally used at      
present on railroads1 as well in this   
kingdom as in other countries4#cc  ,the 

external appearance of the engine and   
tender is shown in the engraving at the 
head of this chapter4 ,in fig4 #ig4 is  
exhibited a vertical section of the     
engine made by a plane carried through  
its length2 and in fig4 #ih4 is         
exhibited a corresponding section of its
 tender1--the tender being supposed to  
be joined on to the engine at the part  
where the connecting points appear to be
 broken in the drawing4 ,in fig4 #ii4 is
 exhibited the plan of the working      
machinery1 including the cylinders1     
pistons1 eccentrics1 c4 which are under 
the boiler1 by the operation of which   
the engine is driven4 ,fig4 #ajj4       
represents the tender1 also taken in    
plan4  ,in fig4 #aja4 is represented an 
elevation of the hinder end of the      
engine next the fire-box2 and in fig4   
#ajb4 is represented a cross vertical   
section through the fire-box1 and at    
right angles to the length of the       
engine1 showing the interior of the     
boiler above and beside the fire-box1   

the rivets and bolts connecting the     
internal and external fire-boxes1 the   
regulator1 steam funnel1 and steam dome4
  ,in fig4 #ajc4 is represented an      
elevation of the front of the engine    
next the smoke-box1 showing the cylinder
 covers ,w1 buffers ,t1 c42 and in fig4 
#ajd4 is represented a section of the   
interior of the smoke-box1 made by a    
vertical plane at right angles to the   
engine1 showing the tube plate forming  
the foremost end of the boiler1 the     
branches ,s of the steam-pipe leading to
 the cylinders1 the blast-pipe p1 the   
cylinders ,h1 and the chimney ,g4  ,the 
same letters of reference are placed at 
corresponding parts in the different    
figures4  ,the boiler1 as has been      
explained in the engines already        
described1 is a cylinder placed upon its
 side1 the section of which is exhibited
 at ,a1 fig4 #ig4 ,the fire-box consists
 of two casings of metal1 one within the
 other4 ,the fire-grate is represented  
at ,d4 ,the tubes by which the products 

of combustion are ,pg#cff drawn from the
 fire-box to the smoke-box ,f are       
represented at ,e4 ,upon the smoke-box  
is erected the chimney ,g4 ,in the      
engine from which this drawing has been 
taken1 and which was used on the ,london
 and ,birmingham ,railway1 the boiler is
 a cylinder #g-a_/b feet long1 and      
#c-a_/b feet in diameter4 ,it is formed 
of wrought-iron plates #e_/af of an inch
 in thickness1 overlapping each other1  
and bound together by iron rivets #g_/h 
of an inch in diameter and #a-c_/d inch 
apart4 ,one of these rivets1 as it joins
 two plates1 is represented in fig4 #ie4
 ,the boiler is clothed with a boarding 
of wood a1 an inch in thickness1 and    
bound round by iron hoops screwed       
together at the bottom4 ,wood being a   
slow conductor of heat1 this covering   
has the effect of keeping the boiler    
warm1 and checking the condensation of  
steam which would otherwise be produced 
by the rapid motion of the engine       
through the cold air4  ,illustration3   

,fig4 #ie4  ,illustration3 ,fig4 #if4   
,the external fire-box1 ,b ,b1 is a     
casing nearly square in its plan1 being 
four feet wide outside1 and three feet  
seven and a half inches long1 measured  
in the direction of the boiler4 ,it is  
constructed of wrought-iron plates1     
similar to those of the boiler4 ,this   
box descends about two feet below the   
boiler1 the top being semi-cylindrical1 
as seen in fig4 #ajb41 of a somewhat    
greater diameter than the boiler1 and   
concentrical with it4 ,the front of the 
fire-box next the end of the boiler has 
a circular opening equal in size to the 
end of the boiler4 ,to the edge of this 
opening the boiler is fastened by angle 
irons1 and rivets in the manner         
represented in fig4 #if4 ,these rivets  
are seen in section in fig4 #ig4  ,the  
internal fire-box ,c1 fig4 #ig41 is     
similar in shape to the external1 only  
it is flat at the top1 and close every  
where except at the bottom4 ,between it 
and the external fire-box an open space 

of three inches and a half is left all  
round1 and on the side next the boiler  
this space is increased to four inches4 
,this internal fire-box is made of      
copper plates1 #g_/af ,pg#cfg of an inch
 in thickness1 every where except next  
the boiler1 where the thickness is      
#g_/h4  ,as the sides and front of the  
external fire-box1 and all the surfaces 
bounding the internal fire-box1 are     
flat1 their form is unfavourable for the
 resistance of pressure4 ,adequate means
 are1 therefore1 provided for           
strengthening them4 ,the plates forming 
the internal fire-box are bent outwards 
near the bottom1 until they are brought 
into contact with those of the external 
fire-box1 to which they are attached by 
copper rivets1 as represented at f in   
fig4 #ig4 ,the plates forming the       
bounding surfaces of the two fire-boxes 
are fastened together by stays          
represented at k in figs4 #ig4 and #ajb4
 ,these stays1 which are of copper1 have
 a screw cut upon them through their    

whole length1 and holes are made through
 the plates of both fire-boxes tapped   
with corresponding threads4 ,the copper 
screws are then passed through them1 and
 rivets formed on their heads within and
 without1 as seen in fig4 #ajb4 ,these  
screw rivets connect all parts of the   
plating of the two fire-boxes which are 
opposed to each other3 they are placed  
at about four inches apart over the     
sides and back of the internal          
fire-place and that part of the front   
which is below the boiler4              
,illustration3 ,fig4 #ig4               
,,longitudinal ,,vertical ,,section ,,of
 ,a ,,locomotive ,,engine4              
,illustration3 ,fig4 #ih4               
,,longitudinal ,,vertical ,,section ,,of
 ,,the ,,tender4  ,illustration3 ,fig4  
#ii4  ,,plan ,,of ,,the ,,working       
,,machinery ,,of ,a ,,locomotive        
,,engine4  ,illustration3 ,fig4 #ajj4   
,,plan ,,of ,,the ,,tender4             
,illustration3 ,fig4 #aja4  ,,elevation 
,,of ,,the ,,hinder ,,end ,,of ,a       

,,locomotive ,,engine4  ,illustration3  
,fig4 #ajb4  ,,cross ,,vertical         
,,section ,,of ,,the ,,engine ,,through 
,,the ,,fire-,,box4  ,illustration3     
,fig4 #ajc4  ,,elevation ,,of ,,the     
,,foremost ,,end ,,of ,,the ,,engine4   
,illustration3 ,fig4 #ajd4  ,,cross     
,,vertical ,,section ,,of ,,engine      
,,through ,,the ,,smoke-,,box4  ,as the 
top of the internal fire-box cannot be  
strengthened by stays of this kind1 ribs
 of wrought-iron1 which are seen in     
their length at l1 in fig4 #ig41 and of 
which an end view is seen in fig4 #ajb41
 are attached by bolts to it4 ,these    
ribs are hollowed out1 as seen in fig4  
#ig41 between bolt and bolt1 in order to
 break their contact with the roof of   
the fire-box1 and allow a more free     
passage to the heat through it4 ,if they
 were in continuous contact with the    
fire-box1 the metal composing them would
 become more highly heated1 and would   
soon wear out1 besides intercepting heat
 from the water4 ,this part of the      

fire-box is subject to rapid wear1      
unless care be taken that the level of  
the water be preserved at its proper    
height in the boiler4 ,even when the    
boiler is properly filled1 the depth of 
water above the roof of the fire-box is 
not considerable1 and on the least      
neglect the roof may be exposed to the  
contact of steam1 in which case it will 
soon be destroyed4  ,to prevent         
accidents arising from this cause1 a    
leaden plug1 ,pg#cfh represented at m1  
figs4 #ig4 and #ajb41 is inserted in the
 roof of the internal fire-box4 ,if the 
water be allowed to subside1 this plug  
will melt out before the copper is very 
injuriously heated1 and the steam       
rushing out at the aperture will cause  
the fire to be extinguished4  ,copper   
fire-boxes are almost universally used2 
but sometimes1 from the consideration of
 cheapness1 the internal fire-box is    
constructed of iron4  ,in the plating   
which forms the back of the external    
fire-box1 an oval aperture is formed1 as

 represented in the back view of the    
engine1 fig4 #aja41 for the fire-door g4
 ,the plating of the internal fire-box  
around this aperture is bent at right   
angles to meet that of the external     
fire-box1 to which it is fastened by a  
row of copper rivets4 ,the fire-door is 
formed of two plates of wrought-iron1   
riveted together with a space of nine   
inches and a half between them4 ,the air
 between these plates being an imperfect
 conductor of heat1 keeps the outer     
plate of the fire-door at a moderate    
temperature4  ,in that part of the      
surface of the internal fire-box which  
forms the end of the boiler1 holes are  
made to receive the extremities of the  
tubes1 by which the air proceeding from 
the fire is drawn to the smoke-box at   
the remote end of the boiler4 ,these    
tubes are represented in longitudinal   
section at ,e1 fig4 #ig41 and their ends
 are seen in the surface of the internal
 fire-box in fig4 #ajb41 and in the     
remote end of the boiler where they     

terminate in the smoke-box in fig4 #ajd4
 ,these tubes are formed of the best    
rolled brass1 and their thickness in the
 engine1 to which we now refer1 is      
#a_/ac of an inch4 ,after the brass     
plating is bent into the form of a tube1
 and being overlapped1 is properly      
soldered together1 and the edges        
smoothed off1 the tubes are made        
perfectly cylindrical by being drawn    
through a circular steel die4           
,illustration3 ,fig4 #aje4  ,the        
tube-plates 7as those parts of the      
boiler ends in which the tubes are      
inserted are called7 are bored with     
holes in corresponding positions1 truly 
cylindrical1 and corresponding in       
magnitude to the tubes1 so that the     
tubes1 when passed into them1 will be   
just in contact with them4 ,the length  
of the tubes is so regulated1 that when 
extending from end to end of the boiler1
 and passing through the holes1 they    
shall ,pg#cfi project at each end a     
little beyond the holes4 ,the manner of 

fastening them so as to be water-tight  
is as follows3--,a steel hoop or        
ferrule1 made slightly conical1 a       
section of which is exhibited at ,c4    
fig4 #aje41 the smaller end of which is 
a little less than the internal diameter
 of the tube1 but which increases       
towards the outer end1 is driven in as  
represented in the figure4 ,it acts as a
 wedge1 and forces the tube into close  
contact with the edges of the hole in   
the tube-plate4  ,when particular tubes 
in a boiler are worn out1 and require to
 be replaced1 their removal is easily   
effected4 ,it is only necessary to cut  
the steel ferrule on the inside1 and to 
bend it off from contact with the tube1 
by which means it can be loosened and   
withdrawn1 and the tube removed4  ,in   
the engine to which this description    
refers there were one hundred and       
twenty-four tubes1 the external diameter
 of which was #a-e_/h inch4 ,the        
distance between tube and tube was #c_/d
 of an inch4 ,the number of tubes vary  

in different engines1 some having so    
many as one hundred and fifty1 while the
 number in some is less than ninety4    
,the evaporating power of an engine     
greatly depends on the proper number and
 magnitude of its tubes2 and the        
experience which engineers have had on  
railways have led them gradually to     
increase the number of tubes1 and       
diminish their magnitude4 ,in the       
,rocket1 already mentioned as having    
gained the prize on the opening of the  
,liverpool and ,manchester ,railway1 the
 number of tubes was twenty-four1 and   
their diameter three inches2 but in all 
the engines subsequently made their     
number was augmented1 and their diameter
 diminished4 ,the practical             
inconvenience which limits the size of  
the tubes is their liability to become  
choked by cinders and ashes1 which get  
wedged in them when they are too small1 
and thereby obstruct the draft1 and     
diminish the evaporating power of the   
boiler4 ,the tubes now in use1 of about 

an inch and a ,pg#cgj half internal     
diameter1 not only require to be cleared
 of the ashes and cinders1 which get    
fastened in them after each journey1 but
 it is necessary throughout a journey of
 any length that the tubes should be    
picked and cleaned by opening the fire  
door at convenient intervals4  ,the     
substitution of brass for copper tubes1 
which has been already mentioned as so  
great an improvement in the construction
 of locomotive engines1 is ascribed to  
,mr4 ,dixon1 who suggested them in      
#ahcc1 being then the resident engineer 
of the ,liverpool and ,manchester       
,railway4 ,they are said to last six or 
eight times as long as copper tubes of  
the same dimensions4  ,when tubes fail1 
they are usually destroyed by the       
pressure of the water crushing them     
inwards3 the water enters through the   
rent made in the tube1 and flowing upon 
the fire extinguishes it4 ,when a single
 tube thus fails upon a journey1 the    
engine1 notwithstanding the accident1   

may generally be made to work to the end
 of its journey by plugging the ends of 
the broken tube with hard wood2 the     
water in contact with which will prevent
 the fire from burning it away4  ,tubes 
of the dimensions here referred to weigh
 about sixteen pounds1 and lose from six
 to seven pounds before they are worn   
out4 ,their cost is about one pound     
each4  ,the tubes act as stays1         
connecting the ends of the boiler to    
strengthen them4 ,besides these1 there  
are rods of wrought iron extended from  
end to end of the boiler above the roof 
of the internal fire-place4 ,these rods 
are represented at o in their length in 
fig4 #ig41 and an end view of them is   
seen in fig4 #ajb4 ,the smoke-box ,f1   
fig4 #ig4 #ajd41 containing the         
cylinders1 steam-pipe1 and blast-pipe1  
is four feet wide1 and two feet long4   
,it is formed of wrought iron plates1   
half an inch thick on the side next the 
boiler1 and a quarter of an inch        
elsewhere4 ,the plates are riveted in   

the same manner as those of the fire-box
 already described4 ,from the top of the
 smoke-box1 which1 like the fire-box1 is
 semi-cylindrical1 as seen in elevation 
in fig4 #ajc41 and in section fig4      
#ajd41 rises the chimney ,g1 fifteen    
inches diameter1 and formed of #a_/h    
inch iron plates1 riveted and bound     
round by hoops4 ,it is flanged to the   
top of the ,pg#cga smoke-box1 as        
represented in fig4 #ajd4 ,near the     
bottom of the smoke-box the working     
cylinders are placed1 side by side1 in a
 horizontal position1 with the slide    
valves upwards4 ,in the top of the      
external fire-box a circular aperture is
 formed fifteen inches in diameter1 and 
upon this aperture is placed the        
steam-dome ,t 7figs4 #ig4 #aja1 #ajb47  
two feet high1 and attached around the  
circular aperture by a flange and screw 
secured by nuts4 ,this steam dome is    
made of brass #c_/h inch thick4 ,in     
stationary boilers1 where magnitude is  
not limited1 it has been already        

explained1 that the space allowed for   
steam is sufficiently large to secure   
the complete separation of the vapour   
from the spray which is mixed with it   
when it issues immediately from the     
water4 ,in locomotive boilers sufficient
 space cannot be allowed for this1 and  
the separation of the water from the    
steam is effected by the arrangement    
here represented4 ,a funnel-shaped tube 
d 7figs4 #ig4 #ajb471 with its wide end 
upwards1 rises into the steam-dome1 and 
reaches nearly to the top of it4 ,this  
funnel bends towards the back of the    
fire-box1 and is attached by a flange   
and screws to the great steam-pipe ,s1  
which traverses the whole length of the 
boiler4 ,the steam rising from the      
boiler fills the steam-dome ,t1 and     
descends in the funnel-shaped tube d4   
,the space it has thus to traverse      
enables the steam to disengage itself   
almost completely from the priming4 ,the
 wider part of the great steam-pipe a is
 flanged and screwed at the hinder end  

to a corresponding aperture in the back 
plate of the fire-box4 ,this opening is 
covered by a circular plate1 secured by 
screws1 having a stuffing-box in its    
centre1 of the same kind as is used for 
the piston-rods of steam-cylinders4     
,through this stuffing-box the spindle a
 of the regulator passes1 and to its end
 is attached a winch h1 by which the    
spindle a is capable of being turned4   
,this winch is limited in its play to a 
quarter of a revolution4 ,the other end 
of the spindle a is attached to a plate 
e seen edgeways in fig4 #ig41 and the   
face of which is seen in fig4 #ajb43    
this circular plate e is perforated with
 two apertures somewhat less than       
quadrants4 ,that part of the plate1     
therefore1 which remains not pierced    
forms two solid pieces somewhat greater 
than quadrants4 ,this plate is ground so
 as to move in steam-tight ,pg#cgb      
contact with a fixed plate under it1    
which terminates at the wide end of the 
conical mouth of the steam-pipe ,s4     

,this fixed circular plate is likewise  
pierced with two nearly quadrantal      
apertures1 corresponding with those in  
the movable plate e4 ,when the movable  
plate e is turned round by the winch h1 
the apertures in it may be made to      
correspond with those of the fixed      
circular plate on which it moves1 in    
which position the steam-pipe ,s        
communicates with the funnel d by the   
two quadrantal apertures thus open4 ,if1
 on the other hand1 the winch h be moved
 from this position through a quarter   
revolution1 then the quadrantal openings
 in the movable plate will be brought   
over the solid parts of the fixed plate 
on which it moves1 and these solid parts
 being a little more than quadrants1    
while the openings are a little less1   
all communication between the steam-pipe
 ,s and the funnel d will be stopped1   
for in this case the quadrantal openings
 in the fixed and movable plates        
respectively will be stopped by the     
solid parts of these plates4 ,it will be

 evident that as the winch h of the     
regulator is moved from the former      
position to the latter1 in every        
intermediate position the aperture      
communicating between the funnel d and  
the steam-pipe ,s will be less in       
magnitude than the complete quadrant4   
,it will in fact be composed of two     
openings having the form of sectors of a
 circle less than a quadrant1 and these 
sectors may be made of any magnitude1   
however small1 until the opening is     
altogether closed4  ,by such means the  
admission of steam from the boiler to   
the steam-pipe ,s may be regulated by   
the winch h4  ,the steam being admitted 
to the steam-pipe passes through it to  
the front end of the boiler1 and the    
pipe being enclosed within the boiler   
the temperature of the steam is         
maintained4 ,the steam-pipe passing     
through the tube-plate at the front end 
of the boiler is carried to a small     
distance from the tube-plate in the same
 direction1 where it is flanged on to a 

cross horizontal pipe proceeding to the 
right and to the left as represented in 
fig4 #ajd4 ,this cross pipe is itself   
flanged to two curved steam-pipes ,s    
7fig4 #ajd471 by which the steam is     
conducted to the valve-boxes ,v ,v4 ,the
 lower ends of these curved arms are    
flanged on to the valve-boxes of the two
 cylinders ,pg#cgc at the ends nearest  
to the boiler4 ,the opening of one of   
these is exhibited in the right hand    
cylinder in fig4 #ii4 ,by these pipes   
the steam is conducted into the         
valve-boxes or steam-chests1 from which 
it is admitted by slide-valves to the   
cylinders to work the pistons in the    
same manner as has been already         
described in the large stationary       
engines4  ,on the upper sides of the    
cylinders are formed the steam-chests or
 valve-boxes1 which are exhibited at ,u 
7figs4 #ig4 #ii4 #ajd474 ,these are made
 of cast-iron half an inch thick1 and   
are bolted to the upper side of each    
cylinder4 ,at the front end they are    

also secured by bolts to the smoke-box1 
and at the hinder end are attached to   
the tube-plate4 ,these valve-boxes      
communicate with the passages m and n   
fig4 #ii4 leading to the top and bottom 
of the cylinder3 these are called the   
steam-ports4 ,they also communicate with
 a passage o leading to the mouth of a  
curved horizontal pipe p connecting the 
front ends of the two cylinders1 as seen
 in figs4 #ii4 #ajd4 ,these curved pipes
 unite in a single vertical pipe p1     
called the blast-pipe1 seen in figs4    
#ig4 #ajd43 this vertical pipe becomes  
gradually small towards the top1 and    
terminates a little above the base of   
the funnel or chimney ,g4 ,in the       
valve-box is placed the slide-valve v to
 which is attached the spindle l4 ,this 
spindle moves through a stuffing-box k1 
and is worked by gearing1 which will be 
described hereafter4 ,according to the  
position given to the slide1 a          
communication may be opened between the 
steam-chest1 or the waste-port1 and     

either end of the cylinders4 ,thus when 
the slide is in the position represented
 in fig4 #ig4 the steam-chest           
communicates with the front end of the  
cylinder1 while the waste-port          
communicates with the hinder end4 ,if1  
on the other hand1 the spindle l being  
pressed forward1 move the slide to its  
extreme opposite position1 the          
steam-port n would communicate with the 
waste-port o1 while the steam-chest     
would communicate with the steam-port m1
 steam would1 therefore1 be admitted to 
the hinder end of the cylinder1 while   
the foremost end would communicate with 
the waste-port4 ,it will be perceived   
that this arrangement is precisely      
similar to that of the slide-valves     
already described 7#acc474 ,the         
slide-valve is represented on a larger  
scale in fig4 #ajf41 where ,a is the    
hinder steam-port1 ,pg#cgd ,b the       
foremost steam-port1 and ,c the         
waste-port4 ,the surfaces ,d1 separating
 the steam-ports from the waste-ports1  

are called the bars3 they are planed    
perfectly smooth1 so that the surfaces  
,f and ,g of the slide-valve1 also      
planed perfectly smooth1 may move in    
steam-tight contact with them4 ,these   
surfaces are kept in contact by the     
pressure of the steam in the            
steam-chest1 by which the slide-valve is
 always pressed down4 ,in its middle    
position1 as represented by the dotted  
lines in the figure1 both the           
steam-ports are stopped by the          
slide-valve1 so that at that moment no  
steam is admitted to either end of the  
cylinder4 ,on either side of this       
intermediate position the slide has an  
inch and a half play1 which is          
sufficient to open successively the two 
steam-ports4  ,illustration3 ,fig4 #ajf4
  ,the cylinders are inserted at one end
 in the plate of the smoke-box1 and at  
the other in the tube-plate of the      
boiler4 ,they are closed at either end  
by cast iron covers1 nearly an inch     
thick1 flanged on by bolts and screws4  

,in the cover of the cylinder attached  
to the tube-plate is a stuffing-box1 in 
which the piston rod plays4 ,the        
metallic pistons used in locomotive     
engines do not differ materially from   
those already described1 and therefore  
need not be here particularly noticed4  
,from their horizontal position they    
have a tendency to wear unequally in the
 cylinders1 their weight pressing them  
on one side only2 but from their small  
magnitude this effect is found to be    
imperceptible in practice4 ,in the      
engine here described the stroke of the 
piston is eighteen inches1 and this is  
the most usual length of stroke in      
locomotive engines4 ,the piston1 in its 
play1 comes at either end within about  
half an inch of the inner surface of the
 covers of the cylinders1 this space    
being allowed to prevent collision4 ,in 
the foremost cover of the cylinder is   
inserted a cock q 7fig4 #ig4 #ii471 by  
which any water which may collect in the
 cylinder by condensation or priming may

 be discharged4 ,a cock r 7fig4 #ig471  
communicating with a small tube         
proceeding from the branches of the     
waste pipe p 7fig4 #ajd471 is likewise  
provided to discharge from that pipe any
 water which may be ,pg#cge collected in
 it4 ,after the steam has been admitted 
to work the piston through the          
slide-valve1 and has been discharged    
through the waste-port by shifting that 
valve1 it passes through the pipe p into
 the blast-pipe p1 from the mouth of    
which it issues1 with great force1 up   
the funnel ,g4 ,when the motion of the  
engine is rapid1 the steam from the two 
cylinders proceeds in an almost         
uninterrupted current from the          
blast-pipe1 and causes a strong draft up
 the chimney4 ,the heated air which     
passes from the mouths of the tubes into
 the smoke-box is drawn up by this      
current1 and a corresponding draft is   
produced in the fire-box4               
,illustration3 ,fig4 #ajg4  ,the        
piston-rods ,y terminate in a fork1 by  

which they are attached to cross heads  
,z1 the ends of which are confined by   
guide-bars ,a1 in which they are allowed
 to play backwards and forwards through 
a space equal to the stroke of the      
piston4 ,to these cross heads ,z1       
between the prongs of the fork in which 
the piston terminates1 are attached the 
foremost ends of the connecting rods ,b4
 ,these rods are1 therefore1 driven     
backwards and forwards by the motion    
imparted to the cross head ,z by the    
piston-rods ,y4 ,the connecting rods ,b 
are attached at the hinder ends to two  
cranks formed upon the axles ,c of the  
driving wheels ,d4 ,these two cranks are
 formed upon the axles precisely at     
right angles to each other4 ,the        
left-hand crank is represented in its   
horizontal position1 in fig4 #ii41 and  
the right-hand crank is seen in its     
vertical position4 ,a cranked axle is   
represented on a larger scale in fig4   
#ajg41 and the two cranks are seen in a 
position oblique to the plane of the    

figure4 ,as this axle is the instrument 
by which the impelling force is conveyed
 to the load1 and as it has to support a
 great portion of the weight of the     
engine1 it is constructed with great    
strength and precision4 ,it is made all 
in one ,pg#cgf piece1 and of the best   
wrought iron called ,back ,barrow1 or   
scrap iron4 ,in the engine here         
described its extreme length is six feet
 and a half1 and its diameter is five   
inches4 ,at the centre part ,a it is    
cylindrical1 and is increased to five   
inches and a quarter at ,c1 where the   
cranks are formed4 ,the sides ,d of the 
cranks are four inches thick1 and the   
crank pins ,b1 which are truly          
cylindrical1 are five inches diameter1  
and three inches in length1 the brasses 
at the extremities of the connecting    
rods which play upon them having a      
corresponding magnitude4 ,the distance  
from the centre of the crank-pins ,b to 
the centre of the axle ,a must be       
exactly equal to half the stroke of the 

piston1 and is1 therefore1 in this case 
precisely nine inches4 ,upon the parts  
,f1 which are seven inches and a half   
long1 the great driving wheels are      
firmly fastened1 so as to be prevented  
from turning or shaking upon the axle4  
,the axle projects beyond the wheels at 
,g1 where it is reduced to three inches 
and an eighth diameter4 ,these          
projecting parts ,g are five inches     
long1 having collars at the outer ends4 
,brasses are fixed at the outside frame 
of the engine which rest upon these     
projections ,g of the axle1 and upon    
these brasses the weight of the engine  
is supported4 ,the entire axle is       
accurately turned in a lathe1 and each  
of the crank-pins ,b is likewise turned 
by suspending the axle on centres       
corresponding with the centres of the   
crank-pins1 and made on strong cast iron
 arms1 which are firmly fixed on the    
ends of the axle1 and project beyond the
 cranks so as to balance the axle1 and  
enable it to turn round on the centre of

 the crank-pin4 ,the axle is by such    
means made perfectly true1 and the      
cranks are made of exactly the proper   
length1 and precisely at right angles to
 each other4 ,the corners of the cranks 
are champered off1 as shown in the      
figure1 and the ends of the cylindrical 
parts well rounded out4  ,the strength  
and accuracy of construction            
indispensable in these cranked axles1 in
 order to make them execute their work1 
render them very expensive4 ,those which
 are here described cost about #ejl4    
each4 ,when properly constructed1       
however1 they are seldom broken1 but are
 sometimes bent when the engine escapes 
from the rails4  ,the proper motion to  
admit and withdraw the steam from       
,pg#cgg either end of the cylinder is   
imparted to the slide-valves by         
eccentrics1 in a manner and on a        
principle so similar to that already    
described in large stationary engines1  
that it will not be necessary here to   
enter into any detailed explanation of  

the apparatus for communicating this    
motion1 which is exhibited in plan and  
section in figs4 #ig4 #ii4 ,the         
eccentrics are attached to the cranked  
axles at ,e ,e4 ,the eccentric ,e       
imparts motion by a rod e to a lever h1 
formed on an axle extending across the  
frame of the engine4 ,this conveys      
motion to another lever l1 projecting   
from the same axle4 ,this lever l is    
jointed to horizontal links m1 which at 
the foremost ends are attached to the   
spindle l1 by which the slide is driven4
 ,by these means the motion received by 
the eccentric from the great working    
axle conveys to the spindle l an        
alternate movement backwards and        
forwards1 and the points at which it is 
reversed will be regulated by the       
position given to the eccentric upon the
 great axle4 ,the eccentric is formed in
 two separate semicircles1 and is keyed 
on to the great axle1 and consequently  
any position may be given to it which   
may be required4 ,the position to be    

given to the eccentrics should be such  
that they shall be at right angles to   
their respective cranks1 and they should
 be fixed a quarter of a revolution     
behind the cranks so as to move the     
slides to that extent in advance of the 
pistons1 since by the position of the   
levers h and l1 the motion of the       
eccentric becomes reversed before it    
reaches the valve spindle4  ,the        
performance of the engine is materially 
affected by the position of the         
eccentrics on the working axle4 ,the    
slide should begin to uncover the       
steam-port a little before the          
commencement of the stroke of the       
piston1 in order that the steam         
impelling the piston should be shut off1
 and the steam about to impel it in the 
contrary direction admitted before the  
termination of the stroke4 ,through this
 small space the steam1 therefore1 must 
act in opposition to the motion of the  
piston4 ,this is called the lead of the 
slide1 and the extent generally given to

 it is about a quarter of an inch4 ,this
 is accomplished by fixing the          
eccentrics not precisely at right angles
 to the respective cranks1 but a little 
in advance of that position4 ,the       
introduction of the steam to ,pg#cgh the
 piston before the termination of the   
stroke has the effect of bringing it    
gradually to rest at the end of the     
stroke1 and thereby diminishing the jerk
 or shock produced by the rapid change  
of motion4 ,in stationary engines1 where
 the reciprocations of the engine are   
slow1 the necessity for this provision  
does not arise2 but in locomotive       
engines in which the motion of the      
piston is changed from four to six times
 in a second1 it becomes necessary4 ,the
 steam admitted to the piston before the
 termination of the stroke acts as a    
spring-cushion to assist in changing its
 motion1 and if it were not applied1 the
 piston could not be kept tight upon the
 piston-rod4 ,another advantage which is
 produced by allowing some lead to the  

slide is that the waste steam which has 
just impelled the piston begins to make 
its escape through the waste-port before
 the commencement of the next stroke1 so
 that when the impelling steam begins to
 produce the returning stroke1 there is 
less waste steam on the other side of   
the piston to resist it4  ,when the     
motion of the engine is very rapid1 the 
resistance of the waste steam1 as it    
escapes from the blast-pipe to the      
piston1 has been generally supposed to  
be very considerable1 though we are not 
aware of any direct experiments by which
 its amount has been ascertained4 ,in   
the account of the locomotive engine    
which has been here described1 supplied 
by ,mr4 ,stephenson for the last edition
 of ,tredgold on the ,steam ,engine1 he 
states1 that the average resisting      
pressure of the waste steam throughout  
the stroke is #f lbs4 per square inch1  
when running at the usual rate of from  
#be to #bh miles an hour1 and that at   
greater velocities this negative        

pressure has been found to increase to  
more than double that amount4 ,no       
experiments are1 however1 cited from    
which this inference has been drawn4    
,it has been also thought that the      
pressure of steam upon the piston in the
 cylinder1 at high velocities1 is       
considerably below the pressure of steam
 in the boiler2 but this has not been1  
so far as we are informed1 ascertained  
by any satisfactory experimental test4  
,mr4 ,stephenson likewise states1 that  
this loss of pressure1 causes the       
negative pressure or resistance of the  
waste steam to amount to ,pg#cgi from   
#cj to #dj per cent4 of the positive    
pressure upon the piston when the engine
 is running very fast1 and that         
therefore the power of the engine is    
diminished nearly one half4  ,but it    
will be perceived that besides the      
uncertainty which attends the estimate  
of the actual amount of pressure on the 
piston compared with the pressure of    
steam in the boiler1 the inference here 

drawn does not appear to be compatible  
with what has been already proved       
respecting the mechanical effect of     
steam4 ,no change of pressure which may 
take place between the boiler and the   
cylinder can affect the practical       
efficacy of the steam4 ,as the steam    
passes through the engine1 whatever     
change of pressure it may be subject to1
 it still remains common steam2 and     
though its pressure may be diminished1  
its volume being increased in a nearly  
equal proportion1 its mechanical effect 
will remain the same4 ,the power of the 
engine1 therefore1 estimated as it ought
 to be1 by the whole mechanical effect  
produced1 will not be altered otherwise 
than by the effect of the increased     
resistance produced by the blast-pipe4  
,what that resistance is1 we repeat1 has
 not1 so far as we know1 been           
ascertained by direct experiment1 and   
there are circumstances attending it    
which render it probable that1 even at  
high velocities1 it is less in amount   

than ,mr4 ,stephenson's estimate4  ,the 
position of the eccentrics which is     
necessary to make the pistons drive the 
engine forward must be directly the     
reverse of that which would cause them  
to drive the engine backwards4 ,to be   
able1 therefore1 to reverse the motion  
of the engine1 it would only be         
necessary to be able to reverse the     
position of the eccentrics1 which may be
 accomplished by either of two          
expedients4  ,first1 ,the eccentrics may
 be capable of revolving on the great   
working axle1 and also of sliding upon  
it through a small space4 ,their        
revolution on the axle may be checked by
 letting a pin attached to a collar     
fastened on the axle fall into a hole on
 the side of the eccentric4 ,such a pin 
will drive the eccentric round with the 
axle1 and the position of this pin and  
the hole will determine the position of 
the eccentric with reference to the     
crank4 ,at a short distance ,pg#chj on  
the other side of the eccentric may be a

 corresponding collar with a pin in the 
opposite position4 ,by moving the       
eccentric longitudinally on the axle1   
the former pin may be withdrawn from the
 hole1 and the latter allowed to fall   
into the hole on the other side4 ,proper
 mechanism may be provided by which the 
position of the eccentric may thus be   
reversed in reference to the crank1 and 
by such means the motion of the engine  
may be reversed4  ,secondly1 ,supposing 
the eccentrics which drive the engine   
forward to be immovably fixed upon the  
axle1 two other eccentrics may be       
provided attached to other parts of the 
same axle1 and having a position exactly
 the reverse with reference to the      
cranks4 ,proper mechanism may be        
provided1 by which either or both pairs 
of eccentrics may be thrown in or out of
 gear4 ,such are the means adopted in   
the engine which has been already       
described4 ,the eccentrics for driving  
the engine backwards are placed outside 
the cranks at ,f ,f4 ,a hand lever w    

fig4 #aja4 is provided1 by which the    
engine man may throw either pair of     
eccentrics into or out of gear1 so as to
 make the engine work either backwards  
or forwards4  ,illustration3 #ajh4      
,illustration3 #aji4  ,illustration3    
#aaj4  ,as all the moving parts of the  
engine require to be constantly         
lubricated with oil to diminish the     
friction1 and keep them cool1 oil-cups  
for this purpose are fixed upon them4   
,in some engines these oil-cups are     
attached separately to all the moving   
parts3 in others they are placed near   
each other in a row on the boiler1 and  
communicate by small tubes with the     
several parts required to be lubricated4
 ,one of these is requisite for each end
 of the connecting rods1 for each of the
 guides of the piston-rods1 for the     
piston-rod itself1 the spindle of the   
slide-valve1 and other parts4 ,an       
elevation of one of these oil-cups is   
shown in fig4 #ajh41 a vertical section 
in fig4 #aji41 and horizontal plan in   

fig4 #aaj4 ,the cup ,a is made of brass 
with a cover ,b4 ,this cover has a piece
 projecting from it turning upon a pin  
in a socket ,c at the side of the cup   
,a1 and square at the end1 resting upon 
a small spring at the bottom of the     
socket to hold it either open or shut4  
,in the bottom of the ,pg#cha cup is    
inserted an iron tube ,d extending      
nearly to the top4 ,this tube projects  
from the bottom of the cup1 where it is 
tapped for the purpose of fixing the cup
 on the part of the engine which it is  
intended to lubricate4 ,the hole into   
which the cup is screwed communicates   
with the rubbing surface1 and some      
cotton thread is passed through the tube
 dipping into the oil in the cup at the 
one end and touching the moving part at 
the other4 ,this thread acts as a       
siphon1 and constantly drops oil on the 
rubbing surface4  ,illustration3 ,fig4  
#aaa4  ,the tender is a carriage        
attached behind the engine and close to 
it1 carrying coke for the supply of the 

furnace1 and water for the boiler4 ,the 
coke is contained in the space ,r1 7fig4
 #ih4 #ajj47 surrounded by a tank ,i    
containing water to feed the boiler4    
,the feed for the boiler is conducted   
from the tank through a pipe descending 
downwards and in a curved direction1 ,p 
,q1 fig4 #ih41 and connected with a     
horizontal pipe ,k1 fig4 #ig4 ,a cock is
 provided at ,p1 by which the supply of 
water to this pipe may be cut off at    
pleasure4 ,another cock is provided at  
t1 fig4 #ig41 where the curved pipe     
joins the horizontal pipe by which the  
quantity of water supplied to ,k may be 
regulated by opening the cock more or   
less fully4 ,the handle of this cock    
rises through the floor of the engine1  
so that the engineer may regulate it at 
discretion4 ,the pipe ,k being conducted
 under the engine1 as represented in    
fig4 #ig41 terminates in a vertical     
pipe1 of greater diameter1 containing   
two valves1 both of which open upwards1 
and between these valves to this        

vertical pipe is attached a force-pump1 
by which the water is drawn from the    
horizontal pipe ,k into the vertical    
pipe ,k1 and from the latter is driven  
into a delivery-pipe by which it is     
forced into the boiler4 ,the details of 
the interior of this feed-pump are      
represented on a larger scale in fig4   
#aaa4 ,the extremity of the horizontal  
pipe ,k is represented in section at ,h1
 where it is joined on by a screw to the
 bottom of the vertical pipe which is   
represented in fig4 #ig4 at ,k1 and     
which is here represented in section4   
,the vertical pipe1 represented in fig4 
#ig4 consists of several parts screwed  
together by nuts and bolts passing      
through flanges4 ,the lowest piece ,i is
 attached by a flange to the piece ,l3  
within these is contained the valve ,q  
resting in a seat made conical1 so that 
the ball ,pg#chb which forms the valve  
shall rest in water-tight contact with  
it4 ,the ball is turned and ground to an
 accurate sphere1 and whatever position 

it assumes upon its seat its contact    
will be perfect4 ,it is guided in its   
upward and downward motion by several   
vertical bars which confine it1 and     
which are united at the top1 so as to   
limit the upward motion of the ball4 ,a 
screw ,v is inserted in the bottom of   
the piece ,i1 by removing which access  
can be obtained to the valve4 ,the piece
 ,l is secured to the short pipe ,g by  
nuts and bolts passed through a flange4 
,the pipe ,g is cast upon the end of the
 feed-pump ,a4 ,on the foremost end of  
this feed-pump is constructed a         
stuffing-box ,c of the usual form1      
having a gland ,d forced against packing
 by nuts and screws ,e4 ,the plunger ,b 
is turned so as to be truly cylindrical1
 and moves in water-tight contact       
through the gland ,d4 ,the plunger not  
being in contact with the inner surface 
of the pump-barrel ,a1 the latter need  
not be ground4 ,the horizontal rod by   
which the plunger ,b is driven is       
attached at its foremost extremity to an

 arm which projects from the rod of the 
steam-piston1 and consequently this     
plunger is moved through a space equal  
to the stroke of the steam-piston4 ,in  
this case that space is eighteen inches4
 ,the ,pg#chc upper end of the vertical 
tube ,g is attached by screws and a     
flange to a piece ,p containing a valve 
,r similar in all respects to the lower 
valve ,q1 and like it opening upwards4  
,a screw ,v is introduced at the top by 
which access may be obtained to this    
valve4 ,this screw also presses on the  
crown of the guides of the valve1 so as 
to hold it down by regulated pressure4  
,at the side of this upper piece ,p is  
inserted a horizontal tube ,m connected 
with the end of the delivery-pipe ,n4   
,this latter is continued to the boiler 
with which it communicates at the       
fire-box4 ,when the plunger ,b is drawn 
out of the pump-barrel ,a1 the spherical
 valve ,q being relieved from its       
downward pressure is raised1 and water  
passes from the pipe ,h through the     

valve ,q into the vertical pipe ,g2 the 
lower valve ,q then closes and stops the
 return of the water4 ,the plunger ,b   
returning into the pump-barrel ,a then  
forces the water against the upper valve
 ,r and drives it through the           
delivery-tube ,n1 from which its return 
is prevented by the valve ,r4 ,when the 
delivery-tube ,n is filled with water   
throughout its whole length1 every      
stroke of the plunger will evidently    
drive into the boiler a volume of water 
equal to the magnitude of a part of the 
plunger eighteen inches in length4      
,until within the last few years1       
locomotive engines were supported on    
only four wheels2 they are1 however1 now
 almost universally supported on six1   
the driving wheels being in the middle4 
,to give greater security to the        
position of the engine between the rails
 it is usual to construct flanges on the
 tires of all the six wheels4 ,mr4      
,stephenson1 however1 has been in the   
practice of constructing the driving    

wheels without flanges1 and with tires  
truly cylindrical1 depending on the     
flanges of the two pairs of smaller     
wheels to maintain the engine between   
the rails4 ,the wheels of the engine    
here described are constructed in this  
manner4 ,the driving wheels ,d are fixed
 on the cranked axle ,c1 and are five   
feet in diameter4 ,the other wheels ,l  
,m1 the one being placed immediately    
behind the smoke-box1 and the other     
immediately behind the fire-box1 are    
each three feet six inches in diameter1 
and have a flange upon their tires1     
which running on the ,pg#chd inside of  
each rail keeps the engine between the  
rails4 ,each pair of these small wheels1
 like the driving-wheels1 is fixed upon 
their axle4 ,the axles are #c-e_/h      
inches diameter1 and project beyond the 
wheels1 the projecting part supporting  
the frame of the engine and turning in  
brasses4 ,upon these brasses rest       
springs1 which bear the whole weight of 
the engine4 ,these springs having       

nothing between them and the road but   
the wheels and axles intercept and      
equalise the sudden shocks produced by  
the rapid motion upon the road4  ,when  
an engine is required for the transport 
of very heavy loads1 such as those of   
merchandise1 the adhesion of one pair of
 working wheels is found to be          
insufficient1 and1 in such cases1 one of
 the two pairs of wheels ,l ,m is made  
of the same diameter as the wheels which
 are placed upon the working axle1 and a
 bar is attached to points on the       
outside of the wheels at equal distances
 from their centre1 connecting them in  
such a manner that any force applied to 
make one pair of wheels revolve must    
necessarily impart the same motion to   
the other pair4 ,by such means the force
 of the steam is made to drive both     
pairs of wheels1 and consequently a     
proportionally increased adhesion is    
obtained4  ,the velocity which an engine
 is capable of imparting to the load    
which it draws depends upon the rate at 

which the pistons are capable of being  
moved in the cylinders4 ,by every motion
 of each piston backwards and forwards  
one revolution of the driving wheels is 
produced1 and by each revolution of the 
driving wheels1 supposing them not to   
slip upon the rails1 the load is driven 
through a distance upon the road equal  
to their circumference4 ,as the two     
cylinders work together1 it follows1    
that a quantity of steam sufficient to  
fill four cylinders supplied by the     
boiler to the engine will move the train
 through a distance equal to the        
circumference of the driving wheels2 and
 in accomplishing this1 each piston must
 move twice from end to end of the      
cylinder2 each cylinder must be twice   
filled with steam from the boiler2 and  
that steam must be twice discharged from
 the cylinder through the blast-pipe    
into the chimney4  ,pg#dja ,if the      
driving wheels be five feet in diameter 
their circumference will be fifteen feet
 seven inches4 ,to drive a train with a 

velocity of thirty miles an hour1 it    
will be necessary that the engine should
 be propelled through a space of        
forty-five feet per second4 ,to         
accomplish this with five-feet wheels   
they must be therefore made to revolve  
at the rate of very nearly three        
revolutions per second2 and as each     
revolution requires two motions of the  
piston in the cylinder1 it follows that 
each piston must move three times       
forwards and three times backwards in   
the cylinder in a second2 that steam    
must be admitted six times per second   
from the steam-chest to each cylinder1  
and discharged six times per second from
 each cylinder into the blast-pipe4 ,the
 motion1 therefore1 of each piston1     
supposing it to be uniform1 must divide 
a second into six equal parts1 and the  
puffs of the blast-pipe in the chimney  
must divide a second into twelve equal  
parts4 ,the motion of the slides and    
other reciprocating parts of the        
machinery must consequently correspond4 

,this motion of the reciprocating parts 
of the machinery being found to be      
injurious to it1 and to produce very    
rapid wear1 attempts have been made to  
remedy the defect1 and to obtain greater
 speed with an equal or diminished rate 
of motion of the piston1 by the adoption
 of driving wheels of greater diameter1 
and on several of the great lines of    
railway the magnitude of the wheels for 
the passenger-engines have been         
increased to five feet and a half and   
six feet diameter2 but such engines have
 not been sufficiently long in use to   
afford grounds for forming a practical  
estimate of their effects4 ,experiments 
of a much bolder description have1      
however1 been tried on one of the great 
lines of railway by the adoption of     
driving wheels of much greater diameter4
 ,in some cases their magnitude has been
 increased even to ten feet2 but from   
various experiments to which these      
engines have been submitted by myself   
and others1 as well as from the         

experience which appears to be obtained 
from the results of their ordinary work1
 it does not appear that any advantages 
have attended them1 and they have been  
accordingly for the most part abandoned4
  ,the pressure of steam in the boiler  
is limited by two safety-valves1 ,pg#djb
 represented in fig4 #ig4 at ,n and ,o4 
,the valve at ,n is under the control of
 the engineer1 but the valve at ,o is   
inaccessible to him4 ,the structure of  
the safety-vale represented at ,n is    
exhibited on a larger scale in fig4     
#aab41 which represents its section1 and
 fig4 #aac41 which shows a plan of the  
valve-seat with the valve removed4 ,the 
valve ,a1 which is made of brass1 is    
mitred round the edge at an angle of    
#de1 and has a spindle1 or stalk ,b1    
cast upon it1 projecting downwards from 
the middle of it4 ,the valve-seat ,c is 
also made of brass1 and cast with a     
flange at the bottom to attach it to the
 boiler4 ,the mitred surface of the     
valve is ground into the valve-seat1 so 

as to rest in steam-tight contact with  
it4 ,across the valve-seat1 which is two
 and a half inches in diameter1 is cast 
a thin piece ,d1 seen in plan in fig4   
#aac4 and in section in fig4 #aab4 which
 extends from the top to the bottom1 and
 has a longitudinal hole through it1 in 
which the spindle ,b of the valve works3
 by this hole it is guided when it rises
 from its seat4 ,a projection ,e is cast
 upon the seat of the valve1 in which a 
standard ,f is inserted4 ,this standard 
is forked at the top1 and receives the  
end of a lever ,g1 which turns in it    
upon a centre4 ,a rod ,h is jointed to  
this lever by another pin at three      
inches from the former1 and the lower   
end of this rod1 ground to a point1     
presses upon the centre of the valve ,a4
 ,at the other end of the lever1 which  
is broken off in fig4 #aab41 at a       
distance of three feet from the centre  
pin1 inserted in the fork of the pillar 
,f1 the rod of a common spring-balance  
w1 fig4 #aja41 is attached by a         

finger-nut n4 ,the bottom of this       
spring-balance is secured on to the     
fire-box4 ,this balance is screwed up by
 the finger-nut on the valve-lever until
 the required pressure on the lever is  
produced through the medium of the rod  
,h1 this pressure being generally fifty 
pounds per square inch above the        
atmosphere4 ,when the pressure of the   
steam in the boiler exceeds this1 the   
valve ,a is raised from its seat1 and   
the steam escapes4  ,illustration3 ,fig4
 #aab4  ,illustration3 ,fig4 #aac4  ,it 
is evident that the sliding weight by   
which the pressure ,pg#djc of the       
safety-valve is sometimes regulated in  
stationary engines would not be         
admissible in a locomotive engine1 since
 the motion of the engine would         
constantly jolt it up and down1 and     
cause the steam to escape4 ,one of the  
disadvantages attending the use of the  
spring-valve is that it cannot be opened
 to let the steam escape without        
increasing its force1 so that the steam1

 when escaping1 must really have a      
greater pressure than that to which the 
valve has been previously adjusted4 ,the
 longer the lever is1 the greater will  
be this difference of pressure1 inasmuch
 as a given elevation of the pin        
governing the rod ,h would cause a      
proportionally greater motion in that   
end of the lever attached to the spring4
  ,the second safety-valve ,o is        
enclosed in a case1 so that it is       
inaccessible1 and its purpose is to     
limit the power of the engineer to      
increase the pressure of steam in the   
boiler4 ,this valve is similar in       
construction to the former1 but instead 
of being held down by a lever1 is       
pressed upon by several small elliptical
 springs placed one above another over  
the valve1 and held down by a screw     
which turns in a frame ,y1 fixed into   
the valve-seat4 ,by this screw the      
pressure on the valve can be adjusted to
 any required degree2 and if the open   
safety-valve be screwed down to a       

greater pressure1 the steam will begin  
to escape from this second valve4  ,also
 in the case where the boiler produces  
surplus steam faster than its escape can
 be effected at the valve ,n1 the       
pressure will sometimes be increased    
until the valve ,o is opened1 and its   
escape will take place from both valves4
  ,the whole weight of the engine bears 
upon those parts of the six axles ,r1   
fig4 #ii41 which project beyond the     
wheels4 ,boxes are formed in which these
 parts of the axles turn1 and through   
the medium of which the weight of the   
engine rests upon them4 ,over these     
boxes are constructed oil or grease     
cups1 by means of which the axles are   
constantly lubricated4 ,it is usual to  
lubricate the axles of the engine itself
 with oil3 the axles of the tender1 and 
other coaches and waggons1 are          
lubricated with a mixture of oil and    
tallow4 ,in the middle of the box in    
which the axle turns1 and between the   
two oil-cups1 is cast a socket1 in which

 the end of the spindle on ,pg#djd which
 the spring presses rests4 ,the springs 
are composed of a number of             
steel-plates1 laid1 in the usual manner1
 one above the other1 increasing in     
length upwards4 ,in the engine here     
described1 the plates forming the       
springs of the driving wheels are       
thirteen in number1 each of which is    
four inches in width1 and #e_/afths of  
an inch in thickness4 ,the springs upon 
the other wheels are three inches in    
width4 ,the springs of the driving      
wheels are below the axle1 while those  
of the smaller wheels are above it4     
,buffers ,d are placed behind the       
tender1 which act upon a spring ,c 7fig4
 #ajj471 to break the collision1 when   
the waggons or carriages strike upon the
 tender1 and similar buffers are        
attached to all passenger-coaches4 ,some
 of these buffers are constructed with a
 system of springs similar to ,c1 but   
more elastic1 and combined in greater   
number under the framing of the         

carriage1 so that a considerable play is
 allowed to them4 ,in some cases the    
rods of the buffers are made to act upon
 strong spiral springs inserted in the  
sides of the framing of the carriage4   
,this arrangement gives greater play to 
the buffers2 and as every coach in a    
train has several buffers1 the combined 
effect of these is such1 that a         
considerable shock given to either end  
of the train may be rendered harmless by
 being spent upon the elasticity of     
these several systems of springs4  ,in  
order to give notice of the approach of 
a train1 a steam-whistle ,z1 fig4 #ig4  
#aja41 is placed immediately above the  
fire-box at the back of the engine4     
,this is an apparatus composed of two   
small hemispheres of brass1 separated   
one from the other by a small space4    
,steam is made to pass through a hollow 
space constructed in the lower          
hemisphere1 and escapes from a very     
narrow circular opening round the edge  
of that hemisphere1 rushing up with a   

force proportionate to its pressure4    
,the edge of the upper hemisphere       
presented downwards encounters this     
steam1 and an effect is produced similar
 to the action of air in organ pipes4 ,a
 shrill whistle is produced1 which can  
be heard at a very considerable         
distance1 and1 differing from all       
ordinary sounds1 it never fails to give 
timely notice of the approach of a      
train4  ,the water tank ,i1 fig4 #ih4   
#ajj41 which is constructed on the      
tender1 is formed of wrought-iron plates
 #a_/h of an inch thick1 ,pg#dje riveted
 at the corners by angle iron already   
described4 ,this tank is #i feet long1  
#f-c_/d feet wide1 and #b-a_/d feet     
deep4 ,the top is covered with a board  
,k1 and a raised platform ,n is         
constructed behind1 divided into three  
parts1 covered with leads1 which open on
 hinges4 ,the middle lid covers an      
opening to the tank by which water is   
let in3 the lids at either side cover   
boxes in which are contained the tools  

necessary to be carried with the engine4
 ,the curved pipe ,p1 fig4 #ih41 leading
 from the bottom of the tank to the pipe
 ,q1 is of copper4 ,the pipe ,q1        
connecting the latter with the feed-pipe
 ,k1 fig4 #ii41 is sometimes formed of  
leather or ,india-rubber cloth1 having a
 spiral spring on the inside to prevent 
it from collapsing4 ,it is necessary    
that this pipe ,q should have a power of
 yielding to a sufficient degree to     
accommodate itself to the inequalities  
of motion between the engine and tender4
 ,a metal pipe is sometimes used1       
supplied with a double ball and socket1 
and a telescopic joint1 having          
sufficient play to allow for the lateral
 and longitudinal inequalities of motion
 of the engine and tender4 ,the weight  
of an engine1 such as that here         
described1 supplied with its proper     
quantity of water and fuel1 is about #ab
 tons3 the tender1 when empty1 weighs   
about #c-a_/d tons2 and when filled with
 water and fuel its weight is #g tons4  

,the tank contains #gjj gallons of      
water1 and the tender is capable of     
carrying about #hjj weight of coke4     
,this supply is sufficient for a trip of
 from thirty to forty miles with an     
ordinary load4   7#aih47 ,it is not     
usual to express the power of locomotive
 engines in the same manner as that of  
other engines by the term horse-power4  
,indeed1 until the actual amount of     
resistance opposed to these machines1   
under the various circumstances in which
 they are worked1 shall be ascertained  
with some degree of precision1 it is    
impossible that their power or          
efficiency can be estimated with any    
tolerable degree of approximation4 ,the 
quantity of water evaporated1 and passed
 in steam through the cylinders1        
supplies a major limit to the power     
exerted2 but even this necessary element
 for the calculation of the efficacy of 
these machines has not been ascertained 
by a sufficiently extensive course of   
observation and experiment4 ,mr4        

,stephenson states1 that the engine     
which ,pg#djf has been here described is
 capable of evaporating #gg cubic feet  
of water per hour1 while the early      
locomotives could only evaporate #af    
cubic feet per hour4 ,this evaporation1 
however1 is inferior to that which ,i   
have ascertained myself to be produced  
by engines in regular operation on some 
of the northern railways4 ,in an        
experiment made in ,july1 #ahci1 with   
the ,hecla engine1 ,i found that the    
evaporation in a trip of ninety-five    
miles1 from ,liverpool to ,birmingham1  
was at the rate of #icb cubic feet per  
hour1 and in returning the same distance
 it was at the rate of #heg cubic feet  
per hour1 giving a mean of #hi cubic    
feet per hour nearly4 ,the ,hecla       
weighed #ab tons2 and its dimensions and
 proportions corresponded very nearly   
with those of the engine above          
described4  ,in a course of experiments 
which ,i made upon the engines then in  
use on the ,grand ,junction ,railway in 

the autumn of #ahch ,i found that the   
ordinary evaporating power of these     
engines varied from eighty to           
eighty-five cubic feet per hour4        
,engines of much greater dimensions1 and
 consequently of greater evaporating    
power1 are used on the ,great ,western  
,railway4 ,in the autumn of #ahch       
experiments were made upon these engines
 by ,mr4 ,nicholas ,wood and myself1    
when we found that the most powerful    
engine on that line1 the ,north ,star1  
drawing a load of #aaj-a_/b tons gross1 
engine and tender inclusive1 at #cj-a_/b
 miles an hour1 evaporated #bjj cubic   
feet of water per hour4 ,the same engine
 drawing a load of #aid-a_/b tons at    
#ah-a_/b miles an hour evaporated #ada  
cubic feet per hour1 and when drawing   
#de tons at #ch-a_/b miles an hour      
evaporated #aih cubic feet of water per 
hour4  ,it has been already shown that a
 cubic foot of water evaporated per hour
 produces a gross amount of mechanical  
force very little less than two-horse   

power1 and consequently the gross amount
 of mechanical power evolved in these   
cases by the evaporation of the         
locomotive boilers will be very nearly  
twice as many horse-power as there are  
cubic feet of water evaporated per hour4
 ,thus the evaporation of the ,hecla1 in
 the experiments made in ,july1 #ahci1  
gave a gross power of about one hundred 
and eighty horses1 while the evaporation
 of the ,north ,star gave a power of    
about four hundred horses4 ,in          
stationary engines about half the gross 
,pg#djg power evolved in the evaporation
 is allowed for waste1 friction1 and    
other sources of resistance not         
connected with the load4 ,what quantity 
should be allowed for this in locomotive
 engines is not yet ascertained1 and    
therefore it is impossible to state what
 proportion of the whole evaporation is 
to be taken as representing the useful  
horse-power4   7#aii47 ,the great       
uniformity of resistance produced by the
 traction of carriages upon a railway is

 such as to render the application of   
steam power to that purpose extremely   
advantageous4 ,so far as this resistance
 depends on mechanical defects1 it is   
probably rendered as uniform as is      
practicable1 and in proportion to the   
quantity of load carried is reduced to  
as small an amount as it is likely to   
attain under any practicable            
circumstances4 ,until a recent period   
this resistance was ascribed altogether1
 or nearly so1 to mechanical causes4    
,the inequalities of the road-surface1  
the friction of the axles of the wheels 
in their bearings1 and the various      
sources of resistance due to the        
machinery of the engine1 being the      
principal of these resistances1 were for
 the most part independent of the speed 
with which the train was moved2 and it  
was accordingly assumed in all          
calculations respecting the power of    
locomotive engines that the resistance  
would be practically the same whatever  
might be the speed of the train4 ,it had

 been well understood that so far as the
 atmosphere might offer resistance to   
the moving power this would be dependent
 on the speed1 and would increase in a  
very high ratio with the speed2 but it  
was considered that the part of the     
resistance due to this cause formed a   
fraction of the whole amount so         
insignificant that it might be fairly   
disregarded in practice1 or considered  
as a part of the actual computed        
resistance taken at an average speed4   
,it has been1 until a late period1      
accordingly assumed that the total      
amount of resistance to railway trains  
which the locomotive engines have had to
 overcome was about the two hundred and 
fiftieth part of the gross weight of the
 load drawn3 some engineers estimated it
 at a two hundred and twentieth2 others 
at a two hundred and fiftieth2 others at
 a three hundred and thirtieth part of  
the load2 and the two hundred and       
fiftieth part of the gross load drawn   
may perhaps be ,pg#djh considered as a  

mean between these much varying         
estimates4 ,what the experiments were1  
if any1 on which these rough estimates  
were based1 has never appeared4 ,each   
engineer formed his own valuation of    
this effect1 but none produced the      
experimental grounds of their opinion4  
,it has been said that the trains run   
down the engine1 or that the drawing    
chains connecting the engine slacken in 
descending an inclination of sixteen    
feet in a mile1 or #a_/ccj4 ,numerous   
experiments1 however1 made by myself1 as
 well as the constant experience now    
daily obtained on railways1 show that   
this is a fallacious opinion1 except at 
velocities so low as are never practised
 on railways4   7#bjj47 ,in the autumn  
of #ahch a course of experiments was    
commenced at the suggestion of some of  
the proprietors of the ,great ,western  
,railway ,company1 with a view to       
determine various points connected with 
the structure and the working of        
railways4 ,a part of these experiments  

were intended to determine the mean     
amount of the resisting force opposed to
 the moving power1 and this part was    
conducted by me4 ,after having tried    
various expedients for determining the  
mean amount of resistance to the moving 
power1 ,i found that no method gave     
satisfactory results except one founded 
on observing the motion of trains by    
gravity down steep inclined planes4     
,when a train of waggons or coaches is  
placed upon an inclined plane so steep  
that it shall descend by its gravity    
without any moving power1 its motion1   
when it proceeds from a state of rest1  
will be gradually accelerated1 and if   
the resistance to that motion was1 as it
 has been commonly supposed to be1      
uniform and independent of the speed1   
the descent would be uniformly          
accelerated3 in other words1 the        
increase of speed would be proportional 
to the time of the motion4 ,whatever    
velocity the train would gain in the    
first minute1 it would acquire twice    

that velocity at the end of the second  
minute1 three times that velocity at the
 end of the third minute1 and so on2 and
 this increase of velocity would        
continue to follow the same law1 however
 extended the plane might be4 ,that such
 would be the law which the descending  
motion of a train would follow had      
always been supposed1 up to the time of 
the experiments now referred to2 and it 
was even maintained by some that ,pg#dji
 such a law was in strict conformity    
with experiments made upon railways and 
duly reported4 ,the first experiments   
instituted by me at the time just       
referred to afforded a complete         
refutation of this doctrine4 ,it was    
found that the acceleration was not     
uniform1 but that with every increase of
 speed the acceleration was lessened4   
,thus if a certain speed were gained by 
a train in one second when moving at    
five miles an hour1 a much less speed   
was gained in one second when moving ten
 miles an hour1 and a comparatively     

small speed was gained in the same time 
when moving at fifteen miles an hour1   
and so on4 ,in fact1 the augmentation of
 the rate of acceleration appeared to   
diminish in a very rapid proportion as  
the speed increased3 this suggested to  
me the probability that a sufficiently  
great increase of speed would destroy   
all acceleration1 and that the train    
would at length move at a uniform       
velocity4 ,in effect1 since the moving  
power which impels a train down an      
inclined plane of uniform inclination is
 that fraction of the gross weight of   
the train which acts in the direction of
 the plane1 this moving power must be   
necessarily invariable2 and as any      
acceleration which is produced must     
arise from the excess of this moving    
power over the resistance opposed to the
 motion of the train1 from whatever     
causes that resistance may arise1       
whenever acceleration ceases1 the moving
 force must necessarily be equal to the 
resistance2 and therefore1 when a train 

descends an inclined plane with a       
uniform velocity1 the gross resistance  
to the motion of the train must be equal
 to the gross weight of the train       
resolved in the direction of the plane2 
or1 in other words1 it must be equal to 
that fraction of the whole weight of the
 train which is expressed by the        
inclination of the plane4 ,thus if it be
 supposed that the plane falls at the   
rate of one foot in one hundred1 then   
the force impelling the train downwards 
will be equal to the hundredth part of  
the weight of the train4 ,so long as the
 resistance to the motion of the train  
continues to be less than the hundredth 
part of its weight1 so long will the    
motion of the train be accelerated2 and 
the more the hundredth part of the      
weight exceeds the resistance1 the more 
rapid will the acceleration be2 and the 
less the hundredth part of the weight   
,pg#daj exceeds the resistance1 the less
 rapid will the acceleration be4 ,if it 
be true that the amount of resistance   

increases with the increase of speed1   
then a speed may at length be attained  
so great that the amount of resistance  
to the motion of the train will be equal
 to the hundredth part of the weight4   
,when that happens1 the moving power of 
a hundredth part of the weight of the   
train being exactly equal to the        
resistance to the motion1 there is no   
excess of power to produce acceleration1
 and therefore the motion of the train  
will be uniform4  ,founded on these     
principles1 a vast number of experiments
 were made on planes of different       
inclinations1 and with loads of various 
magnitudes2 and it was found1 in        
general1 that when a train descended an 
inclined plane1 the rate of acceleration
 gradually diminished1 and at length    
became uniform2 that the uniform speed  
thus attained depended on the weight1   
form1 and magnitude of the train and the
 inclination of the plane2 that the same
 train on different inclined planes     
attained different uniform speeds--on   

the steeper planes a greater speed being
 attained4 ,from such experiments it    
followed1 contrary to all that had been 
previously supposed1 that the amount of 
resistance to railway trains had a      
dependence on the speed2 that this      
dependence was of great practical       
importance1 the resistance being subject
 to very considerable variation at      
different speeds1 and that this source  
of resistance arises from the atmosphere
 which the train encounters4 ,this was  
rendered obvious by the different amount
 of resistance to the motion of a train 
of coaches and to that of a train of low
 waggons of equal weight4  ,the former  
editions of this work having been       
published before the discovery which has
 resulted from these experiments1 the   
average amount of resistance to railway 
trains1 there stated1 and the           
conclusions deduced therefrom1 were in  
conformity with what was then known4 ,it
 was stated that the resistance to the  
moving power was practically independent

 of the speed1 and on level rails was at
 the average rate of about seven pounds 
and a half per ton4 ,this amount would  
be equivalent to the gravitation of a   
load down an inclined plane falling     
#a_/cjj1 and consequently in ascending  
such a plane the moving power would have
 to encounter twice ,pg#daa the         
resistance opposed to it on a level4 ,as
 it was generally assumed that a        
locomotive-engine could not             
advantageously vary its tractive power  
beyond this limit1 it was therefore     
inferred that gradients 7as inclinations
 are called7 ought not to be constructed
 of greater steepness than #a_/cjj4 ,it 
was supposed that in descending         
gradients more steep than this the train
 would be accelerated and would require 
the use of the brake to check its       
motion1 while in ascending such planes  
the engine would be required to exert   
more than twice the ordinary tractive   
power required on level rails4 ,as the  
resistance produced by the air was not  

taken into consideration1 no distinction
 was made between heavy trains of goods 
presenting a frontage and magnitude     
bearing a small proportion to their     
gross weight and lighter trains of      
passenger-coaches presenting great      
frontage and great magnitude in         
proportion to their weight4 ,the result 
of the experiments above explained leads
 to inferences altogether at variance   
with those which have been given in     
former editions of the present work1 and
 which were then universally admitted by
 railway engineers4 ,the tendency of the
 results of these experiments show that 
low gradients on railways are not       
attended with the advantageous effects  
which have been hitherto ascribed to    
them2 that1 on the contrary1 the        
resistance produced by steeper gradients
 can be compensated by slackening the   
speed1 so that the power shall be       
relieved from as much atmospheric       
resistance by the diminution of velocity
 as is equal to the increased resistance

 produced by the gravity of the plane   
which is ascended4 ,and1 on the other   
hand1 in descending the plane the speed 
may be increased until the resistance   
produced by the atmosphere is increased 
to the same amount as that by which the 
train is relieved of resistance by the  
declivity down which it moves4 ,thus1 on
 gradients1 the inclination of which is 
confined within practical limits1 the   
resistance to the moving-power may be   
preserved uniform1 or nearly so1 by     
varying the velocity4   7#bja47 ,the    
series of experiments which have        
established these general conclusions   
have not yet been sufficiently extended 
and varied to supply a correct practical
 estimate of the limit which it would be
 most advantageous to impose upon the   
,pg#dab gradients of railways2 but it is
 certain that railways may be laid down1
 without practical disadvantage1 with   
gradients considerably steeper than     
those to which it has been hitherto the 
practice to recommend as a limit4  ,the 

principle of compensation by varied     
speed being admitted1 it will follow    
that the time of transit between        
terminus and terminus of a line of      
railway laid down with gradients1       
varying from twenty to thirty feet a    
mile1 will be practically the same as it
 would be on a line of the same length  
constructed upon a dead level2 and not  
only will the time of transport be      
equal1 but the quantity of moving power 
expended will not be materially         
different4 ,the difference between the  
circumstances of the transport in the   
two cases will be merely that1 on the   
undulating line1 a varying velocity will
 be imparted to the train and a varying 
resistance opposed to the moving power2 
while on the level line the train would 
be moved at a uniform speed1 and the    
engine worked against a uniform         
resistance4 ,these conclusions have been
 abundantly confirmed by the experiments
 made in last ,july with the ,hecla     
engine above referred to4 ,the line of  

railway between ,liverpool and          
,birmingham on which the experiment was 
made extended over a distance of        
ninety-five miles1 and the gradients on 
which the effects were observed varied  
from a level to thirty feet per mile1 a 
great portion of the line being a dead  
level4 ,the following table shows the   
uniform speed with which the train      
ascended and descended the several      
gradients1 and also the mean of the     
ascent and descent in each case1 as well
 as the speed upon the level parts of   
the line3--                             
----------------------------------------
----------------------------------------
--------------------                    
,speed4                                 
----------------------------------------
--------------------------------------- 
,gradient4  ,ascending4     ,descending4
     ,mean4                             
----------------------------------------
----------------------------------------
--------------------    ,one in  ,miles 

per hour4,miles per hour4     #agg      
#bbbe         #dacb         #cagh       
#bfe         #bdhg         #ciac        
#cbjj     #ccj         #bebf            
#cgjg         #caaf     #djj            
#bfhg         #cfge         #caha       
#ecb         #bgce         #cdcj        
#cjhb     #eij         #bgcg            
#ccaf         #cjba     #fej            
#bijc         #cbeh         #cjhj       
----------------   ,level               
#cjic                                   
----------------------------------------
----------------------------------------
--------------------  ,pg#dac ,from this
 table it is apparent that the gradients
 do possess the compensating power with 
respect to speed already mentioned4 ,the
 discrepancies existing among the mean  
values of the speed are only what may be
 fairly ascribed to casual variations in
 the moving power4 ,the experiment was  
made under favourable circumstances3    
little disturbance was produced from the
 atmosphere2 the day was quite calm4 ,in

 the same experiment it was found that  
the water evaporated varied very nearly 
in proportion to the varying resistance1
 and the amount of that evaporation may 
be taken as affording an approximation  
to the mean amount of resistance4       
,taking the trip to and from ,birmingham
 over the distance of #aij miles1 the   
mean evaporation per mile was #ccf cubic
 feet of water4 ,the volume of steam    
produced by this quantity of water will 
be determined approximately by          
calculating the number of revolutions of
 the driving wheels necessary to move   
the engine one mile4 ,the driving wheels
 being #e feet in diameter1 their       
circumference was #aeg feet1 and        
consequently in passing over a mile they
 would have revolved #ccfc times4 ,since
 each revolution consumes four cylinders
 full of steam1 the quantity of steam   
supplied by the boiler to the cylinders 
per mile will be found by multiplying   
the contents of the cylinder by four    
times #ccfc1 or #acdeb4  ,the cylinders 

of the ,hecla were #ab-a_/b inches      
diameter1 and #ah inches in length1 and 
consequently their contents were #abh   
cubic feet for each cylinder3 this being
 multiplied by #acdeb gives #agbahf or  
#agbb cubic feet of steam per mile4 ,it 
appears1 therefore1 that supposing the  
priming either nothing or insignificant1
 which was considered to be the case in 
these experiments1 #ccf cubic feet of   
water produced #agbb cubic feet of      
steam1 of the density worked in the     
cylinders4 ,the ratio1 therefore1 of the
 volume of this steam to that of the    
water producing it1 was #agbb to #ccf1  
or #eabe to #a4 ,the pressure of steam  
of this density would be #ede pounds per
 square inch4#cd ,such1 therefore1 was  
the limit of the average total pressure 
of the steam in the cylinders4 ,in this 
experiment the safety-valve of the      
boiler was screwed down to #fj pounds   
per square ,pg#dad inch above the       
atmospheric pressure1 which was         
therefore the major limit of the        

pressure of steam in the boiler2 but as 
the actual pressure in the boiler must  
have been less than this amount1 the    
difference between the pressure in the  
cylinder and boiler could not be        
ascertained4 ,this difference1 however1 
would produce no effect on the moving   
power of the steam1 since the pressure  
of steam in the cylinders obtained by   
the above calculation is quite          
independent of the pressure in the      
boiler1 or of any source of error except
 what might arise from priming4 ,the    
pressure of #ede pounds per square inch1
 calculated above1 being the total      
pressure of the steam on the pistons1   
let #ade pounds be deducted from it1 to 
represent the atmospheric pressure      
against which the piston must act1 and  
the remaining #dj pounds per square inch
 will represent the whole available     
force drawing the train and overcoming  
all the resistances arising from the    
machinery of the engine1 including that 
of the blast-pipe4 ,the magnitude of a  

#ab-a_/b inch piston being #abbg square 
inches1 the total area of the two       
pistons would be #bdeb square inches1   
and the pressure upon each of #dj pounds
 per inch would give a total force of   
#ihaf on the two pistons4 ,since this   
force must act through a space of three 
feet1 while the train is impelled       
through a space of #aeg feet1 it must be
 reduced in the proportion of #c to     
#aeg1 to obtain its effect at the point 
of contact of the wheels upon the rails3
 this will give #ahge pounds as the     
total force exerted in the direction of 
the motion of the train4 ,the gross     
weight of the train being #hj tons1     
including the engine and tender1 this   
would give a gross moving force along   
the road of about #bcd pounds per ton of
 the gross load1 this force being       
understood to include all the           
resistances due to the engine4 ,this    
resistance corresponds to the           
gravitation of a plane rising at the    
rate of #a_/ie1 and therefore it appears

 that such would be the inclination of  
the plane by the gravitation of which   
the gross resistance would be doubled1  
instead of such inclination being about 
#a_/cjj1 as has been hitherto supposed4 
,since the remarkable and unexpected    
results of this series of experiments   
became known various circumstances were 
brought to light1 which were before     
unnoticed1 and which ,pg#dae abundantly 
confirm them4 ,among these may be       
mentioned the fact1 that in descending  
the ,madeley plane1 on the ,grand       
,junction ,railway1 which falls for     
above three miles at the rate of        
twenty-nine feet a mile1 the steam can  
never be entirely cut off4 ,but1 on the 
other hand1 to maintain the necessary   
speed in descending1 the power of the   
engine is always necessary4 ,as this    
plane greatly exceeds that which would  
be sufficient to cause the free motion  
of the train down it1 the power of the  
engine expended in descending it1       
besides all that part of the gravitating

 power of the plane which exceeds the   
resistance due to friction and other    
mechanical causes must be worked against
 the atmosphere4  ,this estimate of the 
resistance is also in conformity with   
the results of a variety of experiments 
made by me with trains of different     
magnitudes down inclined planes of      
various inclinations4   7#bjb47 ,in     
laying out a line of railway the        
disposition of the gradients should be  
such as to preserve among them as       
uniform a character as is practicable1  
for the weight and power of the engine  
must necessarily be regulated by the    
general steepness of the gradients4     
,thus if upon a railway which is        
generally level1 like that between      
,liverpool and ,manchester1 one or two  
inclined planes of a very steep         
character occur1 as happens upon that   
line1 then the engine which is          
constructed to work upon the general    
gradients of the road is unfit to draw  
the same load up those inclinations     

which form an exception to the general  
character of the gradients4 ,in such    
cases some extraordinary means must     
generally be provided for surmounting   
those exceptionable inclinations4       
,several expedients have been proposed  
for this purpose1 among which the       
following may be mentioned3--  #a4 ,upon
 arriving at the foot of the plane the  
load is divided1 and the engine carries 
it up in several successive trips1      
descending the plane unloaded after each
 trip4 ,the objection to this method is 
the delay which it occasions--a         
circumstance which is incompatible with 
a large transport of passengers4 ,from  
what has been stated1 it would be       
necessary1 when the engine is fully     
loaded on a level1 to divide its load   
into two or more parts1 to be           
successively ,pg#daf carried up when the
 incline rises #eb feet per mile4 ,this 
method has been practised in the        
transport of merchandise occasionally1  
when heavy loads were carried on the    

,liverpool and ,manchester line1 upon   
the ,rainhill incline4  #b4 ,a          
subsidiary or assistant locomotive      
engine may be kept in constant readiness
 at the foot of each incline1 for the   
purpose of aiding the different trains1 
as they arrive1 in ascending4 ,the      
objection to this method is the cost of 
keeping such an engine with its boiler  
continually prepared1 and its steam up4 
,it is necessary to keep its fire       
continually lighted1 whether employed or
 not2 otherwise1 when the train would   
arrive at the foot of the incline1 it   
should wait until the subsidiary engine 
was prepared for work4 ,in cases where  
trains would start and arrive at stated 
times1 this objection1 however1 would   
have less force4 ,this method is at     
present generally adopted on the        
,liverpool and ,manchester line4  #c4 ,a
 fixed steam-engine may be erected on   
the crest of the incline1 so as to      
communicate by ropes with the train at  
the foot4 ,such an engine would be      

capable of drawing up one or two trains 
together1 with their locomotives1       
according as they would arrive1 and no  
delay need be occasioned4 ,this method  
requires that the fixed engine should be
 kept constantly prepared for work1 and 
the steam continually up in the boiler4 
#d4 ,in working on the level1 the       
communication between the boiler and the
 cylinder in the locomotives may be so  
restrained by partially closing the     
throttle-valve1 as to cause the pressure
 upon the piston to be less in a        
considerable degree than the pressure of
 steam in the boiler4 ,if under such    
circumstances a sufficient pressure upon
 the piston can be obtained to draw the 
load on the level1 the throttle-valve   
may be opened on approaching the        
inclined plane1 so as to throw on the   
piston a pressure increased in the same 
proportion as the previous pressure in  
the boiler was greater than that upon   
the piston4 ,if the fire be sufficiently
 active to keep up the supply of steam  

in this manner during the ascent1 and if
 the rise be not greater in proportion  
than the power thus obtained1 the       
locomotive will draw the load up the    
incline without further assistance4 ,it 
is1 however1 to be observed1 that in    
this case ,pg#dag the load upon the     
engine must be less than the amount     
which the adhesion of its working wheels
 with the railroad is capable of        
drawing2 for this adhesion must be      
adequate to the traction of the same    
load up the incline1 otherwise1 whatever
 increase of power might be obtained by 
opening the throttle-valve1 the drawing 
wheels would revolve without causing the
 load to advance4 ,this method has been 
generally practised upon the ,liverpool 
and ,manchester line in the transport of
 passengers2 and1 indeed1 it is the only
 method yet discovered which is         
consistent with the expedition necessary
 for that species of traffic4  ,in the  
practice of this method considerable aid
 may be derived also by suspending the  

supply of feeding water to the boiler   
during the ascent4 ,it will be          
recollected that a reservoir of cold    
water is placed in the tender which     
follows the engine1 and that the water  
is driven from this reservoir into the  
boiler by a forcing pump1 which is      
worked by the engine itself4 ,this pump 
is so constructed that it will supply as
 much cold water as is equal to the     
evaporation1 so as to maintain          
constantly the same quantity of water in
 the boiler4 ,but it is evident1 on the 
other hand1 that the supply of this     
water has a tendency to check the rate  
of evaporation1 since in being raised to
 the temperature of the water with which
 it mixes it must absorb a considerable 
portion of the heat supplied by the     
fire4 ,with a view to accelerate the    
production of steam1 therefore1 in      
ascending the inclines1 the engine man  
may suspend the action of the forcing   
pump1 and thereby stop the supply of    
cold water to the boiler2 the           

evaporation will go on with increased   
rapidity1 and the exhaustion of water   
produced by it will be repaid by the    
forcing pump on the next level1 or still
 more effectually on the next descending
 incline4 ,indeed the feeding pump may  
be made to act in descending an incline1
 if necessary1 when the action of the   
engine itself is suspended1 and when the
 train descends by its own gravity1 in  
which case it will perform the part of a
 brake upon the descending train4  #e4  
,the mechanical connexion between the   
piston of the cylinder and the points of
 contact of the working wheels with the 
road may be so altered1 upon arriving at
 the incline1 as to ,pg#dah give the    
piston a greater power over the working 
wheels4 ,this may be done in an infinite
 variety of ways1 but hitherto no method
 has been suggested sufficiently simple 
to be applicable in practice2 and even  
were any means suggested which would    
accomplish this1 unless the intensity of
 the impelling power were at the same   

time increased1 it would necessarily    
follow that the speed of the motion     
would be diminished in exactly the same 
proportion as the power of the piston   
over the working wheels would be        
increased4 ,thus1 on the inclined plane1
 which rises fifty-five feet per mile1  
upon the ,liverpool line1 the speed     
would be diminished to nearly one fourth
 of its amount upon the level4          
,illustration    ,,footnotes3    #cj    
,some of the preceding observations on  
inland transport1   as well as other    
parts of the present chapter1 appeared  
in   articles written by me in the      
,edinburgh ,review for ,october1        
#ahcb1 and ,october1 #ahcd4    #ca ,wood
 on ,railroads1 #b;d edit4    #cb ,the  
cost of coke has risen considerably     
since the date of   this report4    #cc 
,i am indebted to the enlarged edition  
of ,tredgold on the   ,steam ,engine1   
published by ,mr4 ,weale1 for the       
drawings of this   engine4 ,the details 
of the machine are very fully given in  

that work1 the description of them being
 supplied by ,mr4   ,stephenson himself4
    #cd ,see ,table of ,pressures1      
,temperatures1 and ,volumes1 in         
appendix4  ,pg#dai     ,illustration    
,,chap4 ,,xii4  ,,locomotive ,,engines  
,,on ,,turnpike ,,roads4      ,,railways
 ,,and ,,stone ,,roads ,,compared4 --   
,,mr4 ,,gurney',s ,,steam     ,,engine4 
-- ,,convenience ,,and ,,safety ,,of    
,,steam ,,carriages4 --     ,,hancock',s
 ,,steam ,,engine4 -- ,,ogle',s ,,steam 
,,engine4 -- ,,trevethick',s            
,,invention4 -- ,,dr4 ,,church',s       
,,steam ,,engine4   7#bjc47 ,we have    
hitherto confined our observations on   
steam-power1 as a means of transport by 
land1 to its application on railways4   
,but modern speculation has not stopped 
there2 various attempts have been made1 
and attended with more or less success1 
to work steam-carriages on common roads4
 ,the mere practicability of this       
project had long been regarded as very  
questionable2 but enough has been done  

to show that the only doubt which can   
attend it1 is as to whether it can be   
profitably resorted to1 as a means of   
transport1 and this question ,pg#dbj has
 been materially affected by the recent 
extension of railways4 ,in comparing the
 effect of a stone road with an iron    
railway1 there are two circumstances    
which give great superiority and        
advantage to the latter3 first1 the     
resistance opposed by a railway to the  
moving power1 no matter what that moving
 power may be1 is considerably less in  
proportion to the load than on a stone  
road4 ,the average resistance on a good 
level stone road1 to the motion of      
carriages drawn at the speed usually    
attained by the application of          
horse-power1 may be taken at about a    
thirty-sixth part of the load1 while the
 resistance to a load drawn upon a      
railway at the same speed probably does 
not amount to a tenth part of this      
resistance4 ,thus the moving power1     
whatever it may be1 would produce on a  

railway ten times the useful effect     
which it would produce on a stone road2 
secondly1 the resistance which is       
opposed to the moving power on a level  
railway is much more uniform than on a  
stone road1 and1 consequently1 the      
moving power is less subjected to jerks 
and inequalities4 ,this renders the     
application of inanimate power more easy
 on the railway4 ,those inequalities of 
surface which increase the amount of    
resistance on stone roads as compared   
with railways also produce a jolting    
motion in the carriage1 to counteract   
which1 the use of springs become        
necessary4 ,these springs render the    
motion of that part of the carriage     
which rests upon them different from    
that part of the carriage which supports
 them2 and in the application of        
steam-machinery it becomes necessary so 
to connect the moving power with the    
wheels that the machinery may have one  
motion1 and the wheels which are put in 
mechanical connexion with that          

machinery1 and driven by it1 shall have 
another motion4 ,this1 it is true1 is   
the case with locomotive engines on     
railways2 but owing to the greater      
smoothness and equality of the railway  
surface the difference between the      
motion of the carriage body suspended on
 springs and that of the wheels is much 
less than it would be on a stone road4  
,but besides the greater smoothness of  
railways compared with stone roads1 the 
latter have another disadvantage1 the   
effects of which have probably been     
exaggerated by those who are opposed to 
this application of steam-power4 ,one of
 the ,pg#dba laws of adhesion long since
 developed by experiment1 and           
established as a principle of practical 
science1 is that the adhesion is greater
 between surfaces of the same than      
between surfaces of a different kind4   
,thus between two metals of the same    
kind1 the adhesion corresponding to any 
given pressure is greater than between  
two metals of different kinds2 between  

two metals of any sort the adhesion is  
greater than between metal and stone1 or
 between metal and wood4 ,hence1 the    
wheels of steam-carriages running on a  
railroad have a greater adhesion with   
the road1 and therefore offer a greater 
resistance to slip round without the    
advance of the carriage1 than wheels    
would offer on a turnpike road2 for on a
 railroad the iron tire of the wheel    
rests in contact with the iron rail1    
while on a common road the iron tire    
rests in contact with the surface of    
stone1 or whatever material the road may
 be composed of4 ,besides this1 the dust
 and loose matter which necessarily     
collect on a common road1 when pressed  
between the wheels and the solid base of
 the road1 act somewhat in the manner of
 rollers1 and give the wheels a greater 
facility to slip than if the road were  
swept clean1 and the wheels rested in   
immediate contact with its hard surface4
 ,the truth of this observation is      
illustrated on the railroads themselves1

 where the adhesion is found to be      
diminished whenever the rails are       
covered with any extraneous matter1 such
 as dust or moist clay4 ,although the   
adhesion of the wheels of a carriage    
with a common road1 however1 be less    
than those of the wheels of a           
steam-carriage with a railroad1 yet     
still the actual adhesion on turnpike   
roads is greater in amount than has been
 generally supposed1 and is quite       
sufficient to propel carriages drawing  
after them loads of large amount4  ,the 
relative facility with which carriages  
are propelled on railroads and          
turnpike-roads equally affects any      
moving power1 whether that of horses or 
steam engines2 and whether loads be     
propelled by the one power or the other1
 the railroad1 as compared with the     
turnpike-road1 will always possess the  
same proportionate advantage2 and a     
given amount of power1 whether of the   
one kind or the other1 will always      
perform a quantity of work less in the  

same proportion on a ,pg#dbb            
turnpike-road than on a rail-road4 ,but1
 on the other hand1 the expense of      
original construction1 and of           
maintaining the repairs of a rail-road1 
is to be placed against the certain     
facility which it offers to draught4    
,in the attempts which have been made to
 adapt locomotive engines to            
turnpike-roads1 the projectors have     
aimed at the accomplishment of two      
objects3 first1 the construction of     
lighter and smaller engines2 and1       
secondly1 increased power4 ,these ends1 
it is plain1 can only be attained1 with 
our present knowledge1 by the production
 of steam of very high temperature and  
pressure1 so that the smallest volume of
 steam shall produce the greatest       
possible mechanical effect4 ,the methods
 of propelling the carriage have been in
 general similar to that used in the    
railroad engines1 viz4 either by cranks 
placed on the axles1 the wheels being   
fixed upon the same axles1 or by        

connecting the piston rods with the     
spokes of the wheels4 ,in some          
carriages1 the boiler and moving power1 
and the body of the carriage which bears
 the passengers1 are placed on the same 
wheels4 ,in others1 the engine is placed
 on a separate carriage1 and draws after
 it the carriage which transports the   
passengers1 as is always the case on    
railways4  ,the chief difference between
 the steam engines used on railways1 and
 those adapted to propel carriages on   
turnpike roads1 is in the structure of  
the boiler4 ,in the latter it is        
essential that1 while the power remains 
undiminished1 the boiler should be      
lighter and smaller4 ,the accomplishment
 of this has been attempted by various  
contrivances for so distributing the    
water as to expose a considerable       
quantity of surface in contact with it  
to the action of the fire3 spreading it 
in thin layers on flat plates2 inserting
 it between plates of iron placed at a  
small distance asunder1 the fire being  

admitted between the intermediate       
plates2 dividing it into small tubes1   
round which the fire has play2          
introducing it between the surfaces of  
cylinders placed one within another1 the
 fire being admitted between the        
alternate cylinders1--have all been     
resorted to by different projectors4    
7#bjd47 ,first and most prominent in the
 history of the application of steam to 
the propelling of carriages on turnpike 
roads stands the name of ,mr4           
,goldsworthy ,gurney1 a medical ,pg#dbc 
gentleman1 and scientific chemist1 of   
,cornwall4 ,in #ahbb1 ,mr4 ,gurney      
succeeded ,dr4 ,thompson as lecturer on 
chemistry at the ,surrey ,institution2  
and1 in consequence of the results of   
some experiments on heat1 his attention 
was directed to the project of working  
steam-carriages on common roads2 and he 
subsequently devoted his exertions in   
perfecting a steam-engine capable of    
attaining the end he had in view4  ,the 
mistake which so long prevailed in the  

application of locomotives on railroads1
 and which1 as we have shown1 materially
 retarded the progress of that          
invention1 was shared by ,mr4 ,gurney4  
,without reducing the question to the   
test of experiment1 he took for granted1
 in his first attempts1 that the        
adhesion of the wheels with the road was
 too slight to propel the carriage4 ,he 
was assured1 he says1 by eminent        
engineers1 that this was a point settled
 by actual experiment4 ,it is strange1  
however1 that a person of his quickness 
and sagacity did not inquire after the  
particulars of these actual experiments4
 ,so1 however1 it was2 and1 taking for  
granted the inability of the wheels to  
propel1 he wasted much labour and skill 
in the contrivance of levers and        
propellers1 which acted on the ground in
 a manner somewhat resembling the feet  
of horses1 to drive the carriage        
forward4 ,after various fruitless       
attempts of this kind1 the experience   
acquired in the trials to which they    

gave rise at last forced the truth upon 
his notice1 and he found that the       
adhesion of the wheels was not only     
sufficient to propel the carriage       
heavily laden on level roads1 but was   
capable of causing it to ascend all the 
hills which occur on ordinary           
turnpike-roads4 ,in this manner it      
ascended all the hills between ,london  
and ,barnet1 ,london and ,stanmore1     
,stanmore ,hill1 ,brockley ,hill1 and   
mounted ,old ,highgate ,hill1 the last  
at one point rising one foot in nine4   
,illustration3 ,fig4 #aad4              
,illustration3 ,fig4 #aae4  ,the boiler 
of ,mr4 ,gurney's engine is so          
constructed1 that there is no part of it
 in which metal exposed to the action of
 the fire is out of contact with water4 
,if it be considered how rapidly the    
action of an intense furnace destroys   
metal when water is not present to      
prevent the heat from accumulating1 the 
advantage of this circumstance will be  
appreciated4 ,in the boiler of ,mr4     

,gurney1 the grate-bars ,pg#dbd         
themselves are tubes filled with water1 
and form1 in fact1 a part of the boiler 
itself4 ,this boiler consists of three  
strong metal cylinders placed in a      
horizontal position one above the other4
 ,a section1 made by a perpendicular or 
vertical plane1 is represented in fig4  
#aad4 ,the ends of the three cylinders  
just mentioned are represented at ,d1   
,h1 and ,i4 ,in the side of the lowest  
cylinder ,d are inserted a row of tubes1
 a ground plan of which is represented  
in fig4 #aae4 ,these tubes1 proceeding  
from the side of the lowest cylinder ,d1
 are inclined ,pg#dbe slightly upwards1 
for a reason which ,i shall presently   
explain4 ,from the nature of the        
section1 only one of these tubes is     
visible in fig4 #aad4 at ,c4 ,the other 
extremities of these tubes at ,a are    
connected with the same number of       
upright tubes1 one of which is shown at 
,e4 ,the upper extremities ,g of these  
upright tubes are connected with another

 set of tubes ,k1 equal in number1      
proceeding from ,g1 inclining slightly  
upwards1 and terminating in the second  
cylinder ,h4  ,illustration3 ,fig4 #aaf4
  ,an end view of the boiler is         
exhibited in fig4 #aaf41 where the three
 cylinders are expressed by the same    
letters4 ,between the cylinders ,d and  
,h there are two tubes of communication 
,b1 and two similar tubes between the   
cylinders ,h and ,i4 ,from the nature of
 the section these appear only as a     
single tube in fig4 #aad4 ,from the top 
of the cylinder ,i proceeds a tube ,n1  
by which steam is conducted to the      
engine4  ,it will be perceived that the 
space ,f is enclosed on every side by a 
grating of tubes1 which have free       
communication with the cylinders ,d and 
,h1 which cylinders have also a free    
communication with each other by the    
tubes ,b4 ,it follows1 ,pg#dbf          
therefore1 that if water be supplied to 
the cylinder ,i1 it will descend through
 the tubes1 and first filling the       

cylinder ,d and the tubes ,c1 will      
gradually rise in the tubes ,b and ,e1  
will next fill the tubes ,k and the     
cylinder ,h4 ,the grating of water-pipes
 ,c ,e ,k forms the furnace1 the pipes  
,c being the fire-bars1 and the pipes ,e
 and ,k being the back and roof of the  
stove4 ,the fire-door1 for the supply of
 fuel1 appears at ,m1 fig4 #aaf4 ,the   
flue issuing between the tubes ,f is    
conducted over the tubes ,k1 and the    
flame and hot air are carried off       
through a chimney4 ,that portion of the 
heat of the burning fuel1 which in other
 furnaces destroys the bars of the      
grate1 is here expended in heating the  
water contained in the tubes ,c4 ,the   
radiant heat of the fire acts upon the  
tubes ,k1 forming the roof of the       
furnace1 on the tube ,e at the back of  
it1 and partially on the cylinders ,d   
and ,h1 and the tubes ,b4 ,the draft of 
hot air and flame passing into the flue 
at ,a acts upon the posterior surfaces  
of the tubes ,e1 and the upper sides of 

the tubes ,k1 and finally passes into   
the chimney4  ,as the water in the tubes
 ,c ,e ,k is heated1 it becomes         
specifically lighter than water of a    
less temperature1 and consequently      
acquires a tendency to ascend4 ,it      
passes1 therefore1 rapidly into ,h4     
,meanwhile the colder portions descend1 
and the inclined positions of the tubes 
,c and ,k give play to this tendency of 
the heated water1 so that a prodigiously
 rapid circulation is produced1 when the
 fire begins to act upon the tubes4     
,when the water acquires such a         
temperature that steam is rapidly       
produced1 steam-bubbles are constantly  
formed in the tubes surrounding the     
fire2 and if these remained stationary  
in the tubes1 the action of the fire    
would not only decompose the steam1 but 
render the tubes red hot1 the water not 
passing through them to carry off the   
heat4 ,but the inclined position of the 
tubes1 already noticed1 effectually     
prevents this injurious consequence4 ,a 

steam-bubble1 which is formed either in 
the tubes ,c or ,k1 having a tendency to
 ascend proportional to its lightness as
 compared with water1 necessarily rushes
 upwards2 if in ,c towards ,a1 and if in
 ,k towards ,h4 ,but this motion of the 
steam is also aided by the rapid        
circulation of the water which is       
continually maintained ,pg#dbg in the   
tubes1 otherwise it might be possible1  
notwithstanding the levity of steam     
compared with water1 that a bubble might
 remain in a narrow tube without rising4
 ,to bring the matter to the test of    
experiment1 ,i have connected two       
cylinders1 such as ,d and ,h1 by a      
system of glass tubes1 such as          
represented at ,c ,e ,k4 ,the rapid and 
constant circulation of the water was   
then made evident3 bubbles of steam were
 formed in the tubes1 it is true2 but   
they passed with great rapidity into the
 upper cylinder1 and rose to the        
surface1 so that the glass tubes never  
acquired a higher temperature than that 

of the water which passed through them4 
,every part of the boiler being         
cylindrical1 it has the form which1     
mechanically considered1 is most        
favourable to strength1 and which1      
within given dimensions1 contains the   
greatest quantity of water4 ,it is also 
free from the defects arising from      
unequal expansion1 which are found to be
 most injurious in tubular boilers4 ,the
 tubes ,c and ,k can freely expand in   
the direction of their length1 without  
being loosened at their joints1 and     
without straining any part of the       
apparatus2 the tubes ,e1 being short1   
are subject to a very slight degree of  
expansion2 and it is obvious that the   
long tubes1 with which they are         
connected1 will yield to this without   
suffering a strain1 and without causing 
any part of the apparatus to be         
loosened4  ,when water is converted into
 steam1 any foreign matter which may be 
combined with it is disengaged1 and is  
deposited on the bottom of the vessel in

 which the water is evaporated4 ,all    
boilers1 therefore1 require occasional  
cleansing1 to prevent the crust thus    
formed from accumulating2 and this      
operation1 for obvious reasons1 is      
attended with peculiar difficulty in    
tubular boilers4 ,in the case before us1
 the crust of deposited matter would    
gather and thicken in the tubes ,c and  
,k1 and if not removed1 would at length 
choke them4 ,but besides this1 it would 
be attended with a still worse effect2  
for1 being a bad conductor1 it would    
intercept the heat in its transit from  
the fire to the water1 and would cause  
the metal of the tube to become unduly  
heated4 ,mr4 ,gurney of course foresaw  
this inconvenience1 and contrived an    
ingenious chemical method of removing   
it1 by occasionally injecting ,pg#dbh   
through the tubes such an acid as would 
combine with the deposit1 and carry it  
away4 ,this method was effectual2 and   
although its practical application was  
found to be attended with difficulty in 

the hands of common workmen1 ,mr4       
,gurney was persuaded to adhere to it by
 the late ,dr4 ,wollaston1 until        
experience proved the impossibility of  
getting it effectually performed1 under 
the circumstances in which boilers are  
commonly used4 ,mr4 ,gurney then adopted
 a method of removing the deposit by    
mechanical means4 ,opposite the mouths  
of the tubes1 and on the other side of  
the cylinders ,d and ,h1 are placed a   
number of holes1 which1 when the boiler 
is in use1 are stopped by pieces of     
metal screwed into them4 ,when the tubes
 require to be cleaned1 these stoppers  
are removed1 and an iron scraper is     
introduced through the holes into the   
tubes1 which1 being passed backwards and
 forwards1 removes the deposit4  ,in    
these engines the draught through the   
furnace was produced by projecting the  
waste steam up the chimneys as is       
practised in railway engines2 a method  
so perfectly effectual1 that it is      
unlikely to be superseded by any other4 

,the objection which has been urged     
against it in locomotive engines1       
working on turnpike-roads1 is1 that the 
noise which it produces has a tendency  
to frighten horses4  ,in the engines on 
the ,liverpool road1 the steam is       
allowed to pass directly from the       
eduction pipe of the cylinder to the    
chimney1 and it there escapes in puffs  
corresponding with the alternate motion 
of the pistons1 and produces a noise1   
which1 although attended with no        
inconvenience on the railroad1 would    
perhaps be objectionable on             
turnpike-roads4 ,in the engine used in  
,mr4 ,gurney's steam-carriage1 the steam
 which passes from the cylinders is     
conducted to a receptacle1 which he     
calls a blowing box4 ,this box serves   
the same purpose as the upper chamber of
 a smith's bellows4 ,it receives the    
steam from the cylinders in alternate   
puffs1 but lets it escape into the      
chimney in a continued stream by a      
number of small jets4 ,regular draught  

is by this means produced1 and no noise 
is perceived4 ,another exit for the     
steam is also provided1 by which the    
conductor is enabled to increase or     
diminish1 or to suspend altogether1 the 
draught ,pg#dbi in the chimney1 so as to
 adapt the intensity of the fire to the 
exigencies of the road4 ,this is a great
 convenience in practice2 because on    
some roads a draught is scarcely        
required1 while on others a powerful    
blast is indispensable4  ,connected with
 this blowing box is another apparatus  
of considerable practical importance4   
,the pipe through which the feeding     
water is conducted from the tank is     
carried through this blowing box1 within
 which it is coiled in a spiral form1 so
 that an extensive thread of the water  
is exposed to the heat of the waste     
steam which has escaped from the        
cylinders1 and which is enclosed in this
 blowing box4 ,in passing through this  
pipe the feeding water is raised from   
the ordinary temperature of about #fj to

 the temperature of #bab4 ,fuel is thus 
economised and weight diminished2 but   
there is another still greater advantage
 attending this process4 ,the feeding   
water in the worm just mentioned1 while 
it takes up the heat from the           
surrounding steam in the blowing box1   
condenses a part of the waste steam1    
which is thence conducted to the tank1  
from which the feeding water is pumped4 
,when steam is generated so rapidly as  
is necessarily the case in locomotive   
boilers1 it rises with great violence in
 numerous bubbles from the bottom of the
 boiler to the surface of the water1 and
 puts the liquid into a state of foaming
 turbulence not unlike the sea in a     
storm4 ,as the steam rushes from the    
surface into the upper part of the      
boiler1 under these circumstances1 it   
carries with it a spray by which water  
is scattered in minute subdivision among
 the steam1 and floats there like the   
spray which rises from the base of a    
cascade4 ,if the steam be conducted     

immediately to the cylinder from the    
boiler in this state1 it will carry with
 it the water which is thus suspended in
 it1 which will pass through the        
cylinder1 and finally be driven into the
 atmosphere upon the returning stroke of
 the piston4 ,the hot water thus carried
 off possesses none of the mechanical   
properties of steam1 and is wholly      
inefficient as a moving power1 and is   
therefore an extensive source of the    
waste of heat4 ,in every boiler1 some   
means should be provided for the        
separation of the water thus suspended  
in the steam1 before the steam is       
conducted to the cylinder4 ,in ordinary 
boilers1 the large space which ,pg#dcj  
remains above the surface of the water  
serves this purpose4 ,the steam being   
there subject to no agitation or        
disturbance1 the water mechanically     
suspended in it descends by its own     
gravity1 and leaves pure steam in the   
upper part4 ,in the small tubular       
boilers1 this has been a matter1        

however1 of greater difficulty4 ,the    
contracted space in which the ebullition
 takes place causes the water to be     
mixed with the steam in a greater       
quantity than could happen in common    
boilers2 and the want of the same       
steam-room renders the separation of the
 water from the steam a matter of some  
difficulty4 ,these inconveniences have  
been attempted to be overcome by various
 contrivances4 ,i have already described
 the rapid and regular circulation      
effected by the arrangement of the      
tubes4 ,by this a regularity in the     
currents is established1 which has a    
tendency to diminish the mixture of     
water with the steam4 ,in addition to   
this1 a method of separation is provided
 in the vessel ,i1 which is a strong    
iron cylinder of some magnitude1 placed 
out of the immediate influence of the   
fire4 ,a partial separation of the steam
 from the water takes place in the      
cylinder ,h2 and the steam with the     
water mechanically suspended in it1     

technically called moist steam1 rises   
into the separator ,i4 ,here1 being free
 from all agitation and currents1 and   
being1 in fact1 quiescent1 the particles
 of water fall to the bottom1 while the 
pure steam remains at the top4 ,this    
separator1 therefore1 serves all the    
purposes of the steam-room above the    
surface of the water in the large plate 
boilers4 ,the dry steam is thus         
collected and ready for the supply of   
the engine through the tube ,n1 while   
the water1 which is disengaged from it1 
is collected at the bottom of the       
separator1 and is conducted through the 
tube ,t to the lowest vessel ,d1 to be  
again circulated through the boiler4    
,the pistons of the engine work on the  
axles of the hind wheels of the carriage
 which bears the engine1 by cranks1 as  
in the locomotives on the ,manchester   
railway1 so that the axle is kept in a  
constant state of rotation while the    
engine is at work4 ,the wheels placed on
 this axle are not permanently fixed or 

keyed upon it1 as in the ,manchester    
locomotives2 but they are capable of    
turning upon it in the same manner as   
ordinary carriage wheels4 ,immediately  
within ,pg#dca these wheels there are   
fixed upon the axles two projecting     
spokes or levers1 which revolve with the
 axle1 and which take the position of   
two opposite spokes of the wheel4 ,these
 may be occasionally attached to the    
wheel or detached from it2 so that they 
are capable of compelling the wheels to 
turn with the axle1 or leaving the axle 
free to turn independently of the wheel1
 or the wheel independent of the axle1  
at the pleasure of the conductor4 ,it is
 by these levers that the engine is made
 to propel either or both of the wheels4
 ,if both pairs of spokes are thrown    
into connexion with the wheels1 the     
crank shaft or axle will cause both     
wheels to turn with it1 and in that case
 the operation of the carriage is       
precisely the same as those of the      
locomotives already described upon the  

,liverpool and ,manchester line2 but    
this is rarely found to be necessary1   
since the adhesion of one wheel with the
 road is generally sufficient to propel 
the carriage1 and consequently only one 
pair of these fixed levers are used1 and
 the carriage propelled by only one of  
the two hind wheels4 ,the fore wheels of
 the carriage turn upon a pivot similar 
to those of a four-wheeled coach4 ,the  
position of these wheels is changed at  
pleasure by a pinion and circular rack1 
which is moved by the conductor1 and in 
this manner the carriage is guided with 
precision and facility4  ,the force of  
traction necessary to propel a carriage 
upon common roads must vary with the    
variable quality of the road1 and       
consequently the propelling power1 or   
the pressure upon the pistons of the    
engine1 must be susceptible of a        
corresponding variation2 but a still    
greater variation becomes necessary from
 the undulations and hills which are    
upon all ordinary roads4 ,this necessary

 change in the intensity of the         
impelling power is obtained by          
restraining the steam in the boiler by  
the throttle-valve1 as already described
 in the locomotive engines on the       
railroad4 ,this principle1 however1 is  
carried much further in the present     
case4 ,the steam in the boiler maybe at 
a pressure of from #ajj to #bjj lbs4 on 
the square inch2 while the steam on the 
working piston may not exceed #cj or #dj
 lbs4 on the inch4 ,thus an immense     
increase of power is always at the      
command of the conductor2 so that when a
 hill is encountered1 or a rough piece  
of road1 ,pg#dcb he is enabled to lay on
 power sufficient to meet the exigency  
of the occasion4  ,the two difficulties 
which have been always apprehended in   
the practical working of steam-carriages
 upon common roads are1 first1 the      
command of sufficient power for hills   
and rough pieces of road2 and1 secondly1
 the apprehended insufficiency of the   
adhesion of the wheels with the road to 

propel the carriage4 ,the former of     
these difficulties has been met by      
allowing steam of very great pressure to
 be constantly maintained in the boiler 
with perfect safety4 ,as to the second1 
all experiments tend to show that there 
is no ground for the supposition that   
the adhesion of the wheels is in any    
case insufficient for the purposes of   
propulsion4 ,mr4 ,gurney states1 that he
 has succeeded in driving carriages thus
 propelled1 up considerable hills on the
 turnpike roads about ,london4 ,he made 
a journey to ,barnet with only one wheel
 attached to the axle1 which was found  
sufficient to propel the carriage up all
 hills upon that road4 ,the same        
carriage1 with only one propelling      
wheel1 also went to ,bath1 and          
surmounted all the hills between        
,cranford ,bridge and ,bath1 going and  
returning4  ,a double stroke of the     
piston produces one revolution of the   
propelling wheels1 and causes the       
carriage to move through a space equal  

to the circumference of those wheels4   
,it will therefore be obvious1 that the 
greater the diameter of the wheels1 the 
better adapted the carriage is for      
speed2 and1 on the other hand1 wheels of
 smaller diameter are better adapted for
 power4 ,in fact1 the propelling power  
of an engine on the wheels will be in   
the inverse proportion of their         
diameter4 ,in carriages designed to     
carry great weights at a moderate speed1
 smaller wheels will be used2 while in  
those intended for the transport of     
passengers at considerable velocities1  
wheels of at least #e feet diameter are 
most advantageous4   7#bje47 ,among the 
numerous popular prejudices to which    
this new invention has given rise1 one  
of the most mischievous in its effects  
and most glaring in its falsehood1 is   
the notion that carriages thus propelled
 are more injurious to roads than       
carriages drawn by horses4 ,this error  
has been successfully exposed in the    
evidence taken before the committee of  

the ,pg#dcc ,house of ,commons upon     
steam carriages4 ,it is there           
demonstrated1 not only that carriages   
thus propelled do not wear a turnpike   
road more rapidly than those drawn by   
horses1 but that1 on the other hand1 the
 wear by the feet of horses is far more 
rapid and destructive than any which    
could be produced by the wheels of      
carriages4 ,steam carriages admit of    
having the tires of the wheels broad1 so
 as to act upon the road more in the    
manner of rollers1 and thereby to give  
consistency and firmness to the material
 of which the road is composed4 ,the    
driving wheels being proved not to slip 
upon the road1 do not produce any       
effects more injurious than the ordinary
 rolling wheels2 consequently the wear  
occasioned by a steam carriage upon a   
road1 is not more than that produced by 
a carriage drawn by horses1 of an       
equivalent weight and the same or equal 
tires2 but the wear produced by the     
pounding and digging of horses' feet in 

draught is many times greater than that 
produced by the wear of any carriage4   
,those who still have doubts upon this  
subject1 if there be any such persons1  
will be fully satisfied by referring to 
the evidence which accompanies the      
report of the committee of the ,house of
 ,commons1 printed in ,october1 #ahca4  
,the weight of machinery necessary for  
steam carriages is sometimes urged as an
 objection to their practical utility4  
,mr4 ,gurney states1 that1 by successive
 improvements in the details of the     
machinery1 the weight of his carriages1 
without losing any of the propelling    
power1 may be reduced to #ce cwt41      
exclusive of the load1 and fuel and     
water3 but thinks that it is possible to
 reduce the weight still further4  ,a   
steam carriage constructed by ,mr4      
,gurney1 weighing #ce cwt41 working for 
#h hours1 is found1 according to his    
statement1 to do the work of about #cj  
horses4 ,he calculates that the weight  
of his propelling carriage1 which would 

be capable of drawing #ah persons1 would
 be equal to the weight of #d horses2   
and the carriage in which these persons 
would be drawn would have the same      
weight as a common stage coach capable  
of carrying the same number of persons4 
,thus the weight of the whole--the      
propelling carriage and the carriage for
 passengers taken together--would be the
 same ,pg#dcd with the weight of a      
common stage coach1 with #d horses      
inclusive4  ,there are two methods of   
applying locomotives upon common roads  
to the transport of passengers or goods2
 the one is by causing the locomotive to
 carry1 and the other to draw the load2 
and different projectors have adopted   
the one and the other method4 ,each is  
attended with its advantages and        
disadvantages4 ,if the same carriage    
transport the engine and the load1 the  
weight of the whole will be less in     
proportion to the load carried2 also a  
greater pressure may be produced on the 
wheels by which the load is propelled4  

,it is also thought that a greater      
facility in turning and guiding the     
vehicle1 greater safety in descending   
the hills1 and a saving in the original 
cost1 will be obtained4 ,on the other   
hand1 when the passengers are placed in 
the same carriage with the engine1 they 
are necessarily more exposed to the     
noise of the machinery and to the heat  
of the boiler and furnace4 ,the danger  
of explosion is so slight1 that1        
perhaps1 it scarcely deserves to be     
mentioned2 but still the apprehension of
 danger on the part of the passengers1  
even though groundless1 should not be   
disregarded4 ,this apprehension will be 
obviously removed or diminished by      
transferring the passengers into a      
carriage separate from the engine2 but  
the greatest advantage of keeping the   
engine separate from the passengers is  
the facility which it affords of        
changing one engine for another in case 
of accident or derangement on the road1 
in the same manner as horses are changed

 at the different stages3 or1 if such an
 accident occur in a place where a new  
engine cannot be procured1 the load of  
passengers may be carried forward by    
horses1 until it is brought to some     
station where a locomotive may be       
obtained4 ,there is also an advantage   
arising from the circumstance1 that when
 the engines are under repair1 or in    
process of cleaning1 the carriages for  
passengers are not necessarily idle4    
,thus the same number of carriages for  
passengers will not be required when the
 engine is used to draw as when it is   
used to carry4  ,in case of a very      
powerful engine being used to carry     
great loads1 it would be quite          
impracticable to place the engine       
,pg#dce and loads on four wheels1 the   
pressure being such as no turnpike road 
could bear4 ,in this case it would be   
indispensably necessary to place a part 
of the load at least upon separate      
carriages to be drawn by the engine4    
,in the comparison of carriages         

propelled by steam with carriages drawn 
by horses1 there is no respect in which 
the advantage of the former is so       
apparent as the safety afforded to the  
passenger4 ,steam power is under the    
most perfect control1 and a carriage    
thus propelled is capable of being      
guided with the most admirable          
precision4 ,it is also capable of being 
stopped almost suddenly1 whatever be its
 speed3 it is capable of being turned   
within a space considerably less than   
that which would be necessary for       
four-horse coaches4 ,in turning sharp   
corners1 there is no danger1 with the   
most ordinary care on the part of the   
conductor4 ,on the other hand1 horse    
power1 as is well known1 is under very  
imperfect control1 especially when      
horses are used adapted to that speed   
which at present is generally considered
 necessary for the purposes of          
travelling4 ,the danger of being run    
away with and overturned1 says ,mr4     
,farey1 in his evidence before the      

,house of ,commons1 is greatly          
diminished in a steam coach4 ,it is very
 difficult to control four such horses  
as can draw a heavy stage coach ten     
miles an hour1 in case they are         
frightened or choose to run away2 and1  
for such quick travelling1 they must be 
kept in that state of courage that they 
are always inclined to run away1        
particularly down hill1 and at sharp    
turns in the road4 ,steam power has very
 little corresponding danger1 being     
perfectly controllable1 and capable of  
having its power reversed1 to retard in 
going down hill4 ,it must be            
carelessness that would occasion the    
overturning of a steam carriage4 ,the   
chance of breaking down has been        
hitherto considerable1 but it will not  
be more than in stage coaches when the  
work is truly proportioned and properly 
executed4 ,the risk from explosion of   
the boiler is the only new cause of     
danger1 and that ,i consider not        
equivalent to the danger from horses4   

,that the risk of accident from         
explosion is extremely slight1 may be   
proved by the fact that the railway     
between ,liverpool and ,manchester has  
now been in operation for about ten     
,pg#dcf years1 and that other railways  
more extensive in length have been      
worked for a considerable time1 and that
 no instance has ever yet occurred of an
 accident to passengers from the        
explosion of a boiler4 ,generally these 
machines1 when they fail1 are attended  
with no other effect than the extinction
 of the fire1 by the water of the boiler
 flowing in upon it4 ,i am not aware of 
more than one instance1 in which a      
serious accident has been produced by   
explosion2 and in that instance1 the    
sufferers were only the engineer and    
stoker4 ,in the steam-engine of ,mr4    
,gurney1 the carriage is drawn after the
 engine1 as represented in fig4 #aag4   
,illustration3 ,fig4 #aag4              
,illustration3 ,fig4 #aah4   7#bjf47 ,in
 the boiler to be used in the steam     

carriage projected by ,mr4 ,walter      
,hancock1 the subdivision of the water  
is accomplished by dividing a case or   
box by a number of ,pg#dcg thin plates  
of metal1 like a galvanic battery1 the  
water being allowed to flow between     
every alternate pair of plates1 at ,e1  
fig4 #aah41 and the intermediate spaces 
,h forming the flue through which the   
flame and hot air are propelled4  ,in   
fact1 a number of thin plates of water  
are exposed on both sides to the most   
intense action of flame and heated air2 
so that steam of a high pressure is     
produced in great abundance and with    
considerable rapidity4 ,the plates      
forming the boiler are bolted together  
by strong iron ties1 extending across   
the boiler1 at right angles to the      
plates1 as represented in the figure4   
,the distance between the plates is two 
inches4  ,there are ten flat chambers of
 this kind for water1 and intermediately
 between them ten flues4 ,under the     
flues is the fire-place1 or grate1      

containing six square feet of fuel in   
vivid combustion4 ,the chambers are all 
filled to about two thirds of their     
depth with water1 and the other third is
 left for steam4 ,the water chambers1   
throughout the whole series1 communicate
 with each other both at top and bottom1
 and are held together by two large     
bolts4 ,by releasing these bolts1 at any
 time1 the chambers fall asunder2 and by
 screwing them up they may be all made  
tight again4 ,the water is supplied to  
the boiler by a forcing-pump1 and the   
steam issues from the centre of one of  
the flues at the top4  ,these boilers   
are constructed to bear a pressure of   
#djj or #ejj lbs4 on the square inch2   
but the average pressure of the steam on
 the safety valve is from #fj to #ajj4  
,there are #ajj square feet of surface  
in contact with the water exposed to the
 fire4 ,the stages which such an engine 
performs are eight miles1 at the end of 
which a fresh supply of fuel and water  
are taken in4 ,it requires about two    

bushels of coke for each stage4  ,the   
steam carriage of ,mr4 ,hancock differs 
from that of ,mr4 ,gurney in this--that 
in the former the passengers and engine 
are all placed on the same carriage4    
,the boiler is placed behind the        
carriage2 and there is an engine-house  
between the boiler and the passengers1  
the latter being placed in the fore part
 of the vehicle2 so that all the        
machinery is behind them4 ,the carriages
 are adapted to carry #ad ,pg#dch       
passengers1 and weigh1 exclusive of     
their load1 about #c-a_/b tons1 the     
tires of the wheels being about #c-a_/b 
inches in breadth4 ,mr4 ,hancock states1
 that the construction of his boiler is 
of such a nature1 that1 even in the case
 of bursting1 no danger is to be        
apprehended1 nor any other inconvenience
 than the stoppage of the carriage4 ,he 
states that1 while travelling about nine
 miles an hour1 and working with a      
pressure of about #ajj lbs4 on the      
square inch1 loaded with thirteen       

passengers1 the carriage was suddenly   
stopped4 ,at first the cause of the     
accident was not apparent2 but1 on      
opening one of the cocks of the boiler1 
it was found that it contained neither  
steam nor water4 ,further examination   
proved that the boiler had burst4 ,on   
unscrewing the bolts1 it was found that 
there were several large holes in the   
plates of the water-chamber1 through    
which the water had flowed on the fire1 
but neither noise nor explosion1 nor any
 dangerous consequences1 ensued4        
7#bjg47 ,mr4 ,nathaniel ,ogle of        
,southampton obtained a patent for a    
locomotive carriage1 and worked it for  
some time experimentally2 but as his    
operations do not appear to have been   
continued1 ,i suppose he was            
unsuccessful in fulfilling those        
conditions1 without which the machine   
could not be worked with economy and    
profit4 ,in his evidence before a       
committee of the ,house of ,commons1 he 
has thus described his contrivance3--   

,the base of the boiler and the summit  
are composed of cross pieces1           
cylindrical within and square without2  
there are holes bored through these     
cross pieces1 and inserted through the  
whole is an air tube4 ,the inner hole of
 the lower surface1 and the under hole  
of the upper surface1 are rather larger 
than the other ones4 ,round the air tube
 is placed a small cylinder1 the collar 
of which fits round the larger aperture 
on the inner surface of the lower frame1
 and the under surface of the upper     
frame-work4 ,these are both drawn       
together by screws from the top2 these  
cross pieces are united by connecting   
pieces1 the whole strongly bolted       
together2 so that we obtain1 in one     
tenth of the space1 and with one tenth  
of the weight1 the same heating surface 
and power as is now obtained in other   
and low-pressure boilers1 with          
incalculably ,pg#dci greater safety4    
,our present experimental boiler        
contains #bej superficial feet of       

heating surface in the space of #c feet 
#h inches high1 #c feet long1 and #b    
feet #d inches broad1 and weighs about  
#h cwt4 ,we supply the two cylinders    
with steam1 communicating by their      
pistons with a crank axle1 to the ends  
of which either one or both wheels are  
affixed as may be required4 ,one wheel  
is found to be sufficient1 except under 
very difficult circumstances1 and when  
the elevation is about one foot in six  
to impel the vehicle forward4  ,the     
cylinders of which the boiler is        
composed are so small as to bear a      
greater pressure than could be produced 
by the quantity of fire beneath the     
boiler2 and if any one of these         
cylinders should be injured by violence1
 or any other way1 it would become      
merely a safety valve to the rest4 ,we  
never1 with the greatest pressure1      
burst1 rent1 or injured our boiler2 and 
it has not once required cleaning1 after
 having been in use twelve months4  ,dr4
 ,church of ,birmingham has obtained a  

succession of patents for contrivances  
connected with a locomotive engine for  
stone roads2 and a company1 consisting  
of a considerable number of individuals1
 possessing sufficient capital1 has been
 formed in ,birmingham1 for carrying    
into effect his designs1 and working    
carriages on his principle4 ,the present
 boiler of ,dr4 ,church is formed of    
copper4 ,the water is contained between 
two sheets of copper1 united together by
 copper nails1 in a manner resembling   
the way in which the cloth forming the  
top of a mattress or cushion is united  
with the cloth which forms the bottom of
 it1 except that the nails or pins1     
which bind the sheets of copper1 are    
much closer together4 ,the water1 in    
fact1 seems to be quilted or padded in  
between two sheets of thin copper4 ,this
 double sheet of copper is formed into  
an oblong rectangular box1 the interior 
of which is the fire-place and ash-pit1 
and over the end of which is the        
steam-chest4 ,the great extent of       

surface exposed to the immediate action 
of the fire causes steam to be produced 
with great rapidity4  ,various other    
projects for the application of steam   
engines on common roads were in a state 
of progressive improvement1 ,pg#ddj when
 the greater advantages attending       
railways were considered so manifest1   
that considerable doubts were raised1   
whether1 supposing the problem of the   
application of the steam engine on      
common roads to be successfully solved1 
it could ever be attended with the same 
economy and effect1 as by the adoption  
of a railway4 ,among the projects which 
promised a successful issue1 may be     
mentioned the locomotive engines        
contrived by ,messrs4 ,maudslay and     
,field1 by ,colonel ,maceroni1 and by   
,mr4 ,scott ,russell4 ,these and others 
have1 however1 been abandoned1 mainly1  
we believe1 from the impression1 that   
wherever traffic can exist1 sufficiently
 extensive to render the application of 
steam power profitable1 a railway must  

always supersede a common road2 and     
that1 even in the limited traffic to be 
expected on branches to the great       
railways1 horse power applied to        
railways would be attended with more    
economy than steam power applied on     
stone roads4  ,illustration  ,pg#dda    
,illustration  ,,chap4 ,,xiii4  ,,steam 
,,navigation4      ,,form ,,and         
,,arrangement ,,of ,,marine ,,engines4  
-- ,,effects ,,of ,,sea ,,water     ,,in
 ,,boilers4 -- ,,remedies ,,for ,,them4 
-- ,,blowing ,,out4 -- ,,indicators     
,,of ,,saltness4 -- ,,seaward',s        
,,indicator4 -- ,,his ,,method ,,of     
,,blowing     ,,out4 -- ,,field',s      
,,brine ,,pumps4 -- ,,tubular           
,,condensers ,,applied ,,by     ,,mr4   
,,watt4 -- ,,hall',s ,,condensers4 --   
,,copper ,,boilers4 -- ,,process ,,of   
,,stoking4 -- ,,marine ,,boilers4 --    
,,means ,,of ,,economising ,,fuel4 --   
,,coating ,,marine ,,boilers ,,with     
,,felt4 -- ,,number ,,and ,,arrangement 
,,of     ,,furnaces ,,and ,,flues4 --   

,,howard',s ,,engine4 -- ,,application  
,,of ,,the     ,,expansive ,,principle  
,,in ,,marine ,,engines4 -- ,,recent    
,,improvements     ,,of ,,messrs4       
,,maudslay ,,and ,,field4 -- ,,humphrys'
 ,,engine4 -- ,,common                  
,,paddle-,,wheel4 -- ,,feathering       
,,paddles4 -- ,,morgan',s ,,wheels4 --  
,,the     ,,split ,,paddle4 --          
,,proportion ,,of ,,power ,,to          
,,tonnage4 -- ,,improved                
,,efficiency ,,of ,,marine ,,engines4 --
 ,,iron ,,steam-,,vessels4 --           
,,steam-,,navigation ,,to ,,india4      
7#bjh47 ,among the many ways in which   
the steam-engine has ministered to the  
advancement of civilisation and the     
social progress of the human race1 there
 is none more ,pg#ddb important or more 
interesting than its application to     
navigation4 ,before it lent its giant   
powers to the propulsion of ships1      
locomotion over the waters of the deep  
was attended with so much danger and    
uncertainty that1 as a common proverb1  

it became the type and the              
representative of every thing which was 
precarious and perilous4 ,the           
application1 however1 of steam to       
navigation has rescued the mariner and  
the voyager from many of the dangers of 
wind and water2 and even in its present 
state1 putting out of view its probable 
improvement1 it has rendered all voyages
 of moderate length as safe1 and very   
nearly as regular1 as journeys          
over-land4 ,as a means of transport by  
sea1 the application of this power may  
be considered as established2 and it is 
now receiving improvements by which its 
extension to the longest class of ocean 
voyages is a question not of            
practicability1 but merely of profit4   
,the manner in which the steam-engine is
 rendered an instrument for the         
propulsion of vessels must in its       
general features be so familiar to every
 one as to require but short            
explanation4 ,a shaft is carried across 
the vessel1 being continued on either   

side beyond the timbers3 to the         
extremities of this shaft1 on the       
outside of the vessel1 are fixed a pair 
of wheels constructed like undershot    
water-wheels1 having attached to their  
rims a number of flat boards called     
paddle-boards4 ,as the wheels revolve1  
these paddle-boards strike the water1   
driving it in a direction contrary to   
that in which it is intended the vessel 
should be propelled4 ,the moving force  
imparted to the water thus driven       
backwards is necessarily accompanied by 
a re-action upon the vessel through the 
medium of the paddle-shaft1 by which the
 vessel is propelled forwards4 ,on the  
paddle-shaft two cranks are constructed1
 similar to the cranks already described
 on the axle of the driving wheels of a 
locomotive engine4 ,these cranks are    
placed at right angles to each other1 so
 that when either is in its highest or  
lowest position the other shall be      
horizontal4 ,they are driven by two     
steam-engines1 which are placed in the  

hull of the vessel below the            
paddle-shaft4 ,in the earlier           
steam-boats a single steam-engine was   
used1 and in that case the unequal      
action of the engine on the crank was   
equalised by a fly-wheel4 ,this1        
however1 has been long ,pg#ddc since    
abandoned in ,european vessels1 and the 
use of two engines is now almost        
universal4 ,by the relative position of 
the cranks it will be seen1 that when   
either crank is at its dead points1 the 
other will be in the positions most     
favourable to its action1 and in all    
intermediate positions the relative     
efficiency of the cranks will be such as
 to render their combined action very   
nearly uniform4  ,the steam-engines used
 to impel vessels may be either         
condensing engines1 similar to those of 
,watt1 and such as are used in          
manufactures generally1 or they may be  
non-condensing and high-pressure        
engines1 similar in principle to those  
used on railways4 ,low-pressure         

condensing engines are1 however1        
universally used for marine purposes in 
,europe and to some extent in the       
,united ,states4 ,in the latter country1
 however1 high-pressure engines are also
 in pretty general use1 on rivers where 
lightness is a matter of importance4    
,the arrangement of the parts of a      
marine engine differs in some respects  
from that of a land engine4 ,the        
limitation of space1 which is           
unavoidable in a vessel1 renders greater
 compactness necessary4 ,the            
paddle-shaft on which the cranks to be  
driven by the engine are constructed    
being very little below the deck of the 
vessel1 the beam and connecting rod     
could not be placed in the position in  
which they usually are in land engines1 
without carrying the machinery to a     
considerable elevation above the deck4  
,this is done in the steam-boat engines 
used on the ,american rivers2 but it    
would be inadmissible in steam-boats in 
general1 and more especially in         

sea-going steamers4 ,the connecting     
rods1 therefore1 instead of being       
presented downwards towards the cranks  
which they drive1 must1 in              
steam-vessels1 be presented upwards1 and
 the impelling force received from      
below4 ,if1 under these circumstances1  
the beam were in the usual position     
above the cylinder and piston-rod1 it   
must necessarily be placed between the  
engine and the paddle-shaft4 ,this would
 require a depth for the machinery which
 would be incompatible with the         
magnitude of the vessel4 ,the beam1     
therefore1 of marine engines1 instead of
 being above the cylinder and piston1 is
 placed below them4 ,to the top of the  
,pg#dde piston-rods cross pieces are    
attached of greater length than the     
diameter of the cylinders1 so that their
 extremities shall project beyond the   
cylinders4 ,to the ends of these cross  
pieces are attached by joints the rods  
of a parallel motion3 these rods are    
carried downwards1 and are connected    

with the ends of two beams below the    
cylinder1 and placed on either side of  
it4 ,the opposite ends of these beams   
are connected by another cross piece1 to
 which is attached a connecting rod1    
which is continued upwards to the       
crank-pin1 to which it is attached1 and 
which it drives4 ,thus the beam1        
parallel motion1 and connecting rod of a
 marine engine1 is similar to that of a 
land engine1 only that it is turned     
upside down2 and in consequence of the  
impossibility of placing the beam       
directly over the piston-rod1 two beams 
and two systems of parallel motion are  
provided1 one on each side of the       
engine1 acted upon by1 and acting on the
 piston-rod and crank by cross pieces4  
,the proportion of the cylinders differs
 from that usually observed in land     
engines1 for like reasons4 ,the length  
of the cylinder of land engines is      
generally greater than its diameter1 in 
the proportion of about two to one4 ,the
 cylinders of marine engines are1       

however1 commonly constructed with a    
diameter very little less than their    
length4 ,in proportion1 therefore1 to   
their power their stroke is shorter1    
which infers a corresponding shortness  
of crank and a greater limitation of    
play of all the moving parts in the     
vertical direction4 ,the valves and the 
gearing by which they are worked1 the   
air-pump1 the condenser1 and other parts
 of the marine engines1 do not          
materially differ from those already    
described in land engines4              
,illustration3 ,fig4 #aai4  ,these      
arrangements of a marine engine will be 
more clearly understood by reference to 
fig4 #aai4ce1 in which is represented a 
longitudinal section of a marine engine 
with its boiler as placed in a          
steam-vessel4 ,the sleepers of oak1     
supporting the engine1 are represented  
at ,x1 the base of the engine being     
secured to these by bolts passing       
through them ,pg#ddf and the bottom     
timbers of the vessel2 ,s is the        

steam-pipe leading from the steam-chest 
in the boiler to the slides c1 by which 
it is admitted to the top and bottom of 
the cylinder4 ,the condenser is         
represented at ,b1 and the air-pump at  
,e4 ,the hot well is seen at ,f1 from   
which the feed is taken for the boiler2 
,l is the piston-rod connected by the   
parallel motion a with the beam ,h1     
working on a centre ,k1 near the base of
 the engine4 ,the other end of the beam 
,i drives the connecting rod ,m1 which  
extends upwards to the crank which it   
works upon the paddle-shaft ,o4 ,q ,r is
 the framing by which the engine is     
supported4 ,the beam here exhibited is  
shown on dotted lines as being on the   
further side of the engine4 ,a similar  
beam similarly placed1 and moving on the
 same axis1 must be understood to be at 
this side connected with the cross head 
of the piston in like manner by a       
parallel motion1 and with a cross piece 
attached to the lower end of the        
connecting rod and to the opposite beam4

 ,the eccentric which works the slides  
is placed upon the paddle shaft ,o1 and 
the connecting arm which drives the     
slides may be easily detached when the  
engine requires to be stopped4 ,the     
section of the boiler1 grate1 and flues1
 is represented at ,w ,u4 ,the          
safety-valve y is enclosed beneath a    
pipe carried up beside the chimney1 and 
is inaccessible to the engine-man2 h are
 the cocks for blowing the salted water 
from the boiler2 and ,i ,i the          
feed-pipe4  ,the general arrangement of 
the engine-room of a steam-vessel is    
represented in fig4 #abj4  ,the nature  
of the effect required to be produced by
 marine engines does not render either  
necessary or possible that great        
regularity of action which is           
indispensable in a steam-engine applied 
to the purposes of manufacture4 ,the    
agitation of the surface of the sea will
 cause the immersion of the             
paddle-wheels to be subject to great    
variation1 and the resistance produced  

by the water to the engine will undergo 
a corresponding change4 ,the governor1  
therefore1 and other parts of the       
apparatus1 contrived for giving to the  
engine that great regularity required in
 manufactures1 are omitted in nautical  
engines1 and nothing is introduced save 
what is ,pg#ddg necessary to maintain   
the machine in its full working         
efficiency4  ,illustration3 ,fig4 #abj4 
,illustration3 ,fig4 #aba4  ,to save    
space1 marine boilers are constructed so
 as to produce the necessary quantity of
 steam within the smallest possible     
dimensions4 ,with this view a more      
extensive surface in proportion to the  
capacity of the boiler is exposed to the
 action of the fire4 ,the flues1 by     
which the flame and heated air are      
conducted to the chimney1 are so        
constructed that the heat may act upon  
the water on every side in thin oblong  
shells or plates4 ,this is accomplished 
by constructing the flues so as to      
traverse the boiler backwards and       

forwards several times before they      
terminate ,pg#ddh in the chimney4 ,such 
an arrangement renders the expense of   
the boilers greater1 but their          
steam-producing power is proportionally 
augmented1 and experiments made by ,mr4 
,watt1 at ,birmingham1 have proved that 
such boilers with the same consumption  
of fuel will produce1 as compared with  
common land boilers1 an increased       
evaporation in the proportion of about  
three to two4  ,illustration3 ,fig4     
#abb4  ,illustration3 ,fig4 #abc4  ,the 
form and arrangement of the water-spaces
 and flues in marine boilers may be     
collected from the sections of the      
boilers used in some of the government  
steamers1 exhibited in figs4 #aba1 #abb1
 #abc4 ,a section made by a horizontal  
plane passing through the flues is      
exhibited in fig4 #aba4 ,the furnaces ,f
 communicate in pairs with the flues ,e1
 the air following the course through   
the flues represented by the arrows4    
,the flue ,e passes to the back of the  

boiler1 then returns to the front1 then 
to the back again1 and is finally       
carried back to the front1 where it     
communicates at ,c with the curved flue 
,b1 represented in the transverse       
vertical section1 fig4 #abb4 ,this      
curved flue ,b finally terminates in the
 chimney ,a4 ,there are in this case    
three independent boilers1 each worked  
by two furnaces communicating with the  
same system of flues2 and in the curved 
flues ,b1 fig4 #abb41 by which the air  
is finally conducted through the        
chimney1 are placed three independent   
,pg#ddi dampers1 by means of which the  
furnace of each boiler can be regulated 
independently of the other1 and by which
 each boiler may be separately detached 
from communication with the chimney4    
,the letters of reference in the        
horizontal section1 fig4 #aba41         
correspond with those in the transverse 
vertical section1 fig4 #abb41 ,e        
representing the commencement of the    
flues1 and ,c their termination4        

,illustration3 ,fig4 #abd4  ,a          
longitudinal section of the boiler made 
by a vertical plane extending from the  
front to the back is given in fig4      
#abc41 where ,f1 as before1 is the      
furnace1 ,g the grate-bars sloping      
downwards from the front to the back1 ,h
 the fire-bridge1 ,c the commencement of
 the flues1 and ,a the chimney4 ,an     
elevation of the front of the boiler is 
represented in fig4 #abd41 showing two  
of the fire-doors closed1 and the other 
two removed1 displaying the position of 
the grate-bars in front4 ,small openings
 are also provided1 closed by proper    
doors1 by which access can be had to the
 under side of the flues between the    
foundation timbers of the engine for the
 purpose of cleaning them4  ,each of    
these boilers can be worked             
independently of the others4 ,by this   
means1 when at sea1 the engine may be   
worked by any two of the three boilers1 
while the third is being cleaned and put
 in order4 ,in all sea-going steamers   

multiple boilers are at present provided
 for this purpose4  ,in the boilers here
 represented the flues are all upon the 
same level1 winding backwards and       
forwards without passing one above the  
other4 ,in other boilers1 however1 the  
flues1 ,pg#dej after passing backwards  
and forwards near the bottom of the     
boiler1 turn upwards and pass backwards 
and forwards through a level of the     
water nearer its surface1 finally       
terminating in the chimney4 ,more       
heating surface is thus obtained with   
the same capacity of boiler4  ,the most 
formidable difficulty which has been    
encountered in the application of the   
steam-engine to sea-voyages has arisen  
from the necessity of supplying the     
boiler with sea-water instead of pure   
fresh water4 ,the sea-water is injected 
into the condenser for the purpose of   
condensing the steam1 and it is thence1 
mixed with the condensed steam1         
conducted as feeding water into the     
boiler4   7#bji47 ,sea-water holds1 as  

is well known1 certain alkaline         
substances in solution1 the principal of
 which is muriate of soda1 or common    
salt4 ,ten thousand grains of pure      
sea-water contain two hundred and twenty
 grains of common salt1 the remaining   
ingredients being thirty-three grains of
 sulphate of soda1 forty-two grains of  
muriate of magnesia1 and eight grains of
 muriate of lime4 ,the heat which       
converts pure water into steam does not 
at the same time evaporate those salts  
which the water holds in solution4 ,as a
 consequence it follows1 that as the    
evaporation in the boiler is continued1 
the salt1 which was held in solution by 
the water which has been evaporated1    
remains in the boiler1 and enters into  
solution with the water remaining in it4
 ,the quantity of salt contained in     
sea-water being considerably less than  
that which water is capable of holding  
in solution1 the process of evaporation 
for some time is attended with no other 
effect than to render the water in the  

boiler a stronger solution of salt4 ,if1
 however1 this process be continued1 the
 quantity of salt retained in the boiler
 having constantly an increasing        
proportion to the quantity of water1 it 
must at length render the water in the  
boiler a saturated solution--that is1 a 
solution containing as much salt as at  
the actual temperature it is capable of 
holding in solution4 ,if1 therefore1 the
 evaporation be continued beyond this   
point1 the salt disengaged from the     
water evaporated instead of entering    
into solution with the water remaining  
in the boiler will be precipitated in   
the form of sediment2 and if the process
 be continued in the ,pg#dea same       
manner1 the boiler would at length      
become a mere salt-pan4  ,but besides   
the deposition of salt sediment in a    
loose form1 some of the constituents of 
sea-water having an attraction for the  
iron of the boiler1 collect upon it in a
 scale or crust in the same manner as   
earthy matters held in solution by      

spring-water are observed to form and   
become incrusted on the inner surface of
 land-boilers and of common culinary    
vessels4  ,the coating of the inner     
surface of a boiler by incrustation and 
the collection of salt sediment in its  
lower parts1 are attended with effects  
highly injurious to the materials of the
 boiler4 ,the crust and sediment thus   
formed within the boiler are almost     
non-conductors of heat1 and placed1 as  
they are1 between the water contained in
 the boiler and the metallic plates     
which form it1 they obstruct the passage
 of heat from the outer surface of the  
plates in contact with the fire to the  
water4 ,the heat1 therefore1            
accumulating in the boiler-plates so as 
to give them a much higher temperature  
than the water within the boiler1 has   
the effect of softening them1 and by the
 unequal temperature which will thus be 
imparted to the lower plates which are  
incrusted1 compared with the higher     
parts which may not be so1 an unequal   

expansion is produced1 by which the     
joints and seams of the boiler are      
loosened and opened1 and leaks produced4
  ,these injurious effects can only be  
prevented by either of two methods2     
first1 by so regulating the feed of the 
boiler that the water it contains shall 
not be suffered to reach the point of   
saturation1 but shall be so limited in  
its degree of saltness that no injurious
 incrustation or deposit shall be       
formed2 secondly1 by the adoption of    
some method by which the boiler may be  
worked with fresh water4 ,this end can  
only be attained by condensing the steam
 by a jet of fresh water1 and working   
the boiler continually by the same      
water1 since a supply of fresh water    
sufficient for a boiler worked in the   
ordinary way could never be commanded at
 sea4   7#baj47 ,the method by which the
 saltness of the water in the boiler is 
most commonly prevented from exceeding a
 certain ,pg#deb limit has been to      
discharge from the boiler into the sea a

 certain quantity of over-salted water1 
and to supply its place by sea-water    
introduced into the condenser through   
the injection-cock for the purpose of   
condensing the steam1 this water being  
mixed with the steam so condensed1 and  
being1 therefore1 a weaker solution of  
salt than common sea-water4 ,to effect  
this1 cocks called blow-off cocks1 are  
usually placed in the lower parts of the
 boiler1 where the over-salted1 and     
therefore heavier1 parts of the water   
collect4 ,the pressure of the steam and 
incumbent weight of the water in the    
boiler force the lower strata of water  
out through these cocks2 and this       
process1 called blowing out1 is1 or     
ought to be1 practised at such intervals
 as will prevent the water from becoming
 over salted4 ,when the salted water has
 been blown out in this manner1 the     
level of the water in the boiler is     
restored by a feed of corresponding     
quantity4  ,this process of blowing out1
 on the due and regular observance of   

which the preservation and efficiency of
 the boiler mainly depend1 is too often 
left at the discretion of the engineer1 
who is1 in most cases1 not even supplied
 with the proper means of ascertaining  
the extent to which the process should  
be carried4 ,it is commonly required    
that the engineer should blow out a     
certain portion of the water in the     
boiler every two hours1 restoring the   
level by a feed of equivalent amount2   
but it is evident that the sufficiency  
of the process founded on such a rule   
must mainly depend on the supposition   
that the evaporation proceeds always at 
the same rate1 which is far from being  
the case with marine boilers4 ,an       
indicator1 by which the saltness of the 
water in the boiler would always be     
exhibited1 ought to be provided1 and the
 process of blowing out should be       
regulated by the indications of that    
instrument4 ,to blow out more frequently
 than is necessary is attended with a   
waste of fuel2 for hot water is thus    

discharged into the sea while cold water
 is introduced in its place1 and        
consequently all the heat necessary to  
produce the difference of the           
temperatures of the water blown out and 
the feed introduced is lost4 ,if1 on the
 other hand1 the process of blowing out 
be observed less frequently than is     
necessary1 then more or less            
incrustation and deposit ,pg#dec may be 
produced1 and the injurious effects     
already described ensue4  ,as the       
specific gravity of water holding salt  
in solution is increased with every     
increase of the strength of the         
solution1 any form of hydrometer capable
 of exhibiting a visible indication of  
the specific gravity of the water       
contained in the boiler would serve the 
purpose of an indicator1 to show when   
the process of blowing out is necessary1
 and when it has been carried to a      
sufficient extent4 ,the application of  
such instruments1 however1 would be     
attended with some practical            

difficulties in the case of sea-boilers4
  ,the temperature at which a solution  
of salt boils under a given pressure    
varies considerably with the strength of
 the solution2 the more concentrated the
 solution is1 the higher will be its    
boiling temperature under the same      
pressure4 ,a comparison1 therefore1 of a
 steam-gauge attached to the boiler1 and
 a thermometer immersed in it1 showing  
the pressure and the temperature1 would 
always indicate the saltness of the     
water2 and it would not be difficult so 
to graduate these instruments as to make
 them at once show the degree of        
saltness4  ,if the application of the   
thermometer be considered to be attended
 with practical difficulty1 the         
difference of pressures under which the 
salt water of the boiler and fresh water
 of the same temperature boil1 might be 
taken as an indication of the saltness  
of the water in the boiler1 and it would
 not be difficult to construct upon this
 principle a self-registering           

instrument1 which would not only        
indicate but record from hour to hour   
the degree of saltness of the water4 ,a 
small vessel of distilled water being   
immersed in the water of the boiler     
would always have the temperature of    
that water1 and the steam produced from 
it communicating with a steam-gauge1 the
 pressure of such steam would be        
indicated by that gauge1 while the      
pressure of the steam in the boiler     
under which pressure the salted water   
boils might be indicated by another     
gauge4 ,the difference of the pressures 
indicated by the two gauges would thus  
become a test by which the saltness of  
the water in the boiler would be        
measured4 ,the two pressures might be   
made to act on opposite ends of the same
 column of ,pg#ded mercury contained in 
a siphon tube1 and the difference of the
 levels of the two surfaces of the      
mercury would thus become a measure of  
the saltness of the water in the boiler4
 ,a self-registering instrument founded 

on this principle formed part of the    
self-registering steam-log which ,i     
proposed to introduce into steam-vessels
 some time since4   7#baa47 ,the        
,messrs4 ,seaward of ,limehouse have    
adopted1 in some of their recently      
constructed engines1 a method of        
indicating the saltness of the water1   
and of measuring the quantity of salted 
water or brine discharged1 by blowing   
out4 ,a glass-gauge1 similar in form to 
that already described in land engines  
7#aef471 is provided to indicate the    
position of the surface of the water in 
the boiler4 ,in this gauge two          
hydrometer balls are provided1 the      
weight of which in proportion to their  
magnitude is such that they would both  
sink to the bottom in a solution of salt
 of the same strength as common         
sea-water4 ,when the quantity of salt   
exceeds #e_/cb parts of the whole weight
 of the water1 the lighter of the two   
balls will float to the top2 and when   
the strength is further increased until 

the proportion of salt exceeds #f_/cb   
parts of the whole1 then the heavier    
ball will float to the top4 ,the actual 
quantity of salt held in solution by    
sea-water in its ordinary state is      
#a_/cb part of its whole weight2 and    
when by evaporation the proportion of   
salt in solution has become #i_/cb parts
 of the whole1 then a deposition of salt
 commences4 ,with an indicator such as  
that above described1 the ascent of the 
lighter hydrometer ball gives notice of 
the necessity for blowing out1 and the  
ascent of the heavier may be considered 
as indicating the approach of an        
injurious state of saltness in the      
boiler4  ,illustration3 ,fig4 #abe4     
,the ordinary method of blowing out the 
salted water from a boiler is by a pipe 
having a cock in it leading from the    
boiler through the bottom of the ship1  
or at a point low down at its side4     
,whenever the engineer considers that   
the water in the boiler has become so   
salted that the process of blowing out  

should commence1 he opens the cock      
communicating by this pipe with the sea1
 and suffers an indefinite and uncertain
 quantity of water to escape4 ,in this  
way he discharges1 according to the     
magnitude of the boiler1 from two to six
 tons ,pg#dee of water1 and repeats this
 at intervals of from two to four hours1
 as he may consider to be sufficient4   
,if1 by observing this process1 he      
prevents the boiler from getting        
incrusted during the voyage1 he         
considers his duty to be effectually    
discharged1 forgetting that he may have 
blown out many times more water than is 
necessary for the preservation of the   
boiler1 and thereby produced a          
corresponding and unnecessary waste of  
fuel4 ,in order to limit the quantity of
 water discharged1 ,messrs4 ,seaward    
have adopted the following method4 ,in  
fig4 #abe4 is represented a transverse  
section of a part of a steam-vessel2 ,w 
is the water-line of the boiler1 ,b is  
the mouth of a blow-off pipe1 placed    

near the bottom of the boiler4 ,this    
pipe rises to ,a1 and turning in the    
horizontal direction1 ,a ,c is conducted
 to a tank ,t1 which contains exactly a 
ton of water4 ,this pipe communicates   
with the tank by a cock ,d1 governed by 
a lever ,h4 ,when this lever is moved to
 ,d1 the cock ,d is open1 and when it is
 moved to ,k1 the cock ,d is closed4    
,from the same tank there proceeds      
another pipe ,e1 which issues from the  
side of the ,pg#def vessel into the sea 
governed by a cock ,f1 which is likewise
 put in connection with the lever ,h1 so
 that it shall be opened when the lever 
,h is drawn to the position ,f1 the cock
 ,d being closed in all positions of the
 lever between ,k and ,f4 ,thus1        
whenever the cock ,f communicating with 
the sea is open1 the cock ,d            
communicating with the boiler is closed1
 and vice vers1 both cocks being closed 
when the lever is in the intermediate   
position ,k4 ,by this arrangement the   
boiler cannot1 by any neglect in blowing

 off1 be left in communication with the 
sea1 nor can more than a ton of water be
 discharged except by the immediate act 
of the engineer4 ,the injurious         
consequences are thus prevented which   
sometimes ensue when the blow-off cocks 
are left open by any neglect on the part
 of the engineer4 ,when it is necessary 
to blow off1 the engineer moves the     
lever ,h1 to the position ,d4 ,the      
pressure of the steam in the boiler on  
the surface of the water ,w forces the  
salted water or brine up the pipe ,b ,a1
 and through the open cock ,c into the  
tank1 and this continues until the tank 
is filled3 when that takes place1 the   
lever is moved from the position ,d to  
the position ,f1 by which the cock ,d is
 closed1 and the cock ,f opened4 ,the   
water in the tank flows through the pipe
 ,e into the sea1 air being admitted    
through the valve ,v1 placed at the top 
of the tank1 opening inwards4 ,a second 
ton of brine is discharged by moving the
 lever back to the position ,d1 and     

subsequently returning it to the        
position ,f2 and in this way the brine  
is discharged ton by ton1 until the     
supply of water from the feed which     
replaces it has caused both the balls in
 the indicator to sink to the bottom4   
7#bab47 ,a different method of          
preserving the requisite freshness of   
the water in the boiler has been adopted
 by ,messrs4 ,maudslay and ,field1 and  
introduced with success into the ,great 
,western and other steam-vessels4 ,pumps
 called brine-pumps are put into        
communication with the lower part of the
 boiler1 and so constructed as to draw  
the brine therefrom1 and drive it into  
the sea4 ,these brine-pumps are worked  
by the engine1 and their operation is   
constant4 ,the feed-pumps are likewise  
worked by the engine1 and they bear such
 a proportion to the brine-pumps that   
the quantity of salt discharged in a    
given time in the brine is equal to the 
quantity of salt ,pg#deg introduced in  
solution by the water of the feed-pumps4

 ,by this means the same actual quantity
 of salt is constantly maintained in the
 boiler1 and consequently the strength  
of the solution remains invariable4 ,if 
the brine discharged by the brine-pumps 
contains #e_/cb parts of salt while the 
water introduced by the feed-pumps      
contains only #a_/cb part1 then it is   
evident that five cubic feet of the     
feeding water will contain no more salt 
than is contained in one cubic foot of  
brine4 ,under such circumstances the    
brine-pumps would be so constructed as  
to discharge #a_/e of the water         
introduced by the feed-pumps1 so that   
#d_/e of all the water introduced into  
the boiler would be evaporated1 and     
rendered available for working the      
engine4  ,to save the heat of the brine1
 a method has been adopted in the marine
 engines constructed by ,messrs4        
,maudslay and ,field similar to one     
which has been long practised in        
steam-boilers1 and in various apparatus 
for the warming of buildings4 ,the      

current of heated brine is conducted    
from the boiler through a tube which is 
contained in another1 through which the 
feed is introduced4 ,the warm current of
 brine1 therefore1 as it passes out1    
imparts a considerable portion of its   
heat to the cold feed which comes in2   
and it is found that by this expedient  
the brine discharged into the sea may be
 reduced to a temperature of about #ajj4
  ,this expedient is so effectual that  
when the apparatus is properly          
constructed1 and kept in a state of     
efficiency1 it may be regarded as nearly
 a perfect preventive against the       
incrustation1 and the deposition of salt
 in the boilers1 and is not attended    
with any considerable waste of fuel4    
7#bac47 ,about the year #aggf1 ,mr4     
,watt invented a tubular condenser1 with
 a view to condense the steam drawn off 
from the cylinder without the process of
 injection4 ,this apparatus consisted of
 a number of small tubes connecting the 
top and bottom of the condenser1        

arranged in a manner not very different 
from that of the tubes which traverse   
the boiler of a locomotive engine4      
,these tubes were continually surrounded
 by cold water1 and the steam1 as it    
escaped from the cylinder passing       
through them1 was condensed by their    
cold surfaces1 and collected in the form
 of water in a reservoir below1 from    
,pg#deh whence it was drawn off by a    
pump in the same manner as in engines   
which condensed by injection4 ,one of   
the advantages proposed by this         
expedient was1 that no atmospheric air  
would be introduced into the condenser1 
as is always the case when condensation 
by injection is practised4 ,cold water1 
which is injected1 has always combined  
with it more or less common air4 ,when  
this water is mixed with the condensed  
steam1 the elevation of its temperature 
disengages the air combined with it1 and
 this air circulating to the cylinder1  
vitiates the vacuum4 ,one of the        
purposes for which the air-pump in      

condensing steam-engines was provided1  
and from which it took its name1 was to 
draw off this air4 ,if1 however1 a      
tubular condenser could be made to act  
with the necessary efficiency1 no       
injection water would be introduced for 
condensation1 and the pump would have no
 other duty except to remove the small  
quantity of water produced by the       
condensed steam4 ,that water being      
subsequently carried back to the boiler 
by the feed-pumps1 a constant system of 
circulation would be maintained1 and the
 boiler would never require any fresh   
supply of water1 except what might be   
necessary to make good the waste by     
leakage and other causes4  ,this        
contrivance has been of late years      
revived by ,mr4 ,samuel ,hall of        
,basford1 near ,nottingham1 with a view 
to supersede in marine engines the      
necessity of using sea-water in the     
boilers4 ,mr4 ,hall proposes to make    
marine boilers with fresh water to      
condense the steam without injection1 by

 a tubulated condenser1 and to provide  
by the distillation of sea-water the    
small quantity of fresh water which     
would be necessary to make good the     
waste4 ,these condensers have been      
introduced into several steam-vessels3  
in some they have been continued1 and in
 others abandoned1 and various opinions 
are entertained of their efficacy4 ,i   
have not been able to obtain the results
 of any satisfactory experiments on     
them1 and cannot therefore form a       
judgment of their usefulness4 ,mr4 ,watt
 abandoned these condensers from finding
 that the condensation of the steam was 
not sufficiently sudden1 and that       
consequently at the commencement of the 
stroke the piston was subject to a      
resistance which ,pg#dei injuriously    
diminished the amount of the moving     
power1 whereas condensation by jet was  
almost instantaneous1 and the efficiency
 of the piston throughout the entire    
stroke was more uniform4  ,mr4 ,watt    
also found that a fur collected around  

the tubes of the condenser1 so as to    
obstruct the free passage of heat from  
the steam to the water of the cold      
cistern2 and that1 consequently1 the    
efficiency of the condenser was         
gradually impaired1 and could only be   
restored by frequent cleansing4  ,it is 
stated by ,mr4 ,hall that a vacuum is   
preserved in his condensers as perfect  
as that which is maintained in the      
ordinary condensers by injection4 ,it is
 objected1 on the other hand1 that      
without the injection water and the air 
which accompanies it being introduced   
into his condensers1 ,mr4 ,hall uses as 
large and powerful an air-pump as those 
which are used in engines of equal power
 condensing by injection2 that1         
consequently1 the vacuum which is       
maintained is produced1 not as it ought 
to be altogether by the condensation of 
steam1 but by the air-pump drawing off  
the uncondensed steam4 ,to whatever     
extent this may be true1 the efficacy of
 the machine1 as indicated by the       

barometer-gauge1 is only apparent2 since
 as much power is necessary to pump away
 any portion of uncondensed vapour as is
 obtained by the vacuum produced by the 
absence of that vapour4  ,a tubular     
condenser of the form proposed by ,mr4  
,hall is represented in fig4 #abf42 a is
 the upper part of the condenser to     
which steam is admitted from the slide  
after having worked the piston2 k is the
 section of a thin plate1 forming the   
top of the condenser1 perforated with   
small holes1 in which the tubes are     
inserted so as to be steam-tight and    
water-tight4 ,water is admitted to flow 
around these tubes between the top k and
 the bottom d of the condenser1 so as to
 keep them constantly at a low          
temperature4 ,the steam passes from a   
through the tubes to the lower chamber f
 of the condenser1 where it is reduced  
to water by the cold to which it has    
been exposed4 ,a supply of cold water is
 constantly pumped through the          
condenser1 so as to keep the tubes at a 

low temperature4 ,the air-pump g is of  
the usual construction1 having valves in
 the piston opening upwards1 and ,pg#dfj
 similar valves in the cover of the pump
 also opening upwards4 ,the water formed
 by the condensed steam in f is drawn   
through the foot-valve1 and after       
passing through the piston-valves1 is   
discharged by the up-stroke of the      
piston into the hot well4 ,any air1 or  
other permanent gas1 which may be       
admitted by leakage through the tubes of
 the condenser1 or by any other means1  
is likewise drawn out by this pump1 and 
when drawn into the hot well is carried 
from thence to the feeding apparatus of 
the boiler1 to which it is transferred  
by the feed-pump4  ,illustration3 ,fig4 
#abf4  ,a provision is likewise made by 
which the steam escaping at the         
safety-valve is condensed and carried   
away to the feeding cistern4   7#bad47  
,one of the remedies proposed for the   
evil consequences arising from          
incrustation is the substitution of     

copper for iron boilers4 ,the attraction
 which produces the adhesion of the     
calcareous matter held in solution by   
salt water to the surface of iron has no
 existence in copper1 and all the saline
 and other alkaline matter precipitated 
in the boiling water in ,pg#dfa copper  
boilers is suspended in a loose form1   
and carried off by the process of       
blowing out4  ,besides the injury       
arising from the deposition of salt and 
the incrustation on the inner surface of
 boilers1 an evil of a formidable kind  
attends the accumulation of soot mixed  
with salt in the flues1 which proceeds  
from the leaks4 ,in the seams of the    
boiler there are numerous apertures1 of 
dimensions so small as to be incapable  
of being rendered stanch by any         
practicable means1 through which the    
water within the boiler filters1 and the
 salt which it carries with it mixes    
with the soot1 forming a compound which 
rapidly corrodes the boilers4 ,this     
process of corrosion in the flues takes 

place not less in copper than in iron   
boilers4 ,in cleansing the flues of a   
copper boiler1 the salt and soot which  
was thrown out upon the iron-plates     
which formed the flooring of the        
engine-room1 having remained there for  
some time1 left behind it a permanent   
appearance of copper on the iron        
flooring1 arising from the precipitation
 of the copper which had combined with  
the soot and salt in the flues4#cf ,in  
this case the leaks from whence the salt
 proceeded were found1 on careful       
examination1 so unimportant1 that the   
usual means to stanch them could not be 
resorted to without the risk of         
increasing the evil4   7#bae47 ,in the  
application of the steam-engine to the  
propulsion of vessels in voyages of     
great extent1 the economy of fuel       
acquires an importance greater than that
 which appertains to it in land-engines1
 even in localities the most removed    
from coal-mines1 and where its expense  
is greatest4 ,the practical limit to    

steam-voyages being determined by the   
greatest quantity of coals which a      
steam-vessel can carry1 every expedient 
by which the efficiency of the fuel can 
be increased becomes a means1 not merely
 of a saving of expense1 but of an      
increased extension of steam-power to   
navigation4 ,much attention has been    
bestowed on the augmentation of the duty
 of engines in the mining districts of  
,cornwall1 where the question of their  
efficiency is merely a question of      
economy1 but far greater care should be 
given to this subject when the          
practicability of maintaining           
intercourse by steam between distant    
points of the globe will perhaps depend 
on the effect produced by a given       
quantity ,pg#dfb of fuel4 ,so long as   
steam-navigation was confined to river  
and channel transport1 and to coasting  
voyages1 the speed of the vessel was a  
paramount consideration1 at whatever    
expenditure of fuel it might be         
obtained2 but since steam-navigation has

 been extended to ocean-voyages1 where  
coals must be transported sufficient to 
keep the engine in operation for a long 
period of time without a fresh relay1   
greater attention has been bestowed upon
 the means of economising it4  ,much of 
the efficiency of fuel must depend on   
the management of the fires1 and        
therefore on the skill and care of the  
stokers4 ,formerly the efficiency of    
firemen was determined by the abundant  
production of steam1 and so long as the 
steam was evolved in superabundance1    
however it might have blown off to      
waste1 the duty of the stoker was       
considered as well performed4 ,the      
regulation of the fires according to the
 demands of the engine were not thought 
of1 and whether much or little steam was
 wanted1 the duty of the stoker was to  
urge the fires to their extreme limit4  
,since the resistance opposed by the    
action of the paddle-wheels of a        
steam-vessel varies with the state of   
the weather1 the consumption of steam in

 the cylinders must undergo a           
corresponding variation2 and if the     
production of steam in the boilers be   
not proportioned to this1 the engines   
will either work with less efficiency   
than they might do under the actual     
circumstances of the weather1 or more   
steam will be produced in the boilers   
than the cylinders can consume1 and the 
surplus will be discharged to waste     
through the safety-valves4 ,the stokers 
of a marine engine1 therefore1 to       
perform their duty with efficiency1 and 
obtain from the fuel the greatest       
possible effect1 must discharge the     
functions of a self-regulating furnace1 
such as has been already described3 they
 must regulate the force of the fires by
 the amount of steam which the cylinders
 are capable of consuming1 and they must
 take care that no unconsumed fuel is   
allowed to be carried away from the     
ash-pit4   7#baf47 ,until within a few  
years of the present time the heat      
radiated from every part of the surface 

of the boiler was allowed to go to      
waste1 and to produce injurious effects 
on those parts of the vessel to which it
 was transmitted4 ,this evil1 ,pg#dfc   
however1 has been lately removed by     
coating the boilers1 steam-pipes1 c4 of 
steam-vessels with felt1 by which the   
escape of heat from the surface of the  
boiler is very nearly1 if not           
altogether1 prevented4 ,this felt is    
attached to the boiler-surface by a     
thick covering of white and red lead4   
,this expedient was first applied in the
 year #ahah to a private steam-vessel of
 ,mr4 ,watt's called the ,caledonia1 and
 it was subsequently adopted in another 
vessel1 the machinery of which was      
constructed at ,soho1 called the ,james 
,watt4  ,the economy of fuel depends in 
a considerable degree on the arrangement
 of the furnaces1 and the method of     
feeding them4 ,in general each boiler is
 worked by two or more furnaces         
communicating with the same system of   
flues4 ,while the furnace is fed1 the   

door being open1 a stream of cold air   
rushes in1 passing over the burning fuel
 and lowering the temperature of the    
flues3 this is an evil to be avoided4   
,but1 on the other hand1 if the furnaces
 be fed at distant intervals1 then each 
furnace will be unduly heaped with fuel1
 a great quantity of smoke will be      
evolved1 and the combustion of the fuel 
will be proportionally imperfect4 ,the  
process of coking in front of the grate1
 which would insure a complete          
combustion of the fuel1 has been already
 described 7#adg474 ,a frequent supply  
of coals1 however1 laid carefully on the
 front part of the grate1 and gradually 
pushed backwards as each fresh feed is  
introduced1 would require the fire-door 
to be frequently opened1 and cold air to
 be admitted4 ,it would also require    
greater vigilance on the part of the    
stokers than can generally be obtained  
in the circumstances in which they work4
 ,in steam-vessels the furnaces are     
therefore fed less frequently1 fuel     

introduced in greater quantities1 and a 
less perfect combustion produced4  ,when
 several furnaces are constructed under 
the same boiler1 communicating with the 
same system of flues1 the process of    
feeding1 and consequently opening one of
 them1 obstructs the due operation of   
the others1 for the current of cold air 
which is thus admitted into the flues   
checks the draft and diminishes the     
efficiency of the furnaces in operation4
 ,it was formerly the practice in       
vessels exceeding one hundred           
horse-power1 to place four furnaces     
under each boiler1 communicating with   
the same system of flues4 ,such an      
arrangement ,pg#dfd was found to be     
attended with a bad draft in the        
furnaces1 and therefore to require a    
greater quantity of heating surface to  
produce the necessary evaporation4 ,this
 entailed upon the machinery the        
occupation of more space in the vessel  
in proportion to its power2 it has      
therefore been more recently the        

practice to give a separate system of   
flues to each pair of furnaces1 or1 at  
most1 to every three furnaces4 ,when    
three furnaces communicate with a common
 flue1 two will always be in operation1 
while the third is being cleared out2   
but if the same quantity of fire were   
divided among two furnaces1 then the    
clearing out of one would throw out of  
operation half the entire quantity of   
fire1 and during the process the        
evaporation would be injuriously        
diminished4 ,it is found by experience1 
that the side plates of furnaces are    
liable to more rapid destruction than   
their roofs1 owing1 probably1 to a      
greater liability to deposit4 ,furnaces1
 therefore1 should not be made narrower 
than a certain limit4 ,great depth from 
front to back is also attended with     
practical inconvenience1 as it renders  
firing tools of considerable length1 and
 a corresponding extent of stoking room 
necessary4 ,it is recommended1 by those 
who have had much practical experience  

in steam-vessels1 that furnaces six feet
 in depth from front to back should not 
be less than three feet in width1 to    
afford means of firing with as little   
injury to the side plates as possible1  
and of keeping the fires in the         
condition necessary for the production  
of the greatest effect4 ,the tops of the
 furnaces almost never decay1 and seldom
 are subject to an alteration of figure1
 unless the level of the water be       
allowed to fall below them4#cg   7#bag47
 ,a form of marine engine was some years
 since proposed and patented by ,mr4    
,thomas ,howard1 possessing much novelty
 and ingenuity1 and having pretensions  
to a very extraordinary economy of fuel1
 in addition to the advantages claimed  
by ,mr4 ,hall4 ,in ,mr4 ,howard's       
engines1 the steam1 as in ,mr4 ,hall's1 
is constantly reproduced from the same  
water1 so that pure or distilled water  
may be used2 but ,mr4 ,howard dispenses 
altogether with the use of a boiler4  ,a
 quantity of mercury is placed in a     

shallow wrought-iron vessel over a coke 
fire1 by which it is maintained at a    
,pg#dfe temperature varying from #djj to
 #ejj4 ,the surface exposed to the fire 
was computed at three fourths of a      
square foot for each horse-power4 ,the  
upper surface of the mercury was covered
 by a very thin plate of iron in contact
 with it1 and so contrived as to present
 about four times as much surface as    
that exposed beneath the fire4 ,adjacent
 to this a vessel of water was placed1  
maintained nearly at the boiling point1 
and communicating by a nozzle and valve 
with the chamber immediately above the  
mercury4 ,at intervals corresponding to 
the motion of the piston a small        
quantity of water was injected from this
 vessel1 and thrown upon the plate of   
iron resting upon the hot mercury4 ,from
 this it received not only the heat     
necessary to convert it into common     
steam1 but to give it the qualities of  
highly superheated steam4 ,in fact1 the 
steam thus produced had a temperature   

considerably above that which           
corresponded to its pressure1 and was1  
therefore1 capable of being deprived of 
more or less of its heat without being  
condensed4 7#id47 ,the quantity of water
 injected into the steam-chamber was    
regulated by the power at which the     
engine was intended to be worked4 ,the  
fire was supplied with air by a blower  
subject to exact regulation4 ,the steam 
thus produced was conducted to a chamber
 surrounding the working cylinder1 and  
this chamber itself was enclosed by     
another space through which the air from
 the furnace passed before it reached   
the flue4 ,by this contrivance the air  
imparted its redundant heat to the      
steam1 as the latter passed to the      
cylinder1 and raised its temperature to 
about #djj1 the pressure1 however1 not  
exceeding #be lbs4 per square inch4 ,the
 valves1 governing the admission of     
steam to the piston1 were adapted for   
expansive action4  ,the vacuum on the   
opposite side was maintained by         

condensation in the following           
manner3--,the condenser was a copper    
vessel placed in a cistern of cold      
water1 and the steam was admitted to it 
from the cylinder by an eduction pipe in
 the usual way4 ,a jet was introduced   
from an adjacent vessel filled with     
distilled water1 and the condensing     
water and condensed steam were pumped   
from the condenser as in common engines4
 ,the warm water thus pumped out of the 
,pg#dff condenser was drawn through a   
copper worm1 carried with many coils    
through a cistern of cold water1 so that
 when it arrived at the end of this pipe
 it was reduced nearly to the           
temperature of the atmosphere4 ,the pipe
 was thus brought to the vessel of      
distilled water already mentioned1 and  
the water supplied by it replaced4 ,the 
water admitted to the condenser through 
the condensing jet being purged of air1 
a small air-pump was sufficient1 since  
it had only to exhaust the condenser and
 tubes at starting1 and to remove the   

air which might be admitted by leakage4 
,mr4 ,howard stated that the            
condensation took place as rapidly and  
perfectly as in the best engines of the 
common kind4  ,an engine of this        
construction was in the spring of #ahce 
placed in the government steamer called 
the ,comet4 ,it was stated1 that though 
the machinery was not advantageously    
constructed1 a part of the engine being 
old1 and not made expressly for a boiler
 of this kind1 the vessel performed a   
voyage from ,falmouth to ,lisbon1 in    
which the consumption of fuel did not   
exceed a third of her former consumption
 when worked by ,boulton and ,watt's    
engines1 the former consumption of coals
 being about eight hundred pounds per   
hour1 and the consumption of ,mr4       
,howard's engine being less than two    
hundred and fifty pounds of coke per    
hour4  ,the advantages claimed for this 
contrivance were the following3 first1  
the small space and weight occupied by  
the machinery1 arising from the absence 

of a boiler2 second1 the diminished     
consumption of fuel2 third1 the reduced 
size of the flues2 fourth1 the removal  
of the injurious effects arising from   
deposit and incrustation2 fifth1 the    
absence of smoke4   7#bah47 ,the method 
by which the greatest quantity of       
practical effect can be obtained from a 
given quantity of fuel must1 however1   
mainly depend on the extended           
application of the expansive principle4 
,this has been the means by which an    
extraordinary amount of duty has been   
obtained from the ,cornish engines4 ,the
 difficulty of the application of this  
principle in marine engines has arisen  
from the objections entertained in      
,europe to the use of steam of high     
pressure under the circumstances in     
which the engine must be worked at sea4 
,to apply the expansive principle1 it is
 necessary that the moving power at the 
commencement of the stroke shall        
considerably exceed the ,pg#dfg         
resistance1 its force being gradually   

attenuated till the completion of the   
stroke1 when it will at length become   
less than the resistance4 ,this         
condition may1 however1 be attained with
 steam of limited pressure1 if the      
engine be constructed with a sufficient 
quantity of piston-surface4 ,this method
 of rendering the expansive principle   
available at sea1 and compatible with   
low-pressure steam1 has recently been   
brought into operation by ,messrs4      
,maudslay and ,field4 ,their improvement
 consists in adapting two               
steam-cylinders in one engine1 in such a
 manner that the steam shall act        
simultaneously on both pistons1 causing 
them to ascend and descend together4    
,the piston-rods are both attached to   
the same horizontal cross-head1 whereby 
their combined action is applied to one 
crank by means of a connecting rod      
placed between the pistons4             
,illustration3 ,fig4 #abg4  ,a section  
of such an engine1 made by a plane      
passing through the two piston-rods ,p  

,p and cylinders1 is represented in fig4
 #abg4 ,the piston-rods are attached to 
a cross-head ,c1 ,pg#dfh which ascends  
and descends with them4 ,this cross-head
 drives upwards and downwards an axle   
,d1 to which the lower end of the       
connecting rod ,e is attached4 ,the     
other end of the connecting rod drives  
the crank-pin ,f1 and imparts revolution
 to the paddle-shaft ,g4 ,a rod ,h      
conveys motion by means of a beam ,i to 
the rod ,k of the air-pump ,e4   7#bai47
 ,connected with this1 and in the same  
patent1 another improvement is included1
 consisting of the application of a     
hollow wrought-iron framing carried     
across the vessel above the machinery1  
to support the whole of the bearings of 
the crank-shaft4 ,a plan of this1       
including the cylinders and             
paddle-wheel1 is represented in fig4    
#abh4 ,the advantages proposed by these 
improvements are simplicity of          
construction1 more direct action on the 
crank1 economy of space and weight of   

material1 combined with increased area  
of the piston1 whereby a given          
evaporating power of the boiler is      
rendered productive1 by extended        
application of the expansive principle1 
of a greater moving power than in former
 arrangements4 ,consequently1 under like
 circumstances1 greater power and       
economy of fuel is obtained1 with the   
further advantage at sea1 that when the 
engine is reduced in its speed1 either  
by the vessel being deeply laden with   
coal1 as is the case at the commencement
 of a long sea voyage1 or by head winds1
 more steam may be given to the         
cylinders1 and consequently more speed  
imparted to the vessel1 all the steam   
produced in the boiler being usefully   
employed4   7#bbj47 ,another            
improvement1 having the same objects1   
and analogous to the preceding1 has been
 likewise patented by ,messrs4 ,maudslay
 and ,field4 ,this consists in the      
adoption of a cylinder of greater       
diameter1 having two piston-rods ,p ,p1 

as represented in fig4 #abi41 of        
considerable length1 connected at the   
top by a cross-head ,c4 ,from this      
cross-head is carried downwards the     
connecting rod ,d1 which drives the     
crank-pin ,e1 and thereby works the     
paddle-shaft ,s4 ,in this case the      
paddle-shaft is extended immediately    
above the piston1 and the double        
piston-rod has sufficient length to be  
above the paddle-shaft when the piston  
is at the bottom of its stroke4 ,this   
improvement is intended to be applied   
more particularly for engines for river 
navigation1 the advantages resulting    
from ,pg#dfi it being that a            
paddle-shaft placed at a given height   
from the bottom of the vessel will be   
enabled to receive a longer stroke of   
piston than by any other arrangement now
 in use4 ,a more ,pg#dgj compact and    
firm connection of the cylinder with the
 crank-shaft bearings is effected by it1
 and a cylinder of much greater diameter
 may be applied by which the expansive  

action of steam may be more fully       
brought into play2 and a more direct    
action of the steam-power on the crank  
with a less weight of materials and a   
greater economy of space may be obtained
 than by any of the arrangements of     
marine engines hitherto used4           
,illustration3 ,fig4 #abh4              
,illustration3 ,fig4 #abi4   7#bba47    
,mr4 ,francis ,humphrys has obtained a  
patent for a form of marine engine1 by  
which some simplification of the        
machinery is attained1 and the same     
power comprised within more limited     
dimensions4 ,in this engine there is    
attached to the piston of the cylinder1 
instead of a piston-rod1 a hollow casing
 ,d ,d 7fig4 #acj471 which moves through
 a stuffing-box ,g1 constructed in a    
manner similar to the stuffing-box of a 
piston-rod4 ,in the figure1 this casing 
is presented in section1 but ,pg#dga its
 form is that of a long narrow slit1 or 
opening1 rounded at either end as       
exhibited in the plan 7fig4 #aca7 of the

 cylinder-cover4 ,the crank ,c is driven
 by the other end of the connecting rod 
,h1 the crank-shaft being immediately   
above the centre of the piston and the  
connecting rod passing through the      
oblong opening ,d1 and descending into  
the hollow piston-rod it is attached to 
an axis ,i at the bottom of the piston4 
,a box or cover ,k ,k encloses the      
cross-piece or axis ,i with its         
bearings1 and is ,pg#dgb attached so as 
to be steam-tight to the bottom of the  
piston4 ,a hollow space ,l ,l is cast in
 the bottom of the cylinder for the     
reception of the box ,k ,k1 when the    
piston is at the bottom of the cylinder4
  ,illustration3 ,fig4 #acj4            
,illustration3 ,fig4 #aca4  ,by this    
arrangement the force by which the      
piston is driven in its ascent and      
descent is communicated to the          
connecting rod1 not1 as usual1 through  
the intervention of a piston-rod1 but   
directly from the piston itself by the  
cross-pin ,i1 and from thence to the    

crank ,c1 which it drives without the   
intervention of beams1 cross-heads1 or  
any similar appendage4  ,the            
slide-valves regulating the admission   
and eduction of steam are represented at
 a2 the rod of the air-pump is shown at 
d1 being worked by a crank placed on the
 centre of the great crank shaft4#ch    
7#bbb47 ,to obtain from the moving power
 its full amount of mechanical effect in
 propelling the vessel1 it would be     
necessary that its force should propel1 
by constantly acting against the water  
in a horizontal direction1 and with a   
motion contrary to the course of the    
vessel4 ,no system of mechanical        
propellers has1 however1 yet been       
contrived capable of perfectly          
accomplishing this4 ,patents have been  
granted for many ingenious mechanical   
combinations to impart to the propelling
 surfaces such angles as appeared to the
 respective contrivers most             
advantageous4 ,in most of these the     
mechanical complexity has formed a fatal

 objection4 ,no part of the machinery of
 a steam-vessel is so liable to become  
deranged at sea as the paddle-wheels2   
and1 therefore1 that simplicity of      
construction which is compatible with   
those repairs which are possible on such
 emergencies is quite essential for safe
 practical use4  ,illustration3 ,fig4   
#acb4  ,the ordinary paddle-wheel1 as   
has been already stated1 is a wheel     
revolving upon a shaft driven by the    
engine1 and carrying upon its           
circumference a number of flat boards1  
called paddle-boards1 which are secured 
by nuts and braces in a fixed position2 
and that position is such that the      
planes ,pg#dgc of the paddle-boards     
diverge nearly from the centre of the   
shaft on which the wheel turns4 ,the    
consequence of this arrangement is that 
each paddle-board can only act in that  
direction which is most advantageous for
 the propulsion of the vessel when it   
arrives near the lowest point of the    
wheel4 ,in fig4 #acb4 let ,o be the     

shaft on which the common paddle-wheel  
revolves2 the position of the           
paddle-boards are represented at ,a1 ,b1
 ,c1 c42 ,x1 ,y represents the water    
line1 the course of the vessel being    
supposed to be from ,x to ,y2 the arrows
 represent the direction in which the   
paddle-wheel revolves4 ,the wheel is    
immersed to the depth of the lowest     
paddle-board1 since a less degree of    
immersion would render a portion of the 
surface of each paddle-board            
mechanically useless4 ,in the position  
,a the whole force of the paddle-board  
is efficient for propelling the vessel2 
but as the paddle enters the water in   
the position ,h1 its action upon the    
water1 not being horizontal1 is only    
partially effective for propulsion3 a   
part of the force which drives the      
paddle is expended in depressing the    
water1 and the remainder in driving it  
contrary to the course of the vessel1   
and1 therefore1 by its re-action        
producing a certain propelling effect4  

,the tendency1 however1 of the paddle   
entering the water at ,h1 is to form a  
hollow or trough1 which the water1 by   
its ordinary property1 has a continual  
tendency to fill up4 ,after passing the 
lowest point ,a1 as the paddle          
approaches the position ,b1 where it    
,pg#dgd emerges from the water1 its     
action again becomes oblique1 a part    
only having a propelling effect1 and the
 remainder having a tendency to raise   
the water1 and throw up a wave and spray
 behind the paddle-wheel4 ,it is evident
 that the more deeply the paddle-wheel  
becomes immersed1 the greater will be   
the proportion of the propelling power  
thus wasted in elevating and depressing 
the water2 and if the wheel were        
immersed to its axis1 the whole force of
 the paddle-boards1 on entering and     
leaving the water1 would be lost1 no    
part of it having a tendency to propel4 
,if a still deeper immersion take place1
 the paddle-boards above the axis would 
have a tendency to retard the course of 

the vessel4 ,when the vessel is1        
therefore1 in proper trim1 the immersion
 should not exceed nor fall short of the
 depth of the lowest paddle2 but for    
various reasons it is impossible in     
practice to maintain this fixed         
immersion3 the agitation of the surface 
of the sea1 causing the vessel to roll1 
will necessarily produce a great        
variation in the immersion of the       
paddle-wheels1 one becoming frequently  
immersed to its axle1 while the other is
 raised altogether out of the water4    
,also the draught of water of the vessel
 is liable to change1 by the variation  
in her cargo2 this will necessarily     
happen in steamers which take long      
voyages4 ,at starting they are heavily  
laden with fuel1 which as they proceed  
is gradually consumed1 whereby the      
vessel is lightened4   7#bbc47 ,to      
remove this defect1 and economise as    
much as possible the propelling effect  
of the paddle-boards1 it would be       
necessary so to construct them that they

 may enter and leave the water edgeways1
 or as nearly so as possible2 such an   
arrangement would be1 in effect1        
equivalent to the process called        
feathering1 as applied to oars4 ,any    
mechanism which would perfectly         
accomplish this would cause the paddles 
to work in almost perfect silence1 and  
would very nearly remove the            
inconvenient and injurious vibration    
which is produced by the action of the  
common paddles4 ,but the construction of
 feathering paddles is attended with    
great difficulty1 under the peculiar    
circumstances in which such wheels work4
 ,any mechanism so complex that it could
 not be easily repaired when deranged1  
with such engineering implements and    
skill ,pg#dge as can be obtained at sea1
 would be attended with great           
objections2 and the efficiency of its   
propelling action would not compensate  
for the dangers which must attend upon  
the helpless state of a steamer1        
deprived of her propelling agents4      

,feathering paddle-boards must          
necessarily have a motion independently 
of the motion of the wheel1 since any   
fixed position which could be given to  
them1 though it might be most favourable
 to their action in one position would  
not be so in their whole course through 
the water4 ,thus the paddle-board when  
at the lowest point should be in a      
vertical position1 or so placed that its
 plane1 if continued upwards1 would pass
 through the axis of the wheel4 ,in     
other positions1 however1 as it passes  
through the water1 it should present its
 upper edge1 not towards the axle of the
 wheel1 but towards a point above the   
highest point of the wheel4 ,the precise
 point to which the edge of the         
paddle-board should be directed is      
capable of mathematical determination4  
,but it will vary according to          
circumstances1 which depend on the      
motion of the vessel4 ,the progressive  
motion of the vessel1 independently of  
the wind or current1 must obviously be  

slower than the motion of the           
paddle-boards round the axle of the     
wheel2 since it is by the difference of 
these velocities that the re-action of  
the water is produced by which the      
vessel is propelled4 ,the proportion1   
however1 between the progressive speed  
of the vessel and the rotative speed of 
the paddle-boards is not fixed3 it will 
vary with the shape and structure of the
 vessel1 and with its depth of          
immersion2 nevertheless it is upon this 
proportion that the manner in which the 
paddle-boards should shift their        
position must be determined4 ,if the    
progressive speed of the vessel were    
nearly equal to the rotative speed of   
the paddle-boards1 the latter should so 
shift their position that their upper   
edges should be presented to a point    
very little above the highest point of  
the wheel4 ,this is a state of things   
which could only take place in the case 
of a steamer of a small draught of      
water1 shallop-shaped1 and so           

constructed as to suffer little         
resistance from the fluid4 ,on the other
 hand1 the greater the depth of         
immersion1 and the less fine the lines  
of the ,pg#dgf vessel1 the greater will 
be the resistance in passing through the
 water1 and the greater will be the     
proportion which the rotative speed of  
the paddle-boards will bear to the      
progressive speed of the vessel4 ,in    
this latter case the independent motion 
of the paddle-boards should be such that
 their edges1 while in the water1 shall 
be presented towards a point            
considerably above the highest point of 
the paddle-wheel4  ,a vast number of    
ingenious mechanical contrivances have  
been invented and patented for          
accomplishing the object just explained4
 ,some of these have failed from the    
circumstance of their inventors not     
clearly understanding what precise      
motion it was necessary to impart to the
 paddle-board3 others have failed from  
the complexity of the mechanism by which

 the desired effect was produced4       
7#bbd47 ,in the year #ahbi a patent was 
granted to ,elijah ,galloway for a      
paddle-wheel with movable paddles1 which
 patent was purchased by ,mr4 ,william  
,morgan1 who made various alterations in
 the mechanism1 not very materially     
departing from the principle of the     
invention4  ,illustration3 ,fig4 #acc4  
,this paddle-wheel is represented in    
fig4 #acc4 ,the contrivance may be      
shortly stated to consist in causing the
 wheel which bears the paddles to       
revolve on one centre1 and the radial   
arms which move the paddles to revolve  
on another centre4 ,let ,a ,b ,c ,d ,e  
,f ,g ,h ,i ,k ,l be the polygonal      
circumference of the paddle-wheel1      
formed of straight bars1 securely       
connected together at the extremities of
 the spokes or radii of the wheel which 
turns on the shaft which is worked by   
the engine2 the centre of this wheel    
being at ,o4 ,so far this wheel is      
similar to the common paddle-wheel2 but 

the paddle-boards are not1 as in the    
common wheel1 fixed at ,a ,b ,c1 c41 so 
as to be always directed to the centre  
,o1 but are so placed that they are     
capable of turning on axles which are   
always horizontal1 so that they can take
 any angle with respect to the water    
which may be given to them4 ,from the   
centres1 or the line joining the pivots 
on which these paddle-boards turn1 there
 proceed short arms ,k1 firmly fixed to 
the paddle-boards at an angle of about  
#abj4 ,on a motion given to this arm ,k1
 it will therefore give a corresponding 
angular motion to the paddle-board1 so  
as to make it turn on its pivots4 ,at   
,pg#dgg the extremities of the several  
arms marked ,k is a pin or pivot1 to    
which the extremities of the radial arms
 ,l are severally attached1 so that the 
angle between each radial arm ,l and the
 short paddle-arm ,k is capable of being
 changed by any motion imparted to ,l2  
the radial arms are connected at the    
other end with a centre1 round which    

they are capable of revolving4 ,now1    
since the points ,a ,b ,c1 c41 which are
 the pivots on which the paddle-boards  
turn1 are moved in the circumference of 
a circle1 of which the centre is ,o1    
they are always at the same distance    
from that point2 consequently they will 
continually vary their distance from the
 other centre ,p4 ,thus1 when a         
paddle-board arrives at that point of   
its revolution at which the centre round
 which it revolves lies precisely       
between it and the centre ,o1 its       
distance from the former centre is less 
than in any other position4 ,as it      
departs from that point1 its distance   
from that centre gradually increases    
until it arrives at the opposite point  
of its revolution1 where the centre ,o  
is exactly between it and the former    
centre2 then the distance of the        
paddle-board from the former centre is  
greatest4 ,pg#dgh ,this constant change 
of distance between each paddle-board   
and the centre ,p is accommodated by the

 variation of the angle between the     
radial arm ,l and the short paddle-board
 arm ,k2 as the paddle-board approaches 
the centre ,p this gradually diminishes2
 and as the distance of the paddle-board
 increases1 the angle is likewise       
augmented4 ,this change in the magnitude
 of the angle1 which thus accommodates  
the varying position of the paddle-board
 with respect to the centre ,p1 will be 
observed in the figure4 ,the            
paddle-board ,d is nearest to ,p2 and it
 will be observed that the angle        
contained between ,l and ,k is there    
very acute2 at ,e the angle between ,l  
and ,k increases1 but is still acute2 at
 ,g it increases to a right angle2 at ,h
 it becomes obtuse2 and at ,k1 where it 
is most distant from the centre ,p1 it  
becomes most obtuse4 ,it again          
diminishes at ,k1 and becomes a right   
angle between ,a and ,b4 ,now this      
continual shifting of the direction of  
the short arm ,k is necessarily         
accompanied by an equivalent change of  

position in the paddle-board to which it
 is attached2 and the position of the   
second centre ,p is1 or may be1 so      
adjusted that this paddle-board1 as it  
enters the water and emerges from it1   
shall be such as shall be most          
advantageous for propelling the vessel1 
and therefore attended with less of that
 vibration which arises chiefly from the
 alternate depression and elevation of  
the water1 owing to the oblique action  
of the paddle-boards4   7#bbe47 ,in the 
year #ahcc1 ,mr4 ,field1 of the firm of 
,maudslay and ,field1 constructed a     
paddle-wheel with fixed paddle-boards1  
but each board being divided into       
several narrow slips arranged one a     
little behind the other1 as represented 
in fig4 #acd4 ,these divided boards he  
proposed to arrange in such cycloidal   
curves that they must all enter the     
water at the same place in immediate    
succession1 avoiding the shock produced 
by the entrance of the common board4    
,these split paddle-boards are as       

efficient in propelling when at the     
lowest point as the common              
paddle-boards1 and when they emerge the 
water escapes simultaneously from each  
narrow board1 and is not thrown up1 as  
is the case with common                 
paddle-boards4#ci  ,illustration3 ,fig4 
#acd4  ,pg#dgi ,the theoretical effect  
of this wheel is the same as that of the
 common wheel1 and experience alone1 the
 result of which has not yet been       
obtained1 can prove its efficiency4 ,the
 number of bars1 or separate parts into 
which each paddle-board is divided1 has 
been very various4 ,when first          
introduced by ,mr4 ,galloway each board 
was divided into six or seven parts3    
this was subsequently reduced1 and in   
the more recent wheels of this form     
constructed for the government vessels  
the paddle-boards consist only of two   
parts1 coming as near to the common     
wheel as is possible1 without altogether
 abandoning the principle of the split  
paddle4   7#bbf47 ,to obtain an         

approximate estimate of the extent to   
which steam-power is applicable to long 
sea-voyages1 it would be necessary to   
investigate the mutual relation which1  
in the existing state of this           
application of steam-power1 exists      
between the capacity or tonnage of the  
vessel1 the magnitude1 weight1 and      
power1 of the machinery1 the available  
stowage for fuel1 and the average speed 
attainable in all ,pg#dhj weathers1 as  
well as the general purposes to which   
the vessel is to be appropriated1       
whether for the transport of goods or   
merchandise1 or merely for despatches   
and passengers1 or for both of these    
combined4 ,that portion of the capacity 
of the vessel which is appropriated to  
the moving power consists of the space  
occupied by the machinery and the fuel4 
,the distribution of it between these   
must mainly depend on the length of the 
voyage which the vessel must make       
without receiving a fresh supply of     
coals4 ,if the trips be short1 and      

frequent relays of fuel can be obtained1
 then the space allotted to the         
machinery may bear a greater proportion 
to that assigned to the fuel2 but in    
proportion as each uninterrupted stage  
of the voyage is increased1 a greater   
stock of coals will be necessary1 and a 
proportionally less space left for the  
machinery4 ,other things being the same1
 therefore1 steam-vessels intended for  
long sea-voyages must be less powerful  
in proportion to their tonnage4  ,it    
will be apparent that every improvement 
which takes place in the application of 
the steam-engine to navigation will     
modify all these data on which such an  
investigation must depend4 ,every       
increased efficiency of fuel1 from      
whatever cause it may be derived1 will  
either increase the useful tonnage of   
the vessel1 or increase the length of   
the voyage of which it is capable4      
,various improvements have been and are 
still in progress1 by which this        
efficiency has undergone continual      

augmentation1 and voyages may now be    
accomplished with moderate economy and  
profit1 to which a few years since      
marine engines could not be applied with
 permanent advantage4 ,the average speed
 of steam-vessels has also undergone a  
gradual increase by such improvements4  
,during the four years ending ,june1    
#ahcd1 it was found that the average    
rate of steaming obtained from fifty-one
 voyages made by the ,admiralty steamers
 between ,falmouth and ,corfu1 exclusive
 of stoppages1 was seven miles and a    
quarter an hour direct distance between 
port and port4 ,the vessels which       
performed this voyage varied from #cej  
to #gjj tons measured burden1 and were  
provided with engines varying from #ajj 
to #bjj horse-power1 with stowage for   
coals varying from #hj to #bdj tons4    
,the proportion of the power to the     
,pg#dha tonnage varied from one horse to
 three tons to one horse to four tons4  
,thus the ,,messenger had a power of    
#bjj horses and measured #gcj tons2 the 

,,flamer had a power of #abj horses1 and
 measured #ejj tons2 the ,,columbia had 
a power of #abj horses1 and measured    
#cfj tons4 ,in general it may be assumed
 that for the shortest class of trips1  
such as those of the ,channel steamers1 
the proportion of the power to the      
tonnage should be about one horse for   
every two tons2 but for the longer class
 of voyages1 the proportion of power to 
tonnage should be about one horse-power 
to from three to four tons measured     
tonnage4 ,these data1 however1 must be  
received as very rough approximations1  
subject to considerable modifications in
 their application to particular        
vessels4 ,we have already stated that   
the nominal horse-power is itself       
extremely indefinite2 and if1 as is now 
customary in the longer class of        
voyages1 the steam be worked            
expansively1 then the nominal power     
almost ceases to have any definite      
relation to the actual performance of   
the vessel4 ,it is usual to calculate   

the horse-power by assuming a uniform   
pressure of steam upon the piston1 and1 
consequently1 by excluding the          
consideration of the effect of          
expansion4 ,the most certain test of the
 amount of mechanical power exerted by  
the machinery would be obtained from the
 quantity of water actually transmitted 
in the form of steam from the boiler to 
the cylinder4 ,but the effect of this   
would also be influenced by the extent  
to which the expansive principle has    
been brought into operation4  ,from the 
reported performances of the larger     
class of steam-ships within the last few
 years1 it would appear that the average
 speed has been increased since the     
estimate above mentioned1 which was     
obtained in #ahcd2 and on comparing the 
consumption of fuel with the actual     
performance1 it would appear that the   
efficiency of fuel has also been        
considerably augmented4 ,no extensive   
course of accurate experiments or       
observations have1 however1 been        

obtained from which correct inferences  
may be drawn of the probable limits to  
which steam-navigation1 in its present  
state1 is capable of being extended4    
,the jealousy of rival companies has    
obstructed the inquiries of those who1  
solicitous more ,pg#dhb for the general 
advancement of the art than for the     
success of individual enterprises1 have 
directed their attention to this        
question2 and it is hardly to be        
expected that sufficiently correct and  
extensive data can be obtained for this 
purpose4   7#bbg47 ,increased facility  
in the extension and application of     
steam-navigation is expected to arise   
from the substitution of iron for wood1 
in the construction of vessels4         
,hitherto iron steamers have been       
chiefly confined to river-navigation2   
but there appears no sufficient reason  
why their use should be thus limited4   
,for sea-voyages they offer many        
advantages2 they are not half the weight
 of vessels of equal tonnage constructed

 of wood2 and1 consequently1 with the   
same tonnage they will have less draught
 of water1 and therefore less resistance
 to the propelling power2 or1 with the  
same draught of water and the same      
resistance1 they will carry a           
proportionally heavier cargo4 ,the      
nature of their material renders them   
more stiff and unyielding than timber2  
and they do not suffer that effect which
 is called hogging1 which arises from a 
slight alteration which takes place in  
the figure of a timber vessel in        
rolling1 accompanied by an alternate    
opening and closing of the seams4 ,iron 
vessels have the further advantage of   
being more proof against fracture upon  
rocks4 ,if a timber vessel strike1 a    
plank is broken1 and a chasm opened in  
her many times greater than the point of
 rock which produces the concussion4 ,if
 an iron vessel strike1 she will either 
merely receive a dinge1 or be pierced by
 a hole equal in size to the point of   
rock which she encounters4 ,some        

examples of the strength of iron vessels
 were given by ,mr4 ,macgregor ,laird1  
in his evidence before the ,committee of
 the ,commons on ,steam ,navigation1    
among which the following may be        
mentioned3--,an iron vessel1 called the 
,,alburkah1 in one of their experimental
 trials got aground1 and lay upon her   
anchor3 in a wooden vessel the anchor   
would probably have pierced her bottom2 
in this case1 however1 the bottom was   
only dinged4 ,an iron vessel1 built for 
the ,irish ,inland ,navigation ,company1
 was being towed across ,lough ,derg in 
a gale of wind1 when the towing rope    
broke1 and she was driven upon rocks1 on
 which she bumped for a considerable    
time ,pg#dhc without any injury4 ,a     
wooden vessel would in this case have   
gone to pieces4 ,a further advantage of 
iron vessels 7which in warm climates is 
deserving of consideration7 is their    
greater coolness and perfect freedom    
from vermin4  ,iron steam-vessels on a  
very large scale are now in preparation 

in the ports of ,liverpool and ,bristol1
 intended for long sea-voyages4 ,the    
largest vessel of this description which
 has yet been projected is stated to be 
in preparation for the voyage between   
,bristol and ,new ,york1 by the company 
who have established the steam-ship     
called the ,great ,western1 plying      
between these places4  ,several projects
 for the extension of steam-navigation  
to voyages of considerable length have  
lately been entertained both by the     
public and by the legislature1 and have 
imparted to every attempt to improve    
steam-navigation increased interest4 ,a 
committee of the ,house of ,commons     
collected evidence and made a report in 
the last session in favour of an        
experiment to establish a line of       
steam-communication between ,great      
,britain and ,india4 ,two routes have   
been suggested by the committee1 each   
being a continuation of the line of     
,admiralty steam-packets already        
established to ,malta and the ,ionian   

,isles4 ,one of the routes proposed is  
through ,egypt1 the ,red ,sea1 and      
across the ,indian ,ocean to ,bombay1 or
 some of the other presidencies2 the    
other across the north part of ,syria to
 the banks of the ,euphrates1 by that   
river to the ,persian ,gulf1 and from   
thence to ,bombay4 ,each of these routes
 will be attended with peculiar         
difficulties1 and in both a long        
sea-voyage will be encountered4  ,in the
 route by the ,red ,sea it is proposed  
to establish steamers between ,malta and
 ,alexandria 7eight hundred and sixty   
miles74 ,a steamer of four hundred tons'
 burden and one hundred horse-power     
would perform this voyage1 upon an      
average of all weathers incident to the 
situation1 in from five to six days1    
consuming ten tons of coal per day4 ,but
 it is probable that it might be found  
more advantageous to establish a higher 
ratio between the power and the tonnage4
 ,from ,alexandria the transit might be 
effected by land across the isthmus to  

,suez--a journey of from four to five   
days--by caravan and camels2 or the     
transit might be made either ,pg#dhd by 
land or water from ,alexandria to       
,cairo1 a distance of one hundred and   
seventy-three miles2 and from ,cairo to 
,suez1 ninety-three miles1 across the   
desert1 in about five days4 ,at ,suez   
would be a station for steamers1 and the
 ,red ,sea would be traversed in three  
runs or more4 ,if necessary1 stations   
for coals might be established at       
,cosseir1 ,judda1 ,mocha1 and finally at
 ,aden or at ,socatra--an island        
immediately beyond the mouth of the ,red
 ,sea1 in the ,indian ,ocean2 the run   
from ,suez to ,cosseir would be three   
hundred miles--somewhat more than twice 
the distance from ,liverpool to ,dublin4
 ,from ,cosseir to ,judda1 four hundred 
and fifty miles2 from ,judda to ,mocha1 
five hundred and seventeen miles2 and   
from ,mocha to ,socatra1 six hundred and
 thirty-two miles4 ,it is evident that  
all this would1 without difficulty1 in  

the most unfavourable weather1 fall     
within the present powers of            
steam-navigation4 ,if the terminus of   
the passage be ,bombay1 the run from    
,socatra to ,bombay will be twelve      
hundred miles1 which would be from six  
to eight days' steaming4 ,the whole     
passage from ,alexandria to ,bombay1    
allowing three days for delay between   
,suez and ,bombay1 would be twenty-six  
days3 the time from ,bombay to ,malta   
would therefore be about thirty-three   
days2 and adding fourteen days to this  
for the transit from ,malta to ,england1
 we should have a total of forty-seven  
days from ,london to ,bombay1 or about  
seven weeks4  ,if the terminus proposed 
were ,calcutta1 the course from ,socatra
 would be one thousand two hundred and  
fifty miles south-east to the ,maldives1
 where a station for coals would be     
established4 ,this distance would be    
equal to that from ,socatra to ,bombay4 
,from the ,maldives1 a run of four      
hundred miles would reach the southern  

point of ,ceylon1 called the ,point de  
,galle1 which is the best harbour       
7,bombay excepted7 in ,british ,india3  
from the ,point de ,galle1 a run of six 
hundred miles will reach ,madras1 and   
from ,madras to ,calcutta would be a run
 of about six hundred miles4 ,the voyage
 from ,london to ,calcutta would be     
performed in about sixty days4  ,at a   
certain season of the year there exists 
a powerful physical opponent to the     
transit from ,india to ,suez3 from      
,pg#dhe the middle of ,june until the   
end of ,september1 the south-west       
monsoon blows with unabated force across
 the ,indian ,ocean1 and more           
particularly between ,socatra and       
,bombay4 ,this wind is so violent as to 
leave it barely possible for the most   
powerful steam-packet to make head      
against it1 and the voyage could not be 
accomplished without serious wear and   
tear upon the vessels during these      
months4  ,the attention of parliament   
has therefore been directed to another  

line of communication1 not liable to    
this difficulty3 it is proposed to      
establish a line of steamers from       
,bombay through the ,persian ,gulf to   
the ,euphrates4  ,the run from ,bombay  
to a place called ,muscat1 on the       
southern shore of the gulf1 would be    
eight hundred and forty miles in a      
north-west direction1 and therefore not 
opposed to the south-west monsoon4 ,from
 ,muscat to ,bassidore1 a point upon the
 northern coast of the strait at the    
mouth of the ,persian ,gulf1 would be a 
run of two hundred and fifty-five miles2
 from ,bassidore to ,bushire1 another   
point on the eastern coast of the       
,persian ,gulf1 would be a run of three 
hundred miles2 and from ,bushire to the 
mouth of the ,euphrates1 would be one   
hundred and twenty miles4 ,it is evident
 that the longest of these runs would   
offer no more difficulty than the       
passage from ,malta to ,alexandria4     
,from ,bussora1 near the mouth of the   
,euphrates1 to ,bir1 a town upon its    

left bank near ,aleppo1 would be one    
thousand one hundred and forty-three    
miles1 throughout which there are no    
physical obstacles to the               
river-navigation which may not be       
overcome4 ,some difficulties arise from 
the wild and savage character of the    
tribes who occupy its banks4 ,it is1    
however1 thought that by proper         
measures1 and securing the co-operation 
of the pacha of ,egypt1 any serious     
obstruction from this cause may be      
removed4 ,from ,bir1 by ,aleppo1 to     
,scanderoon1 a port upon the            
,mediterranean1 opposite ,cyprus1 is a  
land-journey1 said to be attended with  
some difficulty1 but not of great       
length2 and from ,scanderoon to ,malta  
is about the same distance as between   
the latter place and ,alexandria4 ,it is
 calculated that the time from ,london  
to ,bombay by the ,euphrates--supposing 
the passage to be successfully ,pg#dhf  
established--would be a few days shorter
 than by ,egypt and the ,red ,sea4      

,whichever of these courses may be      
adopted1 it is clear that the           
difficulties1 so far as the powers of   
the steam engine are concerned1 lie in  
the one case between ,socatra and       
,bombay1 or between ,socatra and the    
,maldives1 and in the other case between
 ,bombay and ,muscat4 ,this1 however1   
has already been encountered and        
overcome on four several voyages by the 
,,hugh ,,lindsay steamer from ,bombay to
 ,suez3 that vessel encountered a still 
longer run on these several trips1 by   
going1 not to ,socatra1 but to ,aden1 a 
point on the coast of ,arabia1 near the 
,straits of ,babel ,mandeb1 being a run 
of one thousand six hundred and         
forty-one miles1 which she performed in 
ten days and nineteen hours4 ,the same  
trip has since been repeatedly made by  
other steamers2 and1 in the present     
improved state of steam navigation1 no  
insurmountable obstacles are opposed to 
their passage4  ,illustration           
,,footnotes3    #ce ,this cut is taken  

from the plate of the engine of the ,red
   ,rover1 manufactured by ,boulton and 
,watt1 given in the last   edition of   
,tredgold on the ,steam ,engine4    #cf 
,appendix ,i41 on ,marine ,boilers1 by  
,j4 ,dinnen2 ,tredgold   on the ,steam  
,engine1 second edition4    #cg         
,tredgold on the ,steam ,engine1        
,appendix1 ,i4 p4 #aga4    #ch ,engines 
on a very large scale constructed upon  
this   principle are said to be in      
process of construction for an   iron   
steam-vessel of great tonnage1 which is 
in preparation   for the ,new ,york     
passage4 ,it is said that the cylinders 
of   these engines will be one hundred  
and twenty inches in   diameter4    #ci 
,a patent was subsequently taken out for
 these by ,mr4   ,galloway4 ,mr4 ,field 
did not persevere in its use at the time
   he invented it4 ,it has1 however1    
been more generally adopted   since the 
date of ,galloway's patent4  ,pg#dhg    
,illustration  ,,chap4 ,,xiv4           
,,american ,,steam ,,navigation4        

,,steam ,,navigation ,,first            
,,established ,,in ,,america4 --        
,,circumstances     ,,which ,,led ,,to  
,,it4 -- ,,fitch ,,and ,,rumsey4 --     
,,stevens ,,of ,,hoboken4 --            
,,livingstone ,,and ,,fulton4 --        
,,experiments ,,on ,,the ,,seine4 --    
,,fulton',s     ,,first ,,boat4 -- ,,the
 ,,hudson ,,navigated ,,by ,,steam4 --  
,,extension ,,and     ,,improvement ,,of
 ,,river ,,navigation4 -- ,,speed ,,of  
,,american ,,steamers4     --           
,,difference ,,between ,,them ,,and     
,,european ,,steamers4 -- ,,sea-,,going 
,,american ,,steamers4 -- ,,american    
,,paddle-,,wheels4 -- ,,lake ,,steamers4
     -- ,,the ,,missisippi ,,and ,,its  
,,tributaries4 -- ,,steamers            
,,navigating     ,,it4 -- ,,their       
,,structure ,,and ,,machinery4 -- ,,new 
,,orleans ,,harbour4 --     ,,steam     
,,tugs4   7#bbh47 ,the credit of having 
afforded the first practical solution of
 the problem to apply the steam engine  
to the propulsion of ships1 undoubtedly 

belongs to the people of the ,united    
,states of ,america4 ,the geographical  
character of their vast country1 not    
less than the sanguine and enterprising 
spirit of the nation1 contributed to    
this4 ,a coast of four thousand miles in
 extent1 stretching from the ,gulf of   
,st4 ,lawrence to the embouchures of the
 ,mississippi1 indented and ,pg#dhh     
serrated in every part with natural     
harbours and sheltered bays1 and fringed
 with islands forming sounds--capes1 and
 promontories enclosing arms of the sea1
 in which the waters are free from the  
roll of the ocean1 and take the placid  
character of lakes1--rivers of imposing 
magnitude1 navigable for vessels of the 
largest class1 for many hundreds and in 
some instances for many thousands of    
miles1 affording access to the innermost
 population of an empire1 whose area    
vastly exceeds the whole ,european      
continent1--chains of lakes composed of 
the most extensive bodies of fresh water
 in the known world1--and this extensive

 continent peopled by races carrying    
with them the habits and feelings       
together with much of the skill and     
knowledge of the most civilized parts of
 the globe1 endowed also with that      
inextinguishable spirit of enterprise   
which ever belongs to an emigrant       
people1--form a combination of          
circumstances more than sufficient to   
account for the fact of this nation     
snatching from ,england1 the parent of  
the steam engine1 the honour of first   
bringing into practical operation one of
 the most important--if indeed it be not
 altogether the most important--of the  
many applications of that machine to the
 uses of life4  ,the circumstances which
 rendered these extensive tracts of     
inland and coast navigation eminently   
suited to the application of steam      
power1 formed so many obstructions and  
difficulties to the application of other
 more ordinary means of locomotion on   
water4 ,the sheltered bays and sounds   
which offered a smooth and undisturbed  

surface to the action of the infant     
steamer argued the absence of that      
element which gave effect to the sails  
and rigging of the wind-propelled ship1 
and the rapid currents of the gigantic  
streams formed by the drainage of this  
great continent1 though facilitating    
access to the coast1 rendered the oar   
powerless in the ascent4   7#bbi47 ,the 
first great discovery of ,watt had      
scarcely been realized in practice by   
the construction of the single-acting   
steam-engine1 when the speculative and  
enterprising ,americans conceived the   
project of applying it as a moving power
 in their inland navigation4 ,so early  
as the year #aghc ,pg#dhi ,fitch and    
,rumsey made attempts to apply the      
single-acting engine to the propulsion  
of vessels1 and their failure is said to
 have arisen more from the inherent     
defects of that machine in reference to 
this application of it1 than from any   
want of ingenuity or mechanical skill on
 their parts4 ,in #agia1 ,john ,stevens 

of ,hoboken commenced his experiments on
 steam navigation1 which were continued 
for sixteen years2 during a part of this
 period he was assisted by ,livingstone 
7who was subsequently instrumental in   
advancing the views of ,fulton71 and by 
,roosevelt4 ,these projectors had1 at   
that time also1 the assistance and      
advice of ,brunel1 since so celebrated  
for the invention of the block          
machinery1 and the construction of the  
,thames ,tunnel4 ,their proceedings were
 interrupted by the appointment of      
,livingstone as ,american ,minister at  
,paris1 under the ,consular ,government4
  ,at ,paris1 ,livingstone met ,fulton1 
who had been previously engaged in      
similar speculations1 and being struck  
with his mechanical skill1 and the      
soundness of his views1 joined him in   
causing a series of experiments to be   
made1 which were accordingly carried on 
at ,plombires1 and subsequently on a    
still more extensive scale on the       
,seine1 near ,paris4 ,having by this    

course of experiments obtained proofs of
 the efficiency of ,fulton's projects1  
sufficient to satisfy the mind of       
,livingstone1 he agreed to obtain for   
,fulton the funds necessary to construct
 a steam boat on a large scale1 to be   
worked upon the ,hudson4 ,it was        
decided1 in order to give the project   
the best chance of success1 to obtain   
the machinery from ,bolton and ,watt4   
,in #ahjc1 ,fulton accordingly made     
drawings of the engines intended for    
this first steamer1 which were sent to  
,soho1 with an order for their          
construction4 ,fulton1 meanwhile1       
repaired to ,america1 to superintend the
 construction of the boat4 ,the delays  
incidental to these proceedings retarded
 the completion of the boat and         
machinery until the year #ahjg1 when all
 was completed1 and the first successful
 experiment made at ,new ,york4 ,the    
vessel was placed1 for regular work1 to 
ply between ,new ,york and ,albany1 in  
the beginning of #ahjh2 and1 from that  

time to the present1 this river has been
 the theatre of the most ,pg#dij        
remarkable series of experiments on     
locomotion on water which has ever been 
presented in the history of navigation4 
7#bcj47 ,the form and arrangement of    
this first marine engine was1 in many   
respects1 similar to that which is still
 generally used for marine purposes4    
,the cold water cistern was abandoned1  
and an increased condensing power       
obtained by enlarging the condenser4 ,it
 was usual to make the condenser half   
the diameter of the cylinder1 and half  
its length1 and therefore one eighth of 
its capacity4 ,the condenser1 however1  
was now made of the same diameter as the
 cylinder1 being still half its length2 
its capacity therefore1 instead of being
 only an eighth1 was half of the        
cylinder2 the condensing jet was        
admitted by a pipe passing through the  
bottom of the vessel4 ,as in the present
 marine engines1 two working beams were 
provided1 one at either side of the     

cylinder2 but in order to provide       
against the difficulties which might    
arise in the adaptation of machinery    
made at ,birmingham to a vessel made at 
,new ,york1 beams were constructed in   
the form of an inverted 1 the working   
arms being twofold1 one horizontal and  
the other vertical1 so that the         
connecting rod might be carried from the
 crank1 either downwards1 to the end of 
the horizontal arm1 or horizontally1 to 
the end of the vertical arm4 ,in fact   
there was a choice1 to use either a     
straight beam1 or a bell-crank4 ,the    
latter was that which was adopted in    
this instance4 ,the paddle-shaft1 driven
 by the crank1 passed across the vessel1
 and had the paddle-wheels keyed upon it
 as at present2 and in order to equalise
 the effect of the engine spur wheels   
were also placed on the paddle-shaft1 by
 which pinions were driven1 placed upon 
an axle1 which carried a fly-wheel4     
,the speed attained by this steam boat1 
when it first began to ply upon the     

river1 did not exceed four miles an     
hour1 but by a series of improvements   
its rate of motion was soon increased to
 six miles an hour4 ,in the steam boats 
subsequently constructed by ,fulton a   
greater speed was attained2 but in the  
latest vessels built by him he did not  
exceed a speed of nine miles an hour1   
which he considered to be the greatest  
that could be advantageously obtained4  
,while ,fulton was making his plans1 and
 engaged in the ,pg#dia construction of 
his first boat1 ,mr4 ,stevens of        
,hoboken1 already mentioned1 was engaged
 in a like project1 and completed a     
vessel1 to be propelled by a steam      
engine1 within a few weeks after the    
first successful voyage of ,fulton4     
,stevens was likewise completely        
successful2 but the exclusive privilege 
of navigating the ,hudson by steam      
having been granted to ,fulton by an act
 of ,congress1 ,stevens was compelled to
 select another theatre for his         
operations1 and he accordingly sent his 

steam boat by sea to ,philadelphia1 to  
navigate the ,delaware1 thus securing   
for himself the honour of having made   
the first sea voyage by steam4  ,fulton 
did not long retain the monopoly of the 
steam navigation of the ,hudson4        
,fortunately for the progress of steam  
navigation1 the act conferring upon him 
that privilege was declared             
unconstitutional2 and the navigation of 
that noble river was thrown open to the 
spirit and enterprise of ,american      
genius4 ,the number of passengers       
conveyed upon it became enormous beyond 
all precedent1 and inducements of the   
strongest kind were accordingly held out
 to the improvement of its navigation4  
,the distance between ,new ,york and    
,albany1 ascertained by a late survey to
 be one hundred and twenty-five         
geographical miles by water1 had been   
performed by ,fulton's boats            
occasionally in fifteen or sixteen      
hours1 being at the rate of about eight 
miles an hour1 including stoppages4 ,it 

became a great object to increase the   
speed of this trip1 so that it might at 
all times of the year be performed      
between sunrise and sunset4 ,robert ,l4 
,stevens1 the son of the person of that 
name already mentioned1 immediately     
after the abolition of ,fulton's        
monopoly1 placed on the river a vessel  
which had been built for the ,delaware1 
which easily performed the passage in   
twelve hours1 being at the rate of      
nearly ten and a half geographical miles
 an hour4 ,by this increase of speed the
 improved boats so entirely monopolised 
the day work upon the river1 that the   
former steamers were either converted   
into steam tugs to draw barges laden    
with goods1 or used for night trips     
between ,new ,york and ,albany4 ,in the 
night trips the saving of one or two    
hours was immaterial1 it being          
sufficient that the vessel which left   
the one port at night should reach the  
other in the morning4 ,pg#dib  ,the     
river ,hudson rises near ,lake          

,champlain1 the easternmost of the great
 chain of lakes or inland seas which    
extend from east to west across the     
northern boundary of the ,united        
,states4 ,the river follows nearly a    
straight course southwards for two      
hundred and fifty miles1 and empties    
itself into the sea at ,new ,york4 ,the 
influence of the tide is felt as far as 
,albany1 above which the stream begins  
to contract4 ,although this river in    
magnitude and extent is by no means     
equal to several others which intersect 
the ,states1 it is nevertheless rendered
 an object of great interest by reason  
of the importance and extent of its     
trade4 ,the produce of the state of ,new
 ,york and that of the banks of the     
great ,lakes ,ontario and ,erie are     
transported by it to the capital2 and   
one of the most extensive and populous  
districts of the ,united ,states is     
supplied with the necessary imports by  
its waters4 ,a large fleet of vessels is
 constantly engaged in its navigation2  

nor is the tardy but picturesque sailing
 vessel as yet excluded by the more     
rapid steamers4 ,the current of the     
,hudson is said to average nearly three 
miles an hour2 but as the ebb and flow  
of the tide are felt as far as ,albany1 
the passage of the steamers between that
 place and ,new ,york may be regarded as
 equally affected by currents in both   
directions1 or nearly so4 ,the passage  
therefore1 whether in ascending or      
descending the river1 is made nearly in 
the same time4   7#bca47 ,the prevalence
 of smooth water navigation1 whether on 
the surfaces of rivers or in sheltered  
bays and sounds1 has invested the       
problem of steam navigation in ,america 
with conditions so entirely distinct and
 different from those under which the   
same problem presents itself to the     
,european engineer1 that any comparison 
of the performance of vessels1 whether  
with regard to speed or the absorption  
of power in the two cases1 must be      
utterly fallacious4 ,in ,europe a       

steamer is almost invariably a vessel   
designed to encounter the agitated      
surface of an open sea1 and is          
accordingly constructed upon principles 
of suitable strength and stability4 ,it 
is likewise supplied with rigging and   
with sails1 to be used in aid of the    
mechanical power1 and manned and        
commanded by experienced seamen2 in     
fact1 it is a combination of a nautical 
and mechanical structure4 ,in ,america1 
on the other hand1 ,pg#dic with the     
exception of the vessels which navigate 
the great northern lakes1 the steamers  
are structures exclusively mechanical1  
being designed for smooth water4 ,they  
require no other strength or stability  
than that which is sufficient to enable 
them to float and to bear a progressive 
motion through the water4 ,their mould  
is conceived with an exclusive view to  
speed2 they are therefore slender and   
weak in their build1 of great length in 
proportion to their width1 and having a 
very small draught of water4 ,in fact1  

they approach in their form to that of a
 ,thames wherry on a very large scale4  
,the position and form of the machinery 
is likewise affected by these           
conditions4 ,without the necessity of   
being protected from a rough sea1 it is 
placed on the deck in an elevated       
position4 ,the cylinders of large       
diameter and short stroke invariably    
used in ,europe are unknown in ,america1
 and the proportions are reversed1 a    
small diameter and stroke of great      
length being invariably adopted4 ,it is 
rarely that two engines are used4 ,a    
single engine1 placed in the centre of  
the deck1 with a cylinder from forty to 
sixty inches' diameter1 and from eight  
to ten foot stroke1 drives paddle-wheels
 from twenty-one to twenty-five feet in 
diameter1 producing from twenty-five to 
thirty revolutions per minute4 ,the     
great magnitude of the paddle-wheels and
 the velocity imparted to them enable   
them to perform the office of           
fly-wheels1 and to carry the engine     

round its centres1 not however without a
 perceptible inequality of motion1 which
 gives to the ,american steamer an      
effect like that of a row boat advancing
 by starts with each stroke of the      
piston4 ,the length of stroke adopted in
 these engines enables them to apply    
with great effect the expansive         
principle1 which is almost universally  
used1 the steam being generally cut off 
at half stroke4  ,the steamers which    
navigate the ,hudson are vessels of     
considerable magnitude1 splendidly      
fitted up for the accommodation of      
passengers2 they vary from one hundred  
and eighty to two hundred and forty feet
 in length1 and from twenty to thirty   
feet in width of beam4 ,in the following
 table is given the particulars of nine 
steamers plying on this river1 taken    
from ,pg#did the work of ,mr4           
,stevenson1 and from the paper of ,mr4  
,renwick1 inserted in the last edition  
of ,tredgold3--                         
----------------------------------------

----------------------------------------
----------------------------------------
--                  ,length  ,breadth   
,draft   ,drain   ,length      ,names4  
of      of      of       of      of     
,deck4   ,beam4   ,water4  ,wheel4      
,paddles4                               
----------------------------------------
----------------------------------------
----------------------------------------
--                    ,ft4     ,ft4     
,ft4     ,ft4     ,ft4   ,dewit ,clinton
    #bcj     #bh       #ee     #ba      
#acg   ,champlain        #ahj     #bg   
#ee     #bb     #ae   ,erie             
#ahj     #bg       #ee     #bb     #ae  
,north ,america    #bjj     #cj       #e
       #ba     #ac   ,independence      
#adh     #bf       ----      ----       
----   ,albany           #bab     #bf   
----      #bde   #ad   ,swallow         
#bcc     #bbe     #cge    #bd     #aa   
,rochester        #bjj     #be          
#cge    #bce   #aj   ,utica             
#bjj     #ba       #ce     #bb      #ie 

----------------------------------------
----------------------------------------
----------------------------------------
--                                      
----------------------------------------
----------------------------------------
----------------------------------------
------------------                      
,depth   ,number   ,drain   ,length     
,number  ,part of      ,names4        of
      of       of      of     of        
,stroke                  ,paddles       
,engines ,cylinder ,stroke  ,revs   at  
which                                   
it is                                   
cut off4                                
----------------------------------------
----------------------------------------
----------------------------------------
------------------                      
,in4             ,in4      ,ft4         
,dewit ,clinton    #cf      #a       #fe
       #aj    #bi       #c_/d           
,champlain        #cd      #b       #dd 
#aj    #bge     #a_/b   ,erie           

#cd      #b       #dd       #aj    #bge 
#a_/b   ,north ,america    #cj      #b  
#dde      #h    #bd       #a_/b         
,independence     ----      #a       #dd
       #aj             ,albany          
#cj      #a       #fe       ----    #ai 
,swallow          #cj      #a       #df 
----    #bg       ,rochester        #bd 
#a       #dc       #aj    #bh           
,utica            #bd      #a       #ci 
#aj                                     
----------------------------------------
----------------------------------------
----------------------------------------
------------------  ,none of these      
vessels have either masts or rigging1   
and consequently never derive any       
propelling power except from the        
engines3 they are neither manned nor    
commanded by persons having any         
knowledge of navigation3 the works that 
are visible above their decks are the   
beam and framing of the engine1 and the 
chimneys4  ,the engines used for        
steamers on the ,hudson1 and other great

 rivers and bays on the eastern coast of
 ,america1 are most commonly condensing 
engines1 but they nevertheless work with
 steam of very high pressure1 being     
seldom less than twenty-five pounds per 
square inch1 and sometimes as much as   
fifty4 ,by reference to the preceding   
table it will be seen1 that the velocity
 of the piston greatly exceeds the limit
 generally observed in ,europe4 ,it is  
customary in ,european marine engines to
 limit the speed of the piston to about 
two hundred and twenty feet per minute4 
,even the piston of a locomotive engine 
does not much exceed the rate of three  
hundred feet per minute4 ,in the        
,american steamers1 however1 the pistons
 commonly move at the rate of from five 
to six hundred feet per minute1 while   
the circumference of the paddle-wheels  
are driven at the rate of from twenty to
 twenty-two miles an hour4 ,pg#die      
,illustration3 ,fig4 #ace4  ,the hulls  
of these boats are formed with a        
perfectly flat bottom and perpendicular 

sides1 rounded at the angles1 as        
represented in fig4 #ace4 ,at the bow1  
or cutwater1 they are made very sharp1  
and the deck projects to a great        
distance over the sides4 ,the weight of 
the machinery is distributed over an    
extensive surface of the bottom of this 
feeble structure1 by means of a         
frame-work of substantial carpentry to  
which it is attached4  ,at the height of
 from four to six feet above the        
water-line is placed the deck1 which is 
a platform1 having the shape of a very  
elongated ellipse4 ,the extremities of  
its longer axis are supported by the    
sternpost and the cutwater1 and its     
sides expand in gentle curves on either 
hand to a considerable distance beyond  
the limits of the hull2 those parts of  
the deck thus overhanging the water are 
called the wheel guards4  ,beneath the  
first deck is the saloon1 or            
dining-room1 which also1 as is usual in 
,european steamers1 forms the           
gentlemen's sleeping-room4 ,it usually  

extends from end to end of the vessel4  
,the middle of the first deck is        
occupied by the engine1 boilers1        
furnaces1 and chimneys1 of which latter 
there are generally two4 ,between the   
chimneys and the stern1 above the first 
deck1 is constructed the ladies' cabin1 
which is covered by the second deck1    
called the promenade deck4 ,the great   
length of these boats and the elevation 
of the cabins render it impossible for a
 steersman at the stern to see ahead1   
and they are1 consequently1 steered from
 the bow2 the wheel placed there        
communicating with the helm at the      
stern1 by chains or rods carried along  
the sides of the boat4 ,until a recent  
period1 the wheel was connected with the
 stern by ropes1 but some fatal         
accidents1 produced by fire1 ,pg#dif in 
which these ropes were burnt1 and the   
steersman lost all power to guide the   
vessel1 caused metal rods or chains to  
be substituted4   7#bcb47 ,the          
paddle-wheels universally used in       

,american steam-boats are formed1 as if 
by the combination of two or more common
 paddle-wheels1 placed one outside the  
other1 on the same axle1 but so that the
 paddle boards of each may have an      
intermediate position between those of  
the adjacent one1 as represented in fig4
 #acf4  ,illustration3 ,fig4 #acf4  ,the
 spokes1 which are bolted to cast-iron  
flanges1 are of wood4 ,these flanges1 to
 which they are so bolted1 are keyed    
upon the paddle shaft4 ,the outer       
extremities of the spokes are attached  
to circular bands or hoops of iron1     
surrounding the wheel2 and the paddle   
boards1 which are formed of hard wood1  
are bolted to the spokes4 ,the wheels   
thus constructed1 sometimes consist of  
three1 and not unfrequently four1       
independent circles of paddle boards1   
placed one beside the other1 and so     
adjusted in their position1 that the    
boards of no two divisions shall        
correspond4  ,the great magnitude of the
 paddle-wheels1 and the circumstance of 

the navigation being carried on1 for the
 most part1 in smooth water1 have       
rendered unnecessary1 in ,america1 the  
adoption of any of those expedients for 
neutralising the effects of the oblique 
action of the paddles1 which have been  
tried1 but hitherto with so little      
success1 in ,europe4   7#bcc47          
,sea-going steamers are not numerous in 
,america1 the chief of them being those 
which ply between ,new ,york and        
,providence1 and between ,new ,york and 
,charleston4 ,these vessels1 however1 do
 not resemble the sea-going steamers of 
,europe as closely as might be expected2
 and to those who are accustomed to the 
latter1 the sea-going ,pg#dig steamers  
of ,america can hardly be regarded as   
safe means of transport4  ,in the       
following ,table is given the dimensions
 of five of these vessels1 all plying   
between ,new ,york and ,providence3--   
----------------------------------------
----------------------------------------
----------------------------------------

----                  ,length  ,breadth 
,draft  ,diameter  ,length      ,names4 
of      of              of        of    
,deck4   ,beam4          ,wheel4        
,paddles4                               
----------------------------------------
----------------------------------------
----------------------------------------
----                    ,ft4     ,ft4   
,ft4     ,ft4       ,ft4   ,providence  
#ahj     #bg       #i      ----         
----   ,lexington        #bjg     #ba   
----      #bc         #i   ,narragansett
     #baj     #bf       #e      #be     
#aa   ,massachusetts    #bjj     #bie   
#he    #bb        #aj   ,rhode ,island  
#baj     #bf       #fe    #bd        #aa
                                        
----------------------------------------
----------------------------------------
----------------------------------------
----                                    
----------------------------------------
----------------------------------------
----------------------------------------

------------------                      
,depth   ,number  ,diameter ,length     
,number  ,part of      ,names4        of
      of       of      of     of        
,stroke                  ,paddles       
,engines ,cylinder ,stroke  ,revs   at  
which                                   
it is                                   
cut off4                                
----------------------------------------
----------------------------------------
----------------------------------------
------------------                      
,in4             ,in4      ,ft4         
,providence       ----       #a      #aj
       #fe             ,lexington       
#cj       #a      #aa       #dh     #bd 
,narragansett     #cj       #a      #fj 
#ab      #b      #a_/b   ,massachusetts 
#bh       #b      #dd        #h     #bf 
,rhode ,island     #cj       #a      #aa
       #fj     #ba                      
----------------------------------------
----------------------------------------
----------------------------------------

------------------  ,the ,narragansett1 
the finest of these vessels1 is built of
 oak1 strengthened by diagonal straps or
 ties of iron1 by which her timbers are 
connected2 she is driven by a condensing
 engine1 and has two boilers1 exposing  
about three thousand square feet of     
surface to the fire4 ,the steam is      
maintained at a pressure of from twenty 
to twenty-five lbs4 per square inch3 the
 cylinder is horizontal4  ,the cabins of
 these sea-boats are of great magnitude1
 and afford excellent accommodation for 
passengers1 containing generally four   
hundred berths4 ,in the ,massachusetts  
the chief cabin is one hundred and sixty
 feet long1 twenty-two feet wide1 and   
twelve feet in height1 its vast extent  
being uninterrupted by pillars or any   
other obstruction4 ,i have dined1 says  
,mr4 ,stevenson1 with one hundred and   
seventy-five persons in this cabin1 and1
 notwithstanding this numerous assembly1
 the tables1 which were arranged in two 
parallel rows1 extending from one end of

 the cabin to the other1 were far from  
being fully occupied1 the attendance was
 good1 and every thing was conducted    
with perfect regularity and order4      
,there are one hundred and twelve fixed 
berths ranged round this cabin1 and one 
hundred temporary berths can be erected 
in the middle of the floor3 besides     
these there are sixty fixed berths in   
the ladies' cabin1 and several temporary
 sleeping ,pg#dih places can be erected 
in it also4 ,the cabin of the           
,massachusetts is by no means the       
largest in the ,united ,states4 ,some   
steamers have cabins upwards of one     
hundred and seventy-five feet in length4
 ,those large saloons are lighted by    
,argand lamps1 suspended from the       
ceiling1 and their appearance1 when     
brilliantly lighted up and filled with  
company1 is very remarkable4 ,the       
passengers generally arrange themselves 
in parties at the numerous small tables 
into which the large tables are         
converted after dinner1 and engage in   

different amusements4 ,the scene        
resembles much more the coffee-room of  
some great hotel than the cabin of a    
floating vessel4   7#bcd47 ,nothing has 
excited more surprise among engineers   
and others interested in steam          
navigation in ,europe1 than the         
statements which have been so generally 
and so confidently made of the speed    
attained by ,american steamers4 ,this   
astonishment is due to several causes1  
the chief of which is the omission of   
all notice of the great difference      
between the structure and operation of  
the ,american steamers and the nature of
 the navigation in which they are       
engaged1 compared with the structure and
 operation of1 and the navigation in    
which ,european steamers are employed3  
as well might the performance of a      
,thames wherry1 or one of the fly-boats 
on the northern canals1 be compared with
 that of the ,great ,western1 or the    
,british ,queen4 ,the statements alluded
 to all have reference to steamers      

navigating the ,hudson between ,new     
,york and ,albany1 the form and         
structure of which we have already      
described2 and doubtless the greatest   
speed ever attained on the surface of   
water has been exhibited in the passages
 of these vessels4  ,mr4 ,stevenson     
states1 that exclusive of the time lost 
in stoppages1 the voyage between ,new   
,york and ,albany is usually made in ten
 hours4 ,dr4 ,renwick1 however1 who has 
probably more extensive opportunities of
 observation1 states1 that the average  
time1 exclusive of stoppages1 is ten    
hours and a half4 ,the distance being   
#abeah geographical miles1 the average  
rate would therefore be #aa-i_/aj miles 
per hour4 ,if it be observed that the   
average rate of some of the best        
sea-going steamers in ,europe obtained  
from experiments ,pg#dii and            
observations made by myself1 more than  
three years ago1 showed a rate of       
steaming little less than ten           
geographical miles per hour1 and that   

since that time considerable            
improvements in steam navigation have   
been made1 and further1 that these      
performances were made under exposure to
 all the disadvantages of an open sea1  
the difference between them and the     
performance of the ,american river      
steamers will cease to create           
astonishment4  ,dr4 ,renwick states that
 he made1 in a boat called the ,new     
,philadelphia1 one of the most          
remarkable passages ever performed4 ,he 
left ,new ,york at five in the          
afternoon1 with the first of the flood1 
and landed at ,catskill1 distant #ieh   
geographical miles from ,new ,york1 at a
 quarter before twelve4 ,passengers were
 landed and taken in at seven           
intermediate points3 the rate1 including
 stoppages1 was therefore #adb miles per
 hour2 and if half an hour be allowed   
for stoppages1 the actual average rate  
of motion would be fifteen miles and    
three quarters an hour4 ,as the current1
 which in this case was with the course 

of the vessel1 did not exceed three     
miles and a half an hour1 the absolute  
velocity through the water would have   
been somewhat under twelve miles an     
hour4 ,this speed is nearly the same as 
the speed obtained from taking the      
average time of the voyages between ,new
 ,york and ,albany at ten hours and a   
half2 it would therefore appear that the
 great speed attained in this trip must 
have been chiefly1 if not altogether1   
owing to the effect of the current4     
7#bce47 ,the steamers which navigate the
 great northern lakes differ so little  
in their construction and appearance    
from the ,european steam-boats1 that it 
will not be necessary here to devote any
 considerable space to an account of    
them4 ,these vessels were introduced on 
the lakes at about the same time that   
steamers were first introduced on the   
,clyde4 ,these steamers are strongly    
built vessels1 supplied with sails and  
rigging1 and propelled by powerful      
engines4 ,the largest in #ahcg1 when    

,mr4 ,stevenson visited the ,states1 was
 the ,james ,madison4 ,this vessel was  
one hundred and eighty-one feet in      
length on the deck1 thirty feet in      
breadth of beam1 and twelve feet six    
inches in depth of hold3 her draught of 
water was ten feet1 and her measured    
capacity seven hundred ,pg#ejj tons4    
,she plyed between ,buffalo on ,lake    
,erie and ,chicago on ,lake ,michigan1 a
 distance of nine hundred and fifty     
miles4  ,the severe storms and          
formidable sea encountered on the lakes 
render necessary for the navigation1    
vessels in all respects as strong and   
powerful as those which navigate the    
open ocean4   7#bcf47 ,by far the most  
remarkable and important of all the     
,american rivers is the ,mississippi and
 its tributaries4 ,that part of the     
,american continent which extends from  
the southern shores of the great        
northern lakes to the northern shores of
 the ,gulf of ,mexico1 is watered by    
these great streams4 ,the main stream of

 the ,mississippi has its fountains in  
the tract of country lying north of the 
,illinois and east of ,lake ,michigan1  
in latitude forty-three degrees4 ,at    
about latitude thirty-nine degrees1 a   
little north of ,st4 ,louis1 it receives
 the waters of the ,missouri1 and       
further south1 at the latitude of       
thirty-seven degrees1 the ,ohio flows   
into it1 after traversing five degrees  
of longitude and four of latitude1 and  
winding its way from the ,alleghany     
range through several of the states1 and
 forming a navigable communication with 
numerous important towns of the ,union1 
among which may be mentioned ,pittsburg1
 ,cincinnati1 ,frankfort1 ,lexington1   
and ,louisville4 ,the main stream of the
 ,mississippi1 after receiving the      
waters of the ,arkansas1 and numerous   
other minor tributaries1 flows into the 
,gulf of ,mexico by four mouths4 ,the   
main stream of the ,mississippi1        
independently of its tributaries1 forms 
an unbroken course of inland navigation 

for a distance of nearly two thousand   
three hundred miles4 ,its width1 through
 a distance of one thousand one hundred 
miles from its mouth1 is not less than  
half a mile1 and its average depth a    
hundred feet4 ,the ,ohio1 its chief     
eastern tributary1 flowing into it at a 
distance of about a thousand miles from 
its mouth1 traverses also about the same
 extent of country1 and is navigable    
throughout the whole of that extent4    
,this river also has several navigable  
tributaries of considerable extent1     
among which may be mentioned the        
,muskingum1 navigable for one hundred   
and twenty miles2 the ,miami1 navigable 
for seventy-five miles2 the ,scioto1    
navigable for one hundred and twenty    
,pg#eja miles2 the ,tennessee1 navigable
 for two hundred and fifty miles2 the   
,cumberland1 navigable for four hundred 
and forty miles2 the ,kentucky1         
navigable for one hundred and thirty    
miles2 and the ,green ,river1 navigable 
for one hundred and fifty miles4 ,the   

total length of the ,ohio and its       
tributaries is estimated at above seven 
thousand miles4   7#bcg47 ,steam-boats  
were introduced on the ,mississippi     
about the year #ahab1 the period of     
their first introduction in ,europe2 and
 their increase has been rapid beyond   
all precedent4 ,in the year #ahca there 
were one hundred and ninety-eight       
steamers plying on its waters2 and the  
number in #ahcg amounted to nearly four 
hundred4 ,these vessels are built       
chiefly on the banks of the ,ohio1 at   
the towns of ,pittsburg and ,cincinnati1
 at distances of about two thousand     
miles from the mouth of the river they  
are intended to navigate4   7#bch47     
,these steamers1 which are decidedly    
inferior to those which navigate the    
eastern waters1 are generally of a heavy
 build1 fitted to carry goods as well as
 passengers1 and vary from one hundred  
to seven hundred tons burthen4 ,their   
draught of water is also greater than   
that of the eastern river               

steamers--varying from six to eight     
feet4 ,the hull1 at about five feet from
 the water line1 is covered with a deck1
 under which is the hold1 in which the  
heavy part of the cargo is stowed4      
,about the middle of this deck the      
engines are placed1 the boilers and     
furnaces occupying a space nearer to the
 bow1 near which two chimneys are       
placed4 ,the fire-doors of the furnaces 
are presented towards the bow1 and      
exposed so as to increase the draught4  
,that part of the first deck which      
extends from the machinery to the stern 
is the place allotted to the crew and   
the deck passengers1 and is described as
 being filthy and inconvenient in the   
extreme4 ,a second deck is constructed1 
which extends from the chimneys near the
 bow to the stern of the vessel4 ,on    
this is formed the great cabin or       
saloon1 which extends from the chimneys 
to within about thirty feet of the      
stern1 where it is divided by a         
partition from the ladies' cabin1 which 

occupies the remaining space4 ,these    
principal cabins are surrounded by a    
gallery about three feet in width1 from 
which1 at convenient ,pg#ejb places1 an 
ascent is supplied by stairs to the     
highest deck1 called the hurricane or   
promenade deck4   7#bci47 ,the engines  
by which these boats are propelled are  
totally different from the machinery    
already described as used in the eastern
 steamers4 ,they are invariably         
non-condensing engines1 worked by steam 
of extremely high pressure2 the boilers 
are therefore tubular1 and the cylinders
 small in diameter1 but generally having
 a long stroke4  ,the pressure of steam 
used in these machines is such as is    
never used in ,european engines1 even   
when worked on railways4 ,a pressure of 
one hundred pounds per inch is here     
considered extremely moderate4 ,the     
captain of one of these boats1 plying   
between ,pittsburg and ,st4 ,louis1 told
 ,mr4 ,stevenson that under ordinary    
circumstances his safety valves were    

loaded with a pressure equal to one     
hundred and thirty-eight pounds per     
square inch1 but that the steam was     
occasionally raised as high as one      
hundred and fifty pounds to enable the  
vessel to pass parts of the river in    
which there is a strong current2 and he 
added1 by way of consolation1 that this 
pressure was never exceeded except on   
extraordinary occasions6  ,the          
dimensions and power of the ,mississippi
 steamers may be collected from those of
 the ,st4 ,louis1 a boat which was      
plying on that river in #ahcg4 ,that    
vessel measured two hundred and fifty   
feet on deck1 and had twenty-eight feet 
breadth of beam4 ,her draught of water  
was eight feet1 and her measured        
capacity one thousand tons4 ,she was    
propelled by two engines with           
thirty-inch cylinders1 and ten feet     
stroke2 the safety valve being loaded at
 one hundred pounds per square inch4    
,the paddle wheels of these vessels are 
attached to the paddle shaft1 in such a 

manner as to be thrown into and out of  
gear1 at discretion1 by the engineer1 so
 that the paddle shaft may revolve      
without driving the wheels3 by this     
expedient the power of the engine is    
used to feed the boilers while the      
vessel stops at the several stations4   
,the vessel is therefore stopped1 not1  
as is usually the case1 by stopping the 
engines1 but by throwing the wheels out 
of connection with the paddle shaft4    
,the engines continue to work1 but their
 ,pg#ejc power is expended in forcing   
water into the boiler4 ,by this         
expedient the activity of the engines   
may1 within practical limits1 be varied 
with the resistance the vessel has to   
encounter4 ,in working against a strong 
current1 the feed may be cut off from   
the boilers1 and the production of      
steam1 and consequently the power of the
 engines1 thereby stimulated1 while this
 suspension of the feed may be          
compensated at the next station4  ,the  
stoppages to take in goods and          

passengers1 and for relays of fuel1 are 
frequent4 ,the liberty which they take  
with their vessels on these occasions1  
says ,mr4 ,stevenson1 is somewhat       
amusing3 ,i had a good example of this  
on board a large vessel1 called the     
,ontario4 ,she was steered close in     
shore amongst stones and stumps of      
trees1 where she lay for some hours to  
take in goods3 the additional weight    
increased her draught of water1 and     
caused her to heel a good deal2 and when
 her engines were put in motion1 she    
actually crawled into the deep water on 
her paddle wheels3 the steam had been   
got up to an enormous pressure to enable
 her to get off1 and the volume of steam
 discharged from the escapement pipe at 
every half stroke of the piston made a  
sharp sound almost like the discharge of
 fire-arms1 while every timber in the   
vessel seemed to tremble1 and the whole 
structure actually groaned under the    
shocks4  ,besides the steamers used for 
the navigation of the ,mississippi1     

innumerable steam tugs are constantly   
employed in towing vessels between the  
port of ,new ,orleans and the open sea  
of the ,gulf of ,mexico4 ,before the    
invention of steam navigation1 this     
southern capital of the ,united ,states 
laboured under the disadvantage of      
possessing almost the only bad and      
inconvenient harbour in the vast range  
of coast by which the country is        
bounded4 ,new ,orleans lies at a        
distance of about one hundred miles from
 the ,gulf of ,mexico4 ,the force of the
 stream1 the frequency of shoals1 and   
the winding course of the channel       
rendered it scarcely possible for a     
sailing vessel to pass between the port 
and the sea with the same wind4 ,the    
anchorage was every where bad1 and great
 difficulty and risk attended the       
mooring of large vessels to the banks4  
,the steam engine has1 however1 overcome
 all ,pg#ejd these difficulties1 and    
rendered the most objectionable harbour 
of the ,union a safe and good seaport1  

perfectly easy of approach and of egress
 at all times2 a small steam tug will   
take in tow several large ships1 and    
carry them with safety and expedition to
 the offing1 where it will dismiss them 
on their voyage1 and take back vessels  
which may have arrived4  ,illustration3 
,,great ,,western ,,off ,,new ,,york4   
,pg#eje     ,,appendix4    ,on the      
,relation between the ,temperature1     
,pressure1 and ,density     of ,common  
,steam4   ,there is a fixed relation    
between the temperature and pressure of 
common steam1 which has not yet been    
ascertained by theory4 ,various         
empirical formul have been proposed to  
express it1 derived from tables of      
temperatures and corresponding pressures
 which have been founded on experiments 
and completed by interpolation4  ,the   
following formula1 proposed by ,m4      
,biot1 represents with great accuracy   
the relation between the temperature and
 pressure of common steam1 throughout   
all that part of the thermometric scale 

to which experiments have been extended4
  ,let         a      #eifacaccjbei     
log4 a#a  #jhbcdjfhhaic  #a   log4 b#a  
#jacjigcdbie   log4 a#b  #jgdaajieahcg  
log4 b#b  #jjbabeajehc  ,the relation   
between the temperature t with reference
 to the centesimal thermometer1 and the 
pressure p in millimtres of mercury at  
the temperature of melting ice1 will    
then be expressed by the following      
formula3--    log4 p  a  a#a;b#abj  t   
a#b;b#bbj  t4    7#a47  ,formul have1   
however1 been proposed1 which1 though   
not applicable to the whole scale of    
temperatures1 are more manageable in    
their practical application than the    
preceding4  ,for pressures less than an 
atmosphere1 ,southern proposed the      
following formula1 where the pressure is
 intended to be expressed ,pg#ejf in    
pounds per square inch1 and the         
temperature in reference to             
,fahrenheit's thermometer1--    p       
#jjdidh  77#eac  t7 _/ #aeegbef7eac     
4  7#b47   t  #aeegbef 77p  #jjdidh7    

#eac7a_/7eac7      ,the following       
formula was proposed by ,tredgold1 where
 p expresses the pressure in inches of  
mercury3--    p  77#ajj  t7 _/ #agg7f4  
,this was afterwards modified by        
,mellet1 and represents with sufficient 
accuracy experiments from #a to #d      
atmospheres4 ,let p represent pounds per
 square inch1 and t the temperature by  
,fahrenheit's thermometer1--    p       
77#ajc  t7 _/ #bjaah7f                  
4  7#c47   t  #bjaah p#a_/f  #ajc       
,m4 de ,pambour has proposed the        
following formula1 also applicable      
through the same limits of the scale3-- 
p  77#ihhjf  t7 _/ #aihefb7f            
4  7#d47   t  #aihefb p#a_/f  #ihhjf    
,,mm4 ,dulong and ,arago have proposed  
the following formula for all pressures 
between #d and #ej atmospheres3--    p  
7#jbfgic  #jjjfgehe t7#e                
4  7#e47   t  #adgifa p#a_/e  #cifdd    
,it was about the year #ahja1 that      
,dalton1 at ,manchester1 and            
,gay-,lussac1 at ,paris1 instituted a   

series of experiments on gaseous bodies1
 which conducted them to the discovery  
of the law mentioned in art4 7#if471 p4 
#aga4 ,these philosophers found that all
 gases whatever1 and all vapours raised 
from liquids by heat1 as well as all    
mixtures of gases and vapours1 are      
subject to the same quantity of         
expansion between the temperatures of   
melting ice and boiling water2 and by   
experiments subsequently made by ,dulong
 and ,petit1 this uniformity of         
expansion has been proved to extend to  
all temperatures which can come under   
practical inquiries4  ,dalton found that
 #ajjj cubic inches of air at the       
temperature of melting ice dilated to   
#acbe cubic inches if raised to the     
temperature of boiling water4 ,according
 to ,gay-,lussac1 the increased volume  
was #acge cubic inches4 ,the latter     
determination has been subsequently     
found to be the more correct one4#dj    
,pg#ejg ,it appears1 therefore1 that for
 an increase of temperature from #cb to 

#bab1 amounting to #ahj1 the increase of
 volume is #cge parts in #ajjj2 and     
since the expansion is uniform1 the     
increase of volume for #a will be found 
by dividing this by #ahj1 which will    
give an increase of #bjh-a_/c parts in  
#ajj1jjj for each degree of the common  
thermometer4  ,to reduce the expression 
of this important and general law to    
mathematical language1 let v be the     
volume of an elastic fluid at the       
temperature of melting ice1 and let nv  
be the increase which that volume would 
receive by being raised one degree of   
temperature under the same pressure4    
,let ,v be its volume at the temperature
 ,t4 ,then we shall have    ,v  v  nv   
7,t  #cb7  v 7#a  n 7,t  #cb774  ,if ,v 
be its volume at any other temperature  
,t1 and under the same pressure1 we     
shall have1 in like manner1    ,v  v 7#a
  n 7,t  #cb774  ,hence we obtain       
,v_/,v  7#a  n 7,t  #cb77 _/ 7#a  n 7,t 
#cb772   7#f47  which expresses the     
relation between the volumes of the same

 gas or vapour under the same pressure  
and at any two temperatures4 ,the       
co-efficient n1 as explained in the     
text1 has the same value for the same   
gas or vapour throughout the whole      
thermometric scale4 ,but it is still    
more remarkable that this constant has  
the same value for all gases and        
vapours4 ,it is a number1 therefore1    
which must have some essential relation 
to the gaseous or elastic state of fluid
 matter1 independent of the peculiar    
qualities of any particular gas or      
vapour4  ,the value of n1 according to  
the experiments of ,gay-,lussac1 is     
#jjjbjhc1 or #a_/dhj4  ,to reduce the   
law of ,mariotte1 explained in 7#ig47 p4
 #aga41 to mathematical language1 let   
,v1 ,v be the volumes of the same gas or
 vapour under different pressures ,p1   
,p1 but at the same temperature4 ,we    
shall then have    ,,vp  ,v,p4   7#g47  
,if it be required to determine the     
relation between the volumes of the same
 gas or vapour1 under a change of both  

temperature and pressure1 let ,v be the 
volume at the temperature ,t and under  
the pressure ,p1 and let ,v be the      
volume at the temperature ,t and under  
the pressure ,p4 ,let v be the volume at
 the temperature ,t and under the       
pressure ,p4  ,by formula 7#g47 we have 
,,vp  v,p2   ,pg#ejh and by formula     
7#f47 we have    7,v_/v7  7#a  n7,t     
#cb77 _/ 7#a  n7,t  #cb77  ,eliminating 
v1 we shall obtain    7,v_/,v7  7,p_/,p7
  7#a  n7,t  #cb77 _/ 7#a  n7,t  #cb772 
or1    7,,vp_/,v,p7  7#a  n7,t  #cb77 _/
 7#a  n7,t  #cb772    7#h47  which is   
the general relation between the        
volumes1 pressures1 and temperatures of 
the same gas or vapour in two different 
states4  ,to apply this general formula 
to the case of the vapour of water1 let 
,t  #bab4 ,it is known by experiment    
that the corresponding value of ,p1     
expressed in pounds per square inch1 is 
#adgjf2 and that ,v1 expressed in cubic 
inches1 the water evaporated being taken
 as a cubic inch1 is #agjj4 ,if1 then1  

we take #jjjbjhc as the value of n1 we  
shall have by 7#h471    ,,vp  #agjj     
#adgjf  7#a  #jjjbjhc 7,t  #cb77 _/ 7#a 
#jjjbjhc  #ahj7        #ahahc7a         
#jjjbjhc 7,t  #cb774    7#i47  ,if1 by  
means of this formula 7#i471 and any of 
the formul 7#a471 7#b471 7#c471 7#d471  
7#e471 ,t were eliminated1 we should    
obtain a formula between ,v and ,p1     
which would enable us to compute the    
enlargement of volume which water       
undergoes in passing into steam under   
any proposed pressure4 ,but such a      
formula would not be suitable for       
practical computations4 ,by the formul  
7#a47 to 7#e471 a table of pressures and
 corresponding temperatures may be      
computed2 and these being known1 the    
formula 7#i47 will be sufficient for the
 computation of the corresponding values
 of ,v1 or the enlargement of volume    
which water undergoes in passing into   
steam4  ,in the following table1 the    
temperatures corresponding to pressures 
from #a to #bdj lbs4 per square inch are

 given by computation from the formul   
7#b47 to 7#e471 and the volumes of steam
 produced by an unit of volume of water 
as computed from the formula 7#i474     
,the mechanical effect is obtained by   
multiplying the pressure in pounds by   
the expansion of a cubic inch of water  
in passing into steam expressed in feet1
 and is therefore the number of pounds  
which would be raised one foot by the   
evaporation of a cubic inch of water    
under the given pressure4 ,pg#eji       
----------------------------------------
----------------------------------------
------------------------------------    
,volume of    ,mechanical   ,total      
pressure               the ,steam       
,effect of      in ,pounds              
,corresponding compared to  a ,cubic    
,inch     per ,square   ,temperature4   
the ,volume   of ,water       ,inch4    
of the     evaporated                   
,water that   in ,pounds                
has       raised ,one                   
produced it4    ,foot4                  

----------------------------------------
----------------------------------------
----------------------------         #a 
#ajbi       #bjhfh             #agci    
#b           #abfa       #ajhgd         
#ahab         #c           #adaj        
#gdcg             #ahei         #d      
#aebc        #efhe             #ahie    
#e           #afad        #dfag         
#aibd         #f           #afib        
#chig             #aidh         #g      
#agei        #ccgf             #aifi    
#h           #ahbj        #bihc         
#aihi         #i           #ahgd        
#bfgd             #bjjf        #aj      
#aibd        #bdbf             #bjbb    
#aa           #aigj        #bbba        
#bjcf        #ab           #bjac        
#bjej             #bjej        #ac      
#bjec        #aijd             #bjfc    
#ad           #bjia        #aggh        
#bjgd        #ae           #babh        
#affi             #bjhf        #af      
#bafc        #aegc             #bjig    
#ag           #baif        #adhh        

#bajg        #ah           #bbbg        
#adaa             #baag        #ai      
#bbef        #acdc             #babf    
#bj           #bbhe        #abha        
#bace        #ba           #bcab        
#abbe             #badd        #bb      
#bcch        #aagd             #baeb    
#bc           #bcfc        #aabg        
#bafj        #bd           #bchg        
#ajhd             #bafh        #be      
#bdaj        #ajdd             #bage    
#bf           #bdcc        #ajjg        
#bahb        #bg           #bdee        
#igc             #bahi        #bh       
#bdgf         #ida             #baif    
#bi           #bdif         #iaa        
#bbjb        #cj           #beaf        
#hhc             #bbji        #ca       
#becf         #heg             #bbae    
#cb           #beee         #hcc        
#bbba        #cc           #begc        
#haj             #bbbf        #cd       
#beia         #ghh             #bbcb    
#ce           #bfji         #gfg        
#bbch        #cf           #bfbf        

#gdh             #bbdc        #cg       
#bfdc         #gbi             #bbdh    
#ch           #bfei         #gab        
#bbec        #ci           #bfge        
#fie             #bbei        #dj       
#bfia         #fgi             #bbfd    
#da           #bgjf         #ffd        
#bbfh        #db           #bgba        
#fdi             #bbgc        #dc       
#bgcf         #fce             #bbgh    
#dd           #bgej         #fbb        
#bbhb        #de           #bgfd        
#faj             #bbhg        #df       
#bggh         #eih             #bbia    
#dg           #bgib         #ehf        
#bbif        #dh           #bhje        
#ege             #bcjj        #di       
#bhai         #efd             #bcjd    
#ej           #bhcb         #eed        
#bcjh        #ea           #bhdd        
#edd             #bcab        #eb       
#bheg         #ecd             #bcaf    
#ec           #bhfi         #ebe        
#bcbj        #ed           #bhha        
#eaf             #bcbd        #ee       

#bhic         #ejh             #bcbg    
#ef           #bije         #ejj        
#bcca        #eg           #biag        
#dib             #bcce        #eh       
#bibi         #dhd             #bcci    
#ei           #bidb         #dgg        
#bcdc        #fj           #bief        
#dgj             #bcdg        #fa       
#bifi         #dfc             #bcea    
#fb           #biha         #def        
#bcee        #fc           #biib        
#ddi             #bcei        #fd       
#cjjc         #ddc             #bcfb    
#fe           #cjac         #dcg        
#bcfe        #ff           #cjbd        
#dca             #bcfi        #fg       
#cjcd         #dbe             #bcgb    
#fh           #cjdd         #dai        
#bcge        #fi           #cjed        
#dad             #bcgh        #gj       
#cjfd         #djh             #bchb    
#ga           #cjgd         #djc        
#bche        #gb           #cjhd        
#cih             #bchh        #gc       
#cjic         #cic             #bcia    

#gd           #cajc         #chh        
#bcid        #ge           #caab        
#chc             #bcig        #gf       
#cabb         #cgi             #bdjj    
#gg           #caca         #cgd        
#bdjc        #gh           #cadj        
#cgj             #bdje        #gi       
#cadi         #cff             #bdjh    
#hj           #caeh         #cfb        
#bdaa        #ha           #cafg        
#ceh             #bdad        #hb       
#cagf         #ced             #bdag    
#hc           #cahd         #cej        
#bdai        #hd           #caic        
#cdf             #bdbb        #he       
#cbja         #cdb             #bdbe    
#hf           #cbaj         #cci        
#bdbg        #hg           #cbah        
#cce             #bdcj        #hh       
#cbbf         #ccb             #bdcb    
#hi           #cbce         #cbh        
#bdce        #ij           #cbdc        
#cbe             #bdch        #ia       
#cbea         #cbb             #bddj    
#ib           #cbei         #cai        

#bddc        #ic           #cbfg        
#caf             #bdde        #id       
#cbge         #cac             #bddh    
#ie           #cbhb         #caj        
#bdej        #if           #cbij        
#cjg             #bdec        #ig       
#cbih         #cjd             #bdee    
#ih           #ccje         #cja        
#bdeg        #ii           #ccac        
#bih             #bdfj       #ajj       
#ccbj         #bie             #bdfb    
#aaj           #ccib         #bga       
#bdhf       #abj           #cdeh        
#bea             #bejg       #acj       
#ceba         #bcc             #bebg    
#adj           #cegi         #bah       
#bede       #aej           #cfcd        
#bje             #befa       #afj       
#cfhg         #aic             #begg    
#agj           #cgcf         #ahc       
#beic       #ahj           #cghd        
#agd             #bfjh       #aij       
#chbi         #aff             #bfbb    
#bjj           #chgc         #aeh       
#bfcf       #baj           #ciae        

#aea             #bfej       #bbj       
#ciee         #ade             #bffc    
#bcj           #ciid         #adj       
#bfge       #bdj           #djca        
#acd             #bfhg                  
----------------------------------------
----------------------------------------
----------------------------  ,pg#eaa   
,in the absence of any direct method of 
determining the general relation between
 the pressure and volume of common      
steam1 empirical formul expressing it   
have been proposed by different         
mathematicians4  ,the late ,professor   
,navier proposed the following3--,let ,s
 express the volume of steam into which 
an unit of volume of water is converted 
under the pressure ,p1 this pressure    
being expressed in kilogrammes per      
square mtre4 ,then the relation between 
,s and ,p will be    ,s  a_/7b  m,p71   
where a  #ajjj1 b  #jji1 and m          
#jjjjjdhd4  ,this formula1 however1 does
 not agree with experiment at pressures 
less than an atmosphere4 ,m4 de         

,pambour1 therefore1 proposes the       
following changes in the values of its  
co-efficients3--,let ,p express the     
pressure in pounds per square foot2 and 
let    a  #ajjjj  b  #jdbbg  m  #jjjbeh1
  and the formula will be accurate for  
all pressures4 ,for pressures above two 
atmospheres the following values give   
more accuracy to the calculation3--    a
  #ajjjj  b  #adba  m  #jjjbc4  ,in     
these investigations ,i shall adopt the 
following modified formula4 ,the symbols
 ,s and ,p retaining their              
signification1 we shall have    ,s      
a_/7b  ,p7  7#aj47  where    a  #chgeifi
     b  #afd4  ,these values of a and b 
will be sufficiently accurate for       
practical purposes for all pressures1   
and may be used in reference to         
low-pressure engines of every form1 as  
well as for high-pressure engines which 
work expansively4  ,when the pressure is
 not less than #cj pounds per square    
inch1 the following values of a and b   
will be more accurate3--    a  #dcdghbf 

b  #fah4    ,on the ,expansive ,action  
of ,steam4  ,the investigation of the   
effect of the expansion of steam which  
has been given in the text1 is intended 
to convey to those who are not          
conversant with the principles and      
language of analysis1 some notion of the
 nature of that mechanical effect to    
which the advantages attending the      
expansive principle are due4 ,we shall  
now1 however1 explain these effects more
 accurately4 ,pg#eab  ,the dynamical    
effect produced by any mechanical agent 
is expressed by the product of the      
resistance overcome and the space       
through which that resistance is moved4 
,let       ,p  the pressure of steam    
expressed in pounds per square foot4    
,s  the number of cubic feet of steam of
 that pressure             produced by  
the evaporation of a cubic foot of      
water4       ,e  the mechanical effect  
produced by the evaporation of a        
cubic foot of water expressed in pounds 
raised one foot4  ,then we shall have ,e

  ,,ps2 and if ,w be a volume of water  
evaporated under the pressure ,p1 the   
mechanical effect produced by it will be
 ,,wps4  ,by 7#aj47 we have    ,,sp  a  
b,s4  ,hence1 for the mechanical effect 
of a cubic foot of water evaporated     
under the pressure ,p we have    ,e  a  
b,s4                7#aa47  ,let a cubic
 foot of water be evaporated under the  
pressure ,p1 and let it produce a volume
 of steam ,s of that pressure4 ,let this
 steam afterwards be allowed to expand  
to the increased volume ,s and the      
diminished pressure ,p2 and let it be   
required to determine the mechanical    
effect produced during the expansion of 
the steam from the volume ,s to the     
volume ,s4    ,let       ,e  the        
mechanical effect produced by the       
evaporation of               the water  
under the pressure ,p without expansion4
       ,e  the mechanical effect        
produced during the expansion           
of the steam4       ,e   the mechanical 
effect which would be produced by       

the evaporation under the pressure ,p   
without expansion4      ,e  the total   
mechanical effect produced by the       
evaporation               under the     
pressure ,p and subsequent expansion4   
,thus we have    ,e  ,e  ,e4  ,let s be 
any volume of the steam during the      
process of expansion1 p the             
corresponding pressure1 and e the       
mechanical effect produced by the       
expansion of the steam4 ,we have then by
 7#aj47    p  7a_/s7  b2     de         
7ads_/s7  bds4  ,hence by integrating we
 obtain    e  a log4 s  bs  ,c2         
,pg#eac which1 taken between the limits 
s  ,s and s  ,s1 becomes    ,e  a log4  
,s_/,s  b7,s  ,s74   7#ab47  ,but by    
7#aa47 we have            ,e  a  b,s1   
,e  a  b,s2        ,e  ,e  b7,s  ,s72   
,e  a log4 ,s_/,s  ,e  ,e2    ,e  ,e  ,e
  a log4 ,s_/,s  ,e4   7#ac47  ,or1     
,e  a 7#a  log4 ,s_/,s7  b,s4   7#ad47  
,hence it appears that the mechanical   
effect of a cubic foot of water         
evaporated under the pressure ,p may be 

increased by the quantity a log4 ,s_/,s1
 if it be first evaporated under the    
greater pressure ,p1 and subsequently   
expanded to the lesser pressure ,p4     
,the logarithms in these formul are     
hyperbolic4  ,to apply these principles 
to the actual case of a double acting   
steam engine1    ,let       ,l  the     
stroke of the piston in feet4       ,a  
the area of the piston in square feet4  
n  the number of strokes of the piston  
per minute4        #bn ,,al  the number 
of cubic feet of space through which    
the piston moves per minute4   ,let     
c,l,a  the clearage1 or the space       
between the steam valve         and the 
piston at each end of the stroke4       
,the volume of steam admitted through   
the steam valve         at each stroke  
of the engine will be #bn ,,al7#a  c74  
,let       ,v  the mean speed of the    
piston in feet per minute1        #bn,l 
,v4  ,the volume of steam admitted to   
the cylinder per minute will therefore  
be ,,va 7#a  c71 the part of it employed

 in working the piston being ,,va4      
,let       ,w  the water in cubic feet  
admitted per minute in the form         
of steam through the steam valve4       
,s  the number of cubic feet of steam   
produced by a cubic             foot of 
water4  ,pg#ead ,hence we shall have    
,,ws  ,,va 7#a  c72    ,s  7,,va7#a     
c77_/,w4          7#ae47  ,since by     
7#aj47 we have    ,p  a_/,s  b2    ,p   
,wa_/7,,va7#a  c77  b4   7#af47  ,by    
which the pressure of steam in the      
cylinder will be known1 when the        
effective evaporation1 the diameter of  
the cylinder1 and speed of the piston1  
are given4  ,if it be required to       
express the mechanical effect produced  
per minute by the action of steam on the
 piston1 it is only necessary to        
multiply the pressure on the surface of 
the piston by the space per minute      
through which the piston moves4 ,this   
will give    ,,vap  ,w7a_/7#a  c77      
,v,ab2     7#ag47  which expresses the  
whole mechanical effect per minute in   

pounds raised one foot4  ,if the steam  
be worked expansively1 let it be cut off
 after the piston has moved through a   
part of the stroke expressed by e4  ,the
 volume of steam of the undiminished    
pressure ,p admitted per minute through 
the valve would then be    ,,va 7e  c72 
and the ratio of this volume to that of 
the water producing it being expressed  
by ,s1 we should have    ,s  7,,va7e    
c77_/,w4  ,the final volume into which  
this steam is subsequently expanded     
being ,,va7#a  c71 its ratio to that of 
the water will be    ,s  7,,va 7#a      
c77_/,w4  ,the pressure ,p1 till the    
steam is cut off1 will be    ,p  ,wa _/ 
7,,va7e  c77  b4   7#ah47  ,the         
mechanical effect ,e produced per minute
 by the steam of full pressure will be  
,e  ,p,a,ve  ,wae _/ 7e  c7  ,a,vbe2    
and the effect ,e per minute produced by
 the expansion of the steam will by     
7#ab47 be ,pg#eae    ,e  ,wa log47#a  c7
 _/ 7e  c7  b,v,a7#a  e74  ,hence the   
total effect per minute will be    ,e   

,wa 7e_/7e  c77  log47#a  c_/e  c7      
b,v,a4   7#ai47  ,if the engine work    
without expansion1 e  #a2     ,e  7     
,wa_/7#a  c77  b,v,a1  7#bj47  as       
before2 and the effect per minute gained
 by expansion will therefore be    ,e   
,e       ,wa 7e_/7e  c77  7#a_/7a  c77  
log47#a  c_/e  c72   7#ba47  which      
therefore represents the quantity of    
power gained by the expansive action1   
with a given evaporating power4  ,in    
these formul the total effect of the    
steam is considered without reference to
 the nature of the resistances which it 
has to overcome4  ,these resistances may
 be enumerated as follows3--    #a4 ,the
 resistance produced by the load which  
the engine is   required to move4    #b4
 ,the resistance produced by the vapour 
which remains   uncondensed if the      
engine be a condensing engine1 or of the
   atmospheric pressure if the engine do
 not condense the steam4    #c4 ,the    
resistance of the engine and its        
machinery1 consisting   of the friction 

of the various moving parts1 the        
resistances   of the feed pump1 the cold
 water pump1 c4 ,a part of these        
resistances are of the same amount1     
whether the engine be   loaded or not1  
and part are increased1 in some         
proportion   depending on the load4     
,when the engine is maintained in a     
state of uniform motion1 the sum of all 
these resistances must always be equal  
to the whole effect produced by the     
steam on the piston4 ,the power expended
 on the first alone is the useful       
effect4  ,let ,r  the pressure per      
square foot of the piston surface1 which
 balances the resistances produced by   
the load4  m,r  the pressure per square 
foot1 which balances that part of the   
friction of the engine which is         
proportional to the load4  r  the       
pressure per square foot1 which balances
 the sum of all those resistances that  
are not proportional to the load4  ,the 
total resistance1 therefore1 being ,r   
m,r  r1 which1 when the mean motion of  

the piston is uniform1 must be equal to 
the mean pressure on the piston4 ,the   
total mechanical effect ,pg#eaf must    
therefore be equal to the total         
resistance multiplied by the space      
through which that resistance is driven4
 ,hence we shall have    ,r7#a  m7      
r,,va  ,wa7e_/7e  c77  log47#a  c_/e  c7
  ,v,ab2     ,,rva7#a  m7  ,wa7e_/7e    
c77  log47#a  c_/e  c7  ,,va7b  r74     
,for brevity1 let        e  a7e_/7e  c77
  log47#a  c_/e  c72     ,,rva7#a  m7   
,we  ,,va7b  r74        7#bb47  ,by     
solving this for ,,va1 we obtain    ,,va
  ,we_/7,r7#a  m7  b  r72     ,,rva     
,we,r_/7,r7#a  m7  b  r74      7#bc47   
,this quantity ,,rva1 being the product 
of the resistance ,,ra1 of the load     
reduced to the surface of the piston1   
multiplied by the space through which   
the piston is moved1 will be equal to   
the load itself multiplied by the space 
through which it is moved4 ,this being1 
in fact1 the useful effect of the       
engine1 let it be expressed by ,u1 and  

we shall have    ,u  ,we,r_/7,r7#a  m7  
b  r74       7#bd47  ,or by 7#bb471     
,u7#a  m7  ,we  ,,va7b  r74      7#be47 
,the value of the useful effect obtained
 from these formul will be expressed in 
pounds1 raised one foot per minute1 ,w  
being the effective evaporation in cubic
 feet per minute1 ,a the area of the    
piston in square feet1 and ,v the space 
per minute through which it is moved1 in
 feet4  ,since a resistance amounting to
 #cc1jjj pounds moved through one foot  
per minute is called one-horse power1 it
 is evident that the horse power ,h of  
the engine is nothing more than the     
useful effect per minute referred to a  
larger unit of weight or resistance2    
that is to #cc1jjj pounds instead of one
 pound4 ,hence we shall have    ,h      
,u_/#ccjjj4         7#bf47  ,since the  
useful effect expressed in 7#bd47 and   
7#be47 is that due to a number of cubic 
feet of water1 expressed by ,w1 we shall
 obtain the effect due to one cubic foot
 of water1 by dividing ,u by ,w4 ,if1   

therefore1 ,u be the effect produced by 
the effective evaporation of a cubic    
foot of water1 we shall have ,pg#eag    
,u  ,u_/,w4         7#bg47  ,if the     
quantity of fuel consumed per minute be 
expressed by ,f1 the effect produced by 
the unit of fuel1 called the ,,duty of  
the engine1 will1 for like reason1 be   
,d  ,u_/,f4         7#bh47  ,if the fuel
 be expressed in hundredweights of coal1
 then ,d will express the number of     
pounds' weight raised one foot by a     
hundredweight of coal4  ,by solving     
7#bd47 and 7#be47 for ,w1 we obtain     
,w  ,u7,r7#a  m7  b  r7_/,re1           
7#bi47    ,w  7#a_/;e7,u7#a  m7  ,,va7b 
r74       7#cj47  ,by eliminating ,u1 by
 7#bf471 we shall have    ,w  #ccjjj    
,h7,r7#a  m7  b  r7_/,re1       7#ca47  
,w  7#a_/;e7#ccjjj ,h7#a  m7  ,,va7b    
r74    7#cb47  ,the evaporation         
necessary per horse power per minute    
will be found by putting ,h  #a in these
 formul4#da  ,it will be observed that  
the quantities ,a and ,v1 the area of   

the cylinder and the speed of the       
piston1 enter all these formul as       
factors of the same product4 ,other     
things1 therefore1 being the same1 the  
speed of the piston will be always      
inversely as the area of the cylinder4  
,in fact1 ,,va is the volume of steam   
per minute employed in working the      
piston1 and if the piston be increased  
or diminished in magnitude1 its speed   
must be inversely ,pg#eah varied by the 
necessity of being still moved through  
the same number of cubic feet by the    
same volume of steam4  ,it has been     
already stated in the text1 that no     
satisfactory experiments have yet been  
made1 by which the numerical value of   
the quantity r can be exactly known4 ,in
 engines of different magnitudes and    
powers1 this resistance bears very      
different proportions to the whole power
 of the machine4 ,in general1 however1  
the larger and more powerful the engine1
 the less that proportion will be4      
,that part of this resistance which     

arises from the reaction of the         
uncondensed vapour on the piston is very
 variable1 owing to the more or less    
perfect action of the condensing        
apparatus1 the velocity of the piston1  
and the magnitude and form of the steam 
passages4 ,m4 de ,pambour states1 that1 
by experiments made with indicators1 the
 mean amount of this resistance in the  
cylinder is #b-a_/b lbs4 per square inch
 more than in the condenser1 and that   
the pressure in the latter being usually
 #a-a_/b lb4 per square inch1 the mean  
amount of the pressure of the condensed 
vapour in the cylinder is about #d lbs4 
per square inch4 ,engineers1 however1   
generally consider this estimate to be  
above the truth in well-constructed     
engines1 when in good working order4    
,in condensing low pressure engines of  
forty horse power and upwards1 working  
with an average load1 it is generally   
considered that the resistance produced 
by the friction of the machine and the  
force necessary to work the pumps may be

 taken at about #b lbs4 per square inch 
of piston surface4  ,thus the whole     
resistance represented by r in the      
preceding formul1 as applied to the     
larger class of low pressure engines1   
may be considered as being under #f lbs4
 per square inch1 or #hfd lbs4 per      
square foot1 of the piston4 ,it is      
necessary1 however1 to repeat1 that this
 estimate must be regarded as a very    
rough approximation2 and as representing
 the mean value of a quantity subject to
 great variation1 not only in one engine
 compared with another1 but even in the 
same engine compared with itself at     
different times and in different states4
  ,in the same class of engines1 the    
magnitude of the clearage is generally  
about a twentieth part of the capacity  
of the cylinder1 so that c  #jje4  ,that
 part of the resistance which is        
proportional to the load1 and on which  
the value of m in the preceding formul  
depends1 is still more variable1 and    
depends so much on the form1 magnitude1 

and the arrangement of its parts1 that  
no general rule can be given for its    
value4 ,it must1 in fact1 be determined 
in every particular case4  ,in the      
practical application of the preceding  
formul in condensing engines we shall   
have ,pg#eai    a  #chgeifi   b  #afd   
c #jje2    e  #chgeifi7;e_/7e  #jje7    
log4#aje_/7;e  #jje774  ,in engines     
which work without condensation1 and    
therefore with high pressure steam1 we  
shall have    a  #dcdghbf   b  #fah   c 
#jje    e  #dcdghbf7;e_/7e  #jje7       
log4#aje_/7;e  #jje77  ,to facilitate   
computation1 the values of e            
corresponding to all values of e1 from e
  #aj to e  #ij1 are given in the       
following table3--                      
----------------------------------------
----------------------------------------
----------------------------------------
------       ,condensing,non-condensing 
,condensing,non-condensing              
,engines     ,engines         ,engines  
,engines    e      e4         e4      e 

e4        e4                            
----------------------------------------
----------------------------------------
----------------------------------   #aj
  #ajabfbfe    #aaceijbi   #ea  #eiffcfg
     #ffibgjh   #aa   #iiefhfg          
#aaafijjh   #eb  #eijchcg     #ffbbefe  
#ab   #igicacf    #ajihecdd   #ec       
#ehdbbhh     #feecebe   #ac   #ifcdibf  
#ajhjghge   #ed  #eghafic     #fdheeeb  
#ad   #idhbjbi    #ajfcfcfd   #ee       
#egbbjbd     #fdahfai   #ae   #iccdbai  
#ajdgjefj   #ef  #effcbea     #fcebfic  
#af   #iaiabea    #ajcajahf   #eg       
#efjecec     #fbhggde   #ag   #ijebhhh  
#ajaedigh   #eh  #eedhbig     #fbbcgdb  
#ah   #hiahhif    #ajjjdfge   #ei       
#edibjfd     #fafjffb   #ai   #hghijdc  
#iheijad   #fj  #edcffbh     #fjihdgh   
#bj   #hffcabj     #igaggfj   #fa       
#echaifi     #fjcgaff   #ba   #hedjiah  
#iehjfhb   #fb  #ecbhjfe     #eigffii   
#bb   #hdbbbdb     #iddgeei   #fc       
#ebgdhif     #eiagjeg   #bc   #hcjfiaf  
#icahaic   #fd  #ebbbddd     #ehehbai   

#bd   #haidggj     #iaibcif   #fe       
#eagjfhd     #ehjjaei   #be   #hjhefdd  
#ijfiihd   #ff  #eaaifje     #egdbhfj   
#bf   #gigicib     #hiejgif   #fg       
#ejfiahf     #efhfcjd   #bg   #ghgehgj  
#hhcdfgd   #fh  #ejaidaj     #efcjdfi   
#bh   #gggdieb     #hgbadfh   #fi       
#digjbfc     #eegecdj   #bi   #gfgfead  
#hfaajdh   #gj  #dibagbg     #eebjhid   
#cj   #gehjddg     #hejcbhd   #ga       
#dhgcgij     #edfgaba   #ca   #gdhffdj  
#hcihjef   #gb  #dhbfdcd     #edadjjj   
#cb   #gcidiij     #hbiebej   #gc       
#dggifdh     #ecfaeai   #cc   #gcjedjg  
#haidgfj   #gd  #dgccdag     #ecjifei   
#cd   #gbaghjg     #hjifdif   #ge       
#dfhggbh     #ebehdjh   #ce   #gacbjig  
#hjjjceb   #gf  #dfdbefi     #ebjggea   
#cf   #gjdhbjf     #gijfbdi   #gg       
#deigibh     #eaegfgf   #cg   #fiffjeh  
#ghadajj   #gh  #deecgid     #eajhagj   
#ch   #fhheehe     #ggbchcb   #gi       
#deajaee     #ejeibah   #ci   #fhjfgbj  
#gfcecfe   #hj  #ddffiii     #ejajhjh   
#dj   #fgbidjh     #gedhfdb   #ha       

#ddbdcag     #difbica   #da   #ffecegh  
#gdfcehj   #hb  #dchbjif     #diaeefi   
#db   #fegiahg     #gchjacb   #hc       
#dcdjccb     #dhfhgbj   #dc   #fejfagd  
#gbihbcj   #hd  #dbiijaj     #dhbbcfh   
#dd   #fdcddia     #gbaghbb   #he       
#dbehabj     #dggfejj   #de   #fcfdjii  
#gachheh   #hf  #dbagfeh     #dgcaaac   
#df   #fbididd     #gjfabhe   #hg       
#daggfac     #dfhfaib   #dg   #fbbfihi  
#fihejeh   #hh  #dacgigd     #dfdagbh   
#dh   #fafjaij     #fiajabf   #hi       
#djihgcg     #deiggac   #di   #fjideaj  
#fhcfdej   #ij  #djeihic     #deedadj   
#ej   #fjbiiaf     #fgfciib             
----------------------------------------
----------------------------------------
----------------------------------      
,pg#ebj ,in engines which work without  
expansion we have    e  a_/7#a  c74     
,for condensing engines without         
expansion1 we shall then have    e      
#chgeifi_/aje  #cfiacii2  7#cc47  and   
for non-condensing engines1    e        
#dcdghbf_/aje  #dadjghg4  7#cd47  ,as   

the diameters of the cylinders of       
engines are generally expressed in      
inches1 the corresponding areas of the  
pistons expressed in square feet are    
given in the following table1 so that   
the values of ,a may be readily found3--
                                        
----------------------------------------
----------------------------------------
----------------------------------------
--------------------  ,diam4   ,area4   
,diam4  ,area4    ,diam4  ,area4        
,diam4  ,area4                          
----------------------------------------
----------------------------------------
----------------------------------------
------  ,inches4 ,sq4feet4,inches4      
,sq4feet4,inches4 ,sq4feet4,inches4     
,sq4feet4    #aj     #jede    #dh       
#abeff    #hf    #djcci   #abd          
#hchfc    #aa     #jffj    #di    #acjie
    #hg    #dabhc   #abe     #hebba     
#ab     #jghe    #ej    #acfce    #hh   
#dbbcg   #abf     #hfeij    #ac         
#jibb    #ea    #adahf    #hi    #dcbjb 

#abg     #hgigj    #ad     #ajfi    #eb 
#adgdh    #ij    #ddagi   #abh          
#hicfa    #ae     #abbg    #ec    #aecba
    #ia    #deaff   #abi     #ijgfc     
#af     #acif    #ed    #aeijd    #ib   
#dfafd   #acj     #ibage    #ag         
#aegf    #ee    #afdii    #ic    #dgagc 
#aca     #iceii    #ah     #agfg    #ef 
#agajd    #id    #dhaic   #acb          
#iejcc    #ai     #aifi    #eg    #aggba
    #ie    #dibbd   #acc     #ifdgi     
#bj     #bahb    #eh    #ahcdh    #if   
#ejbfe   #acd     #igice    #ba         
#bdje    #ei    #ahihf    #ig    #eacah 
#ace     #iidjb    #bb     #bfdj    #fj 
#aifce    #ih    #ebchb   #acf          
#ajjhhj    #bc     #bhhe    #fa         
#bjbie    #ii    #ecdef   #acg          
#ajbcfi    #bd     #cadb    #fb         
#bjiff   #ajj    #ededb   #ach          
#ajchfi    #be     #cdji    #fc         
#bafdh   #aja    #eefch   #aci          
#ajechj    #bf     #cfhg    #fd         
#bbcdj   #ajb    #efgde   #adj          
#ajfija    #bg     #cigf    #fe         

#bcjdd   #ajc    #eghfc   #ada          
#ajhdcd    #bh     #dbgf    #ff         
#bcgeh   #ajd    #ehiib   #adb          
#ajiigg    #bi     #dehg    #fg         
#bddhd   #aje    #fjacb   #adc          
#aaaecb    #cj     #diji    #fh         
#bebbj   #ajf    #fabhc   #add          
#aacjig    #ca     #ebda    #fi         
#beifg   #ajg    #fbdde   #ade          
#aadfgd    #cb     #eehe    #gj         
#bfgbe   #ajh    #fcfag   #adf          
#aafbfa    #cc     #eidj    #ga         
#bgdid   #aji    #fdhja   #adg          
#aaghei    #cd     #fcje    #gb         
#bhbgd   #aaj    #feiie   #adh          
#aaidfh    #ce     #ffha    #gc         
#bijfe   #aaa    #fgbja   #adi          
#abajhh    #cf     #gjfi    #gd         
#bihfg   #aab    #fhdag   #aej          
#abbgai    #cg     #gdfg    #ge         
#cjfhj   #aac    #fifdd   #aea          
#abdcfa    #ch     #ghgf    #gf         
#caejc   #aad    #gjhhb   #aeb          
#abfjac    #ci     #hbif    #gg         
#cbcch   #aae    #gbaca   #aec          

#abgfgf    #dj     #hgbg    #gh         
#ccahc   #aaf    #gccia   #aed          
#abicea    #da     #iafh    #gi         
#cdjci   #aag    #gdffb   #aee          
#acajcf    #db     #ifba    #hj         
#cdijg   #aah    #geidd   #aef          
#acbgcb    #dc    #ajjhe    #ha         
#ceghe   #aai    #ggbcf   #aeg          
#acddci    #dd    #ajeei    #hb         
#cffgd   #abj    #ghedj   #aeh          
#acfaeg    #de    #aajde    #hc         
#cgegd   #aba    #gihed   #aei          
#acghhf    #df    #aaeda    #hd         
#chdhe   #abb    #haahj   #afj          
#acifbf    #dg    #abjdh    #he         
#cidjf   #abc    #hbeaf   #afa          
#adacgg                                 
----------------------------------------
----------------------------------------
----------------------------------------
--   ,pg#eba ,the practical application 
of the preceding formul will be shown by
 the following examples4   ,,examples4  
#a4 ,a #cf-;inch cylinder with #e-a_/b  
feet stroke is supplied by a boiler     

evaporating effectively #fj cubic feet  
of water per hour1 and the piston makes 
#bj strokes per minute without          
expansion2-- what is the power of the   
engine and the pressure of steam in the 
cylinder8  ,let it be assumed that r  #f
  #add  #hfd and m  #ja4 ,since the     
engine is a condensing engine1 we have b
  #afd and e  #cfiacii4 ,by the formul  
7#be47 and 7#bf47 we have    ,h  ,we    
,,va7b  r7_/#ccjjj7a  m72  and since by 
the data we have    ,w  #a   ,a  #gjfi  
,v  #bn,l  #dj  #ee  #bbj1  the formula1
 by these substitutions1 becomes    ,h  
7#cfiacii  #bbj  #ajbh  #gjfi7 _/       
7#ccjjj  #aa72    ,h  #egf4  ,since e   
#a1 the pressure ,p of steam in the     
cylinder1 by 7#ah471 is    ,p           
7,we_/,,va7  b4  ,therefore    ,p       
7#cfiacii_/aeeeah7  #afd  #bbaj2  which 
being the pressure in pounds per square 
foot1 the pressure per square inch will 
be #ae-a_/c lbs4  #b4 ,to find the      
effective evaporation necessary to      
produce a power of #hj horses with the  

same engine4 ,also1 find the pressure of
 steam in the cylinder1 the speed of the
 piston being the same4  ,by the formula
 7#cb471 with the above substitutions1  
we have    ,w  7#ccjjj  #hj  #aa  #bbj  
#gjfi  #ajbh7_/cfiacii  #abb4  ,the     
evaporating power would therefore be    
only increased #bb per cent41 while the 
working power of the engine would be    
increased nearly #dj per cent4  ,the    
pressure ,p in the cylinder will be     
given1 by 7#ah471 as before4    ,p      
7#abb  #cfiacii7_/aeeeah  #afd  #bgcb2  
which is equivalent to #ai lbs4 per     
square inch4 ,pg#ebb  #c4 ,what must be 
the diameter of a cylinder to work with 
a power of a hundred horses1 supplied by
 a boiler evaporating effectively #gj   
cubic feet of water per hour1 the mean  
speed of the piston being #bdj feet per 
minute1 and the steam being cut off at  
half stroke8 ,also1 what will be the    
full pressure of steam on the piston8   
,taking1 as in the former examples1 m   
#ja1 b  #afd1 and r  #hfd1 we shall have

    ,h  #ajj  ,w  #g_/f   ,v  #bdj1  and
 by the column for condensing engines1  
in table1 p4 #eai1 we have e  #fjbiiaf1 
where e  #jej4 ,making these            
substitutions in    ,we  #ccjjj ,h 7#a  
m7  ,,va 7b  r71  we shall have         
7#g_/f7  #fjbiiaf  #ccjjjjj  #aa  #bdj  
#ajbh  ,a4  ,whence we find    ,a  #ach2
  and by the table1 p4 #ebj1 the        
corresponding diameter of the cylinder  
will be #ej-a_/c inches4  ,if ,p be the 
full pressure of the steam1 we shall    
have1 by 7#ah471    ,p  7,wa_/,,va7e    
c77  b4  ,making in this the proper     
substitutions1 we have    ,p  77#g_/f7  
#chgeifi7 _/ 7#bdj  #ach  #jee7  #afd   
#bcah2  which being in pounds per square
 foot1 the pressure per square inch will
 be #af-a_/aj lbs4    ,,footnotes3      
#dj ,m4 de ,pambour states that the     
increased volume is #acfd   cubic       
inches4    #da ,formul equivalent to    
some of the preceding are given1   with 
numerous others1 by ,m4 de ,pambour1 in 
his ,theory of the   ,steam ,engine4    

,these mathematical details contain     
nothing new   in principle1 being merely
 the application of the known           
principles of general mechanics to this 
particular machine4 ,m4   de ,pambour   
objects against the methods of          
calculating the   practical effects of  
steam engines generally adopted by      
engineers in this country4 ,their       
estimates of the loss of   power by     
friction1 imperfect condensation1 and   
other causes1   are1 as ,i have stated  
in this volume1 vague1 and can be       
regarded at best as very rough          
approximations2 but1 subject to   the   
restrictions under which their methods  
of calculation are   always applied1    
they are by no means so defective as ,m4
 de   ,pambour supposes4 ,he proves what
 he considers to be their   inaccuracy1 
by applying them in cases in which they 
are never   intended to be applied by   
,english engineers4 ,those who desire   
to reduce to general algebraical formul 
the effects of the   different kinds of 

steam engines will1 however1 find the   
volume of ,m4 de ,pambour of            
considerable use4  ,pg#ebc     ,,index4 
,air1 elasticity of1 #bh2     ,may be   
partially expelled from a vessel by the 
application of       heat1 #dd4         
,america1 steam navigation first        
established in1 #dhg2     ,circumstances
 which led to it1 #dhh2     ,fitch and  
,rumsey1 their attempts to apply the    
single-acting       engine to the       
propulsion of vessels1 #dhi2            
,stevens of ,hoboken commences          
experiments on steam navigation1        
#dhi2     ,experiments of ,livingstone  
and ,fulton1 #dhi2     ,fulton's first  
boat1 #dij2     ,the ,hudson navigated  
by steam1 #dia2     ,extension and      
improvement of river navigation1 #dib2  
,american steamers1 #did2               
,difference between them and ,european  
steamers1 #did2     ,steamers on the    
,hudson1 #did2     ,american            
paddle-wheels1 #die2     ,sea-going     
,american steamers1 #dif2     ,speed    

attained by ,american steamers1 #dig2   
,lake steamers1 #dii2     ,the          
,mississippi and its tributaries1 #dii2 
,steam-boats navigating it1 #ejj2       
,their structure and machinery1 #ejj2   
,new ,orleans ,harbour1 #ejc2     ,steam
 tugs1 #ejc4    ,atmosphere1 #ch2       
,weight of1 #ci4    ,atmospheric air1   
mechanical properties of1 #ch2          
,composition of1 #bec4    ,atmospheric  
engine1 ,thomas ,newcomen the reputed   
inventor of1 #fb2     ,description of1  
as first constructed by ,newcomen1 #fg2 
,the operation of considered1 #fi2      
,not unfrequently used in preference to 
the modern steam       engine1 #gb2     
,advantages which it possessed over     
,savery's1 #gc2     ,considerably       
improved by ,beighton1 #ge2     ,john   
,smeaton investigates this machine1 #gf2
     ,brindley obtains a patent for     
improvements in1 #gf2     ,applied by   
,champion of ,bristol to raise water1   
#aha2     ,possessed but limited power  
of adaptation to a varying load1        

#aea2     ,expedient to remedy this1    
#aea2     ,working-beam1 cylinder1 and  
piston applied to by ,newcomen1         
#cbb4    ,atmospheric pressure rendered 
available as a mechanic agent by        
,denis ,papin1 #ch2     ,means of       
measuring the force of1 #ci2     ,the   
idea of using against a vacuum or       
partial vacuum to work        a piston  
in a cylinder1 suggested by ,otto       
,guericke1 #gc4     ,barometer gauge1   
#bgb4    ,barton's piston1 #bdh4        
,beighton1 his improvement of the       
atmospheric engine1 #ge4    ,black1     
,dr41 his doctrine of latent heat1 #ic4 
,blasco de ,garay1 his contrivance to   
propel vessels1 #af2     ,the           
contrivance of1 probably identical with 
that of ,hero1 #ag4    ,blinkensop1 his 
locomotive engine1 #ccg4                
,blowing-box1 #dbi4    ,blowing out1    
,seaward's method of1 #ded4    ,blow-off
 cocks1 #deb4    ,boiler1 forms of1 most
 convenient1 #bee2     ,the waggon      
boiler adopted by ,watt1 #bee2          

,furnace1 #bef2     ,method of feeding1 
#beg2     ,combustion of gas in flues1  
#bfj2     ,mr4 ,williams's method of    
consuming the unburned gases which      
escape from the grate1 and are carried  
through the flues1       #bfj2          
,construction of grate and ash-pit1     
#bfa2     ,magnitude of heating surface 
of boiler1 #bfb2     ,capacity of1 must 
be proportioned to the quantity of water
 to       be evaporated1 #bfc2          
,water-space and steam-space in boiler1 
#bfc2     ,proportion of water-space in 
the boiler1 how to be regulated1        
#bfd2     ,position of flues1 #bfd2     
,method of feeding1 #bfe2     ,the      
magnitude of the feed should be equal to
 the quantity of       water evaporated1
 #bfe2     ,different methods for       
indicating the level of the water in    
the boiler1 #bff2     ,level guages1    
#bff2     ,self-regulating feeder1 #bfg2
     ,another method of arranging1 #bfi2
     ,steam gauge1 #bgj2                
,thermometer gauge1 #bga2     ,barometer

 gauge1 #bgb2     ,the indicator to     
measure the mean efficient force of the 
piston invented by ,watt1 #bgd2     ,the
 counter contrived by ,watt1 #bgh2      
,safety valve1 #bgi2     ,fusible plugs 
used in high pressure boilers1 #bhj2    
,self-regulating damper1 #bha2          
,self-regulating furnace invented by    
,brunton1 #bhc2     ,duty of a boiler1  
#bid2     ,boilers of locomotive        
engines1 #cea2     ,construction of the 
boiler of ,gurney's steam carriage1     
#dbc2     ,all boilers require          
occasional cleansing1 #dbg2             
,gurney's method of removing crust of   
deposited matter in       boilers1 #dbg2
     ,the boiler of ,dr4 ,church's      
engine formed of copper1 #dci2          
,boilers in marine engines1 #ddi2       
,effects of sea-water in1 #dej2         
,remedies for them1 #dea2               
,substitution of copper for iron1 #dfj2 
,expedient of coating boilers with felt1
 applied by ,watt1 #dfc4    ,booth1     
,mr41 his report on locomotive engines1 

#cfa4    ,boulton and ,watt's           
experiments on the horse power of       
engines1       #bhh4    ,branca1        
,giovanni1 his machine for propelling a 
wheel by a blast     of steam1 #bb4     
,brindley 7,james7 obtains a patent for 
improvements in       atmospheric       
engine1 #gf2     ,undertook to erect an 
engine at ,newcastle-under-,lyne1 #gf2  
,discouraged by the obstacles thrown in 
his way1 #gf4    ,brougham1 ,lord1 his  
sketch of ,watt's character1 #cac2      
,inscription from the pen of1 on ,watt's
 monument in ,westminster       ,abbey1 
#cbj4    ,buffers1 #djd4                
,cartwright's engine to use the vapour  
of alcohol to work the       piston1    
#bde2     ,his piston1 #bdg4    ,cawley 
and ,newcomen obtain a patent for the   
atmospheric engine1       #fd4          
,champion applies atmospheric engine to 
raise water1 #aha4    ,chapman1         
,messrs41 their locomotive engine1 #ccg4
    ,chlorine introduced in bleaching by
 ,watt1 #caj4    ,church1 ,dr41 his     

steam engine1 #dci2     ,the boiler     
formed of copper1 #dci4    ,coals1 the  
virtues and powers which steam has      
conferred upon1       #f2     ,the      
amount of labour a bushel of performs by
 means of the       steam engine1       
compared with horse power1 #g2          
,constituents of1 #beb2     ,process of 
combustion1 #beb4    ,coal mines1       
apprehensions as to the possibility of  
the       exhaustion of groundless1 #h4 
,cocks1 friction on1 #bdj4    ,cocks and
 valves1 #bbg4    ,combustion of gas in 
flues1 #bfj4    ,condensation by        
injection1 accidental discovery of1 #fi4
    ,condensation in the cylinder       
incompatible with a due economy       of
 fuel1 #abj4    ,condensing principle1  
circumstance which led to ,savery's     
discovery of1 #dg4    ,condensing pipe  
in ,savery's engine1 #eb4    ,condensing
 out of the cylinder1 #abj4             
,condensing jet1 #aia4    ,conical steam
 valves1 #bbh4    ,conversion of ice    
into water1 #ajc2     ,of water into    

steam1 #aje4    ,copying press invented 
by ,watt1 #cjb4    ,cornish system of   
inspection1 #big4    ,cornish engines1  
improvement of1 #bih2     ,historical   
detail of the duty of1 #bii4            
,cylinders1 ,wilkinson's machine for    
accurately boring the       insides of1 
#adi4     ,d valve1 #bcj4    ,dalton and
 ,gay-,lussac1 law of1 relating to the  
pressure of       elastic bodies1 #aga4 
,dixon1 ,mr4 ,the substitution of brass 
for copper tubes in       locomotive    
engines ascribed to him1 #cgj4          
,double clack-valve1 #bbh4              
,eccentric1 #bbe2     ,two expedients to
 reverse the position of1 #cgi4         
,effect of an engine1 #bhe4    ,elastic 
fluids4 ,the law according to which the 
pressure of1       increases with their 
temperature1 discovered by ,dalton and  
,gay-,lussac1 #aga4    ,evaporation of  
water and other liquids1 physical and   
mechanical principles connected with1   
#ig4    ,expansion of common steam1     
effects of1 #agc4    ,expansive action  

of steam1 #aei2     ,stated by ,watt in 
a letter to ,dr4 ,small1 #aeg2     ,its 
principle explained1 #aeh2              
,mechanical effect resulting from it1   
#afa2     ,computed effect of cutting   
off steam at different portions       of
 the stroke1 #afb2     ,involves the    
condition of a variation in the         
intensity of       the moving power1    
#afc2     ,expedients for equalising the
 power1 #afd2     ,the expansive        
principle in the engines constructed by 
,boulton and ,watt1 limited1 #afe2      
,its more extensive application in the  
,cornish engines1 #afe2     ,methods of 
equalising1 #agd2     ,description of   
,hornblower's engine for this purpose1  
#agd4    ,expansive principle1          
application of in marine engines1 #dff4 
,farey on the steam engine1 quotation   
from1 relative to       ,savery's       
engine1 #eh2     ,his evidence before   
the ,house of ,commons1 #dce4    ,field1
 construction of his split paddle1 #dgh4
    ,fitch and ,rumsey1 their attempts  

to apply the single-acting       engine 
to the propulsion of vessels1 #dhi4     
,flues1 position of1 #bfd4    ,fluids1  
of two kinds1 #be2     ,mechanical      
properties of1 #be2     ,elastic1 #bg2  
,experimental proof that they press     
equally in all       directions1 #da4   
,fly-wheel1 #bje4    ,four-way cock1    
#bci2     ,disadvantages of1 #bdj4      
,fuel1 means of economising1 in marine  
furnaces1 #dfc4    ,fulton and          
,livingstone1 their experiments in steam
 navigation1       #dhi4    ,fulton's   
first boat1 #dij4    ,furnace1          
self-regulating1 invented by ,brunton1  
#bhc4    ,fusible plugs used in         
high-pressure boilers1 #bhj4            
,galloway1 his paddle-wheel described1  
#dgf4    ,gas1 elasticity of1 #bh4      
,gay-,lussac and ,dalton1 law of1       
relating to the pressure of             
elastic bodies1 #aga4    ,governor1     
adaptation of1 #bji4    ,gradients1     
restrictions on1 #daa2     ,disposition 
of1 should be uniform1 #dae4    ,great  

,western ,railway1 ,dr4 ,lardner's      
experiments on1 #djh4    ,griff1        
proposals to drain a colliery at1       
mentioned by       ,desaguliers1 #fd4   
,gurney's steam carriage1 #dbc2         
,construction of the boiler of1 #dbc2   
,his method of removing crust of        
deposited matter in boilers1       #dbg2
     ,his experiments on common roads1  
#dcb4     ,hall1 his condensers         
described1 #deh4    ,hancock1 his steam 
carriage1 #dcf2     ,in what manner it  
differs from that of ,gurney1 #dcg4     
,harris1 ,dr41 mentions ,savery's engine
 in his ,lexicon       ,technicum1 #ef4 
,heat1 effects of upon water1 #bi2      
,waste of in atmospheric engine1 #hi2   
,an examination of the analogous effects
 produced by the       continued        
application of1 to water in the liquid  
state1       #ajb2     ,radiation of1   
#bed4    ,heating by steam brought      
forward by ,watt1 #cjc4    ,hecla1      
experiments with the1 #dab4    ,hero of 
,alexandria1 description of his machine1

 #ab4    ,high pressure engines         
described1 #cba2     ,one of the        
earliest forms of the steam engine1     
#cbb2     ,obscurely described in the   
,century of ,inventions1 #cbb2          
,construction of the first1 by ,messrs4 
,trevethick and ,vivian1       #cbd4    
,hooke exposes the fallacy of ,papin's  
project1 #fd4    ,horse carriages       
compared with steam1 #dce4    ,horse    
power of steam engines1 #bhh2           
,smeaton's estimation of1 #bhh2         
,boulton and ,watt's experiments on1    
#bhh4    ,howard's description of his   
marine engine1 #dfd4    ,hudson1 the1   
navigated by steam1 #dia4    ,hull1     
,jonathan1 his application of the steam 
engine to water       wheels1 #ahj4     
,humphrey4 ,his marine engine described1
 #dgj4    ,huskisson1 ,mr41 death of1   
#cbi4    ,hydrogen1 #bec4     ,india1   
steam navigation to1 #dhc4    ,indicator
 invented by ,watt1 #bgd4     ,jeffrey1 
,lord2 his sketch of the character of   
,watt1 #cae4     ,kinneal1 description  

of ,watt's experimental engine at1 #aca4
     ,lake steamers1 #dii4              
,lardner's1 ,dr41 experiments on the    
,manchester ,railway in #ahcb1          
#ceg2     ,his experiments in #ahch1    
#djf2     ,experiments on the ,great    
,western ,railway1 #djh4    ,leupold's  
engine1 description of1 #cbc4    ,level 
gauges1 #bff4    ,linen1 machine for    
drying by steam1 invented by ,watt1     
#cjc4    ,liverpool and ,manchester     
railroad1 effects of the introduction   
of steam transport on1 #cbi2     ,want  
of experience in the construction of the
 engines1 #cbi2     ,death of ,mr4      
,huskisson1 #cbi2     ,proceedings of   
the directors1 #cdb2     ,premium       
offered by them for the best engine1    
#cdd2     ,experimental trial1 #cdd4    
,livingstone and ,fulton1 experiments of
 in steam navigation1       #dhi4       
,locomotive engine1 history of1 #cbh2   
,blinkensop's engine1 #ccg2             
,chapman's engine1 #ccg2     ,walking   
engine1 #ccg2     ,mr4 ,stephenson's    

engine at ,killingworth1 #cci2          
,defect of1 #cda2     ,description of   
the ,rocket1 #cde2     ,the ,sanspareil1
 #cdg2     ,the ,novelty1 #cdi2         
,superiority of the ,rocket1 #cej2      
,subsequent improvements in the         
locomotive engine1 #ceb2     ,table1    
showing the economy of fuel gained by   
subdividing the       flue into tubes1  
#ced2     ,engines constructed in the   
form of the ,rocket subject to       two
 principal defects1 #ced2     ,these    
defects remedied1 #cee2     ,improved by
 the adoption of a more contracted blast
 pipe1       #cef2     ,dr4 ,lardner's  
experiments in #ahcb1 #ceg2             
,adoption of brass tubes1 #cfa2     ,mr4
 ,booth's report1 #cfa2     ,detailed   
description of the most improved        
locomotive       engines1 #cfd2         
,substitution of brass for copper tubes 
ascribed to ,mr4       ,dixon1 #cgj2    
,mr4 ,stephenson constructed the driving
 wheels without       flanges1 #chc2    
,pressure of steam in the boiler limited

 by two safety-       valves1 #djb2     
,buffers1 #djd2     ,steam whistle1     
#djd2     ,water tank1 #djd2     ,power 
of locomotive engines1 #dje2            
,evaporation of boilers1 #djf2     ,dr4 
,lardner's experiments in #ahch1 #djf2  
,resistance to railway trains1 #djg2    
,dr4 ,lardner's experiments on the      
,great ,western ,railway1 #djh2         
,restriction on gradients1 #daa2        
,experiment with the ,hecla1 #dab2      
,disposition of gradients should be     
uniform1 #dae2     ,method of           
surmounting steep inclinations1 #dae2   
,steam carriages on common roads1 #dai2 
,difference between steam engines on    
railways and those used       to propel 
carriages on turnpike roads1 #dbb2      
,gurney's steam carriage1 #dbc2         
,construction of the boiler of1 #dbc2   
,escape of steam from the engines on the
 ,liverpool road1 #dbh2                 
,blowing-box1 #dbi2     ,separator1     
#dcj2     ,difficulties in the practical
 working of steam carriages       upon  

common roads1 #dcb2     ,gurney's       
experiments on common roads1 #dcb2      
,prejudice against locomotive engines on
 common roads1 #dcb2     ,not more      
destructive to roads than carriages     
drawn by       horses1 #dcc2     ,report
 of the committee of the ,house of      
,commons1 #dcc2     ,weight of steam    
carriages1 #dcc2     ,two methods of    
applying locomotives upon common roads1 
#dcd2     ,horse carriages compared     
with1 #dce2     ,farey's evidence before
 the ,house of ,commons1 #dce2     ,risk
 of accident from explosion extremely   
slight1 #dce2     ,hancock's steam      
carriage1 #dcf2     ,in what manner it  
differs from that of ,gurney1 #dcg2     
,ogle's steam carriage1 #dch2     ,his  
evidence before the ,house of ,commons1 
#dci2     ,dr4 ,church's steam engine1  
#dci2     ,the boiler of formed of      
copper1 #dci4    ,lunar ,society1       
,boulton and ,watt leading members in1  
#cjb4     ,marine engines1 form and     
arrangement of1 #dda2     ,difference   

between marine and land engines1 #ddc2  
,engine-room1 arrangement of1 #ddf2     
,boilers in1 #ddi2     ,effects of      
sea-water on boilers1 #dej2             
,remedies for them1 #dea2     ,blow-off 
cocks1 #deb2     ,indicators of         
saltness1 #deb2     ,seaward's          
indicator1 #ded2     ,his method of     
blowing out1 #ded2     ,method of       
,maudslay and ,field to preserve        
freshness of water       in the boiler1 
#def2     ,brine pumps1 #deg2           
,tubular condensers applied by ,mr4     
,watt1 #deg2     ,hall's condensers1    
#deh2     ,substitution of copper for   
iron boilers1 #dfa2     ,process of     
stoking1 #dfb2     ,marine furnaces1    
#dfc2     ,expedient of coating boilers 
with felt applied by ,watt1 #dfc2       
,means of economising fuel1 #dfc2       
,description of ,howard's engine1 #dfd2 
,application of the expansive principle 
in marine engines1       #dff2          
,recent improvements of ,messrs4        
,maudslay and ,field1 #dfg2             

,humphrey's engine1 #dgj2     ,common   
paddle-wheel1 #dgb2     ,defect of1     
#dgd2     ,feathering paddles1 #dgd2    
,galloway's paddle-wheel1 #dgf2         
,field's split paddle1 #dgh2            
,proportion of power to tonnage1 #dhj2  
,iron steam vessels1 #dhb4              
,mariotte's law relating to pressure1   
#aga4    ,maudslay and ,field1 their    
method to preserve the requisite        
freshness of water in the boiler1 #def2 
,brine pumps1 #deg2     ,recent         
improvements of in marine engines1 #dff4
    ,metallic pistons1 #bdd2            
,cartwright's engine1 #bde2     ,an     
improved form given to by ,barton1 #bdh4
    ,mill work1 ,stewart's application  
of the steam engine to1 #ahb4    ,mines1
 the drainage of1 ,watt endeavours to   
bring to perfection       the           
application of the steam engine to1     
#agh4    ,mississippi and its           
tributaries1 #dii2     ,steam-boats on1 
#ejj2     ,their structure and          
machinery1 #ejj4    ,morland1 ,sir      

,samuel1 his application of steam to    
raise water1       #cd2     ,the reputed
 inventor of several ingenious          
contrivances1 #cd2     ,his work in     
,french upon the raising of water1 #ce2 
,extract from it1 #ce2     ,evelyn's    
account of his visit to1 #cf4           
,murray's slide-valve1 #bbi4            
,newcomen1 ,thomas1 the reputed inventor
 of the atmospheric       engine1 #fb2  
,his acquaintance with ,dr4 ,hooke1 #fb2
     ,acquainted with ,papin's writings1
 #fd2     ,the merits of his engine     
ascribed principally to its             
mechanism and combinations1 #gc2        
,obtains with ,cawley a patent for the  
atmospheric engine1 #fd2     ,resumes   
the old method of raising water from    
mines by       ordinary pumps1 #fe2     
,the means proposed to effect this1 #ff2
     ,first conception of the           
atmospheric engine1 #ff2                
,description of his construction of     
atmospheric engine1 #fg2     ,suggestion
 of a better method of condensation than

 the       application of cold water on 
the external surfaces of the            
cylinder1 #fi2     ,he abandons the     
external cylinder1 #fi2     ,applied the
 working-beam1 cylinder1 and piston to  
the       atmospheric engine1 #cbb4     
,new ,orleans ,harbour1 #ejc4           
,novelty1 description of the1 a         
locomotive engine1 #cdi4     ,ogle1 his 
steam carriage1 #dch2     ,his evidence 
before the ,house of ,commons1 #dci4    
,otto ,guericke1 his suggestion relative
 to atmospheric       pressure1 #gc4    
,oxley made the first attempt to drive  
water-wheels by the       steam engine1 
#ahb4     ,paddle-wheel described1 #dgb2
     ,defect of1 #dgd2     ,feathering  
paddles1 #dgd2     ,galloway's          
paddle-wheel1 #dgf2     ,field's split  
paddle1 #dgh4    ,paddle-wheels of      
,american steamers1 #die4    ,papin1    
,denis1 conceived the idea of rendering 
atmospheric       pressure available as 
a mechanical agent1 #cg2                
,description of his contrivance1 #cg2   

,his discovery of condensation of steam1
 #de2     ,quotation from his work      
relative to this discovery1 #de2        
,explanation of this important          
discovery1 #df2     ,discovers the      
method of producing a vacuum by the     
condensation of steam1 #agh2     ,his   
projected applications of the steam     
engine1 #agh2     ,his proposition for  
the construction of an engine working by
       atmospheric pressure1 #fb2       
,abandons the project when informed of  
the principle and       structure of    
,savery's engine1 #fb2     ,his engine  
described1 #fb2     ,this project       
nothing more than a reproduction of the 
,marquis       of ,worcester's engine1  
#fc2     ,the fallacy of his project    
exposed by ,hooke1 #fd2     ,his project
 for producing a vacuum under a piston  
by       condensing the steam1 published
 in the ,act ,eruditorum1       #fd4    
,parallel motion1 #aie4    ,physical    
science1 the rapid progress of1 #h4     
,pistons1 #bdb2     ,the common         

hemp-packed1 #bdb2     ,woolf's method  
of tightening the packing of1 without   
removing the lid of the cylinder1 #bdd2 
,this method further simplified1 #bdd2  
,metallic1 #bdd2     ,cartwright's      
engine1 #bde2     ,cartwright's piston1 
#bdg2     ,invention of the indicator by
 ,watt to measure the mean              
efficient force of1 #bgd4    ,piston rod
 and beam1 methods of connecting in the 
double-       acting engine1 #aic4      
,pneumatic institution at ,clifton1     
,watt one of the founders of1           
#caj4    ,potter1 ,humphrey1 his        
contrivance for working the valves1 #ga2
     ,improved by the substitution of a 
plug-frame1 #gb4    ,power1 proportion  
of1 to tonnage in marine engines1 #dhj4 
,power and duty of steam engines1 #bhg4 
,priestley1 ,watt's letter to1 relative 
to the composition of       water1 #cjg4
    ,pump1 an illustration of force     
attained by a vacuum1 #dc4    ,puppet   
clacks1 or button valves1 #add4         
,rack and ,sector1 #aid4    ,railways1  

speed of coaches on1 compared with that 
of stage-       coaches on a common     
road1 #g4    ,railway transport1 effects
 of1 #cbh4 #ccj4    ,railways and stone 
roads compared1 #dbj4    ,river         
navigation1 extension and improvement   
of1 #dib4    ,rocket1 description of    
the1 a locomotive engine1 #cde2         
,engines constructed in the form of1    
subject to two principal       defects1 
#ced2     ,these defects remedied1 #cee2
     ,improved by the adoption of a more
 contracted blast-pipe1 #cef4           
,roebuck1 ,dr41 ,watt's partnership     
with1 #acj4    ,rotatory motion1 method 
of producing by sun and planet wheels1  
#ahg4     ,safety-valve not adopted by  
,savery1 #eg2     ,invented by ,papin1  
#eg2     ,description of1 #eg2          
,first applied to ,savery's engine by   
,desaguliers1 #eh4    ,sanspareil1      
description of the1 a locomotive engine1
 #cdg4    ,savery1 ,thomas1 obtains a   
patent for an engine to raise water1    
#dg2     ,circumstance which led to his 

discovery of the condensing             
principle1 #dg2     ,an account of his  
engine1 #di2     ,description of the    
working apparatus in which the steam is 
used as a moving power1 #ea2     ,his   
engine described in a work entitled ,the
 ,miner's ,friend1       #ef2           
,mentioned by ,dr4 ,harrison in his     
,lexicon ,technicum1 #ef2     ,quotation
 from his address to the ,royal         
,society1 #ef2     ,quotation from his  
address to the ,miners of ,england1 #eg2
     ,mentioned by ,bradley in his      
,improvements of ,planting and          
,gardening1 #eg2     ,the safety-valve  
not adopted by him1 #eg2     ,the       
safety-valve first applied to his engine
 by ,desaguliers1       #eh2     ,farey 
on the steam engine quoted1 #eh2        
,further ,improvements made by          
,desaguliers1 #eh2     ,defects of his  
engine1 #ei2     ,his engine applied to 
the drainage of mines1 #ei2     ,further
 defects of1 #fj2     ,the first to     
suggest the method of expressing the    

power of       an engine with reference 
to that of horses1 #fa2     ,failure of 
his engine in the work of drainage1 #fa2
     ,the tendency of high pressure to  
weaken and gradually destroy       the  
vessels1 #gb2     ,the power of his     
engines restricted1 #gc2     ,the       
atmospheric engine superior to1 #gc2    
,the boiler1 guage-pipes1 and regulator 
borrowed from his       engine1 #gc2    
,proposes to apply his engine as a prime
 mover for all sorts       of machinery1
 #ahj4    ,scott1 ,sir ,walter1 his     
sketch of the character of ,watt1 #cad4 
,sculpture1 ,watt's invention of machine
 for copying1 #cah4    ,sea-going       
,american steamers1 #dif4    ,sea-water1
 effects of upon boilers1 #dej4         
,seaward's slides1 #bce2     ,indicator 
of saltness1 #ded2     ,his method of   
blowing out1 #ded4    ,self-regulating  
damper1 #bha2     ,furnace1 #bhc4       
,separator1 #dcj4    ,single-acting     
engine1 description of ,watt's1 #acc4   
#add4    ,single clack-valve1 #bbg4     

,single cock1 #bch4    ,slide-valves1   
#bbi2     ,that contrived by ,mr4       
,murray1 #bbi4    ,smeaton1 ,john1      
investigates the atmospheric engine1    
#gf2     ,applies himself to the        
improvement of wind and water mills1    
#aha2     ,his estimate of the horse    
power of engines1 #bhh4    ,solomon ,de 
,caus1 description of the apparatus of1 
#ag2     ,m4 ,arago claims for him a    
share of the honour of the              
invention of the steam engine1 #ba2     
,republished1 with additions1 the work  
of ,isaac ,de ,caus1 #bb4    ,somerset1 
,edward1 ,marquis of ,worcester4        
,invention of the steam       engine    
ascribed to him1 #bc2     ,description  
of his contrivance1 #bc2     ,his       
,century of ,inventions1 #bd2     ,brief
 account of his engine described in this
 work1 #ca2     ,his contrivance        
compared with that of ,de ,caus1 #cc2   
,many of his inventions have been       
reproduced and brought into             
general use1 #cd4    ,steam cannot be   

applied immediately to any useful       
purpose1       but requires the         
interposition of mechanism1 #aa2        
,elastic force of1 recognised by the    
ancients only in vague       and general
 terms1 #ad2     ,the power of1 formerly
 made to minister to the objects of     
superstition1 mentioned by ,arago1 #ae2 
,anecdote showing the knowledge which   
the ancients had of the       mechanical
 force of1 #ae2     ,the discovery of   
the condensation of1 by ,papin1 #de2    
,mechanical power obtained from the     
direct pressure of the       elastic    
force of1 suggested by ,de ,caus and    
,lord ,worcester1       #gc2     ,latent
 heat of1 #ajg2     ,the mechanical     
force of considered1 #aae2     ,watt's  
early experiments on1 #hg2              
,discovery of the expansive action of1  
#aeg2     ,expansive action of stated by
 ,watt in a letter to ,dr4 ,small1      
#aeg2     ,its principle explained1     
#aeh2     ,mechanical effect resulting  
from it1 #afa2     ,properties of1 #afh2

     ,common and super-heated steam1    
#afh2     ,pressure and temperature of1 
#aga2     ,relation between the         
temperatures of common steam and its    
pressure and density1 #agb2     ,effects
 of the expansion of common steam1 #agc2
     ,mechanical effects of1 #agc2      
,methods of equalising the varying force
 of expanding steam1       #agd2        
,method of producing a vacuum by the    
condensation of1       discovered by    
,papin1 #agh2     ,applied to move      
machinery1 #agi2     ,steam guage1 #bgj2
     ,heating by steam brought forward  
by ,watt1 #cjc2     ,a machine for      
drying linen by1 invented by ,watt1     
#cjc2     ,mode of escape of1 from the  
engines on the ,liverpool road1         
#dbi4    ,steam case or jacket1 invented
 by ,watt1 #abd4    ,steam engine1 a    
subject of popular interest1 #c2        
,the effects which it has produced upon 
the well-being of the       human race  
considered1 #d2     ,presents peculiar  
claims upon the attention of the people 

of       ,great ,britain1 #e2     ,the  
exclusive offspring of ,british genius1 
#e2     ,the virtues and powers which it
 has conferred upon coals1 #f2          
,water the means of calling these powers
 into activity1 #f2     ,used in the    
drainage of ,cornish mines1 #g2         
,comparison of its power with human     
labour1 #h2     ,investigation of the   
origin of1 #aj2     ,a combination of a 
great variety of contrivances and the   
production of several inventions1 #ab2  
,before the discoveries of ,james ,watt 
was of extremely       limited power1   
#ab2     ,invention of1 ascribed to the 
,marquis of ,worcester1 #bc2            
,account of ,savery's1 #di2     ,farey  
quoted1 #eh2     ,improvements made by  
,desaguliers1 #eh2     ,applied to the  
drainage of mines1 #ei2     ,humphrey   
,potter's contrivance1 #gb2             
,advantages of the atmospheric engine   
over that of ,savery1 #gc2     ,progress
 of the atmospheric engine1 #ge2        
,description of ,papin's engine1 #fb2   

,smeaton's improvements1 #gf2     ,first
 experiments of ,watt and subsequent    
improvements1 #hc2     ,watt's          
experiments on the force of steam at    
high pressure1       #hc2     ,watt     
discovers the great defects of the      
atmospheric engine1       #he2          
,waste of heat in atmospheric engine1   
#hi2     ,dr4 ,black's theory of latent 
heat1 #ic2     ,description of ,watt's  
experimental engine at ,kinneal1 #aca2  
,description of his single-acting       
engine1 #acc2     ,disadvantages of the 
atmospheric compared with the old       
engine1 #aej2     ,expedients to force  
the atmospheric engines into use1 #aeb2 
,watt's exertions to improve the        
manufacture of1 at ,soho1 #aee2         
,efficiency of fuel in the new engines1 
#aef2     ,hornblower's engine1 #age2   
,woolf's engine1 #agf2     ,watt        
endeavours to bring to perfection the   
application of1       to the drainage of
 mines1 #agh2     ,papin's projected    
application of1 #agh2     ,savery       

proposed to apply his steam engine as a 
prime mover       for all sorts of      
machinery1 #ahj2     ,jonathan ,hull's  
application of1 to water-wheels1 #ahj2  
,steam engine used for driving water    
wheels1 #ahb2     ,first attempt of this
 kind made by ,oxley1 #ahb2             
,stewart's application of1 to mill work1
 #ahb2     ,wasbrough's application of  
the fly-wheel and crank1 #ahc2          
,reasons why ,watt's single-acting      
engine was not adapted to       produce 
continuous uniform motion of rotation1  
#ahd2     ,watt's second patent1 #ahf2  
,valves of double-acting engine1 #ahi2  
,condensing jet1 #aia2     ,methods of  
connecting the piston-rod and beam in   
the double-       acting engine1 #aic2  
,rack and sector1 #aid2     ,parallel   
motion1 #aie2     ,connecting rod and   
crank1 #bjb2     ,fly-wheel1 #bje2      
,throttle-valve1 #bjg2     ,adaptation  
of the governor1 #bji2                  
,double-acting engine considered as a   
whole1 #baf2     ,process of its        

operation investigated1 #bag2     ,the  
eccentric1 #bbe2     ,cocks and valves1 
#bbg2     ,single clack-valve1 #bbg2    
,double clack-valve1 #bbh2     ,conical 
steam-valves1 #bbh2     ,slide-valves1  
#bbi2     ,murray's slide-valve1 #bbi2  
,d valve1 #bcj2     ,seaward's slides1  
#bce2     ,single cock1 #bch2           
,four-way cock1 #bci2     ,pistons1     
#bdb2     ,gross effect and useful      
effect of engines1 #bhe2     ,power and 
duty of1 #bhg2     ,horse power of1     
#bhh2     ,the means whereby mechanical 
power is expended in working       the  
engines enumerated1 #bij2     ,common   
rules followed by engine makers1 #bib2  
,duty of engines1 #bid2     ,duty       
distinguished from power1 #bie2         
,proportion of stroke to diameter of    
cylinder1 #bie2     ,cornish system of  
inspection1 #big2     ,improvement of   
the ,cornish engines1 #bih2             
,historical detail of the duty of       
,cornish engines1 #bii2                 
,high-pressure engines1 #cba2           

,leupold's engine described1 #cbc2      
,construction of the first high-pressure
 engine by ,messrs4       ,trevethick   
and ,vivian1 #cbd2     ,first           
application of the steam engine to      
propel carriages       on railroads1    
#cbh2     ,computation of how much corn 
could be saved by the       substitution
 of steam engines for horse power1 #ccb2
     ,marine engines1 form and          
arrangement of1 #dda2     ,difference   
between marine and land engines1 #ddc2  
,mr4 ,howard's patent engine described1 
#dfd2     ,humphrey's engine described1 
#dgj4    ,steam navigation to ,india1   
#dhc2     ,first established in         
,america1 #dhg2     ,circumstances which
 led to it1 #dhh2     ,attempts of      
,fitch and ,rumsey to apply the         
single-acting       engine to the       
propulsion of vessels1 #dhi2            
,stevens of ,hoboken commences          
experiments in1 #dhi2     ,experiments  
of ,livingstone and ,fulton1 #dhi2      
,fulton's first boat1 #dij2     ,the    

,hudson navigated by steam1 #dia2       
,extension and improvement of river     
navigation1 #dib2     ,american         
steamers1 #did2     ,difference between 
them and ,european steamers1 #did2      
,steamers on the ,hudson1 #did2         
,sea-going ,american steamers1 #dif2    
,speed attained by ,american steamers1  
#dig2     ,lake steamers1 #dii2         
,steam-boats on the ,mississippi1 #ejj4 
,steam tugs1 #ejc4    ,steep            
inclinations1 method of surmounting1    
#dae4    ,stephenson1 his locomotive    
engine at ,killingworth1 #cci2          
,defect of1 #cda2     ,constructed the  
driving wheels without flanges1 #chc4   
,stevens1 of ,hoboken1 commences        
experiments on steam navigation1        
#dhi4    ,stewart1 his application of   
the steam engine to mill work1 #ahb4    
,stoking1 process of1 #dfb4             
,stuffing-box1 contrivance of1 #adg4    
,sun and planet wheels1 method of       
producing rotatory motion1       #ahg4  
,thermometers1 the process of filling   

described1 #dd2     ,explanation of the 
principle of1 #ih2     ,construction of 
mercurial thermometer1 #ih2     ,method 
of graduating1 #ii4    ,thermometer     
gauge1 #bgj4    ,throttle-valve1        
description of1 #bjg4    ,tredgold1 his 
remark relative to ,newcomen's engine1  
#gc4    ,trevethick and ,vivian's engine
 described1 #cbe4     ,vacuum1 force    
obtained by a1 #dc2     ,the pump an    
illustration of this1 #dc4    ,valves of
 double-acting engine1 #ahi4            
,wasbrough1 his application of the      
fly-wheel and crank1 #ahc4    ,water1 a 
pint of1 the mechanical force produced  
by its       evaporation1 #f2     ,the  
alternate decomposition and             
recomposition of1 by       magnetism and
 electricity1 analogous to vaporisation 
and       condensation1 #h2     ,the    
fixed temperature which it assumes in   
boiling subject to       variation1     
#ajh2     ,experiments to illustrate    
this1 #aji2     ,table to show the      
temperature at which it will boil under 

different pressures of the atmosphere1  
#aac2     ,mechanical force of a cubic  
inch of1 converted into steam1          
#aah2     ,discovery of the composition 
of1 #cjc2     ,the merit of this        
discovery shared between ,cavendish1    
,lavoisier1 and ,watt1 #cje2     ,latent
 heat of1 #aja2     ,conversion of ice  
into1 #ajc4    ,water tank1 #djd4       
,water-wheels1 steam engine used for    
turning1 #ahb4    ,watt 7,james71 birth 
of1 #gg2     ,his infancy1 #gh2         
,anecdotes respecting1 #gh2     ,his    
boyhood1 #gi2     ,goes to ,london1 #hj2
     ,returns to ,glasgow1 #hj2         
,appointed mathematical instrument-maker
 to the university1       #ha2     ,adam
 ,smith one of his earliest friends and 
patrons1 #ha2     ,also ,black and      
,robert ,simson1 #ha2     ,extract from 
an unpublished manuscript of ,robison   
respecting       the character of1 #hb2 
,his first experiments on steam1 #hc2   
,observes defects of atmospheric engine1
 #hd2     ,his first attempt to improve 

it1 by using a wooden instead       of  
an iron cylinder1 #he2     ,his method  
to ascertain the temperatures at which  
water would       boil under pressures  
less than that of the atmosphere1 #hf2  
,his early experiments on steam1 #hg2   
,his notice of the waste of heat in     
atmospheric engines1 #hi2     ,his      
experiments to determine the extent to  
which water       enlarged its volume   
when it passed into steam1 #ij2         
,discovers the latent heat of steam1    
#ia2     ,learns the theory of latent   
heat1 #ic2     ,his letter to ,dr4      
,brewster1 explaining the circumstances 
which led to the error that a large     
share of the merit of       his         
discoveries were due to ,black1 #ic2    
,finds that condensation in the cylinder
 is incompatible with       a due       
economy of fuel1 #abj2     ,conceives   
the notion of condensing out of the     
cylinder1 #abj2     ,discovers separate 
condensation1 #aba2     ,invents the    
air-pump1 #abb2     ,substitutes steam  

pressure for atmospheric pressure1 #abc2
     ,invents the steam case or jacket1 
#abd2     ,his first experiments to     
realise these inventions1 #abe2     ,his
 experimental apparatus1 #abf2          
,difficulties of bringing the improved  
engines into use1 #abh2     ,practises  
as a civil engineer1 #abi2     ,makes a 
survey of the river ,clyde1 #abi2       
,his partnership with ,dr4 ,roebuck1    
#acj2     ,his first patent1 #acj2      
,description of his experimental engine 
at ,kinneal1 #aca2     ,removes to      
,soho1 #aca2     ,abstract of the act of
 parliament for the extension of his    
patent1 #acb2     ,description of his   
single-acting engine1 #acc-add2     ,his
 condenser worked by an injection1 #adf2
     ,objections attending condensation 
by surface1 #adf2     ,improvements in  
construction of piston1 #adg2           
,effected by a contrivance called a     
stuffing-box1 #adg2     ,method of      
packing1 #adh2     ,improved methods of 
boring the cylinder1 #adi2     ,his     

letter to ,smeaton on this subject1     
#adi2     ,used black-lead dust for the 
purpose of lubrication1 #adi2     ,this 
found to wear the cylinder1 #adi2       
,disadvantages of the atmospheric       
compared with the old       engines1    
#aej2     ,greatly increased economy of 
fuel1 #aea2     ,expedients to force the
 atmospheric engines into use1 #aeb2    
,his correspondence with ,boulton1 #aec2
     ,his correspondence with ,smeaton1 
#aed2     ,exertions to improve the     
manufacture of engines at ,soho1 #aee2  
,efficiency of fuel in the new engines1 
#aef2     ,endeavours to bring to       
perfection the application of the       
steam engine to the drainage of mines1  
#agh2     ,the reasons why his          
single-acting engine was not adapted to 
produce continuous uniform motion of    
rotation1 #ahd2     ,his notes upon ,dr4
 ,robison's article on the steam engine1
       #ahd2     ,his second patent1    
#ahf2     ,his third patent1 #ahi2      
,his application of the fly-wheel1 #bje2

     ,his application of the            
throttle-valve1 #bjg2     ,his          
adaptation of the governor1 #bji2       
,his double-acting engine considered as 
a whole1 #baf2     ,investigation of the
 process of its operation1 #bag2        
,eccentric1 #bbe2     ,cocks and valves1
 #bbg2     ,single clack-valve1 #bbg2   
,double clack-valve1 #bbh2     ,conical 
steam-valve1 #bbh2     ,slide-valves1   
#bbi2     ,the waggon boiler adopted by 
him1 #bbe2     ,invents the indicator1  
#bgd2     ,the counter contrived by him1
 #bgh2     ,the ,lunar ,society in which
 ,watt and ,boulton were leading        
members1 #cjb2     ,invents the copying 
press1 #cjb2     ,his friends and       
associates at ,birmingham1 #cjb2        
,method of heating by steam brought     
forward by him1 #cjc2     ,his invention
 of a machine for drying linen by steam1
 #cjc2     ,his share in the discovery  
of the composition of water1 #cjc2      
,his letter to ,priestley on this       
subject1 #cjg2     ,anecdote of his     

inventive genius1 #cji2     ,introduces 
the use of chlorine in bleaching1 #caj2 
,one of the founders of the ,pneumatic  
institution at ,clifton1       #caj2    
,his first marriage1 #caj2     ,private 
life of1 #caa2     ,death of his first  
wife1 #caa2     ,his second marriage1   
#caa2     ,he retires from business1    
#caa2     ,death of his younger son1    
#caa2     ,extracts from his letters1   
#cab2     ,his death1 #cac2             
,character of1 by ,lord ,brougham1 #cac2
     ,by ,sir ,walter ,scott1 #cad2     
,by ,lord ,jeffrey1 #cae2               
,occupation of his old age1 #cah2       
,invention of machine for copying       
sculpture1 #cah2     ,his last days1    
#cah2     ,monuments1 #cai2             
,inscription on the monument in         
,westminster ,abbey from the       pen  
of ,lord ,brougham1 #cai2     ,his      
application of tubular condensers1 #deg2
     ,his expedient for coating boilers 
with felt1 #dfc4    ,wilkinson1 his     
machine for accurately boring the       

insides of       cylinders1 #adi4       
,williams's method of consuming the     
unburned gases which escape       from  
the grate1 and are carried through the  
flues1 #bfj4    ,woolf's engine1 #agf2  
,woolf's piston1 #bdc4   ,illustration3 
,,richmond ,,bridge4   ,,london3        
,printed by ,a4 ,,spottiswoode1         
,new-,street-,square4            99     
99       99       99       99           
,transcriber's endnote3    ,original    
spelling and grammar has mostly been    
retained4 ,for   example1 the forms     
,cyclopoedia1 cyclopdia1 ,encyclopdia1  
,encyclopoedia1 guage1 and gauge are all
 retained4 ,figures   were moved from   
within paragraphs to between paragraphs4
   ,footnotes were re-indexed and moved 
to the ends of chapters4    ,an entry   
for the ,,index was inserted into the   
,table of ,contents4    ,in the ,table  
of ,contents1 changed ,,mm4 ,dulong and 
,arrago to ,,mm   ,dulong and ,arago4   
,also ,blinkinsop to ,blinkensop4 ,also 
,wasborough's to ,wasbrough's4    ,figs4

 #d1 #e and #f are all in one image4    
,two tubes in ,fig4 #d   were           
incorrectly labeled ,t'2 one of these   
has been crossed out   and changed to   
,t4 ,both tubes in ,fig4 #f were        
incorrectly   labeled ,g4 ,one of these 
was crossed out and replaced by ,g'4    
,note also that ,figs4 #d1 #e1 #f are   
repeated in the text on   different     
pages2 this feature has been retained4  
,page #aj3 it s already to it is        
already4    ,page #dc3 ,thu if heat     
changed to ,thus if heat4    ,page #de3 
had a diameter of only one square foot  
changed to   had a diameter of only one 
foot4    ,page #dg3 immedate to         
immediate4    ,page #ea3 a a level to a 
level4 ,also1 comma removed from ,a     
gauge1 pipe is inserted4    ,page #ec3  
proportionably to proportionally4       
,page #gi3 ,a paragraph beginning ,he   
was not fourteen contains three   double
 quotation marks2 this is presumably an 
error4 ,possibly there   should be two  
double quotation marks and two single   

quotation   marks4    ,page #hj3 ,s'4   
,gravesande is retained1 although this  
probably   refers to a person known as  
's ,gravesande4    ,page #ajc3 gases n  
general to gases in general4    ,page   
#abb3 comma removed from process may1 be
 continued4    ,page #abc3 two thin     
pipes ,f ,g of tin to two thin pipes ,f1
 ,g   of tin4    ,page #agb3 empyrical  
to empirical4    ,page #ahg1 ,fig4 #cb43
 ,the text refers to end ,i of the      
connecting rod1 but this was labeled ,l 
on the ,figure4 ,this ,l   has been     
crossed out and replaced by ,i4    ,page
 #bhe3 ,in surrounding the boiler with  
iron-conducting   substances1 changed   
iron- to non-4    ,page #cjh3 exeitement
 to excitement4    ,page #cfb3 acomplish
 to accomplish4    ,there were several  
extended quotations1 for example        
beginning on   page #cab1 in which each 
line began with a quotation mark1 with  
ending quotation marks at the end of    
each paragraph4 ,in this   edition1     
these passages have been marked by      

indentation1 and all   but the first and
 last quotation marks from each         
paragraph were   removed4    ,page #cff3
 ,figs4 #ig-ajd appeared originally     
between pages #che   and #cii1 as       
full-page prints4 ,numerically1 however1
 they   belong between ,figs4 #if and   
#aje--therefore between pages   #cff and
 #cfi4 ,therefore1 they have been moved 
to a location   between two paragraphs  
on page #cfg4    ,page #cfh3 rivetted to
 riveted4    ,page #dai3 ,,trevitheck',s
 ,,invention changed to ,,trevethick',s 
,,invention1 in the chapter heading4    
,however1 the references to             
,trevethick occur in a previous chapter1
 around page #cbd4    ,page #dfh3       
,period added to end sentence 444 piston
 is at the   bottom of its stroke4      
,page #dij3 ,period added to end        
sentence 444 therefore one   eighth of  
its capacity4    ,pages #did1 #dig3     
large data tables were split into two   
pieces   each4    ,page #eje3 ,the      
logarithm originally given as log x     

#ahbcdjfhhaic1 where #a represents a    
numeral one with   a horizontal line    
over it1 is herein changed to log x     
#jhbcdjfhhaic - #a1 as that is the      
meaning of this convention4    ,page    
#eac formul are hyberbolic to formul are
 hyperbolic4    ,in the ,appendix1 pp   
#eje-ebb1 mathematical variables such as
   a1 p1 t1 etc4 were originally        
italicized4 ,in these text   file       
versions1 italicized variables have been
 removed from this   section of the     
book4 ,this rule has two unfortunate    
exceptions3   ,e1 ,e1 ,e'1 and ,e' on pp
 #eab-eae are different variables1 and  
have been retained4 ,italics have been  
removed from tables   throughout the    
work4    ,the tables on page #did and   
#dig were divided into two parts1       
better to fit the width constraints of  
this format4 ,most of the   tables will 
not look good unless viewed with a      
monospace font1   such as ,courier ,new 
or ,lucida ,console4