,illustration3 ,pl4 ,,xiii4 ,,american ,,high-,,pressure ,,engine ,,the ,,steam ,,engine ,,familiarly ,,explained ,,and ,,illustrated2 ,,with ,,an ,,historical ,,sketch ,,of ,,its ,,invention ,,and ,,progressive ,,improvement2 ,,its ,,applications ,,to ,,navigation ,,and ,,railways2 ,,with ,,plain ,,maxims ,,for ,,railway ,,speculators4 ,,by ,,the ,,rev4 ,,dionysius ,,lardner1 ,,ll4 ,d41 ,f4 ,r4 ,s41 ,,fellow ,,of ,,the ,,royal ,,society ,,of ,,edinburgh2 ,,of ,,the ,,royal ,,irish ,,academy2 ,,of ,,the ,,royal ,,astronomical ,,society2 ,,of ,,the ,,cambridge ,,philosophical ,,society2 ,,of ,,the ,,statistical ,,society ,,of ,,paris2 ,,of ,,the ,,linn,,an ,,and ,,zoological ,,societies2 ,,of ,,the ,,society ,,for ,,promoting ,,useful ,,arts ,,in ,,scotland1 ,,etc4 ,,with ,,additions ,,and ,,notes1 ,,by ,,james ,,renwick1 ,,ll4 ,d41 ,,professor ,,of ,,natural ,,experimental ,,philosophy ,,and ,,chemistry ,,in ,,columbia ,,college1 ,,new ,,york4 ,,illustrated ,,by ,,engravings ,,and ,,woodcuts4 ,,second ,,american1 ,,from ,,the ,,fifth ,,london1 ,,edition1 ,,considerably ,,enlarged4 ,,philadelphia3 ,e4 ,l4 ,,carey ,a4 ,,hart4 #ahcf ,entered1 according to the ,act of ,congress1 in the year #ahcf1 by ,e4 ,l4 ,,carey ,a4 ,,hart1 in the ,clerk's office of the ,district ,court for the ,eastern ,district of ,pennsylvania4 ,,preface ,,of ,,the ,,american ,,editor4 ,several of the additions1 which were made by the ,editor to the first ,american edition1 have been superseded by the great extension1 which the original has from time to time received from its author4 ,this is more particularly the case1 with the sections which had reference to the character of steam at temperatures other than that of boiling water1 to the use of steam in navigation1 and to its application to locomotion4 ,these sections have of course been omitted4 ,a few new sections1 and several notes have been added1 illustrative of such points as may be most interesting to the ,american reader4 ,,columbia ,,college1 ,new ,york1 ,march1 #ahcf4 ,,preface ,,to ,,the ,,fifth ,,edition4 ,this volume should more properly be called a new work than a new edition of the former one4 ,in fact the book has been almost rewritten4 ,the change which has taken place1 even in the short period which has elapsed since the publication of the first edition1 in the relation of the steam engine to the useful arts1 has been so considerable as to render this inevitable4 ,the great extension of railroads1 and the increasing number of projects which have been brought forward for new lines connecting various points of the kingdom1 as well as the extension of steam navigation1 not only through the seas and channels surrounding and intersecting these islands1 and throughout other parts of ,europe1 but through the larger waters which are interposed between our dominions in the ,east and the countries of ,egypt and ,syria1 have conferred so much interest on the application of steam to transport1 that ,i have thought it adviseable to extend the limits of the present edition considerably beyond those of the last4 ,the chapter on railroads has been enlarged and improved4 ,three chapters have been added4 ,the twelfth chapter contains a view of steam navigation2 the thirteenth contains several important points connected with the economy of steam power1 which1 when this work was first published1 would not have offered sufficient interest to justify their admission into a popular treatise2 and the fourteenth chapter contains a series of compendious maxims1 for the instruction and guidance of persons desirous of making investments or speculating in railway property4 ,london1 ,december1 #ahce4 ,,preface ,,to ,,the ,,first ,,edition4 ,there are two classes of persons whose attention may be attracted by a treatise on such a subject as the ,steam ,engine4 ,one consists of those who1 by trade or profession1 are interested in mechanical science1 and who therefore seek information on the subject of which it treats1 as a matter of necessity1 and a wish to acquire it in a manner and to an extent which may be practically available in their avocations4 ,the other and more numerous class is that part of the public in general1 who1 impelled by choice rather than necessity1 think the interest of the subject itself1 and the pleasure derivable from the instances of ingenuity which it unfolds1 motives sufficiently strong to induce them to undertake the study of it4 ,without leaving the former class altogether out of view1 it is for the use of the latter principally that the following lectures are designed4 ,to this class of readers the ,steam ,engine is a subject which1 if properly treated of1 must present strong and peculiar attractions4 ,whether we consider the history of its invention as to time and place1 the effects which it has produced1 or the means by which it has caused these effects1 we find everything to gratify our national pride1 stimulate our curiosity1 excite our wonder1 and command our admiration4 ,the invention and progressive improvement of this extraordinary machine1 is the work of our own time and our own country2 it has been produced and brought to perfection almost within the last century1 and is the exclusive offspring of ,british genius fostered and supported by ,british capital4 ,to enumerate the effects of this invention1 would be to count every comfort and 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 never could have hoped to share them4 ,nor are its effects confined to ,england alone3 they extend over the whole civilized world2 and the savage tribes of ,america1 ,asia1 and ,africa1 must ere long feel the benefits1 remote or immediate1 of this all-powerful agent4 ,if the effect which this machine has had on commerce and the wealth of nations raise our astonishment1 the means by which this effect has been produced will not less excite our admiration4 ,the history of the ,steam ,engine presents a series of contrivances1 which1 for exquisite and refined ingenuity1 stand without a parallel in the annals of human invention4 ,these admirable contrivances1 unlike other results of scientific investigation1 have also this peculiarity1 that to understand and appreciate their excellence requires little previous or subsidiary knowledge4 ,a simple and clear explanation1 divested as far as possible of technicalities1 and assisted by well selected diagrams1 is all that is necessary to render the principles of the construction and operation of the ,steam ,engine intelligible to a person of plain understanding and moderate information4 ,the purpose for which this volume is designed1 as already explained1 has rendered necessary the omission of many particulars which1 however interesting and instructive to the practical mechanic or professional engineer1 would have little attraction for the general reader4 ,our readers require to be informed of the general principles of the construction and operation of ,steam ,engines1 rather than of their practical details4 ,for the same reasons we have confined ourselves to the more striking and important circumstances in the history of the invention and progressive improvement of this machine1 excluding many petty disputes which arose from time to time respecting the rights of invention1 the interest of which is buried in the graves of their respective claimants4 ,in the descriptive parts of the work we have been governed by the same considerations4 ,the application of the force of steam to mechanical purposes has been proposed on various occasions1 in various countries1 and under a great variety of forms4 ,the list of ,british patents alone would furnish an author of common industry and application with matter to swell his book to many times the bulk of this volume4 ,by far the greater number of these projects have1 however1 proved abortive4 ,descriptions of such unsuccessful1 though frequently ingenious machines1 we have thought it adviseable to exclude from our pages1 as not possessing sufficient interest for the readers to whose use this volume is dedicated4 ,we have therefore strictly confined our descriptions either to those ,steam ,engines which have come into general use1 or to those which form an important link in the chain of invention4 ,december #bf1 #ahbg4 ,,contents4 ,,chapter ,i4 ,,preliminary ,,matter4 ,motion the ,agent in ,manufactures4 -- ,animal ,power4 -- ,power depending on physical ,phenomena4 -- ,purpose of a ,machine4 -- ,prime ,mover4 -- ,mechanical qualities of the ,atmosphere4 -- ,its ,weight4 -- ,the ,barometer4 -- ,fluid ,pressure4 -- ,pressure of rarefied ,air4 -- ,elasticity of ,air4 -- ,bellows4 -- ,effects of ,heat4 -- ,thermometer4 -- ,method of making one4 -- ,freezing and ,boiling ,points4 -- ,degrees4 -- ,dilatation of bodies4 -- ,liquefaction and ,solidification4 -- ,vaporisation and ,condensation4 -- ,latent ,heat of ,steam4 -- ,expansion of ,water in ,evaporating4 -- ,effects of ,repulsion and ,cohesion4 -- ,effect of ,pressure upon ,boiling ,point4 -- ,formation of a ,vacuum by ,condensation4 ,page #ag ,,chapter ,,ii4 ,,first ,,steps ,,in ,,the ,,invention4 ,futility of early ,claims4 -- ,watt the real ,inventor4 -- ,hero of ,alexandria4 -- ,blasco ,garay4 -- ,solomon ,de ,caus4 -- ,giovanni ,branca4 -- ,marquis of ,worcester4 -- ,sir ,samuel ,morland4 -- ,denis ,papin4 -- ,thomas ,savery4 #ch ,,chapter ,,iii4 ,,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 ,jet4 -- ,potter's discovery of the ,method of working the ,valves4 #ea ,,chapter ,,iv4 ,,engine ,,of ,,james ,,watt4 ,advantages of the ,atmospheric ,engine over that of ,captain ,savery4 -- ,it contained no new ,principle4 -- ,papin's ,engine4 -- ,james ,watt4 -- ,particulars of his ,life4 -- ,his first conceptions of the ,means of economising ,heat4 -- ,principle of his projected ,improvements4 #fi ,,chapter ,v4 ,,watt',s ,,single-,,acting ,,steam ,,engine4 ,expansive ,principle applied4 -- ,failure of ,roebuck1 and partnership with ,bolton4 -- ,patent extended to #ahjj4 -- ,counter4 -- ,difficulties in getting the ,engines into ,use4 #hj ,,chapter ,,vi4 ,,double-,,acting ,,steam ,,engine4 ,the ,single-acting ,engine unfit to impel ,machinery4 -- ,various ,contrivances to adapt it to this ,purpose4 -- ,double-,cylinder4 -- ,double-acting ,cylinder4 -- ,various modes of connecting the ,piston with the ,beam4 -- ,rack and ,sector4 -- ,double ,chain4 -- ,parallel ,motion4 -- ,crank4 -- ,sun and ,planet ,motion4 -- ,fly ,wheel4 -- ,governor4 #ia ,,chapter ,,vii4 ,,double-,,acting ,,steam ,,engine1 continued4 ,on the ,valves of the ,double-acting ,steam ,engine4 -- ,original ,valves4 -- ,spindle ,valves4 -- ,sliding ,valve4 -- ,d ,valve4 -- ,four-,way ,cock4 #ajh ,,chapter ,,viii4 ,,boiler ,,and ,,its ,,appendages4 ,level ,gauges4 -- ,feeding apparatus4 -- ,steam ,gauge4 -- ,barometer ,gauge4 -- ,safety ,valves4 -- ,self-regulating ,damper4 -- ,edelcrantz's ,valve4 -- ,furnace4 -- ,smoke-consuming ,furnace4 -- ,brunton's ,self-regulating ,furnace4 -- ,oldham's ,modification4 #aag ,,chapter ,,ix4 ,,double-,,cylinder ,,engines4 ,hornblower's ,engine4 -- ,woolf's ,engine4 -- ,cartwright's ,engine4 #acd ,,chapter ,x4 ,,locomotive ,,engines ,,on ,,railways4 ,high-pressure ,engines4 -- ,leupold's ,engine4 -- ,trevithick and ,vivian4 -- ,effects of ,improvement in ,locomotion4 -- ,historical ,account of the ,locomotive ,engine4 -- ,blenkinsop's ,patent4 -- ,chapman's ,improvement4 -- ,walking ,engine4 -- ,stephenson's ,first ,engines4 -- ,his ,improvements4 -- ,liverpool and ,manchester ,railway ,company4 -- ,their ,preliminary ,proceedings4 -- ,the ,great ,competition of #ahbi4 -- ,the ,rocket4 -- ,the ,sanspareil4 -- ,the ,novelty4 -- ,qualities of the ,rocket4 -- ,successive ,improvements4 -- ,experiments4 -- ,defects of the ,present ,engines4 -- ,inclined ,planes4 -- ,methods of surmounting them4 -- ,circumstances of the ,manchester ,railway ,company4 -- ,probable ,improvements in ,locomotives4 -- ,their capabilities with respect to speed4 -- ,probable ,effects of the ,projected ,railroads4 -- ,steam ,power compared with ,horse ,power4 -- ,railroads compared with ,canals4 #ade ,,chapter ,,xi4 ,,locomotive ,,engines ,,on ,,turnpike ,,roads4 ,railway and ,turnpike ,roads compared4 -- ,mr4 ,gurney's inventions4 -- ,his ,locomotive ,steam ,engine4 -- ,its performances4 -- ,prejudices and errors4 -- ,committee of the ,house of ,commons4 -- ,convenience and safety of ,steam ,carriages4 -- ,hancock's ,steam ,carriage4 -- ,mr4 ,n4 ,ogle4 -- ,trevithick's invention4 -- ,proceedings against ,steam ,carriages4 -- ,turnpike ,bills4 -- ,steam ,carriage between ,gloucester and ,cheltenham4 -- ,its discontinuance4 -- ,report of the ,committee of the ,commons4 -- ,present ,state and ,prospects of ,steam ,carriages4 #bac ,,chapter ,,xii4 ,,steam ,,navigation4 ,propulsion by paddle-wheels4 -- ,manner of driving them4 -- ,marine ,engine4 -- ,its form and arrangement4 -- ,proportion of its cylinder4 -- ,injury to boilers by deposites and incrustation4 -- ,not effectually removed by blowing out4 -- ,mr4 ,samuel ,hall's condenser4 -- ,its advantages4 -- ,originally suggested by ,watt4 -- ,hall's steam saver4 -- ,howard's vapour engine4 -- ,morgan's paddle-wheels4 -- ,limits of steam navigation4 -- ,proportion of tonnage to power4 -- ,average speed4 -- ,consumption of fuel4 -- ,iron ,steamers4 -- ,american steam raft4 -- ,steam navigation to ,india4 -- ,by ,egypt and the ,red ,sea to ,bombay4 -- ,by same route to ,calcutta4 -- ,by ,syria and the ,euphrates to ,bombay4 -- ,steam communication with the ,united ,states from the west coast of ,ireland to ,st4 ,johns1 ,halifax1 and ,new ,york4 #bda ,,chapter ,,xiii4 ,,general ,,economy ,,of ,,steam ,,power4 ,mechanical efficacy of steam -- proportional to the quantity of water evaporated1 and to the fuel consumed4 -- ,independent of the pressure4 -- ,its mechanical efficacy by condensation alone4 -- ,by condensation and expansion combined -- by direct pressure and expansion -- by direct pressure and condensation -- by direct pressure1 condensation1 and expansion4 -- ,the power of engines4 -- ,the duty of engines4 -- ,meaning of horse power4 -- ,to compute the power of an engine4 -- ,of the power of boilers4 -- ,the structure of the grate-bars4 -- ,quantity of water and steam room4 -- ,fire surface and flue surface4 -- ,dimensions of steam pipes4 -- ,velocity of piston4 -- ,economy of fuel4 -- ,cornish duty reports4 #bgg ,,chapter ,,xiv4 ,plain ,rules for ,railway ,speculators4 #cjg ,,the ,,steam ,,engine ,,explained ,,and ,,illustrated4 ,,chapter ,i4 ,,preliminary ,,matter4 ,motion the ,agent in ,manufactures4 -- ,animal ,power4 -- ,power depending on ,physical ,phenomena4 -- ,purpose of a ,machine4 -- ,prime ,mover4 -- ,mechanical qualities of the ,atmosphere4 -- ,its ,weight4 -- ,the ,barometer4 -- ,fluid ,pressure4 -- ,pressure of ,rarefied ,air4 -- ,elasticity of ,air4 -- ,bellows4 -- ,effects of ,heat4 -- ,thermometer4 -- ,method of making one4 -- ,freezing and ,boiling ,points4 -- ,degrees4 -- ,dilatation of ,bodies4 -- ,liquefaction and ,solidification4 -- ,vaporisation and ,condensation4 -- ,latent heat of ,steam4 -- ,expansion of ,water in ,evaporating4 -- ,effects of ,repulsion and ,cohesion4 -- ,effect of ,pressure upon ,boiling-,point4 -- ,formation of a ,vacuum by ,condensation4 7#a47 ,of the various productions designed by nature to supply the wants of man1 there are few which are suited to his necessities in the state in which the earth spontaneously offers them3 if we except atmospheric air1 we shall scarcely find another instance3 even water1 in most cases1 requires to be transported from its streams or reservoirs2 and food itself1 in almost every form1 requires culture and preparation4 ,but if1 from the mere necessities of physical existence in a primitive state1 we rise to the demands of civil and social life1--to say nothing of luxuries and refinements1--we shall find that everything which contributes to our convenience1 or ministers to our pleasure1 requires a previous and extensive expenditure of labour4 ,in most cases1 the objects of our enjoyment derive all their excellences1 not from any qualities originally inherent in the natural substances out of which they are formed1 but from those qualities which have been bestowed upon them by the application of human labour and human skill4 ,in all those changes to which the raw productions of the earth are submitted in order to adapt them to our wants1 one of the principal agents is motion4 ,thus1 for example1 in the preparation of clothing for our bodies1 the various processes necessary for the culture of the cotton require the application of moving power1 first to the soil1 and subsequently to the plant from which the raw material is obtained3 the wool must afterwards be picked and cleansed1 twisted into threads1 and woven into cloth4 ,in all these processes motion is the agent3 to cleanse the wool and arrange the fibres of the cotton1 the wool must be beaten1 teased1 carded1 and submitted to other processes1 by which all the foreign and coarser matter may be separated1 and the fibres or threads arranged evenly1 side by side4 ,the threads must then receive a rotatory motion1 by which they may be twisted into the required form2 and finally peculiar motions must be given to them in order to produce among them that arrangement which characterises the cloth which it is our final purpose to produce4 ,in a rude state of society1 the motions required in the infant manufactures are communicated by the immediate application of the hand4 ,observation and reflection1 however1 soon suggest more easy and effectual means of attaining these ends3 the strength of animals is first resorted to for the relief of human labour4 ,further reflection and inquiry suggest still better expedients4 ,when we look around us in the natural world1 we perceive inanimate matter undergoing various effects in which motion plays a conspicuous part3 we see the falls of cataracts1 the currents of rivers1 the elevation and depression of the waters of the ocean1 the currents of the atmosphere2 and the question instantly arises1 whether1 without sharing our own means of subsistence with the animals whose force we use1 we may not equally1 or more effectually1 derive the powers required from these various phenomena of nature8 ,a difficulty1 however1 immediately presents itself3 we require motion of a particular kind2 but wind will not blow1 nor water fall as we please1 nor as suits our peculiar wants1 but according to the fixed laws of nature4 ,we want an upward motion2 water falls downwards3 we want a circular motion2 wind blows in a straight line4 ,the motions1 therefore1 which are in actual existence must be modified to suit our purposes3 the means whereby these modifications are produced1 are called machines4 ,a machine1 therefore1 is an instrument interposed between some natural force or motion1 and the object to which force or motion is desired to be transmitted4 ,the construction of the machine is such as to modify the natural motion which is impressed upon it1 so that it may transmit to the object to be moved that peculiar species of motion which it is required to have4 ,to give a very obvious example1 let us suppose that a circular or rotatory motion is required to be produced1 and that the only natural source of motion at our command is a perpendicular fall of water3 a wheel is provided1 placed upon the axle destined to receive the rotatory motion2 this wheel is furnished with cavities in its rim2 the water is conducted into the cavities near the top of the wheel on one side2 and being caught by these1 its weight bears down that side of the wheel1 the cavities on the opposite side being empty and in an inverted position4 ,as the wheel turns1 the cavities on the descending side discharge their contents as they arrive near the lowest point1 and ascend empty on the other side4 ,thus a load of water is continually pressing down one side of the wheel1 from which the other side is free1 and a continued motion of rotation is produced4 ,in every machine1 therefore1 there are three objects demanding attention3--first1 ,the power which imparts motion to it1 this is called the prime mover2 secondly1 ,the nature of the machine itself2 and thirdly1 ,the object to which the motion is to be conveyed4 ,in the steam engine the first mover arises from certain phenomena which are exhibited when heat is applied to liquids2 but in the details of the machine and in its application there are several physical effects brought into play1 which it is necessary perfectly to understand before the nature of the machine or its mode of operation can be rendered intelligible4 ,we propose therefore to devote the present chapter to the explanation and illustration of these phenomena4 7#b47 ,the physical effects most intimately connected with the operations of steam engines are some of the mechanical properties of atmospheric air4 ,the atmosphere is the thin transparent fluid in which we live and move1 and which1 by respiration1 supports animal life4 ,this fluid is apparently so light and attenuated1 that it might be at first doubted whether it be really a body at all4 ,it may therefore excite some surprise when we assert1 not only that it is a body1 but also that it is one of considerable weight4 ,we shall be able to prove that it presses on every square inch#a of surface with a weight of about #aelb4 avoirdupois4 ,footnote #a3 ,as we shall have frequent occasion to mention this magnitude1 it would be well that the reader should be familiar with it4 ,it is a square1 each side of which is an inch4 ,such as ,a ,b ,c ,d1 ,fig4 #a4 7#c47 ,take a glass tube ,a ,b 7fig4 #b47 more than #cb inches long1 open at one end ,a1 and closed at the other end ,b1 and let it be filled with mercury 7quicksilver47 ,let a glass vessel or cistern ,c1 containing a quantity of mercury1 be also provided4 ,applying the finger at ,a 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 #c47 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 open 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 about #cj inches above the level ,c of the mercury in the cistern4 7#d47 ,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 ,c as the weight of the atmosphere is able to support4 ,if we suppose the section of the tube to be equal to the magnitude of a square inch1 the weight of the column of mercury in the tube above the level ,c will be exactly equal to the weight of the atmosphere on each square inch of the surface ,c4 ,the height of the level ,d above ,c being about #cj inches1 and a column of mercury two inches in height1 and having a base of a square inch1 weighing about one pound avoirdupois1 it follows that the weight with which the atmosphere presses on each square inch of a level surface is about #aelb4 avoirdupois4 ,an apparatus thus constructed1 and furnished with a scale to indicate the height of the level ,d above the level ,c1 is the common barometer4 ,the difference of these levels is subject to a small variation1 which indicates a corresponding change in the atmospheric pressure4 ,but we take #cj inches as a standard or average4 7#e47 ,it is an established property of fluids that they press equally in all directions2 and air1 like every other fluid1 participates in this quality4 ,hence it follows1 that since the downward pressure or weight of the atmosphere is about #aelb4 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 ,let four glass tubes ,a1 ,b1 ,c1 ,d1 7fig4 #d47 be constructed of sufficient length1 closed at one end ,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 inverted so as to have their closed ends up as here represented4 ,it will be found that the mercury will be sustained in all1#b and that the difference of the levels in all will be the same4 ,thus the mercury is sustained in ,a by the upward pressure of the atmosphere1 in ,b by its horizontal or lateral pressure1 in ,c by its downward pressure1 and in ,d by its oblique pressure2 and as the difference of the levels is the same in all1 these pressures are exactly equal4 ,footnote #b3 ,this experiment with the tube ,a requires to be very carefully executed1 and the tube should be one of small bore4 7#f47 ,in the experiment described in 7#c47 the space ,b ,d 7fig4 #c47 at the top of the tube from which the mercury has fallen is perfectly void and empty1 containing neither air nor any other fluid3 it is called therefore a vacuum4 ,if1 however1 a small quantity of air be introduced into that space1 it will immediately begin to exert a pressure on ,d1 which will cause the surface ,d to descend1 and it will continue to descend until the column of mercury ,c ,d is so far diminished that the weight of the atmosphere is sufficient to sustain it1 as well as the pressure exerted upon it by the air in the space ,b ,d4 ,the quantity of mercury which falls from the tube in this case is necessarily an equivalent for the pressure of the air introduced1 so that the pressure of this air may be exactly ascertained by allowing about one pound per square inch for every two inches of mercury which has fallen from the tube4 ,the pressure of the air or any other fluid above the mercury in the tube1 may at once be ascertained by comparing the height of the mercury in the tube with the height of the barometer2 the difference of the heights will always determine the pressure on the surface of the mercury in the tube4 ,this principle will be found of some importance in considering the action of the modern steam engines4 ,the air which we have supposed to be introduced into the upper part of the tube1 presses on the surface of the mercury with a force much greater than its weight4 ,for example1 if the space ,b ,d 7fig4 #c47 were filled with atmospheric air in its ordinary state1 it would exert a pressure on the surface ,d equal to the whole pressure of the atmosphere1 although its weight might not amount to a single grain4 ,the property in virtue of which the air exerts this pressure is its elasticity1 and this force is diminished in precisely the proportion in which the space which the air occupies is increased4 ,thus it is known that atmospheric air in its ordinary state exerts a pressure on the surface of any vessel in which it is confined1 amounting to about #aelb4 on every square inch4 ,if the capacity of the vessel which contains it be doubled1 it immediately expands and fills the double space1 but in doing so it loses half its elastic force1 and presses only with the force of #g-a_/blb4 on every square inch4 ,if the capacity of the vessel had been enlarged five times1 the air would still have expanded so as to fill it1 but would exert only a fifth part of its first pressure1 or #clb4 on every square inch4 ,this property of losing its elastic force as its volume or bulk is increased1 is not peculiar to air4 ,it is common to all elastic fluids1 and we accordingly find it in steam2 and it is absolutely necessary to take account of it in estimating the effects of that agent4 7#g47 ,there are numerous instances of the effects of these properties of atmospheric air which continually fall under our observation4 ,if the nozzle and valve-hole of a pair of bellows be stopped1 it will require a very considerable force to separate the boards4 ,this effect is produced by the diminished elastic force of the air remaining between the boards upon the least increase of the space within the bellows1 while the atmosphere presses1 with undiminished force1 on the external surfaces of the boards4 ,if the boards be separated so as to double the space within1 the elastic force of the included air will be about #g-a_/blb4 on every square inch1 while the pressure on the external surfaces will be #aelb4 on every square inch2 consequently1 it will require as great a force to sustain the boards in such a position1 as it would to separate them if each board were forced against the other1 with a pressure of #g-a_/blb4 per square inch on their external surfaces4 ,when boys apply a piece of moistened leather to a stone1 so as to exclude the air from between them1 the stone1 though it be of considerable weight1 may be lifted by a string attached to the leather3 the cause of which is the atmospheric pressure1 which keeps the leather and the stone in close contact4 7#h47 ,the next class of physical effects which it is necessary to explain1 are those which are produced when heat is imparted or abstracted from bodies4 ,in general1 when heat is imparted to a body1 an enlargement of bulk will be the immediate consequence1 and at the same time the body will become warmer to the touch4 ,these two effects of expansion and increase of warmth going on always together1 the one has been taken as a measure of the other2 and upon this principle the common thermometer is constructed4 ,that instrument consists of a tube of glass1 terminated in a bulb1 the magnitude of which is considerable1 compared with the bore of the tube4 ,the bulb and part of the tube are filled with mercury1 or some other liquid4 ,when the bulb is exposed to any source of heat1 the mercury contained in it1 being warmed or increased in temperature1 is at the same time increased in bulk1 or expanded or dilated1 as it is called4 ,the bulb not having sufficient capacity to contain the increased bulk of mercury1 the liquid is forced up in the tube1 and the quantity of expansion is determined by observing the ascent of the column in the tube4 ,an instrument of this kind1 exposed to heat or cold1 will fluctuate accordingly1 the mercury rising as the heat to which it is exposed is increased1 and falling by exposure to cold4 ,in order1 however1 to render it an accurate measure of temperature1 it is necessary to connect with it a scale by which the elevation or depression of the mercury in the tube may be measured4 ,such a scale is constructed for thermometers in this country in the following manner3--,let us suppose the instrument immersed in a vessel of melting ice3 the column of mercury in the tube will be observed to fall to a certain point1 and there maintain its position unaltered3 let that point be marked upon the tube4 ,let the instrument be now transferred to a vessel of boiling water at a time when the barometer stands at the altitude of #cj inches3 the mercury in the tube will be observed to rise until it attain a certain elevation1 and will there maintain its position4 ,it will be found1 that though the water continue to be exposed to the action of the fire1 and continue to boil1 the mercury in the tube will not continue to rise1 but will maintain a fixed position3 let the point to which the mercury has risen1 in this case1 be likewise marked upon the tube4 ,the two points1 thus determined1 are called the freezing and the boiling points4 ,if the distance upon the tube between these two points be divided into #ahj equal parts1 each of these parts is called a degree2 and if this division be continued1 by taking equal divisions below the freezing point1 until #cb divisions be taken1 the last division is called the zero1 or nought of the thermometer4 ,it is the point to which the mercury would fall1 if the thermometer were immersed in a certain mixture of snow and salt4 ,when thermometers were first invented1 this point was taken as the zero point1 from an erroneous supposition that the temperature of such a mixture was the lowest possible temperature4 ,the degrees upon the instrument thus divided are counted upwards from the zero1 and are expressed1 like the degrees of a circle1 by placing a small over the number4 ,thus it will be perceived that the freezing point is #cb of our thermometer1 and the boiling-point will be found by adding #ahj to #cb2 it is therefore #bab4 ,the temperature of a body is that elevation to which the thermometer would rise when the mercury enclosed in it would acquire the same temperature4 ,thus1 if we should immerse the thermometer1 and should find that the mercury would rise to the division marked #ajj1 we should then affirm that the temperature of the water was #ajj4 7#i47 ,the dilatation which attends an increase of temperature is one of the most universal effects of heat4 ,it varies1 however1 in different bodies3 it is least in solid bodies2 greater in liquids2 and greatest of all in bodies in the aeriform state4 ,again1 different solids are differently susceptible of this expansion4 ,metals are the most susceptible of it2 but metals of different kinds are differently expansible4 ,as an increase of temperature causes an increase of bulk1 so a diminution of temperature causes a corresponding diminution of bulk1 and the same body always has the same bulk at the same temperature4 ,a flaccid bladder1 containing a small quantity of air1 will1 when heated1 become quite distended2 but it will again resume its flaccid appearance when cold4 ,a corked bottle of fermented liquor1 placed before the fire1 will burst by the effort of the air contained in it to expand when heated4 ,let the tube ,a ,b 7fig4 #e47 open at both ends1 have one end inserted in the neck of a vessel ,c ,d1 containing a coloured liquid1 with common air above it2 and let the tube be fixed so as to be air-tight in the neck3 upon heating the vessel1 the warm air inclosed in the vessel ,c ,d above the liquid will begin to expand1 and will press upon the surface of the liquid1 so as to force it up in the tube ,a ,b4 ,in bridges and other structures1 formed of iron1 mechanical provisions are introduced to prevent the fracture or strain which would take place by the expansion and contraction which the metal must undergo by the changes of temperature at different seasons of the year1 and even at different hours of the day4 ,thus all nature1 animate and inanimate1 organized and unorganized1 may be considered to be incessantly breathing heat2 at one moment drawing in that principle through all its dimensions1 and at another moment dismissing it4 7#aj47 ,change of bulk1 however1 is not the only nor the most striking effect which attends the increase or diminution of the quantity of heat in a body4 ,in some cases1 a total change of form and of mechanical qualities is effected by it4 ,if heat be imparted in sufficient quantity to a solid body1 that body1 after a certain time1 will be converted into a liquid4 ,and again1 if heat be imparted in sufficient quantity to this liquid1 it will cease to exist in the liquid state1 and pass into the form of vapour4 ,by the abstraction of heat1 a series of changes will be produced in the opposite order4 ,if from the vapour produced in this case1 a sufficient quantity of heat be taken1 it will return to the liquid state2 and if again from this liquid heat be further abstracted1 it will at length resume its original solid state4 ,the transmission of a body from the solid to the liquid state1 by the application of heat1 is called fusion or liquefaction1 and the body is said to be fused1 liquefied1 or melted4 ,the reciprocal transmission from the liquid to the solid state1 is called congelation1 or solidification2 and the liquid is said to be congealed or solidified4 ,the transmission of a body from the liquid to the vaporous or aeriform state1 is called vaporization1 and the liquid is said to be vaporized or evaporated4 ,the reciprocal transmission of vapour to the liquid state is called condensation1 and the vapour is said to be condensed4 ,we shall now examine more minutely the circumstances which attend these remarkable and important changes in the state of body4 7#aa47 ,let us suppose that a thermometer is imbedded in any solid body2 for example1 in a mass of sulphur2 and that it stands at the ordinary temperature of #fj degrees3 let the sulphur be placed in a vessel1 and exposed to the action of fire4 ,the thermometer will now be observed gradually to rise1 and it will continue to rise until it exhibit the temperature of #bah4 ,here1 however1 notwithstanding the continued action of the fire upon the sulphur1 the thermometer will become stationary2 proving1 that notwithstanding the supply of heat received from the fire1 the sulphur has ceased to become hotter4 ,at the moment that the thermometer attains this stationary point1 it will be observed that the sulphur has commenced the process of fusion2 and this process will be continued1 the thermometer being stationary1 until the whole mass has been liquefied4 ,the moment the liquefaction is complete1 the thermometer will be observed again to rise1 and it will continue to rise until it attain the elevation of #egj4 ,here1 however1 it will once more become stationary2 and notwithstanding the heat supplied to the sulphur by the fire1 the liquid will cease to become hotter3 when this happens1 the sulphur will boil2 and if it continue to be exposed to the fire a sufficient length of time1 it will be found that its quantity will gradually diminish1 until at length it will all disappear from the vessel which contained it4 ,the sulphur will1 in fact1 be converted into vapour4 ,from this process we infer1 that all the heat supplied during the processes of liquefaction and vaporization is consumed in effecting these changes in the state of the body2 and that under such circumstances1 it does not increase the temperature of the body on which the change is produced4 ,these effects are general3 all solid bodies would pass into the liquid state by a sufficient application of heat2 and all liquid bodies would pass into the vaporous state by the same means4 ,in all cases the thermometer would be stationary during these changes1 and consequently the temperature of the body1 in those periods1 would be maintained unaltered4 7#ab47 ,solids differ from one another in the temperatures at which they become liquid4 ,these temperatures are called their melting points4 ,thus the melting point of ice is #cb2 that of lead #fab2 that of gold #ebcg4c ,the heat which is supplied to a body during the processes of fusion or vaporization1 and which does not affect the thermometer1 or increase the temperature of the body fused or vaporized1 is said to become latent4 ,it can be proved to exist in the body fused or vaporized1 and may even be taken from that body4 ,in parting with it the body does not fall in temperature1 and consequently the loss of this heat is not indicated by the thermometer any more than its reception4 ,the term latent heat is merely intended to express this fact1 of the thermometer being insensible to the presence or absence of this portion of heat1 and is not intended to express any theoretical notions concerning it4 ,footnote #c3 ,temperatures above #fej cannot be measured by the mercurial thermometer4 ,they can be inferred only with probability by pyrometers4 7#ac47 ,in explaining the construction and operation of the steam engine1 although it is necessary occasionally to refer to the effects of heat upon bodies in general1 yet the body1 which is by far the most important to be attended to1 so far as the effects of heat upon it are concerned1 is water4 ,this body is observed to exist in the three different states1 the solid1 the liquid1 and the vaporous1 according to the varying temperature to which it is exposed4 ,all the circumstances which have been explained in reference to metals1 and the substance sulphur in particular1 will1 mutatis mutandis1 be applicable to water4 ,but in order perfectly to comprehend the properties of the steam engine1 it is necessary to render a more rigorous and exact account of these phenomena1 so far as they apply to the changes produced upon water by the effects of heat4 ,let us suppose a mass of ice immersed in the mixture of snow and salt which determines the zero point of the thermometer3 this mass1 if allowed to continue a sufficient length of time submerged in the mixture1 will necessarily acquire its temperature1 and the thermometer immersed in it will stand at zero4 ,let the ice be now withdrawn from the mixture1 still keeping the thermometer immersed in it1 and let it be exposed to the atmosphere at the ordinary temperature1 say #fj4 ,at first the thermometer will be observed gradually and continuously to rise until it attain the elevation of #cb2 it will then become stationary1 and the ice will begin to melt3 the thermometer will continue standing at #cb until the ice shall be completely liquefied4 ,the liquid ice and the thermometer being contained in the same vessel1 it will be found1 when the liquefaction is completed1 that the thermometer will again begin to rise1 and will continue to rise until it attain the temperature of the atmosphere1 viz4 #fj4 ,hitherto the ice or water has received a supply of heat from the surrounding air2 but now an equilibrium of temperature having been established1 no further supply of heat can be received2 and if we would investigate the further effects of increased heat1 it will be necessary to expose the liquid to fire1 or some other source of heat4 ,but previous to this1 let us observe the time which the thermometer remains stationary during the liquefaction of the ice3 if noted by a chronometer1 it would be found to be a hundred and forty times the time during which the water in the liquid state was elevated one degree2 the inference from which is1 that in order to convert the solid ice into liquid water1 it was necessary to receive from the surrounding atmosphere one hundred and forty times as much heat as would elevate the liquid water one degree in temperature2 or1 in other words1 that to liquefy a given weight of ice requires as much heat as would raise the same weight of water #adj in temperature3 or from #cb to #agb4 ,the latent heat of water acquired in liquefaction is therefore #adj4 7#ad47 ,let us now suppose that1 a spirit lamp being applied to the water already raised to #fj1 the effects of a further supply of heat be observed3 the thermometer will continue to rise until it attain the elevation of #bab1 the barometer being supposed to stand at #cj inches4 ,the thermometer having attained this elevation will cease to rise2 the water will therefore cease to become hotter1 and at the same time bubbles of steam will be observed to be formed at the bottom of the vessel containing the water1 near the flame of the spirit lamp4 ,these bubbles will rise through the water1 and escape at the surface1 exhibiting the phenomena of ebullition1 and the water will undergo the process of boiling4 ,during this process1 the thermometer will constantly be maintained at the same elevation of #bab2 but if the time be noted1 it will be found that the water will be altogether evaporated1 if the same source of heat be continued to be applied to it six and a half times as long as was necessary to raise it from the freezing to the boiling-point4 ,thus1 if the application of the lamp to water at #cb1 be capable of raising that water to #bab in one hour1 the same lamp will require to be applied to the boiling water for six hours and a half1 in order to convert the whole of it into steam4 ,now if the steam into which it is thus converted were carefully preserved in a receiver1 maintained at the temperature of #bab1 this steam would be found to have that temperature1 and not a greater one2 but it would be found to fill a space about #agjj times greater than the space it occupied in the liquid state1 and it would possess an elastic force equal to the pressure of the atmosphere under which it was boiled2 that is to say1 it would press the sides of the vessel which contained it with a pressure equivalent to that of a column of mercury of #cj inches in height2 or what is the same thing1 at the rate of about #aelb4 on every square inch of surface4 7#ae47 ,as the quantity of heat expended in raising the water from #cb to #bab1 is #ahj2 and as the quantity of heat necessary to convert the same water into steam is six and a half times this quantity1 it follows that the quantity of heat requisite for converting a given weight of water into steam1 will be found by multiplying #ahj by #e-a_/b4 ,the product of these numbers being #iij1 it follows1 that1 to convert a given weight of water at #bab into steam of the same temperature1 under the pressure of the atmosphere1 when the barometer stands at #cj inches1 requires as much heat as would be necessary to raise the same water #iij higher in temperature4 ,the heat1 not being sensible to the thermometer1 is latent heat2 and accordingly it may be stated1 that the latent heat1 necessary to convert water into steam under this pressure is1 in round numbers1 #ajjj4 7#af47 ,all the effects of heat which we have just described may be satisfactorily accounted for1 by supposing that the principle of heat imparts to the constituent atoms of bodies a force1 by virtue of which they acquire a tendency to repel each other4 ,but in conjunction with this1 it is necessary to notice another force1 which is known to exist in nature3 there is observable among the corpuscles of bodies a force1 in virtue of which they have a tendency to cohere1 and collect themselves together in solid concrete masses3 this force is called the attraction of cohesion4 ,these two forces--the natural cohesion of the particles1 and the repulsive energy introduced by heat--are directly opposed to one another1 and the state of the body will be decided by the predominance of the one or the other1 or their mutual equilibrium4 ,if the natural cohesion of the constituent particles of the body considerably predominate over the repulsive energy introduced by the heat1 then the cohesion will take effect2 the particles of the body will coalesce1 the mass will become rigid and solid1 and the particles will hold together in one invariable mass1 so that they cannot drop asunder by the mere effect of their weight4 ,in such cases1 a more or less considerable force must be applied1 in order to break the body1 or to tear its parts asunder4 ,such is the quality which characterises the state1 which in mechanics is called the state of solidity4 ,if the repulsive energy introduced by the application of heat be equal1 or nearly equal1 to the natural cohesion with which the particles of the body are endued1 then the predominance of the cohesive force may be insufficient to resist the tendency which the particles may have to drop asunder by their weight4 ,in such a case1 the constituent particles of the body cannot cohere in a solid mass1 but will separate by their weight1 fall asunder1 and drop into the various corners1 and adapt themselves to the shape of any vessel in which the body may be contained4 ,in fact1 the body will take the liquid form4 ,in this state1 however1 it does not follow that the cohesive principle will be altogether inoperative3 it may1 and does1 in some cases1 exist in a perceptible degree1 though insufficient to resist the separate gravitation of the particles4 ,the tendency which particles of liquids have1 in some cases1 to collect in globules1 plainly indicates the predominance of the cohesive principle3 drops of water collected upon the window pane2 drops of rain condensed in the atmosphere2 the tear which trickles on the cheek2 drops of mercury1 which glide over any flat surface1 and which it is difficult to subdivide or scatter into smaller parts2 are all obvious indications of the predominance of the cohesive principle in liquids4 ,by the due application of heat1 even this small degree of cohesion may be conquered1 and a preponderance of the opposite principle of repulsion may be created4 ,but another physical influence here interposes its aid1 and conspires with cohesion in resisting the transmission of the body from the liquid to the vaporous state3 this force is no other than the pressure of the atmosphere1 already explained4 ,this pressure has an obvious tendency to restrain the particles of the liquid1 to press them together1 and to resist their separation4 ,the repulsive principle of the heat introduced must therefore not only neutralize the cohesion1 but must also impart to the atoms of the liquid a sufficient elasticity or repulsive energy to enable them to fly asunder1 and assume the vaporous form in spite of this atmospheric resistance4 ,now it is clear1 that if this atmospheric resistance be subject to any variation in its intensity1 from causes whether natural or artificial1 the repulsive energy necessary to be introduced by the heat1 will vary proportionally3 if the atmospheric pressure be diminished1 then less heat will be necessary to vaporize the liquid4 ,if1 on the other hand1 this pressure be increased1 a greater quantity of heat will be required to impart the necessary elasticity4 7#ag47 ,from this reasoning we must expect that any cause1 whether natural or artificial1 which diminishes the atmospheric pressure upon the surface of a liquid1 will cause that liquid to boil at a lower temperature3 and on the other hand1 any cause which may increase the atmospheric pressure upon the liquid1 will render it necessary to raise it to a higher temperature before it can boil4 ,these inferences we accordingly find supported by experience4 ,under a pressure of #aelb4 on the square inch1 i4 e4 when the barometer is at #cj inches1 water boils at the temperature of #bab of the common thermometer4 ,but if water at a lower temperature1 suppose #ahj1 be placed under the receiver of an air-pump1 and1 by the process of exhaustion the atmospheric pressure be removed1 or very much diminished1 the water will boil1 although its temperature still remain at #ahj1 as may be indicated by a thermometer placed in it4 ,on the other hand1 if a thermometer be inserted air-tight in the lid of a close digester containing water with common atmospheric air above it1 when the vessel is heated the air acquires an increased elasticity2 and being confined by the cover1 presses1 with increased force1 on the surface of the water4 ,by observing the thermometer while the vessel is exposed to the action of heat1 it will be seen to rise considerably above #bab1 suppose to #bcj1 and would continue so to rise until the strength of the vessel could no longer resist the pressure within it4 ,the temperature at which water boils is commonly said to be #bab1 which is called the boiling-point of the thermometer2 but1 strictly speaking1 this is only true when the barometer stands at #cj inches4 ,if it be lower1 water will boil at a lower temperature1 because the atmospheric pressure is less2 and if it be higher1 as at #ca1 water will not boil until it receives a higher temperature1 the pressure being greater4 ,according as the cohesive forces of the particles of liquids are more or less active1 they boil at greater or less temperatures4 ,in general the lighter liquids1 such as alcohol and ether1 boil at lower temperatures4 ,these fluids1 in fact1 would boil by merely removing the atmospheric pressure1 as may be proved by placing them under the receiver of an air-pump1 and withdrawing the air4 ,from this we may conclude that these and similar substances would never exist in the liquid state at all1 but for the atmospheric pressure4 7#ah47 ,the elasticity of vapour raised from a boiling liquid1 is equal to the pressure under which it is produced4 ,thus1 steam raised from water at #bab1 and1 therefore1 under a pressure of #aelb4 on the square inch1 is endued with an elastic force which would exert a pressure on the sides of any vessel which confines it1 also equal to #aelb4 on the square inch4 ,since an increased pressure infers an increased temperature in boiling1 it follows1 that where steam of a higher pressure than the atmosphere is required1 it is necessary that the water should be boiled at a higher temperature4 7#ai47 ,we have already stated that there is a certain point at which the temperature of a liquid will cease to rise1 and that all the heat communicated to it beyond this is consumed in the formation of vapour4 ,it has been ascertained1 that when water boils at #bab1 under a pressure equal to #cj inches of mercury1 a cubic inch of water forms a cubic foot#d of steam1 the elastic force of which is equal to the atmospheric pressure1 and the temperature of which is #bab4 ,since there are #agbh cubic inches in a cubic foot1 it follows1 that when water at this temperature passes from the liquid to the vaporous state1 it is dilated into #agbh times its bulk4 ,footnote #d3 ,the terms cubic inch and cubic foot are easily explained4 ,a common die1 used in games of chance1 has the figure which is called a cube4 ,it is a solid having twelve straight edges equal to one another4 ,it has six sides1 each of which is square1 and which are also equal to one another4 ,if its edges be each one inch in length1 it is called a cubic inch1 if one foot1 a cubic foot1 if one yard1 a cubic yard1 c4 ,this figure is represented in perspective1 in fig4 #f4 7#bj47 ,we have seen that about #ajjj degrees of heat must be communicated to any given quantity of water at #bab1 in order to convert it into steam of the same temperature1 and possessing a pressure amounting to about #ae pounds on the square inch1 and that such steam will occupy above #agjj times the bulk of the water from which it was raised4 ,now we might anticipate1 that by abstracting the heat thus employed in converting the liquid into vapour1 a series of changes would be produced exactly the reverse of those already described2 and such is found to be actually the case4 ,let us suppose a vessel1 the capacity of which is #agbh cubic inches1 to be filled with steam1 of the temperature of #bab1 and exerting a pressure of #ae pounds on the square inch2 let #e-a_/b cubic inches of water1 at the temperature of #cb1 be injected into this vessel1 immediately the steam will impart the heat1 which it has absorbed in the process of vaporisation to the water thus injected1 and will itself resume the liquid form4 ,it will shrink into its primitive dimensions of one cubic inch1 and the heat which it will dismiss will be sufficient to raise the #e-a_/b cubic inches of injected water to the temperature of #bab4 ,the contents of the vessel will thus be #f-a_/b cubic inches of water at the temperature of #bab4 ,one of these cubic inches is in fact the steam which previously filled the vessel reconverted into water1 the other #e-a_/b are the injected water which has been raised from the temperature of #cb to #bab by the heat which has been dismissed by the steam in resuming the liquid state4 ,it will be observed that in this transmission no temperature is lost1 since the cubic inch of water into which the steam is converted has the same temperature as the steam had before the cold water was injected4 ,these consequences are in perfect accordance with the results already obtained from observing the time necessary to convert a given quantity of water into steam by the application of heat4 ,from the present result it follows1 that in the reduction of a given quantity of steam to water it parts with as much heat as is sufficient to raise #e-a_/b cubic inches from #cb to #bab1 that is1 #e-a_/b times #ahj or #iij4 7#ba47 ,there is an effect produced in this process to which it is material that we should attend4 ,the steam which filled the space of #agbh cubic inches shrinks when reconverted into water into the dimensions of #a cubic inch4 ,it therefore leaves #agbg cubic inches of the vessel it contains unoccupied4 ,by this property steam is rendered instrumental in the formation of a vacuum4 ,by allowing steam to circulate through a vessel1 the air may be expelled from it1 and its place filled by steam4 ,if the vessel be then closed and cooled the steam will be reduced to water1 and1 falling in drops on the bottom and sides of the vessel1 the space which it filled will become a vacuum4 ,this may be easily established by experiment4 ,let a long glass tube be provided with a hollow ball at one end1 and having the other end open4#e ,let a small quantity of spirits be poured in at the open end1 and placing the glass ball over the flame of a lamp1 let the spirits be boiled4 ,after some time the steam will be observed to issue copiously from the open end of the tube which is presented upwards4 ,when this takes place1 let the tube be inverted1 and its open end plunged in a basin of cold water4 ,the heat being thus removed1 the cool air will reconvert the steam in the tube into liquid1 and a vacuum will be produced1 into which the pressure of the atmosphere on the surface of the water in the basin will force the water through the tube1 and it will rush up with considerable force1 and fill the glass ball4 ,footnote #e3 ,a common glass flask with a long neck will answer the purpose4 ,in this experiment it is better to use spirits than water1 because they boil at a lower heat1 and expose the glass to less liability to break1 and also the tube may more easily be handled4 ,,chapter ,,ii4 ,,first ,,steps ,,in ,,the ,,invention4 ,futility of early claims4 -- ,watt1 the real ,inventor4 -- ,hero of ,alexandria4 -- ,blasco ,garay4 -- ,solomon de ,caus4 -- ,giovanni ,branca4 -- ,marquis of ,worcester4 -- ,sir ,samuel ,morland4 -- ,denis ,papin4 -- ,thomas ,savery4 7#bb47 ,in the history of the progress of the useful arts and manufactures1 there is perhaps no example of any invention the credit of which has been so keenly contested as that of the steam engine4 ,claims to it have been advanced by different nations1 and by different individuals of the same nation4 ,the partisans of the competitors for this honour have argued their pretensions1 and pressed their claims1 with a zeal which has occasionally outstripped the bounds of discretion2 and the contest has not unfrequently been tinged with prejudices1 both national and personal1 and marked with a degree of asperity quite unworthy of so noble a cause1 and altogether beneath the dignity of science4 ,the efficacy of the steam engine considered as a mechanical agent depends1 first1 on the several physical properties from which it derives its operation1 and1 secondly1 on the various pieces of mechanism and details of mechanical arrangement by which these properties are rendered practically available4 ,if the merit of the invention must be ascribed to the discoverer and contriver of these1 then the contest will be easily decided1 because it will be obvious that the prize is not due to any one individual1 but must be distributed in different proportions among several4 ,if1 however1 he is best entitled to the credit of the invention1 who has by the powers of his mechanical genius imparted to the machine that form and those qualities from which it has received its present extensive utility1 and by which it has become an agent of transcendent power1 which has spread its beneficial effects throughout every part of the civilized globe1 then the universal consent of mankind will1 as it were by acclamation1 award the prize 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 have rendered it a topic of interest to every individual for whom the progress of human civilization has any attractions4 ,before the era marked 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 greatly inferior in importance to most other mechanical contrivances used as prime movers4 ,but from that time it is scarcely necessary here to state that it became a subject not of ,british interest only1 but one with which the progress of the human race became intimately mixed up4 ,since1 however1 the question of the progressive developement of those physical principles on which the steam engine depends1 and of their mechanical application1 has of late years received some importance1 as well from the interest which the public manifest towards them as from the rank of the writers who have investigated them1 we have thought it expedient to state briefly1 but we trust with candour and fairness1 the successive steps which appear to have led to this invention4 ,the engine as it exists at present is not1 strictly speaking1 the exclusive invention of any one individual3 it is the result of a series of discoveries and inventions which have for the last two centuries been accumulating4 ,when we attempt to trace back its history1 and to determine its first inventor1 we experience the same difficulty as is felt in tracing the head of a great river3 as we ascend its course1 we are embarrassed by the variety of its tributary streams1 and find it impossible to decide which of those channels into which it ramifies ought to be regarded as the principal stream2 and it terminates at length in a number of threads of water1 each in itself so insignificant as to be unworthy of being regarded as the source of the majestic object which has excited the inquiry4 ,from a very early period the effects of heat upon liquids1 and more especially the production of steam or vapour1 was regarded as a probable source of mechanical power1 and numerous speculators directed their attention to it1 and exerted their inventive faculties to derive from it an effective mover4 ,it was not1 however1 until the commencement of the eighteenth century that any invention was produced which was practically applied1 even unsuccessfully4 ,all the attempts previous to that time were either suggestions which were limited to paper or experiments confined to models2 or1 if they exceeded this1 they never outlived a single trial on a larger scale4 ,nevertheless many of these suggestions and experiments being recorded and accessible to future inquirers doubtless offered useful hints and some practical aid to those more successful investigators who subsequently contrived engines in such forms as to be practically available on a large scale for mechanical purposes4 ,it is right and just1 therefore--mere suggestions and abortive experiments though they may have been--to record them1 that each inventor and discoverer may receive the just credit due to his share in this splendid mechanical invention4 ,we shall then in the present chapter briefly enumerate1 in chronological order1 the successive steps so far as they have come to our knowledge4 ,,hero ,,of ,,alexandria1 #abj ,b4 ,c4 ,illustration3 ,fig4 #a4 7#bc47 ,in a work entitled ,spiritalia seu ,pneumatica1 one of the numerous works of this philosopher which has remained to us1 is contained a description of a machine moved by vapour of water4 ,a hollow sphere1 of which ,a ,b represents a section1 is supported on two pivots at ,a and ,b1 which are the extremities of tubes ,a ,c ,d and ,b ,e ,f1 which pass into a boiler where steam is generated4 ,this steam flows through small apertures at the extremities ,a and ,b1 and fills the hollow sphere4 ,one or more horizontal arms ,k ,g1 ,i ,h1 project from this sphere1 and are likewise filled with steam1 but are closed at their extremities4 ,conceive a small hole made near the extremity ,g1 but at one side of one of the tubes2 the steam confined in the tube and globe would immediately rush from the hole with a force proportionate to its pressure within the globe4 ,on the common principle of mechanics a re-action would be produced1 and the tube would recoil in the same manner as a gun when discharged4 ,the tubular arm ,k ,g being thus pressed in a direction opposed to that in which the steam issues1 the sphere would revolve accordingly1 and would continue to revolve so long as the steam would continue to flow from the aperture4 ,the force of recoil would be increased by making a similar aperture in two or more arms1 care being taken that all the apertures should be placed so as to cause the sphere to revolve in the same direction4 ,this motion being once produced might be transmitted by ordinary mechanical contrivance to any machinery which its power might be adequate to move4 ,this method of using steam is not adopted in any part or any form of the modern steam engine4 ,,blasco ,,de ,,garay1 ,a4 ,d4 #aedc4 7#bd47 ,in the year #ahbf there appeared in ,zach's ,correspondence a communication from ,thomas ,gonsalez1 ,director of the ,royal ,archives of ,simancas1 giving an account of an experiment reported to have been made in the year #aedc by order of ,charles ,v4 in the port of ,barcelona4 ,blasco de ,garay1 a sea captain1 had contrived a machine by which he proposed to propel vessels without oars or sails4 ,garay concealed altogether the nature of the machine which he used3 all that was seen during the experiment was that it consisted of a great boiler for water1 and that wheels were kept in revolution at each side of the vessel4 ,the experiment was made upon a vessel called the ,trinity1 of #bjj tons burden1 and was witnessed by several official personages1 whose presence on the occasion was commanded by the king4 ,one of the witnesses reported that it was capable of moving the vessel at the rate of two leagues in three hours1 that the machine was too complicated and expensive1 and was exposed to the danger of explosion4 ,the other witnesses1 however1 reported more favourably4 ,the result of the experiment was thought to be favourable3 the inventor was promoted1 and received a pecuniary reward1 besides having all his expenses defrayed4 ,from the circumstance of the nature of the impelling power having been concealed by the inventor it is impossible to say in what this machine consisted1 or even whether steam exerted any agency whatever in it1 or1 if it did1 whether it might not have been1 as was most probably the case1 a reproduction of ,hero's contrivance4 ,it is rather unfavourable to the claims advanced by the advocates of the ,spaniard1 that although it is admitted that he was rewarded and promoted in consequence of the experiment1 yet it does not appear that it was again tried1 much less brought into practical use4 ,,solomon ,,de ,,caus1 #afae4 ,illustration3 ,fig4 #b4 7#be47 ,a work entitled ,les ,raisons des ,forces ,mouvantes1 avec diverses ,machines tant utiles que plaisantes1 published at ,frankfort in #afae1 by ,solomon de ,caus1 a native of ,france1 contains the following theorem3-- ,water will mount by the help of fire higher than its level1 which is explained and proved in the following terms3-- ,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 ,a1 well soldered in every part1 to which is attached a tube and stopcock 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 stopcock ,d1 and opening the stopcock in the vertical tube ,b ,c1 let the ball be placed upon a fire1 the heat acting upon the said ball will cause the water to rise in the tube ,b ,c4 ,such is the description of the apparatus of ,de ,caus as given by himself2 and on this has been founded a claim to the invention of the steam engine4 ,it will be observed1 that neither in the original theorem nor in the description of the machine which accompanies it1 is the word steam anywhere used4 ,now it was well known1 by all conversant in physics1 long before the date of the publication containing this description1 that atmospheric air when heated acquires an increased elastic force4 ,as the experiment is described1 the other part of the ball ,a is filled with atmospheric air2 the heat of the fire acting upon the air through the external surface of the ball1 and likewise transmitted through the water1 would of course raise the temperature of the air contained in the vessel1 would thereby increase its elasticity1 and would cause the water to rise in the tube ,b ,c1 upon a physical principle altogether independent of the qualities of steam4 ,the effect produced1 therefore1 is just what might have been expected by any one acquainted with the common properties of air1 though entirely ignorant of those of steam2 and1 in point of fact1 the pressure of the air is as much concerned in this case in raising the water as the pressure of the steam4 ,this objection1 however1 is combated by another theorem contained in the same work1 in which ,de ,caus speaks of the strength of the vapour produced by the action of the fire1 which causes water to mount2 which vapour will issue from the stopcock with great violence after the water has been expelled4 ,if ,de ,caus be admitted to have understood the elastic property of the vapour of water1 and to have attributed the ascent of the water in the tube ,c ,b to the pressure of that vapour upon the surface of the water confined in the copper ball1 it must be admitted that he suggested one of the ways of using the power of steam as a mechanical agent4 ,in the modern steam engine this pressure is not now used against a liquid surface1 but against the solid surface of a piston4 ,this1 however1 should not take from ,de ,caus whatever credit be due to the suggestion of the physical property in question4 ,,giovanni ,,branca1 #afbi4 7#bf47 ,in a work published at ,rome in #afbi1 entitled ,le ,machine del ,g4 ,branca1 is contained a description of a machine for propelling a wheel by a blast of steam4 ,this contrivance 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 of a pipe4 ,being directed against the vanes1 it causes the wheel to revolve1 and this motion may be imparted by the usual mechanical contrivances to any machinery which it was intended to move4 ,this contrivance has no analogy whatever to any part of the modern steam engines in any of their various forms4 ,,edward ,,somerset1 ,,marquis ,,of ,,worcester1 #affc4 7#bg47 ,of all the individuals to whom the invention of the steam engine has been ascribed the most celebrated was the ,marquis of ,worcester1 the author of a work entitled ,the ,scantling of ,one ,hundred ,inventions1 but which is more commonly known by the title ,a ,century of ,inventions4 ,it is to him that by far the greater number of writers and inquirers on this subject ascribe the merit of the discovery of the invention4 ,this contrivance is described in the following terms in the sixty-eighth invention in the work above named3-- ,i have invented an admirable and forcible way to drive up water by fire2 not by drawing or sucking it upwards1 for that must be1 as the philosopher terms it1 infra spram 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-hole 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 ,these experiments must have been made before the year #affc1 in which the ,century of ,inventions was published4 ,the description of the machine here given1 like other descriptions in the same work1 was only intended to express the effects produced1 and the physical principle on which their production depends4 ,it is1 however1 sufficiently explicit to enable any one conversant with the subsequent contrivance of ,savery1 to perceive that ,lord ,worcester must have contrived a machine containing all that part of ,savery's engine in which the direct force of steam is employed4 ,as in the above description1 the separate boiler or generator of steam is distinctly mentioned2 that the steam from this is conducted into another vessel containing the cold water to be raised2 that this water is raised by the pressure of steam acting upon its surface2 that when one vessel of water has thus been discharged1 the steam acts upon the water contained in another vessel1 while the first is being replenished2 and that a continued upward current of water is maintained by causing the steam to act alternately upon two vessels1 employing the interval to fill one while the water is discharged from the other4 ,on comparing this with the contrivance previously suggested by ,de ,caus1 it will be observed1 that even if ,de ,caus knew the physical agent by which the water was driven upwards in the apparatus contrived by him1 still it was only a means of causing a vessel of boiling water to empty itself2 and before a repetition of the process could be obtained1 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 and 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 ,,sir ,,samuel ,,morland1 #afhc4 7#bh47 ,it appears1 by a ,,ms4 in the ,harleian ,collection in the ,british ,museum1 that a mode of applying steam to raise water was proposed to ,louis ,,xiv4 by ,sir ,samuel ,morland4 ,it contains1 however1 nothing more than might have been collected from ,lord ,worcester's description1 and is only curious1 because of the knowledge the writer appears to have had of the expansion which water undergoes in passing into steam4 ,the following is extracted from the ,,ms43 ,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 horses17 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' ,,denis ,,papin1 #afie4 7#bi47 ,denis ,papin1 a native of ,blois in ,france1 and professor of mathematics at ,marbourg1 had been engaged about this period in the contrivance of a machine in which the atmospheric pressure should be made available as a mechanical agent by creating a partial vacuum in a cylinder under a piston4 ,his first attempts were directed to the production of this vacuum by mechanical means1 having proposed to apply a water-wheel to work an air-pump1 and so maintain the degree of rarefaction required4 ,this1 however1 would eventually have amounted to nothing more than a mode of transmitting the power of the water-wheel to another engine1 since the vacuum produced in this way could only give back the power exerted by the water-wheel diminished by the friction of the pumps2 still this would attain the end first proposed by ,papin1 which was merely to transmit the force of the stream of a river1 or a fall of water1 to a distant point1 by partially exhausted pipes or tubes4 ,he next1 however1 attempted to produce a partial vacuum by the explosion of gunpowder2 but this was found to be insufficient1 since so much air remained in the cylinder under the piston1 that at least half the power due to a vacuum would have been lost4 ,i have1 therefore1 proceeds ,papin1 attempted to attain this end by another method4 ,since water being converted into steam by heat acquires the property of elasticity like air1 and may afterwards be recondensed so perfectly by cold that there will no longer remain the appearance of elasticity in it1 ,i have thought that it would not be difficult to construct machines in which1 by means of a moderate heat1 and at a small expense1 water would produce that perfect vacuum which has been vainly sought by means of gunpowder4 ,papin accordingly constructed the model of a machine1 consisting of a small pump1 in which was placed a solid piston1 and in the bottom of the cylinder under the piston was contained 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 cylinder steam was produced1 the elastic force of which raised the piston to the top of the cylinder3 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 generally that the same end may be attained by various forms of machines easy to be imagined4#f ,footnote #f3 ,recueil de diverses pices touchant quelques nouvelles machines1 p4 #ch4 ,,thomas ,,savery1 #afih4 7#cj47 ,the discovery of the method of producing a vacuum by the condensation of steam was reproduced before #afhh1 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 ,worcester1 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 in #afie1 and states that his discovery of the condensing principle arises from the following circumstance3-- ,having drunk a flask of ,florence at a tavern 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 boil 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 flask1 and the moment he plunged its mouth in the water1 the liquid immediately rushed up into the flask and filled it4 7#ba47 ,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 steam and then condensing the same steam1 the atmospheric pressure would force the water from the well into the pump-barrel and into any vessel connected with it1 provided that vessel were not more than about #cd feet above the elevation of the water in the well4 ,he perceived1 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 serve by its subsequent condensation to repeat the vacuum 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 ,,chapter ,,iii4 ,,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 ,jet4 -- ,potter's ,discovery of the ,method of ,working the ,valves4 7#ca47 ,the steam engine contrived by ,savery1 like every other which has since been constructed1 consists of two parts essentially distinct4 ,the first is that which is employed to generate the steam1 which is called the boiler1 and the second1 that in which the steam is applied as a moving power4 ,the former apparatus in ,savery's engine consists of two strong boilers1 sections of which are represented at ,d and ,e in fig4 #g42 ,d the greater boiler1 and ,e the less4 ,the tubes ,t and ,t communicate with the working apparatus which we shall presently describe4 ,a thin plate of metal ,r is applied closely to the top of the greater boiler ,d 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 described17 are alternately opened and closed1 the lever which effects this being constantly wrought by the hand of the attendant4 ,two gauge-pipes are represented at ,g1 ,g1 the use of which is to determine the depth of water in the boiler4 ,one ,g has its lower aperture a little above the proper depth1 and the other ,g 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 water 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 them1 there is too much water in the boiler1 since the mouth of ,g is below its level4 ,if steam issue from both there is too little water in the boiler1 since the mouth of ,g is above its level4 ,but if steam issue from ,g and water from ,g 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 ,g should be at a level of a little less than one-third of the whole depth1 and the mouth of ,g at a level a 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 extends which is continued to a cistern ,c 7fig4 #h47 and a cock is placed at ,m 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 ,g1 ,g being all closed4 ,the fire being lighted beneath ,d and the water boiled1 steam is produced and is transmitted through one or other of the tubes ,t ,t1 to the working apparatus4 ,when evaporation has reduced the water in ,d below the level of ,g it will be necessary to replenish the boiler ,d4 ,this is effected thus4 ,a fire being lighted beneath the feeding boiler ,e1 steam is produced in it above the surface of the water1 which having no escape 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 #h47 through the pipe ,f 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 #h47 be two steam vessels communicating by the tubes ,t ,t 7marked by the same letters in fig4 #g47 with the greater boiler ,d4 ,let ,s be a pipe1 called the suction pipe1 descending into the well or reservoir from which the water is to be raised1 and communicating with each of the steam vessels through tubes ,d ,d by valves ,a ,a which open upwards4 ,let ,f be a pipe continued from the level of the engine of whatever higher level it is intended to elevate the water4 ,the steam vessels ,v ,v communicate with the force-pipe ,f by valves ,b ,b which open upward1 through the tubes ,e ,e4 ,over the steam vessels and on the force-pipe is placed a small cistern ,c 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 #g47 by the cock ,m4#g ,footnote #g3 ,this pipe in fig4 #i4 is represented as proceeding from the force-pipe above the cistern ,c4 ,the communication of the pipes ,t ,t with the boiler can be opened and closed1 alternately1 by the regulator ,r1 7fig4 #g47 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 condensed 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 ,v that it will cease to condense it4 ,mixed with the heated air 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 ,v 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 well or reservoir1 will open ,a1 so that a part of this air will rush in 7#f47 and occupy the vessel ,v4 ,the air in the suction pipe ,s1 being thus allowed an increased space1 will be proportionably diminished in its elastic force 7#f471 and its pressure will no longer balance that of the atmosphere acting on the external surface ,l#h 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 pressure on ,l 7#g474 ,when this has taken place1 the water will cease to ascend4 ,footnote #h3 ,not in the diagram4 ,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 on ,l 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 ,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 first 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 on the surface of the water in ,v1 so as to form a surface as hot as boiling water4#i ,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 open and the water1 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 ,footnote #i3 ,hot water being lighter than cold1 it floats on the surface4 ,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 on ,l will force the water1 and fill the vessel ,v4 ,the condensing pipe being then closed 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 which as far as we have described1 would have remained filled with common atmospheric air1 the pressure of which1 on the valve ,a1 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 notice1 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 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 this opens the communication between ,t and the boiler2 for the sliding plate ,r 7fig4 #g47 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 and1 while the air in ,s is rushing up through ,a into ,v followed by the water raised in ,s by the atmospheric pressure on ,l1 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 #g47 from the tube ,t to ,t2 at the same time the condensing pipe is removed from over ,v 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 ,v 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 ,v into which water is raised by the atmospheric pressure at ,l4 ,thus each of the vessels ,v ,v is alternately filled from ,s 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 ,s 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 ,v which is done by the lever placed upon it4 ,again 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#aj ,a perspective view of this engine is presented in fig4 #i4 ,the different parts already described will easily be recognised1 being marked with the same letters as in figs4 #f1 #g4 ,footnote #aj3 ,in the diagrams used for explaining the principles and operations of machines1 ,i have found it contribute much to the clearness of the description to adopt an arrangement of parts somewhat different from that of the real machine4 ,when once the nature and principles on which the machine acts are well understood1 the reader will find no difficulty in transferring every part to its proper place1 which is represented in the perspective drawings4 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 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 stated1 that the pressure of the atmosphere amounts to about #ae lbs4 7#c47 on every square inch4 ,now1 a column of water1 whose base is one square inch1 and whose height is #cd feet1 weighs about #aelbs4 ,if we suppose that a perfect vacuum were produced in the steam-vessels ,v ,v 7fig4 #h47 by condensation1 the atmospheric pressure on ,l would fail to force up the water1 if the height of the top of these vessels exceeded #cd feet4 ,it is plain1 therefore1 that the engine cannot be more than #cd 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 temperature 7#ag472 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 it was found that the engine could never be placed with practical advantage at a greater height than #bf 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 #aelbs4 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 #cd feet in height2 and if steam of triple the force be used1 it will raise a column of #fh feet high1 which1 added to #bf feet raised by the atmosphere1 gives a total lift of #id 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 of the pressure is balanced by the pressure of the atmosphere on the external surface of the vessels2 but an effective pressure of #cjlbs4 per square inch still remains1 tending to burst the vessels4 ,it was found1 that the apparatus could not be constructed to bear more than this with safety2 and1 therefore1 in practice the lift of such an engine was limited to about #ij 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 #ij feet of the depth2 so that the water raised by one through the first #ij feet should be received in a reservoir1 from which it was to be elevated the next #ij 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 enhanced 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 cool 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 begin to act until a quantity of hot water1 formed by condensed steam1 is collected on the surface of the cold water which fills the vessel ,v ,v4 ,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 vessel 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 water in ,f1 and in producing a vacuum1 bears a very small proportion indeed to what is consumed in heating the apparatus after condensation4 ,illustration3 ,pl4 ,i4 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 #fh feet of water4 ,steam is therefore required of a pressure of #delbs4 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 #bab 7#ag471 even so high as #bfg2 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 ,besides the drainage of mines1 ,savery proposed to apply his steam engine to a variety of other purposes2 such as supplying cities with water1 forming ornamental waterworks in pleasure grounds1 turning mills1 c4 ,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 #h hours a day1 while the engine works for #bd 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 great work of drainage1 from the causes which have been just mentioned and the increasing necessity for effecting this object arising from the circumstance of the large property in mines1 which became every year unproductive by it1 stimulated the ingenuity of mechanics to contrive some means of rendering those powers of steam exhibited in ,savery's engine practically available4 ,among others1 ,thomas ,newcomen1 a blacksmith of ,dartmouth1 and ,john ,cawley1 a plumber of the same place1 turned their attention to this inquiry4 ,newcomen appears to have 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 this was by connecting the end of a pump rod ,d 7fig4 #aj471 by a chain1 with the arch-head ,a of a 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 #ae lbs4 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 neutralize the downward pressure1 the piston will be in a state of indifference as to 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 c4 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 ,illustration3 ,pl4 ,,ii4 ,,savery',s ,,steam ,,engine4 ,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 a 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 #ae times as many pounds as there are square inches in the section of the piston4#aa ,thus1 if the base of the piston were #ajj square inches1 a pressure equal to #aejjlbs4 would be obtained4 ,footnote #aa3 ,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 ,thus if there be #ab inches in the diameter1 this multiplied by itself gives #add1 which divided by #ad gives #aj-d_/ad1 which multiplied by #aa gives #aae1 neglecting fractions4 ,there are1 therefore1 #aae square inches in a circle whose diameter is #ab inches4 7#ch47 ,in order to accomplish this design1 two things were necessary3 #a4 ,to make a speedy and effectual vacuum below the piston in the descent2 and #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 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-pipes ,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 ,the great steam-tube is represented at ,s1 which conducts steam from the boiler to the cylinder2 and a feeding pipe ,t 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 water 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 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 this 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 diffusion 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#ab ,into this space cold water is allowed to flow from a cock ,m placed over it1 which is supplied by a pipe from the cistern ,n4 ,this cistern is supplied with water by a pump ,o1 which is worked by the engine itself1 from the beam above it4 ,footnote #ab3 ,the external cylinder is not represented in the diagram4 ,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 immediately 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 it has 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 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 in the bottom of the cylinder1 and resist the descent of the piston4 ,it is1 therefore1 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 effusion 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 ,h furnished with a cock ,q into the bottom of the cylinder1 so that on turning the cock 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 a jet formed a very important improvement in the engine1 and is the method 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 working the weight of the pump-rod ,d 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 in and is first condensed by the cold cylinder4 ,after a short time the cylinder acquires the temperature of the steam1 which then 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#ac7 the steam and air rush in a constant stream 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 ,footnote #ac3 ,also called the snifting valve1 from the peculiar noise made by the air and steam escaping from 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 ,h1#ad 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 regulator ,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 cylinder through the tube ,y1 containing a valve which opens outwards1 7called the eduction valve17 which leads to the hot cistern ,l1 into which this water is therefore discharged4 ,footnote #ad3 ,also called the injection valve4 ,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 produced as before1 and so the process is continued4 ,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 ,from the imperfect attention which even an assiduous attendant could give to the management of these valves1 the performance of the engines was very irregular1 and the waste of fuel very great1 until a boy named ,humphrey ,potter contrived means of making the engine work its own valves4 ,this contrivance1 although made with no other design than the indulgence of an idle disposition1 nevertheless constituted a most important step in the progressive improvement of the steam-engine2 for by its means1 not only the irregularity arising from the negligence of attendants was avoided1 but the speed of the engine was doubled4 ,potter attached strings to the levers which worked the valves1 and carrying these strings to the working beam1 fastened them upon it in such a manner that as the beam ascended and descended1 it pulled the strings so as to open and close the proper valves with the most perfect regularity and certainty4 ,this contrivance was afterwards much improved by an engineer named ,beighton1 who attached to the working beam a straight beam called a plug frame1 carrying pins which1 in the ascent and descent of the beam1 struck the levers attached to the valves1 and opened and closed them exactly at the proper moment4 ,the engine thus improved required no other attendance except to feed the boiler occasionally by the cock ,t1 and to attend the furnace4 ,,chap4 ,,iv4 ,,engine ,,of ,,james ,,watt4 ,advantages of the ,atmospheric ,engine over that of ,captain ,savery4 -- ,it contained no new ,principle4 -- ,papin's ,engine4 -- ,james ,watt4 -- ,particulars of his ,life4 -- ,his first conceptions of the means of ,economising ,heat4 -- ,principle of his projected ,improvements4 7#dc47 ,considered practically1 the engine described in the last chapter possessed considerable advantages over that of ,savery2 and even at the present day this machine is not unfrequently used in districts where fuel is very abundant and cheap1 the first cost being considerably less than that of a modern engine4 ,the low pressure of the steam necessary to work it rendered the use of the atmospheric engine perfectly safe2 there being only a bursting pressure of about #alb4 per inch1 while in ,savery's there was a bursting pressure amounting to #cjlbs4 ,the temperature of the steam not exceeding #baf1 did not weaken or destroy the materials2 while ,savery's engines required steam raised from water at #bfg1 which in a short time rendered the engine unable to sustain the pressure4 ,the power of ,savery's engines was also very limited1 both as to the quantity of water raised1 and the height to which it was elevated 7#cd474 ,on the other hand1 the atmospheric engine had no other limit than the dimensions of the piston4 ,in estimating the power of these engines1 however1 we cannot allow the full atmospheric pressure as an effective force4 ,the condensing water being mixed with the condensed steam1 forms a quantity of hot water in the bottom of the cylinder1 which1 not being submitted to the atmospheric pressure 7#ag471 produces a vapour which resists the descent of the piston4 ,in practice we find that an allowance of at least #clbs4 per square inch should be made for the resistance of this vapour1 and #alb4 per square inch for friction1 c42 so that the effective force will be found by subtracting these #dlbs4 per square inch from the atmospheric pressure2 which1 if estimated at #aelbs41 leaves an effective working power of about #aalbs4 per square inch4 ,this1 however1 is rather above what is commonly obtained4 ,another advantage which this engine has over those of ,savery1 is the facility with which it might be applied to drive machinery by means of the working beam4 ,the merit of this engine as an invention1 must be ascribed principally to its mechanism and combinations4 ,we find in it no new principle2 the agency of atmospheric pressure acting against a vacuum1 or a partial vacuum1 was long known4 ,the formation of a vacuum by the condensation of steam had been suggested by ,papin and ,savery1 and carried into practical effect by the latter4 ,the mechanical power derivable from the direct pressure of the elastic force of steam was distinctly pointed out by ,lord ,worcester1 and even prior to his time2 the boiler1 gauge-pipes1 and regulator of the atmospheric engine1 were evidently borrowed from ,savery's engine4 ,the idea of working a piston in a cylinder by the atmospheric pressure against a vacuum below1 was suggested by ,otto ,guericke1 an ingenious ,german philosopher1 the inventor of the air-pump1 and subsequently by ,papin2 and the use of a working beam could not have been unknown4 ,nevertheless1 considerable credit must be acknowledged to be due to ,newcomen for the judicious combination of those scattered principles4 ,the mechanism contrived by him1 says ,tredgold1 produces all the difference between an efficient and inefficient engine1 and should be more highly valued than the fortuitous discovery of a new principle4 ,the rapid condensation of steam by the injection of water1 the method of clearing the cylinder of air and water after the stroke1 are two contrivances not before in use1 and which are quite essential to the effective operation of the engine3 these are wholly due to ,newcomen and his associates4 7#dd47 ,the patent of ,newcomen was granted in #agje2 and in #agjg1 ,papin published a work1 entitled ,a ,new ,method of raising ,water by ,fire1 in which a steam engine is described1 which would scarcely merit notice here but for the contests which have arisen upon the claims of different nations for a share in the invention of the steam engine4 ,the publication of this work of ,papin was nine years after ,savery's patent1 with which he acknowledges himself acquainted1 and two years after ,newcomen's4 ,the following is a description of ,papin's steam engine3-- ,an oval boiler1 ,a 7fig4 #aa471 is filled to about two thirds of its entire capacity with water1 through a valve ,b in the top1 which opens upwards1 and is kept down by a lever carrying a sliding weight4 ,the pressure on the valve is regulated by moving the weight to or from ,b1 like the common steelyard4 ,this boiler communicates with a cylinder1 ,c1 by a syphon tube furnished with a stopcock at ,d4 ,the cylinder ,c has a valve ,f in the top1 closed by a lever and weight similar to ,b1 and a tube with a stopcock ,g opening into the atmosphere4 ,in this cylinder is placed a hollow copper piston ,h1 which moves freely in it1 and floats upon the water4 ,another tube forms a communication between the bottom of this cylinder and the bottom of a close cylindrical vessel ,i1 called the air-vessel4 ,in this tube is a valve at ,k1 opening upwards2 also a pipe terminated in a funnel1 and furnished with a valve ,l1 which opens downwards4 ,from the lower part of the air-vessel a tube proceeds1 furnished also with a stopcock ,m1 which is continued to whatever height the water is to be raised4 ,water being poured into the funnel1 passes through the valve ,l1 which opens downwards2 and filling the tube1 ascends into the cylinder ,c1 carrying the floating piston ,h on its surface1 and maintains the same level in ,c which it has in the funnel4 ,in this manner the cylinder ,c may be filled to the level of the top of the funnel4 ,in this process the cock ,g should be left open1 to allow the air in the cylinder to escape as the water rises4 ,let us now suppose that1 a fire being placed beneath the boiler1 steam is being produced4 ,on opening the cock ,d1 and closing ,g1 the steam1 flowing through the syphon tube into the top of the cylinder1 presses down the floating piston1 and forces the water into the lower tube4 ,the passage at ,l being stopped1 since ,l opens downwards1 the water forces open the valve ,k1 and passes into the air-vessel ,i4 ,when the piston ,h has been forced to the bottom of the cylinder1 the cock ,d is closed1 and ,g is opened1 and the steam allowed to escape into the atmosphere4 ,the cylinder is then replenished from the funnel as before2 and the cock ,g being closed1 and ,d opened1 the process is repeated1 and more water forced into the air-vessel ,i4 ,by continuing this process1 water is forced into the air-vessel1 and the air which originally filled that vessel is compressed into the space above the water2 and its elastic force increases exactly in the same proportion as its bulk is diminished4 7#f47 ,now1 suppose that half of the vessel ,i has been filled by the water which is forced in1 the air above the water being reduced to half its bulk has acquired twice the elastic force1 and therefore presses on the surface of the water with twice the pressure of the atmosphere4 ,again1 if two thirds of the air-vessel be filled with water1 the air is compressed into one third of its bulk1 and presses on the surface of the water with three times the pressure of the atmosphere1 and so on4 ,illustration3 ,pl4 ,,iii4 ,now if the cock ,m be opened1 the pressure of the condensed air will force the water up in the tube ,n1 and it will continue to rise until the column balances the pressure of the condensed air4 ,if1 when the water is suspended in the tube1 and the cock ,m open1 the vessel ,i is half filled1 the height of the column in ,n will be #cd feet1 because #cd feet of water has a pressure equal to the atmosphere2 and this1 added to the atmospheric pressure on it1 gives a total pressure equal to twice that of the atmosphere1 which balances the pressure of the air in ,i reduced to half its bulk4 ,if two thirds of ,i be filled with water1 a column of #fh feet will be supported in ,n2 for such a column1 united with the atmospheric pressure on it1 gives a total pressure equal to three times that of the atmosphere1 which balances the air in ,i compressed into one third of its original bulk4 ,by omitting the principle of condensation1 this machine loses #bf feet in the perpendicular lift4 ,but1 indeed1 in every point of view1 it is inferior to the engines of ,savery and ,newcomen4 7#de47 ,from the construction of the atmospheric engine by ,newcomen1 in #agje1 for about half a century1 no very important step had been made in the improvement of the steam engine4 ,during this time the celebrated ,smeaton had given much attention to the details of the atmospheric engine1 and brought that machine to as high a state of perfection as its principle seemed to admit1 and as it has ever since reached4 ,in the year #agfc1 ,,james ,,watt1 a name illustrious in the history of mechanical science1 commenced his experiments on steam4 ,he was born at ,greenock1 in the year #agcf2 and at the age of #af was apprenticed to a mathematical instrument-maker1 with whom he spent four years4 ,at the age of #bj he removed to ,london1 where he still pursued the same trade under a mathematical instrument-maker in that city4 ,after a short time1 however1 finding his health declining1 he returned to ,scotland1 and commenced business on his own account at ,glasgow4 ,in #ageg he was appointed mathematical instrument-maker to the university of ,glasgow1 where he resided and carried on business4 ,this circumstance produced an acquaintance between him and the celebrated ,dr4 ,robison1 then a student in ,glasgow1 who directed ,watt's attention to the steam engine4 ,in his first experiments he used steam of a high-pressure2 but found it attended with so much danger of bursting the boiler1 and difficulty of keeping the joints tight1 and other objections1 that he relinquished the inquiry at that time4 7#df47 ,in the winter of #agfc1 ,watt was employed to repair the model of an atmospheric engine1 belonging to the natural philosophy class in the university--a circumstance which again turned his attention to the subject of the steam engine4 ,he found the consumption of steam in working this model so great1 that he inferred that the quantity wasted1 must have had a very large proportion to that used in working the piston4 ,his first conclusion was1 that the material of the cylinder 7brass7 was too good a conductor of heat1 and that much was thereby lost4 ,he made some experiments1 accordingly1 with wooden cylinders1 soaked in linseed oil1 which1 however1 he soon laid aside4 ,further consideration convinced him that a prodigious waste of steam was essential to the very principle of the atmospheric engine4 ,this will be easily understood4 ,when the steam has filled the cylinder so as to balance the atmospheric pressure on the piston1 the cylinder must have the same temperature as the steam itself4 ,now1 on introducing the condensing jet1 the steam mixed with this water forms a mass of hot water in the bottom of the cylinder4 ,this water1 not being under the atmospheric pressure1 boils at very low temperatures1 and produces a vapour which resists the descent of the piston4 ,the heat of the cylinder itself assists this process2 so that in order to produce a tolerably perfect vacuum1 it was found necessary to introduce a quantity of condensing water1 sufficient to reduce the temperature of the water in the cylinder lower than #ajj1 and consequently to cool the cylinder itself to that temperature4 ,under these circumstances1 the descent of the piston was found to suffer very little resistance from any vapour within the cylinder3 but then on the subsequent ascent1 an immense waste of steam ensued2 for the steam1 on being admitted under the piston1 was immediately condensed by the cold cylinder and water of condensation1 and this continued until the cylinder became again heated up to #bab1 to which point the whole cylinder should be heated before the ascent could be completed4 ,here1 then1 was an obvious and an extensive cause of the waste of heat4 ,at every descent of the piston1 the cylinder should be cooled below #ajj2 and at every ascent it should be again heated to #bab4 ,it1 therefore1 became a question whether the force gained by the increased perfection of the vacuum was adequate to the waste of fuel in producing the vacuum2 and it was found1 on the whole1 more profitable not to cool the cylinder to so low a temperature1 and consequently to work with a very imperfect vacuum1 and a diminished power4 ,watt1 therefore1 found the engine involved in this dilemma3 either much or little condensation-water must be used4 ,if much were used1 the vacuum would be perfect2 but then the cylinder would be cooled1 and would entail an extensive waste of fuel in heating it4 ,if little were used1 a vapour would remain1 which would resist the descent of the piston1 and rob the atmosphere of a part of its power4 ,the great problem then pressed itself on his attention1 to condense the steam without cooling the cylinder4 ,from the small quantity of water in the form of steam which filled the cylinder1 and the large quantity of injected water to which this communicated heat1 ,watt was led to inquire what proportion the bulk of water in the liquid state bore to its bulk in the vaporous state2 and also what proportion subsisted between the heat which it contained in these two states4 ,he found by experiment that a cubic inch of water formed about a cubic foot of steam2 and that the cubic foot of steam contained as much heat as would raise a cubic inch of water to about #ajjj4 7#ae47 ,this gave him some surprise1 as the thermometer indicated the same temperature1 #bab1 for both the steam and the water from which it was raised4 ,what then became of all the additional heat which was contained in the steam1 and not indicated by the thermometer8 ,watt concluded that this heat must be in some way engaged in maintaining the water in its new form4 ,struck with the singularity of this circumstance1 he communicated it to ,dr4 ,black1 who then explained to ,watt his doctrine of latent heat1 which he had been teaching for a short time before that1 but of which ,watt had not previously heard2 and thus1 says ,watt1 ,i stumbled upon one of the material facts on which that theory is founded4 7#dg47 ,watt now gave his whole mind to the discovery of a method of condensing the steam without cooling the cylinder4 ,the idea occurred to him of providing a vessel separate from the cylinder1 in which a constant vacuum might be sustained4 ,if a communication could be opened between the cylinder and this vessel1 the steam1 by its expansive property1 would rush from the cylinder to this vessel1 where1 being exposed to cold1 it would be immediately condensed1 the cylinder meanwhile being sustained at the temperature of #bab4 ,this happy conception formed the first step of that brilliant career which has immortalized the name of ,watt1 and which has spread his fame to the very skirts of civilization4 ,he states1 that the moment the notion of separate condensation struck him1 all the other details of his improved engine followed in rapid and immediate succession1 so that in the course of a day his invention was so complete that he proceeded to submit it to experiment4 ,his first notion was1 as we have stated1 to provide a separate vessel1 called a condenser1 having a pipe or tube communicating with the cylinder4 ,this condenser he proposed to keep cold by being immersed in a cistern of cold water1 and by providing a jet of cold water to play within it4 ,when the communication with the cylinder is opened1 the steam1 rushing into the condenser1 is immediately condensed by the jet and the cold surface4 ,but here a difficulty presented itself1 viz4 how to dispose of the condensing water1 and condensed steam1 which would collect in the bottom of the condenser4 ,but besides this1 a quantity of air or permanent uncondensible gas would collect from various sources4 ,water in its ordinary state always holds more or less air in combination with it3 the air thus combined with the water in the boiler passes through the tubes and cylinder with the steam1 and would collect in the condenser4 ,air also would enter in combination with the condensing water1 which would be set free by the heat it would receive from admixture with the steam4 ,the air proceeding from these sources would1 as ,watt foresaw1 accumulate in the condenser1 even though the water might be withdrawn from it1 and would at length resist the descent of the piston4 ,to remedy this he proposed to form a communication between the bottom of the condenser and a pump which he called the ,,air ,,pump1 so that the water and air which might be collected in the condenser would be drawn off2 and it was easy to see how this pump could be worked by the machine itself4 ,this constituted the second great step in the invention4 ,to make it air-tight in the cylinder1 it had been found necessary to keep a quantity of water supplied above the piston4 ,in the present case1 any of this water which might escape through the piston1 or between it and the cylinder1 would boil1 the cylinder being kept at #bab2 and would thus1 by the steam it would produce1 vitiate the vacuum4 ,to avoid this inconvenience1 ,watt proposed to lubricate the piston1 and keep it air-tight1 by employing melted wax and tallow4 ,another inconvenience was still to be removed4 ,on the descent of the piston1 the air which must then enter the cylinder would lower its temperature2 so that upon the next ascent1 some of the steam which would enter it would be condensed1 and hence would arise a source of waste4 ,to remove this difficulty1 ,watt proposed to close the top of the cylinder altogether by an air-tight and steam-tight cover1 allowing the piston-rod to play through a hole furnished with a stuffing-box1 and to press down the piston by steam instead of the atmosphere4 ,this was the third step in this great invention1 and one which totally changed the character of the machine4 ,it now became really a steam engine in every sense2 for the pressure above the piston was the elastic force of steam1 and the vacuum below it was produced by the condensation of steam2 so that steam was used both directly and indirectly as a moving power2 whereas1 in the atmospheric engine1 the indirect force of steam only was used1 being adopted merely as an easy method of producing a vacuum4 ,the last difficulty respecting the economy of heat which remained to be removed1 was the circumstance of the cylinder being liable to be cooled on the external surface by the atmosphere4 ,to obviate this1 he first proposed casing the cylinder in wood1 that being a substance which conducted heat slowly4 ,he subsequently1 however1 adopted a different method1 and inclosed one cylinder within another1 leaving a space between them1 which he kept constantly supplied with steam4 ,thus the inner cylinder was kept continually at the temperature of the steam which surrounded it4 ,the outer cylinder was called the jacket4#ae ,footnote #ae3 ,it is a remarkable circumstance1 that ,watt used the same means for keeping the cylinder hot as ,newcomen used in his earlier engines to cool it4 7#ch47 7#dh47 ,watt computed that in the atmospheric engine three times as much heat was wasted in heating the cylinder1 c4 as was spent in useful effect4 ,and1 as by the improvements proposed by him nearly all this waste was removed1 he contemplated1 and afterwards actually effected1 a saving of three fourths of the fuel4 ,the honour due to ,watt for his discoveries is enhanced by the difficulties under which he laboured from contracted circumstances at the time he made them4 ,he relates1 that when he was endeavouring to determine the heat consumed in the production of steam1 his means did not permit him to use an efficient and proper apparatus1 which would have been attended with expense2 and it was by experiments made with apothecaries' phials1 that he discovered the property already mentioned1 which was one of the facts on which the doctrine of latent heat was founded4 ,a large share of the merit of ,watt's discoveries has1 by some writers1 been attributed to ,dr4 ,black1 to whose instructions on the subject of latent heat it is said that ,watt owed the knowledge of those facts which led to his improvements4 ,such1 however1 was not the case2 and the mistake arose chiefly from some passages respecting ,watt in the works of ,dr4 ,robison1 in one of which he states that ,watt had been a pupil and intimate friend of ,dr4 ,black2 and that he attended two courses of his lectures at college in ,glasgow4 ,such1 however1 was not the case2 for ,unfortunately for me1 says ,watt in a letter to ,dr4 ,brewster1 the necessary avocations of my business prevented me from attending his or any other lectures at college4 ,in further noticing ,dr4 ,black's opinion1 that his fortunate observation of what happens in the formation and condensation of elastic vapour 'has contributed in no inconsiderable degree to the public good1 by suggesting to my friend ,mr4 ,watt of ,birmingham1 then of ,glasgow1 his improvements on the steam-engine1' it is very painful for me to controvert any opinion or assertion of my revered friend2 yet1 in the present case1 ,i find it necessary to say1 that he appears to me to have fallen into an error4 ,these improvements proceeded upon the established fact1 that steam was condensed by the contact of cold bodies1 and the later known one1 that water boiled at heats below #ajj1 and consequently that a vacuum could not be obtained unless the cylinder and its contents were cooled every stroke below the heat4 ,,chapter ,v4 ,,watt',s ,,single-,,acting ,,steam ,,engine4 ,expansive ,principle applied4 -- ,failure of ,roebuck1 and ,partnership with ,bolton4 -- ,patent extended to #ahjj4 -- ,counter4 -- ,difficulties in getting the ,engines into use4 7#di47 ,the first machine in which ,watt realised the conceptions which we mentioned in the last chapter1 is that which was afterwards called his ,single-acting ,steam ,engine4 ,we shall now describe the working apparatus in this machine4 ,the cylinder is represented at ,c 7fig4 #ab47--;in which the piston ,p moves steam-tight4 ,it is closed at the top1 and the piston-rod being very accurately turned1 runs in a steam-tight collar ,b furnished with a stuffing-box1 and constantly supplied with melted tallow or wax4 ,through a funnel in the top of the cylinder1 melted grease flows upon the piston so as to maintain it steam-tight4 ,two boxes ,a ,a1 containing the valves for admitting and withdrawing the steam1 connected by a tube of communication ,t1 are attached to the cylinder2 the action of these valves will be presently described4 ,below the cylinder1 placed in a cistern of cold water1 is a close cylindrical vessel ,d1 called the condenser1 communicating with the cylinder by a tube ,t1 leading to the lower valve-box ,a4 ,in the side of this condenser is inserted a tube1 the inner end of which is pierced with holes like the rose of a watering-pot2 and a cock ,e in the cold cistern is placed on the outside1 through which1 when open1 the water passing1 rises in a jet on the inside4 ,the tube ,s1 which conducts steam from the boiler1 enters the top of the upper valve-box at ,f4 ,immediately under it is placed a valve ,g1 which is opened and closed by a lever or rod ,g4 ,this valve1 when open1 admits steam to the top of the piston1 and also to the tube ,t1 which communicates between the two valve-boxes1 and when closed suspends the admission of steam4 ,there are two valves in the lower box1 one ,h in the top worked by the lever ,h1 and one ,i in the bottom worked by the lever ,i4 ,the valve ,h1 when open1 admits steam to pass from the cylinder above the piston1 by the tube ,t1 to the cylinder below the piston1 the valve ,i being supposed in this case to be closed4 ,this valve ,i1 when open1 7the valve ,h being closed17 admits steam to pass from below the cylinder through ,t to the condenser4 ,this steam1 entering the condenser1 meets the jet1 admitted to play by the valve ,e1 and is condensed4 ,the valve ,g is called the upper steam valve2 ,h1 lower steam valve2 ,i1 the exhausting-valve2 and ,e1 the condensing valve4 ,let us now consider how these valves must be worked in order to produce the alternate ascent and descent of the piston4 ,it is in the first place necessary that all the air which fills the cylinder1 tubes1 and condenser should be expelled4 ,to accomplish this it is only necessary to open at once the valves ,g1 ,h1 and ,i4 ,the steam then rushing from ,f through the valve ,g will pass into the upper part of the cylinder1 and through the tube ,t and the valve ,h into the lower part1 and also through the valve ,i into the condenser4 ,after the steam ceases to be condensed by the cold of the apparatus1 it will rush out mixed with air through the valve ,m1 which opens outward2 and this will continue until all the air has been expelled1 and the apparatus filled with pure steam4 ,then suppose all the valves again closed4 ,the cylinder both above and below the piston is filled with steam2 and the steam which filled the condenser being cooled by the cold surface1 a vacuum has been produced in that vessel4 ,the apparatus being in this state1 let the upper steam valve ,g1 the exhausting-valve ,i1 and the condensing valve ,e be opened4 ,steam will thus be admitted through ,g to press on the top of the piston2 and this steam will be prevented from circulating to the lower part of the cylinder by the lower steam-valve ,h being closed4 ,also the steam which filled the cylinder below the piston rushes through the open exhausting-valve ,i to the condenser1 where it meets the jet allowed to play by the open condensing valve ,e4 ,it is thus instantly condensed1 and a vacuum is left in the cylinder below the piston4 ,into this vacuum the piston is pressed without resistance by the steam which is admitted through ,g4 ,when the piston has thus been forced to the bottom of the cylinder1 let the three valves ,g1 ,i1 and ,e1 which were before opened1 be closed1 and let the lower steam-valve ,h be opened4 ,the effects of this change are easily perceived4 ,by closing the upper steam-valve ,g1 the further admission of steam to the apparatus is stopped4 ,by closing the exhausting-valve ,i1 all transmission of steam from the cylinder to the condenser is stopped4 ,thus the steam which is in the cylinder1 valve-boxes1 and tubes is shut up in them1 and no more admitted1 nor any allowed to escape4 ,by closing the condensing valve ,e1 the play of the jet in the condenser is suspended4 ,previously to opening the valve ,h1 the steam contained in the apparatus was confined to the part of the cylinder above the piston and the tube ,t and the valve-box ,a4 ,but on opening this valve1 the steam is allowed to circulate above and below the piston2 and in fact through every part included between the upper steam valve ,g1 and the exhausting-valve ,i4 ,the same steam circulating on both sides1 the piston is thus equally pressed upward and downward4 ,in this case there is no force tending to retain the piston at the bottom of the cylinder except its own weight4 ,its ascent is produced in the same manner as the ascent of the piston in the atmospheric engine4 ,the piston-rod is connected by chains ,g to the arch-head of the beam1 and the weight of the pump-rod ,r1 or any other counterpoise acting on the chains suspended from the other arch-head1 draws the piston to the top of the cylinder4 ,when the piston has arrived at the top of the cylinder1 suppose the three valves ,g1 ,i1 and ,e to be again opened1 and ,h closed4 ,steam passes from the steam-pipe ,f through the upper steam-valve ,g to the top of the piston1 and at the same time the steam which filled the cylinder below the piston is drawn off through the open exhausting-valve ,i into the condenser1 where it is condensed by the jet allowed to play by the open condensing valve ,e4 ,the pressure of the steam above the piston then forces it without resistance into the vacuum below it1 and so the process is continued4 ,it should be remembered1 that of the four valves necessary to work the piston1 three are to be opened the moment the piston reaches the top of the cylinder1 and the fourth is to be closed2 and on the piston arriving at the bottom of the cylinder1 these three are to be closed and the fourth opened4 ,the three valves which are thus opened and closed together are the upper steam-valve1 the exhausting-valve1 and the condensing valve4 ,the lower steam-valve is to be opened at the same instant that these are closed1 and vice vers4 ,the manner of working these valves we shall describe hereafter4 ,the process which has just been described1 if continued for any considerable number of reciprocations of the piston1 would be attended with two very obvious effects which would obstruct and finally destroy the action of the machine4 ,first1 the condensing water and condensed steam would collect in the condenser ,d1 and fill it2 and secondly1 the water in the cistern in which the condenser is placed would gradually become heated1 until at last it would not be cold enough to condense the steam when introduced in the jet4 ,besides this1 it will be recollected that water boils in a vacuum at a very low temperature 7#ag72 and1 therefore1 the hot water collected in the bottom of the condenser would produce steam which1 rising into the cylinder through the exhausting-valve1 would resist the descent of the piston1 and counteract the effects of the steam above it4 ,a further disadvantage arises from the air or other permanently elastic fluid which enters in combination with the water1 both in the boiler and condensing jet1 and which is disengaged by its own elasticity4 ,to remove these difficulties1 a pump is placed near the condenser communicating with it by a valve ,m1 which opens from the condenser into the pump4 ,in this pump is placed a piston which moves air-tight1 and in which there is a valve ,n1 which opens upwards4 ,now suppose the piston at the bottom of the pump4 ,as it rises1 since the valve in it opens upwards1 no air can pass down through it1 and consequently it leaves a vacuum below it4 ,the water and any air which may be collected in the condenser open the valve ,m1 and pass into the lower part of the pump from which they cannot return in consequence of the valve ,m opening outwards4 ,on the descent of the pump-piston1 the fluids which occupy the lower part of the pump1 force open the piston-valve ,n2 and passing through it1 get above the piston1 from which their return is prevented by the valve ,n4 ,in the next ascent1 the piston lifts these fluids to the top of the pump1 whence they are discharged through a conduit into a small cistern ,b by a valve ,k which opens outwards4 ,the water which is thus collected in ,b is heated by the condensed steam1 and is reserved in ,b1 which is called the hot well for feeding the boiler1 which is effected by means which we shall presently explain4 ,the pump which draws off the hot water and air from the condenser is called the air-pump4 7#ej47 ,we have not yet explained the manner in which the valves and the air-pump piston are worked4 ,the rod ,q of the latter is connected with the working beam1 and the pump is therefore wrought by the engine itself4 ,it is not very material to which arm of the beam it is attached4 ,if it be on the same side of the centre of the beam with the cylinder1 it rises and falls with the steam-piston2 but if it be on the opposite side1 the pump-piston rises when the steam-piston falls1 and vice vers4 ,in the single-engine there are some advantages in the latter arrangement4 ,as the steam-piston descends1 the steam rushes into the condenser1 and the jet is playing2 and this1 therefore1 is the most favourable time for drawing out the water and condensed steam from the condenser by the ascent of the pump-piston1 since by this means the descent of the steam-piston is assisted2 an effect which would not be produced if the steam-piston and pump-piston descended together4 ,with respect to the method of opening and closing the valves1 it is evident that the three valves which are simultaneously opened and closed may be so connected as to be worked by the same lever4 ,this lever may be struck by a pin fixed upon the rod ,q of the air-pump1 so that when the pistons have arrived at the top of the cylinders the pin strikes the lever and opens the three valves4 ,a catch or detent is provided for keeping them open during the descent of the piston1 from which they are disengaged in a similar manner on the arrival of the piston at the bottom of the cylinder1 and they close by their own weight4 ,in exactly the same way the lower steam-valve is opened on the arrival of the piston at the bottom of the cylinder1 and closed on its arrival at the top by the action of a pin placed on the piston-rod of the air-pump4 7#ea47 ,soon after the invention of these engines1 ,watt found that in some instances inconvenience arose from the too rapid motion of the steam-piston at the end of its stroke1 owing to its being moved with an accelerated motion4 ,this was owing to the uniform action of the steam-pressure upon it3 for upon first putting it in motion at the top of the cylinder1 the motion was comparatively slow2 but from the continuance of the same pressure the velocity with which the piston descended was continually increasing1 until it reached the bottom of the cylinder1 where it acquired its greatest velocity4 ,to prevent this1 and to render the descent as nearly as possible uniform1 it was proposed to cut off the steam before the descent was completed1 so that the remainder might be effected merely by the expansion of the steam which was admitted to the cylinder4 ,to accomplish this1 he contrived1 by means of a pin on the rod of the air-pump1 to close the upper steam-valve when the steam-piston had completed one-third of its entire descent1 and to keep it closed during the remainder of the descent1 and until the piston again reached the top of the cylinder4 ,by this arrangement the steam pressed the piston with its full force through one-third of the descent1 and thus put it into motion2 during the other two thirds the steam thus admitted acted merely by its expansive force1 which became less in exactly the same proportion as the space given to it by the descent of the piston increased4 ,thus1 during the last two thirds of the descent the piston is urged by a gradually decreasing force1 which in practice was found just sufficient to sustain in the piston a uniform velocity4 7#eb47 ,we have already mentioned the difficulty arising from the water in the cistern1 in which the condenser and air-pump are placed1 becoming heated1 and the condensation therefore being imperfect4 ,to prevent this1 a waste-pipe is placed in this cistern1 from which the water is continually discharged1 and a pump ,l 7called the cold-water-pump7 is worked by the engine itself1 which raises a supply of cold water and sends it through a pipe in a constant stream into the cold cistern4 ,the waste-pipe1 through which the water flows from the cistern1 is placed near the top of it1 since the heated water1 being lighter than the cold1 remains on the top4 ,thus the heated water is continually flowing off1 and a constant stream of cold water supplied4 ,the piston-rod of the cold-water-pump is attached to the beam 7by which it is worked71 usually on the opposite side from the cylinder4 ,another pump ,o 7called the hot-water-pump7 enters the hot well ,b2 and raising the water from it1 forces it through a tube to the boiler for the purpose of feeding it4 ,the manner in which this is effected will be more particularly described hereafter4 ,a part of the heat which would otherwise be lost1 is thus restored to the boiler to assist in the production of fresh steam4 ,we may consider a portion of the heat to be in this manner circulating continually through the machine4 ,it proceeds from the boiler in steam1 works the piston1 passes into the condenser1 and is reconverted into hot water2 thence it is passed to the hot well1 from whence it is pumped back into the boiler1 and is again converted into steam1 and so proceeds in constant circulation4 ,from what has been described1 it appears that there are four pistons attached to the great beam and worked by the piston of the steam-cylinder4 ,on the same side of the centre with the cylinder is the piston-rod of the air-pump1 and on the opposite side are the piston-rods of the hot-water pump and the cold-water-pump2 and lastly1 at the extremity of the beam opposite to that at which the steam-piston works1 is the piston of the pump to be wrought by the engine4 7#ec47 ,the position of these piston-rods with respect to the centre of the beam depends on the play necessary to be given to the piston4 ,if the play of the piston be short1 its rod will be attached to the beam near the centre2 and if longer1 more remote from the centre4 ,the cylinder of the air-pump is commonly half the length of the steam-cylinder1 and its piston-rod is attached to the beam at the point exactly in the middle between the end of the beam and the centre4 ,the hot-water pump not being required to raise a considerable quantity of water1 its piston requires but little play1 and is therefore placed near the centre of the beam1 the piston-rod of the cold-water pump being farther from the centre4 7#ed47 ,it appears to have been about the year #agfc1 that ,watt made these improvements in the steam engine1 and constructed a model which fully realized his expectations4 ,either from want of influence or the fear of prejudice and opposition1 he did not make known his discovery or attempt to secure it by a patent at that time4 ,having adopted the profession of a land surveyor1 his business brought him into communication with ,dr4 ,roebuck1 at that time extensively engaged in mining speculations1 who possessed some command of capital1 and was of a very enterprising disposition4 ,by ,roebuck's assistance and countenance1 ,watt erected an engine of the new construction at a coal mine on the estate of the ,duke of ,hamilton1 at ,kinneil near ,burrowstoness4 ,this engine being a kind of experimental one1 was improved from time to time as circumstances suggested1 until it reached considerable perfection4 ,while it was being erected1 ,watt in conjunction with ,roebuck applied for and obtained a patent to secure the property in the invention4 ,this patent was enrolled in #agfi1 six years after ,watt invented the improved engine4 ,watt was now preparing to manufacture the new engines on an extensive scale1 when his partner ,roebuck suffered a considerable loss by the failure of a mining speculation in which he had engaged1 and became involved in embarrassments1 so as to be unable to make the pecuniary advances necessary to carry ,watt's designs into execution4 ,again disappointed1 and harassed by the difficulties which he had to encounter1 ,watt was about to relinquish the further prosecution of his plans1 when ,mr4 ,matthew ,bolton1 a gentleman who had established a factory at ,birmingham a short time before1 made proposals to purchase ,dr4 ,roebuck's share in the patent1 in which he succeeded2 and in #aggc1 ,watt entered into partnership with ,bolton4 ,his situation was now completely changed4 ,bolton was not only a man of extensive capital1 but also of considerable personal influence1 and had a disposition which led him1 from taste1 to undertakings which were great and difficult1 and which he prosecuted with the most unremitting ardency and spirit4 ,mr4 ,watt1 says ,playfair1 was studious and reserved1 keeping aloof from the world2 while ,mr4 ,bolton was a man of address1 delighting in society1 active1 and mixing with people of all ranks with great freedom1 and without ceremony4 ,had ,mr4 ,watt searched all ,europe1 he probably would not have found another person so fitted to bring his invention before the public1 in a manner worthy of its merit and importance2 and although of most opposite habits1 it fortunately so happened that no two men ever more cordially agreed in their intercourse with each other4 ,the delay in the progress of the manufacture of engines occasioned by the failure of ,dr4 ,roebuck was such1 that ,watt found that the duration of his patent would probably expire before he would even be reimbursed the necessary expenses attending the various arrangements for the manufacture of the engines4 ,he therefore1 with the advice and influence of ,bolton1 ,roebuck1 and other friends1 in #agge1 applied to parliament for an extension of the terms of his patent1 which was granted for #be years from the date of his application1 so that his exclusive privilege should expire in #ahjj4 ,an engine was now erected at ,soho 7the name of ,bolton's factory7 as a specimen for the examination of mining speculators1 and the engines were beginning to come into demand4 ,the manner in which ,watt chose to receive remuneration from those who used his engines was as remarkable for its ingenuity as for its fairness and liberality4 ,he required that one-third of the saving of coals effected by his engines1 compared with the atmospheric engines hitherto used1 should be paid to him1 leaving the benefit of the other two-thirds to the public4 ,accurate experiments were made to ascertain the saving of coals2 and as the amount of this saving in each engine depended on the length of time it was worked1 or rather on the number of descents of the piston1 ,watt invented a very ingenious method of determining this4 ,the vibrations of the great working beam were made to communicate with a train of wheelwork1 in the same way as those of a pendulum communicate with the work of a clock4 ,each vibration of the beam moved one tooth of a small wheel1 and the motion was communicated to a hand or index1 which moved on a kind of graduated plate like the dial plate of a clock4 ,the position of this hand marked the number of vibrations of the beam4 ,this apparatus1 which was called the counter1 was locked up and secured by two different keys1 one of which was kept by the proprietor1 and the other by ,bolton and ,watt1 whose agents went round periodically to examine the engines1 when the counters were opened by both parties and examined1 and the number of vibrations of the beam determined1 and the value of the patent third found4#af ,footnote #af3 ,the extent of the saving in fuel may be judged from this3 that for three engines erected at ,chacewater mine in ,cornwall1 it was agreed by the proprietors that they would compound for the patent third at #bdjjl4 per annum2 so that the whole saving must have exceeded #gbjjl4 per annum4 ,notwithstanding the manifest superiority of these engines over the old atmospheric engines2 yet such were the influence of prejudice and the dislike of what is new1 that ,watt found great difficulties in getting them into general use4 ,the comparative first cost also probably operated against them2 for it was necessary that all the parts should be executed with great accuracy1 which entailed proportionally increased expense4 ,in many instances they felt themselves obliged to induce the proprietors of the old atmospheric engines to replace them by the new ones1 by allowing them in exchange an exorbitant price for the old engines2 and in some cases they were induced to erect engines at their own expense1 upon an agreement that they should only be paid if the engines were found to fulfil the expectations1 and brought the advantages which they promised4 ,it appeared since1 that ,bolton and ,watt had actually expended a sum of nearly #ej1jjjl4 on these engines before they began to receive any return4 ,when we contemplate the immense advantages which the commercial interests of the country have gained by the improvements in the steam engine1 we cannot but look back with disgust at the influence of that fatal prejudice which opposes the progress of improvement under the pretence of resisting innovation4 ,it would be a problem of curious calculation to determine what would have been lost to the resources of this country1 if chance had not united the genius of such a man as ,watt with the spirit1 enterprise1 and capital1 of such a man as ,bolton6 ,the result would reflect little credit on those who think novelty alone a sufficient reason for opposition4 ,,chapter ,,vi4 ,,double-,,acting ,,steam ,,engine4 ,the ,single-,acting ,engine unfit to impel ,machinery4 -- ,various contrivances to adapt it to this purpose4 -- ,double-,cylinder4 -- ,double-,acting ,cylinder4 -- ,various mode of connecting the ,piston with the ,beam4 -- ,rack and ,sector4 -- ,double ,chain4 -- ,parallel ,motion4 -- ,crank4 -- ,sun and ,planet ,motion4 -- ,fly ,wheel4 -- ,governor4 ,in the atmospheric engine of ,newcomen1 and in the improved steam engine of ,watt1 described in the last chapter1 the action of the moving power is an intermitting one4 ,while the piston descends1 the moving power is in action1 but its action is suspended during the ascent4 ,thus the opposite or working end of the beam can only be applied in cases where a lifting power is required4 ,this action is quite suitable to the purposes of pumping1 which was the chief or only object to which the steam engine had hitherto been applied4 ,in a more extended application of the machine1 this intermission of the moving power and its action taking place only in one direction would be inadmissible4 ,to drive the machinery generally employed in manufactures a constant and uniform force is required2 and to render the steam engine available for this purpose1 it would be necessary that the beam should be driven by the moving power as well in its ascent as in its descent4 ,when ,watt first conceived the notion of extending the application of the engine to manufactures generally1 he proposed to accomplish this double action upon the beam by placing a steam cylinder under each end of it1 so that while each piston would be ascending1 and not impelled by the steam1 the other would be descending1 being urged downwards by the steam above it acting against the vacuum below4 ,thus1 the power acting on each during the time when its action on the other would be suspended1 a constant force would be exerted upon the beam1 and the uniformity of the motion would be produced by making both cylinders communicate with the same boiler1 so that both pistons would be driven by steam of the same pressure4 ,one condenser might also be used for both cylinders1 so that a similar vacuum would be produced under each4 ,this arrangement1 however1 was soon laid aside for one much more simple and obvious4 ,this consisted in the production of exactly the same effect by a single cylinder in which steam was introduced alternately above and below the piston1 being at the same time withdrawn by the condenser at the opposite side4 ,thus the piston being at the top of the cylinder1 steam is introduced from the boiler above it1 while the steam in the cylinder below it is drawn off by the condenser4 ,the piston1 therefore1 is pressed from above into the vacuum below1 and descends to the bottom of the cylinder4 ,having arrived there1 the top of the cylinder is cut off from all communication with the boiler2 and1 on the other hand1 a communication is opened between it and the condenser4 ,the steam which has pressed the piston down is therefore drawn off by the condenser1 while a communication is opened between the boiler and the bottom of the cylinder1 so that steam is admitted below the piston3 the piston1 thus pressed from below into the vacuum above1 ascends1 and in the same way the alternate motion is continued4 ,such is the principle of what is called the ,double-acting ,steam ,engine1 in contradistinction to that described in the last chapter1 in which the steam acts only above the piston while a vacuum is produced below it4 ,it is evident that1 in the arrangement now described1 the condenser must be in constant action3 while the piston is descending the condenser must draw off the steam below it1 and while it is ascending1 it must draw off the steam above it4 ,as steam1 therefore1 must be constantly drawn into the condenser1 the jet of cold water which condenses the steam must be kept constantly playing4 ,this jet1 therefore1 will not be worked by the valve alternately opening and closing1 as in the single engine1 but will be worked by a cock1 the opening of which will be adjusted according to the quantity of cold water necessary to condense the steam4 ,when the steam is used at a low pressure1 and1 therefore1 in a less compressed state1 less condensing water would be necessary than when it is used at a higher pressure and in a more compressed state4 ,in the one case1 therefore1 the condensing cock would be less open than in the other4 ,again1 the quantity of condensing water must vary with the speed of the engine1 because the greater the speed of the engine1 the more rapidly will the steam flow from the cylinder into the condenser2 and1 as the same quantity of steam requires the same quantity of condensing water1 the supply of the condensing water must be proportional to the speed of the engine4 ,in the double-acting engine1 then1 the jet cock is regulated by a lever or index which moves upon a graduated arch1 and which is regulated by the engineer according to the manner in which the engine works4 ,this change in the action of the steam upon the piston rendered it necessary to make a corresponding change in the mechanism by which the piston-rod was connected with the beam4 ,in the single acting engine1 the piston-rod pulled the end of the beam down during the descent1 and was pulled up by it in the ascent4 ,the connection by which this action was transmitted between the beam and piston was1 as we have seen1 a flexible chain passing from the end of the piston and playing upon the arch-head of the beam4 ,now1 where the mechanical action to be transmitted is a pull1 and not a push1 a flexible chain1 or cord1 or strap1 is always sufficient2 but if a push or thrust is required to be transmitted1 then the flexibility of the medium of mechanical communication afforded by a chain1 renders it inapplicable4 ,in the double-acting engine1 during the descent1 the piston-rod still pulls the beam down1 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 ascent 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 counter weight 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 ,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 beam as represented in fig4 #ac4 ,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 ,in fact1 it was necessary to turn these piston-rods very accurately in the lathe1 so that they may work with sufficient precision in the cylinder4 ,under these circumstances1 the motion of 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 bar 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 mechanism1 since called the ,parallel ,motion1 one of the most ingenious mechanical combinations connected with the history of the steam engine4 ,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 a circle1 the end of the piston-rod connected with the beam should move exactly 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 connexion1 it is evident that1 being moved up and down in the arch of a circle1 it would be bent to the left and the right alternately1 and would consequently either be broken1 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 rods 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 accomplish this1 he conceived the notion of connecting three rods in the following manner3--,a ,b and ,c ,d 7fig4 #ad471 are two rods or levers turning on fixed pivots or centres at ,a and ,c4 ,a third rod1 ,b ,d1 is connected with them by pivots placed at their extremities1 ,b and ,d1 and the lengths of the rods are so adjusted that when ,a ,b and ,c ,d are horizontal1 ,b ,d shall be perpendicular or vertical1 and that ,a ,b and ,c ,d shall be of equal lengths4 ,now1 let a pencil be imagined to be placed at ,p1 exactly in the middle of the rod ,b ,d3 if the rod ,a ,b be caused to move up and down like the beam of the steam engine in the arch represented in the figure1 it is clear1 from the mode of their connexion1 that the rod ,c ,d will be moved up and down in the other arch4 ,now ,watt conceived that1 under such circumstances1 the pencil ,p would be moved up and down in a perpendicular straight line4 ,however difficult the first conception of this mechanism may have been1 it is easy to perceive why the desired effect will be produced by it4 ,when the rod ,a ,b rises to the upper extremity of the arch1 the point ,b departs a little to the right2 at the same time1 the point ,d is moved a little to the left4 ,now the extremities of the rod ,b ,d being thus at the same time1 carried slightly in opposite directions1 the pencil in the middle of it will ascend directly upwards2 the one extremity of the rod having a tendency to draw it as much to the right as the other has to draw it to the left4 ,in the same manner1 when the rod ,a ,b moves to the lower extremity of the arch1 the rod ,c ,d will be likewise moved to the lower extremity of its arch4 ,the point ,b is thus transferred a little to the right1 and the point ,d to the left2 and1 for the same reason as before1 the point ,p in the middle will move neither to the right nor to the left1 but straight downwards4#ag ,footnote #ag3 ,in a strict mathematical sense1 the path of the point ,p is a curve of a high order1 but in the play which is given to it in the application used in the steam engine1 it describes only a part of its entire locus2 and this part extending equally on each side of a point of inflection1 its radius of curvature is infinite1 so that1 in practice1 the deviation from a straight line1 when proper proportions are observed in the rods1 and too great a play not given to them1 is insignificant4 ,now ,watt conceived that his object would be attained if he could contrive to make the beam perform the part of ,a ,b in fig4 #ad41 and to connect with it other two rods1 ,c ,d and ,d ,b1 attaching the end of the piston to the middle of the rod ,d ,b4 ,the practical application of this principle required some modification1 but is as elegant as the notion itself is ingenious4 ,the apparatus adopted for carrying it into effect is represented on the arm which works the piston in fig4 #ae4 ,the beam1 moving on its axis ,c1 every point in its arm moves in the arc of a circle of which ,c is the centre4 ,let ,b be the point which divides the arm ,a ,c into equal parts1 ,a ,b and ,b ,c2 and let ,d ,e be a straight rod equal in length to ,c ,b1 and playing on the fixed centre or pivot ,d4 ,the end ,e of this rod is connected by a straight bar1 ,e ,b1 with the point ,b1 by pivots at ,b and ,e on which the rod ,b ,e plays freely4 ,if the beam be supposed to move alternately on its axis ,c1 the point ,b will move up and down in a circular arc1 of which ,c is the centre1 and at the same time the point ,e will move in an equal circular arc round the point ,d as a centre4 ,according to what we have just explained1 the middle point ,f of the rod ,b ,e will move up and down in a straight line4 ,also1 let a rod1 ,a ,g1 equal in length to ,b ,e1 be attached to the end ,a of the beam by a pivot on which it moves freely1 and let its extremity ,g be connected with ,e by a rod1 ,g ,e1 equal in length to ,a ,b1 and playing on pivots at ,g and ,e4 ,by this arrangement the joint ,a ,g being always parallel to ,b ,e1 the three points ,c1 ,a1 and ,g will be in circumstances precisely similar to the points ,c1 ,b1 and ,f1 except that the system ,c ,a ,g will be on a scale of double the magnitude of ,c ,b ,f3 ,c ,a being twice ,c ,b1 and ,a ,g twice ,b ,f1 it is clear1 then1 that whatever course the point ,f may follow1 the point ,g must follow a similar line1#ah but will move twice as fast4 ,but1 since the point ,f has been already shown to move up and down in a straight line1 the point ,g must also move up and down in a straight line1 but of double the length4#ai ,footnote #ah3 ,it is1 in fact1 the principle of the pantograph4 ,the points ,c1 ,f1 and ,g evidently lie in the same straight line1 since ,c ,b 3 ,c ,a 33 ,b ,f 3 ,a ,g1 and the latter lines are parallel4 ,taking ,c as the common pole of the loci of the points ,f ,g1 the radius vector of the one will always be twice the corresponding radius vector of the other2 and therefore these curves are similar1 similarly placed1 and parallel4 ,hence1 by the last note1 the point ,g must move in a line differing imperceptibly from a right line4 ,footnote #ai3 ,it is not necessary that the rods1 forming the parallel motion1 should have the proportions which we have assigned to them4 ,there are various proportions which answer the purpose1 and which will be seen by reference to practical works on the steam engine4 ,by this arrangement the pistons of both the steam cylinder and air-pump are worked2 the rod of the latter being attached to the point ,f1 and that of the former to the point ,g4 ,this beautiful contrivance1 which is incontestably one of the happiest mechanical inventions of ,watt1 affords an example with what facility the mind of a mere mechanician can perceive1 as it were instinctively1 a result to obtain which by strict reasoning would require a very complicated mathematical analysis4 ,watt1 when asked1 by persons whose admiration was justly excited by this invention1 to what process of reasoning he could trace back his discovery1 replied that he was aware of none2 that the conception flashed upon his mind without previous investigation1 and so as to excite in himself surprise at the perfection of its action2 and that on looking at it for the first time1 he experienced all that pleasurable sense of novelty which arises from the first contemplation of the results of the invention of others4 ,this and the other inventions of ,watt seem to have been the pure creations of his natural genius1 very little assisted by the results of practice1 and not at all by the light of education4 ,it does not even appear that he was a dexterous mechanic2 for he never assisted in the construction of the first models of his own inventions4 ,his dwelling-house was two miles from the factory1 to which he never went more than once in a week1 and then did not stay half an hour4 7a7 ,however beautiful and ingenious in principle the parallel motion may be1 it has recently been shown in the ,united ,states that much simpler means are sufficient to subserve the same purpose4 ,in the engines constructed recently1 under the direction of ,mr4 ,r4 ,l4 ,stevens1 a substitute for the parallel motion has been introduced that performs the task equally well1 and is much less complex4 ,on the head of the piston-rod a bar is fixed1 at right angles to it1 and to the longitudinal section of the engine4 ,the ends of this bar work in guides formed of two parallel and vertical bars of iron1 by which the upper end of the piston-rod is constrained to move in a straight line4 ,the cross-bar that moves in the guides is connected with the end of the working beam by an inflexible bar1 having a motion on two circular gudgeons1 one of which is in the working beam1 the other in the cross-bar4 ,this is therefore free to accommodate itself to the changes in the respective position of the piston-rod and working beam1 and yet transmits the power exerted by the steam upon the former whether it be ascending or descending1 to the latter and through it to the other parts of the machine4--,a4 ,e4 7b7 ,the most improved form of ,watt's engine was reached by successive additions to the old atmospheric engine of ,newcomen and ,cawley4 ,hence1 the working-beam1 derived from the pump brake of that engine1 always formed a part2 and the parallel motion1 or some equivalent contrivance was absolutely necessary4 ,in many ,american engines1 and particularly in those used in steam boats1 the working beam is no longer used for the purpose of transmitting motion to the machinery4 ,this is effected by applying a bar1 called the cross-head1 at right angles to the upper ends of the piston-rod4 ,the ends of the cross-head work in iron guides1 adapted to a gallows-frame of wood4 ,on each side of the cylinder1 connecting rods are applied1 which take hold of the cranks of the shafts of the water-wheel4 ,two other connecting rods give motion to a short beam1 which works the air and supply pumps4 ,the working beam is also suppressed in engines which work horizontally4 ,the connecting rod is in them merely a jointed prolongation of the piston-rod1 extending to the crank1 whose axis lies in the same horizontal plane with and at right angles to the axis of the cylinder4--,a4 ,e4 7#ee47 ,a perfect motion being thus obtained of conveying the alternate motion of the piston to the working beam1 the use of a counterpoise to lift the piston was discontinued1 and the beam was made to balance itself exactly on its centre4 ,the next end to be obtained was to adapt the reciprocating motion of the working end of the beam to machinery4 ,the motion most generally useful for this purpose is one of continued rotation4 ,the object1 therefore1 was by the alternate motion of the end of the beam to transmit to a shaft or axis a continued circular motion4 ,in the first instance1 ,watt proposed effecting this by a crank1 connected with the working end of the beam by a metal connector or rod4 ,let ,k be the centre or axis1 or shaft by which motion is given to the machinery1 and to which rotation is to be imparted by the beam ,c ,h4 ,on the axle ,k1 suppose a lever1 ,k ,i1 fixed1 so that when ,k ,i is turned round the centre ,k1 the wheel must be turned with it4 ,let a connector or rod1 ,h ,i1 be attached to the points ,h and ,i1 playing freely on pivots or joints4 ,as the end ,h is moved upwards and downwards1 the lever ,k ,i is turned round the centre ,k1 so as to give a continued rotatory motion to the shaft which revolves on that centre4 ,the different positions which the connector and lever ,k ,i assume in the different parts of a revolution are represented in fig4 #af4 7#ef47 ,this was the first method which occurred to ,watt for producing a continued rotatory motion by means of the vibrating motion of the beam1 and is the method now universally used4 ,a workman1 however1 from ,mr4 ,watt's factory1 who was aware of the construction of a model of this1 communicated the method to ,mr4 ,washborough of ,bristol1 who anticipated ,watt in taking out a patent2 and although it was in his power to have disputed the patent1 yet rather than be involved in litigation1 he gave up the point1 and contrived another way of producing the same effect1 which he called the sun and planet wheel1 and which he used until the expiration of ,washborough's patent1 when the crank was resumed4 ,the toothed wheel ,b 7fig4 #ag47 is fixed on the end of the connector1 so that it does not turn on its axis4 ,the teeth of this wheel work in those of another wheel1 ,a1 which is the wheel to which rotation is to be imparted1 and which is turned by the wheel ,b revolving round it1 urged by the rod ,h ,i1 which receives its motion from the working-beam4 ,the wheel ,a is called the sun-wheel1 and ,b the planet-wheel1 from the obvious resemblance to the motion of these bodies4 ,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 simple crank1 for in the simple crank one revolution only on the axle is produced by one revolution of the crank1 but in the sun and planet-wheel 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 higher position1 must now be distant from it by half the circumference of the wheel1 and must therefore be again in the highest position1 so that while the planet-wheel has been carried from the top to the bottom1 the sun-wheel has made a complete revolution4 ,a little reflection1 however1 on the nature of the motion1 will render this plainer than any description can4 ,this advantage of giving an increased velocity1 may be obtained also by the simple 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 decidedly inferior to the crank1 which has now entirely superseded it4 7#eh47 ,whether the simple crank or the sun and planet wheel be used1 there still remains a difficulty of a peculiar nature attending the continuance of the rotatory motion4 ,there are two positions in which the engine can give no motion whatever to the crank4 ,these are when the end of the beam1 the axle of the crank1 and the pivot which joins the connector with the crank1 are in the same straight line4 ,this will be easily understood4 ,suppose the beam1 connector1 and crank to assume the position represented in fig4 #ae4 ,if steam urge the piston downwards1 the point ,h and the connector ,h ,i will be drawn directly upwards4 ,but it must be very evident that in the present situation of the connector ,h ,i1 and the lever ,i ,k1 the force which draws the point ,i in the direction ,i ,k can have no effect whatever in turning ,i ,k round the centre ,k1 but will merely exert a pressure on the axle or pivots of the wheel4 ,again1 suppose the crank and connector to be in the position ,h ,i ,k 7fig4 #af471 the piston being consequently at the bottom of the cylinder4 ,if steam now press the piston upwards1 the pivot ,h and the connector ,h ,i will be pressed downwards1 and this pressure will urge the crank ,i ,k in the direction ,i ,k4 ,it is evident that such a force cannot turn the crank round the centre ,k1 and can be attended with no other effect than a pressure on the axle or pivots of the wheel4 ,hence in these two positions1 the engine can have no effect whatever in turning the crank4 ,what1 then1 it may be asked1 extricates the machine from this mechanical dilemma in which it is placed twice in every revolution1 on arriving at those positions in which the crank escapes the influence of the power8 ,there is a tendency in bodies1 when once put in motion1 to continue that motion until stopped by some opposing force1 and this tendency carries the crank out of those two critical situations4 ,the velocity which is given to it1 while it is under the influence of the impelling force of the beam1 is retained in a sufficient degree to carry it through that situation in which it is deserted by this impelling force4 ,although the rotatory motion intended to be produced by the crank is1 therefore1 not absolutely destroyed by this circumstance1 yet it is rendered extremely irregular1 since1 in passing through the two positions already described1 where the machine loses its power over the crank1 the motion will be very slow1 and1 in the positions of the crank most remote from these1 where the power of the beam upon it is greatest1 the motion will be very quick4 ,as the crank revolves from each of those positions where the power of the machine over it is greatest1 to where that power is altogether lost1 it is continually diminished1 so that1 in fact1 the crank is driven by a varying power1 and therefore produces a varying motion4 ,this will be easily understood by considering the successive positions of the crank and connector represented in fig4 #af4 ,this variable motion becomes particularly objectionable when the engine is employed to drive machinery4 ,to remove this defect1 we have recourse to the property of bodies just mentioned1 viz4 their tendency to retain a motion which is communicated to them4 ,a large metal wheel called a fly-wheel is placed upon the axis of the crank 7fig4 #ae471 and is turned by it4 ,the effect of this wheel is to equalize the motion communicated by the action of the beam on the crank1 that action being just sufficient to sustain in the fly-wheel a uniform velocity1 and the tendency of this wheel to retain the velocity it receives1 renders its rotation sufficiently uniform for all practical purposes4 ,this uniformity of motion1 however1 will only be preserved on two conditions2 first1 that the supply of steam from the boiler shall be uniform2 and secondly1 that the machine have always the same resistance to overcome or be loaded equally4 ,if the supply of steam from the boiler to the cylinder be increased1 the motion of the piston will be rendered more rapid1 and1 therefore1 the revolution of the fly-wheel will also be more rapid1 and1 on the other hand1 a diminished supply of steam will retard the fly-wheel4 ,again1 if the resistance or load upon the engine be diminished1 the supply of steam remaining the same1 the velocity will be increased1 since a less resistance is opposed to the energy of the moving power2 and1 on the other hand1 if the resistance or load be increased1 the speed will be diminished1 since a greater resistance will be opposed to the same moving power4 ,to insure a uniform velocity1 in whatever manner the load or resistance may be changed1 it is necessary to proportion the supply of steam to the resistance1 so that1 upon the least variation in the velocity1 the supply of steam will be increased or diminished1 so as to keep the engine going at the same rate4 7#ei47 ,one of the most striking and elegant appendages of the steam engine is the apparatus contrived by ,watt for effecting this purpose4 ,an apparatus1 called a regulator or governor1 had been long known to mill-wrights for rendering uniform the action of the stones in corn-mills1 and was used generally in machinery4 ,mr4 ,watt contrived a beautiful application of this apparatus for the regulation of the steam engine4 ,in the pipe which conducts steam from the boiler to the cylinder he placed a thin circular plate1 so that when placed with its face presented towards the length of the pipe1 it nearly stopped it1 and allowed little or no steam to pass to the cylinder1 but when its edge was placed in the direction of the pipe1 it offered no resistance whatever to the passage of the steam4 ,this circular plate1 called the throttle valve1 was made to turn on a diameter as an axis1 passing consequently through the centre of the tube1 and was worked by a lever outside the tube4 ,according to the position given to it1 it would permit more or less steam to pass4 ,if the valve be placed with its edge nearly in the direction of the tube1 the supply of steam is abundant2 if it be placed with its face nearly in the direction of the tube1 the supply of steam is more limited1 and it appears that1 by the position given to this valve1 the steam may be measured in any quantity to the cylinder4 ,at first it was proposed that the engine-man should adjust this valve with his hand2 when the engine was observed to increase its speed too much1 he would check the supply of steam by partially closing the valve2 but if1 on the other hand1 the motion was too slow1 he would open the valve and let in a more abundant supply of steam4 ,watt1 however1 was not content with this1 and desired to make the engine itself discharge this task with more steadiness and regularity than any attendant could1 and for this purpose he applied the governor already alluded to4 ,this apparatus is represented in fig4 #ae42 ,l is a perpendicular shaft or axle to which a wheel1 ,m1 with a groove is attached4 ,a strap or rope1 which is rolled upon the axle of the fly-wheel1 is passed round the groove in the wheel ,m1 in the same manner as the strap acts in a turning lathe4 ,by means of this strap the rotation of the fly-wheel will produce a rotation of the wheel ,m and the shaft ,l1 and the speed of the one will always increase or diminish in the same proportion as the speed of the other4 ,n1 ,n are two heavy balls of metal placed at the ends of rods1 which play on an axis fixed on the revolving shaft at ,o1 and extend beyond the axis to ,q ,q4 ,connected with these by joints at ,q ,q are two other rods1 ,q ,r1 which are attached to a broad ring of metal1 moving freely up and down the revolving shaft4 ,this ring is attached to a lever whose centre is ,s1 and is connected by a series of levers with the throttle-valve ,t4 ,when the speed of the fly-wheel is much increased1 the spindle ,l is whirled round with considerable rapidity1 and by their natural tendency#bj the balls ,n ,n fly from the centre4 ,the levers which play on the axis ,o1 by this motion1 diverge from each other1 and thereby depress the joints ,q ,q1 and draw down the joints ,r1 and with them the ring of metal which slides upon the spindle4 ,by these means the end of the lever playing on ,s is depressed1 and the end ,v raised1 and the motion is transmitted to the throttle-valve1 which is thereby partially closed1 and the supply of steam to the cylinder checked4 ,if1 on the contrary1 the velocity of the fly-wheel be diminished1 the balls will fall towards the axis1 and the opposite effects ensuing1 the supply of steam will be increased1 and the velocity restored4 ,footnote #bj3 ,the centrifugal force4 ,illustration3 ,pl4 ,,iv4 ,,watt',s ,,single ,,acting ,,steam ,,engine4 ,the peculiar beauty of this apparatus is1 that in whatever position the balls settle themselves1 the velocity with which the governor revolves must be the same1#ba and in this1 in fact1 consists its whole efficacy as a regulator4 ,its regulating power is limited1 and it is only small changes of velocity that it will correct4 ,it is evident that such a velocity as1 on the one hand1 would cause the balls to fly to the extremity of their play1 or1 on the other1 would cause them to fall down on their rests1 would not be influenced by the governor4 ,footnote #ba3 ,strictly speaking1 this is only true when the divergence of the rods from the spindle is not very great1 and1 in practice1 this divergence is never sufficient to render the above assertion untrue4 ,this property of the conical pendulum arises from the circumstance of the centrifugal force1 in this instance1 varying as the radius of the circle in which the balls are moved2 and when this is the case1 as is well known1 the periodic time is constant4 ,the time of one revolution of the balls is equal to twice the time in which either ball1 as a common pendulum1 would vibrate on the centre1 and as all its vibrations1 though the arcs be unequal1 are equal in time1 provided those arcs be small1 so also is the periodic time of the revolving ball invariable4 ,these observations1 however1 only apply when the balls settle themselves steadily into a circular motion2 for while they are ascending they describe a spiral curve with double curvature1 and the period will vary4 ,this takes place during the momentary changes in the velocity of the engine4 ,we have thus described the principal parts of the double-acting steam engine4 ,the valves and the methods of working them have been reserved for the next chapter1 as they admit of considerable variety1 and will be better treated of separately4 ,we have also reserved the consideration of the boiler1 which is far from being the least interesting part of the modern steam engine1 for a future chapter4 ,,chapter ,,vii4 ,,double-,,acting ,,steam ,,engine 7continued47 ,on the ,valves of the ,double-,acting ,steam ,engine4 -- ,original ,valves4 -- ,spindle ,valves4 -- ,sliding ,valve4 -- ,d ,valve4 -- ,four-,way ,cock4 7#fj47 ,the various improvements described in the last chapter were secured to ,watt by patent in the year #aghb4 ,the engine now acquired an enlarged sphere of action2 for its dominion over manufactures was decided by the fly-wheel1 crank1 and governor4 ,by means of these appendages1 its motions were regulated with the most delicate precision2 so that while it retained a power whose magnitude was almost unlimited1 that power was under as exact regulation as the motion of a time-piece4 ,there is no species of manufacture1 therefore1 to which this machine is not applicable1 from the power which spins the finest thread1 or produces the most delicate web1 to that which is necessary to elevate the most enormous weights1 or overcome the most unlimited resistances4 ,although it be true1 that in later times the steam engine has received many improvements1 some of which are very creditable to the invention and talents of their projectors1 yet it is undeniable that all its great and leading perfections1 all those qualities by which it has produced such wonderful effects on the resources of these countries1 by the extension of manufactures and commerce1--those qualities by which its influence is felt and acknowledged in every part of the civilized globe1 in increasing the happiness1 in multiplying the enjoyments1 and cheapening the pleasures of life1--that these qualities are due to the predominating powers of one man1 and that man one who possessed neither the influence of wealth1 rank1 nor education1 to give that first impetus which is so often necessary to carry into circulation the earlier productions of genius4 ,the method of working the valves of the double-acting steam engine1 is a subject which has much exercised the ingenuity of engineers1 and many elegant contrivances have been suggested1 some of which we shall now proceed to describe4 ,but even in this the invention of ,watt has anticipated his successors2 and the contrivances suggested by him are those which are now almost universally used4 ,in order perfectly to comprehend the action of the several systems of valves which we are about to describe1 it will be necessary distinctly to remember the manner in which the steam is to be communicated to the cylinder1 and withdrawn from it4 ,when the piston is at the top of the cylinder1 the steam below it is to be drawn off to the condenser1 and the steam from the boiler is to be admitted above it4 ,again1 when it has arrived at the bottom of the cylinder1 the steam above is to be drawn off to the condenser1 and the steam from the boiler is to be admitted below it4 ,in the earlier engines constructed by ,watt1 this was accomplished by four valves1 which were opened and closed in pairs4 ,valve boxes were placed at the top and bottom of the cylinder1 each of which communicated by tubes both with the steam-pipe from the boiler and the condenser4 ,each valve-box accordingly contained two valves1 one to admit steam from the steam-pipe to the cylinder1 and the other to allow that steam to pass into the condenser4 ,thus each valve-box contained a steam valve and an exhausting valve4 ,the valves at the top of the cylinder are called the upper steam valve and the upper exhausting-valve1 and those at the bottom1 the lower steam valve and the lower exhausting-valve4 ,in fig4 #ae4 ,a is the upper steam valve1 which1 when open1 admits steam above the piston2 ,b is the upper exhausting-valve1 which1 when open1 draws off the steam from the piston to the condenser4 ,c is the lower steam valve1 which admits steam below the piston2 and ,d1 the lower exhausting-valve1 which draws off the steam from below the piston to the condenser4 ,now1 suppose the piston to be at the top of the cylinder1 the cylinder below it being filled with steam1 which has just pressed it up4 ,let the upper steam valve ,a1 and the lower exhausting-valve ,d be opened1 and the other two valves closed4 ,the steam which fills the cylinder below the piston will immediately pass through the valve ,d into the condenser1 and a vacuum will be produced below the piston4 ,at the same time1 steam is admitted from the steam-pipe through the valve ,a above the piston1 and its pressure will force the piston to the bottom of the cylinder4 ,on the arrival of the piston at the bottom of the cylinder1 the upper steam valve ,a1 and lower exhausting-valve ,d1 are closed2 and the lower steam valve ,c1 and upper exhausting-valve ,b are opened4 ,the steam which fills the cylinder above the piston now passes off through ,b into the condenser1 and leaves a vacuum above the piston4 ,at the same time1 steam from the boiler is admitted through the lower steam valve ,c1 below the piston1 so that it will press the piston to the top of the cylinder2 and so the process is continued4 ,it appears1 therefore1 that the upper steam valve1 and the lower exhausting-valve1 must be opened together1 on the arrival of the piston at the top of the cylinder4 ,to effect this1 one lever1 ,e1 is made to communicate by jointed rods with both these valves1 and this lever is moved by a pin placed on the piston-rod of the air-pump2 and such a position may be given to this pin as to produce the desired effect exactly at the proper moment of time4 ,in like manner1 another lever1 ,f1 communicates by jointed rods with the upper exhausting valve and lower steam valve1 so as to open them and close them together2 and this lever1 in like manner1 is worked by a pin on the piston-rod of the air-pump4 7#fa47 ,this method of connecting the valves1 and working them1 has been superseded by another1 for which ,mr4 ,,murray of ,leeds obtained a patent1 which was1 however1 set aside by ,messrs4 ,bolton and ,watt1 who showed that they had previously practised it4 ,this method is represented in figs4 #ah1 #ai4 ,the stems of the valves are perpendicular1 and move in steam-tight sockets in the top of the valve-boxes4 ,the stem of the upper steam valve ,a is a tube through which the stem of the upper exhausting-valve ,b passes1 and in which it moves steam-tight2 both these stems moving steam-tight through the top of the valve-box4 ,the lower steam valve ,c1 and exhausting-valve ,d1 are similarly circumstanced2 the stem of the former being a tube through which the stem of the latter passes4 ,the stems of the upper steam valve and lower exhausting-valve are then connected by a rod1 ,e2 and those of the upper exhausting-valve and lower steam valve by another rod1 ,f4 ,these rods1 therefore1 are capable of moving the valves in pairs1 when elevated and depressed4 ,the motion which works the valves is1 however1 not communicated by the rod of the air-pump1 but is received from the axis of the fly-wheel4 ,this axis works an apparatus called an eccentric2 the principle which regulates the motion of this may be thus explained3-- ,d ,e 7figs4 #bj1 #ba47 is a circular metallic ring1 the inner surface of which is perfectly smooth4 ,this ring is connected with a shaft1 ,f ,b1 which communicates motion to the valves by levers which are attached to it at ,b4 ,a circular metallic plate is fitted in the ring so as to be capable of turning within it1 the surfaces of the ring and plate which are in contact being smooth and lubricated with oil or grease4 ,this circular plate revolves1 but not on its centre4 ,it turns on an axis ,c1 at some distance from its centre ,a2 the effect of which1 evidently1 is that the ring within which it is turned is moved alternately in opposite directions1 and through a space equal to twice the distance 7,c ,a7 of the axis of the circular plate from the common centre of it and the ring4 ,the eccentric in its two extreme positions is represented in figs4 #bj1 #ba4 ,the plate and ring ,d ,e are placed on the axis of the fly-wheel1 or on the axis of some other wheel which is worked by the fly-wheel4 ,so that the motion of continued rotation in the fly-wheel is thus made to produce an alternate motion in a straight line in the shaft ,f ,b4 ,this rod is made to communicate by levers with the rods ,e and ,f 7figs4 #ah1 #ai471 which work the valves in such a manner1 that1 when the eccentric is in the position fig4 #bj41 one pair of valves are opened1 and the other pair closed2 and when it is brought to the position fig4 #ba41 the other pair are opened and the former closed and so on4 ,it is by means of such an apparatus as this that the valves are worked almost universally at present4 ,the piston being supposed to be at the top of the cylinder 7fig4 #ah471 and the rod ,e raised1 the valves ,a and ,d are opened1 and ,b and ,c closed4 ,the steam enters from the steam-pipe at an aperture immediately above the valve ,a1 and1 passing through the open valve1 enters the cylinder above the piston4 ,at the same time1 the steam which is below the piston1 and which has just pressed it up1 flows through the open valve ,d1 and through a tube immediately under it to the condenser4 ,a vacuum being thus produced below the piston1 and steam pressure acting above it1 it descends2 and when it arrives at the bottom of the cylinder 7fig4 #ai47 the rod ,f is drawn down1 and the valves ,a and ,d fall into their seats1 and at the same time the rod ,f is raised1 and the valves ,b and ,c are opened4 ,steam is now admitted through an aperture above the valve ,c1 and passes below the piston1 while the steam above it passes through the open valve ,b into a tube immediately under it1 which leads to the condenser4 ,a vacuum being thus produced above the piston1 and steam pressure acting below it1 the piston ascends1 and thus the alternate ascent and descent is continued by the motion communicated to the rods ,e ,f from the fly-wheel4 ,illustration3 ,pl4 ,v4 ,,watt',s ,,double-,,acting ,,steam ,,engine4 ,illustration3 ,pl4 ,,vi4 7c7 ,an improvement has been made in the ,united ,states in the mode of working the puppet valve4 ,it consists in placing them by pairs in two different vertical planes instead of one4 ,the rods then work through four separate stuffing boxes1 and the necessity of making two of them hollow cylinders is avoided4--,a4 ,e4 7#fb47 ,there are various other contrivances for regulating the circulation of steam through the cylinder4 ,in figs4 #bb1 #bc4 is represented a section of a slide valve suggested by ,mr4 ,murray of ,leeds4 ,the steam-pipe from the boiler enters the valve-box ,d ,e at ,s4 ,curved passages1 ,a ,a1 ,b ,b1 communicate between this valve-box and the top and bottom of the cylinder2 and a fourth passage leads to the tube ,c1 which passes to the condenser4 ,a sliding piece within the valve-box opens a communication alternately between each end of the cylinder and the tube ,c1 which leads to the condenser4 ,in the position of the apparatus in fig4 #bb4 steam is passing from the steam-pipes1 through the curved passage ,a ,a above the piston1 and at the same time the steam below the piston is passing through the passage ,b ,b into the tube ,c1 and thence to the condenser4 ,a vacuum is thus formed below the piston1 and steam is introduced above it4 ,the piston1 therefore1 descends2 and when it arrives at the bottom of the cylinder1 the slide is moved into the position represented in fig4 #bc4 ,steam now passes from ,s through ,b ,b below the piston1 and the steam above it passes through ,a ,a and ,c to the condenser4 ,a vacuum is thus produced above the piston1 and steam pressure is introduced below it1 and the piston ascends2 and in this way the motion is continued4 ,the slide is moved by a lever1 which is worked by the eccentric from the fly-wheel4 7#fc47 ,watt suggested a method of regulating the circulation of steam1 which is called the ,d valve1 from the resemblance which the horizontal section of the valve has to the letter ,d4 ,this method1 which is very generally used1 is represented in section in figs4 #bd1 #be4 ,steam from the boiler enters through ,s4 ,a rod of metal connects two solid plugs1 ,a ,b1 which move steam-tight in the passage ,d4 ,in the position of the apparatus represented in fig4 #bd4 the steam passes from ,s through the passage ,d1 and enters the cylinder above the piston2 while the steam below the piston passes through the open passage by the tube ,c to the condenser4 ,a vacuum is thus formed below the piston1 while the pressure of steam is introduced above it1 and it accordingly descends4 ,when it has arrived at the bottom of the cylinder1 the plugs ,a ,b are moved into the position in fig4 #be4 ,steam now passing from ,s through ,d1 enters the cylinder below the piston2 while the steam which is above the piston1 and has just pressed it down1 passes through the open passage into the condenser4 ,a vacuum is thus produced above the piston1 and the steam pressure below forces it up4 ,when it has arrived at the top of the cylinder1 the position of the plugs ,a ,b is again changed to that represented in fig4 #bd41 and a similar effect to that already described is produced1 and the piston is pressed down2 and so the process is continued4 ,the plugs ,a ,b1 and the rod which connects them1 are moved up and down by proper levers1 which receive their motion from the eccentric4 ,this contrivance is frequently modified1 by conducting the steam from above the piston to the condenser1 through a tube in the plugs ,a ,b1 and their connecting rod4 ,in figs4 #bf1 #bg4 a tube passes through the plugs ,a ,b and the rod which joins them4 ,in the position fig4 #bf4 steam entering at ,s passes through the tube to the cylinder above the piston1 while the steam below the piston passes through ,c into the condenser4 ,a vacuum being thus made below the piston1 and steam pressing above it1 it descends2 and when it has arrived at the bottom of the cylinder1 the position of the plugs ,a ,b and the tube is changed to that represented at fig4 #bg4 ,the steam now entering at ,s passes to the cylinder below the piston1 while the steam above the piston passes through ,c into the condenser4 ,a vacuum is thus produced above the piston1 and steam pressure introduced below it1 so that it ascends4 ,when it has arrived at the top of the cylinder1 the plugs are moved into the position represented in fig4 #bf41 and similar effects being produced1 the piston again descends2 and so the motion is continued4 ,the motion of the sliding tube may be produced as in the former contrivances1 by the action of the eccentric4 ,it is also sometimes done by a bracket fastened on the piston-rod of the air-pump4 ,this bracket1 in the descent of the piston1 strikes a projection on the valve-rod1 and drives it down2 and in the ascent meets a similar projection1 and raises it4 7#fd47 ,another method1 worthy of notice for its elegance and simplicity1 is the four-way cock4 ,a section of this contrivance is given in figs4 #bh1 #bi43 ,c ,t ,s ,b are four passages or tubes2 ,s leads from the boiler1 and introduces steam2 ,c1 opposite to it1 leads to the condenser2 ,t is a tube which communicates with the top of the cylinder2 and ,b one which communicates with the bottom of the cylinder4 ,these four tubes communicate with a cock1 which is furnished with two curved passages1 as represented in the figures2 and these passages are so formed1 that1 according to the position given to the cock1 they may be made to open a communication between any two adjacent tubes of the four just mentioned4 ,when the cock is placed as in fig4 #bh4 communication is opened between the steam-pipe and the top of the cylinder by one of the curved passages1 and between the condenser and the bottom of the cylinder by the other curved passage4 ,in this case the steam passes from below the piston to the condenser1 leaving a vacuum under it1 and steam is introduced from the boiler above the piston4 ,the piston therefore descends2 and when it has arrived at the bottom of the cylinder1 the position of the cock is changed to that represented in fig4 #bi4 ,this change is made by turning the cock through one fourth of an entire revolution1 which may be done by a lever moved by the eccentric1 or by various other means4 ,one of the curved passages in the cock now opens a communication between the steam-pipe and the bottom of the cylinder2 while the other opens a communication between the condenser and the top of the cylinder4 ,by these means1 the steam from the boiler is introduced below the piston1 while the steam above the piston is drawn off to the condenser4 ,a vacuum being thus made above the piston1 and steam introduced below it1 it ascends2 and when it has arrived at the top of the cylinder1 the cock being moved back1 it resumes the position in fig4 #bh41 and the same consequences ensue1 the piston descends2 and so the process is continued4 ,in figs4 #cj1 #ca4 the four-way cock with the passages to the top and bottom of the cylinder is represented on a larger scale4 ,this beautiful contrivance is not of late invention4 ,it was used by ,papin1 and is also described by ,leupold in his ,theatrum ,machinarum1 a work published about the year #agbj1 in which an engine is described acting with steam of high pressure1 on a principle which we shall describe in a subsequent chapter4 ,the four-way cock is liable to some practical objections4 ,the quantity of steam which fills the tubes between the cock and the cylinder1 is wasted every stroke4 ,this objection1 however1 also applies to the sliding valve 7figs4 #bb1 #bc471 and to the sliding tube or ,d valves 7figs4 #bd1 #be1 #bf1 #bg474 ,in fact1 it is applicable to every contrivance in which means of shutting off the steam are not placed at both top and bottom of the cylinder4 ,besides this1 however1 the various passages and tubes cannot be conveniently made large enough to supply steam in sufficient abundance2 and consequently it becomes necessary to produce steam in the boiler of a more than ordinary strength to bear the attenuation which it suffers in its passage through so many narrow tubes4 ,illustration3 ,pl4 ,,vii4 ,one of the greatest objections1 however1 to the use of the four-way cock1 particularly in large engines1 is its unequal wear4 ,the parts of it near the passages having smaller surfaces1 become more affected by the friction1 and in a short time the steam leaks between the cock and its case1 and becomes wasted1 and tends to vitiate the vacuum4 ,these cocks are seldom used in condensing engines1 except they be small engines1 but are frequently adopted in high-pressure steam-engines2 for in these the leakage is not of so much consequence1 as will appear hereafter4 ,,chapter ,,viii4 ,,boiler ,,and ,,its ,,appendages4--,,furnace4 ,the ,boiler and its ,appendages4 -- ,level ,gauges4 -- ,feeding ,apparatus4 -- ,steam ,gauge4 -- ,barometer ,gauge4 -- ,safety ,valves4 -- ,self-regulating ,damper4 -- ,edelcrantz's ,valve4 -- ,furnace4 -- ,self-consuming ,furnace4 -- ,brunton's ,self-regulating ,furnace4 -- ,oldham's ,modification4 7#fe47 ,the regular action of a steam engine1 as well as the economy of fuel1 depends in a great degree on the construction of the boiler or apparatus for generating the steam4 ,the boiler may be conceived as a great magazine of steam for the use of the engine2 and care must be taken not only that a sufficient quantity be always ready for the supply of the machine1 but also that it shall be of the proper quality2 that is1 that its pressure shall not exceed that which is required1 nor fall short of it4 ,precautions should1 therefore1 be taken that the production of steam should be exactly proportioned to the work to be done1 and that the steam so produced shall be admitted to the cylinder in the same proportion4 ,to accomplish this1 various contrivances1 eminently remarkable for their ingenuity1 have been resorted to1 and which we shall now proceed to describe4 7d7 ,it may be premised that boilers have been made of various figures1 each having its own peculiar advantages and defects4 ,that which possesses the greatest degree of strength1 is one of the shape of a cylinder4 ,this form was originally introduced by ,oliver ,evans1 in the ,united ,states4 ,it will have its entire superiority when the fire is made beneath it in a furnace of masonry4 ,but this method is not applicable to steam boats or locomotive engines4 ,in these instances the weight of the separate furnace is an objection2 when1 therefore1 this form is applied in them1 the fire is usually made in a chamber of cylindric shape1 within the boiler1 and the smoke is conveyed to the chimney by flues1 which pass through the water4 ,these flues have1 in some cases1 been reduced to the size of small tubes1 and of this method an example will be found in a subsequent part of this work4--,a4 ,e4 7#ff47 ,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#ca472 and which are still generally continued4 ,there are1 however1 some other methods which merit our attention4 ,a weight1 ,f 7fig4 #cb471 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 string or chain passing over a wheel1 ,w1 with a counterpoise1 ,a1 which is just sufficient to balance ,f1 when half immersed4 ,if ,f be raised above the water1 ,a being lighter1 will no longer balance it1 and ,f will descend1 pulling up ,a1 and turning the wheel ,w4 ,if1 on the other hand1 ,f be plunged deeper in the water1 ,a1 will more than balance it1 and will pull it up4 ,so that the only position in which ,f and ,a will balance each other is when ,f is half immersed4 ,the wheel ,w is so adjusted1 that when two pins1 placed on its rim1 are in the horizontal position1 as in fig4 #cb41 the water is at its proper level4 ,consequently it follows1 that if the water rise above this level1 the weight ,f is lifted1 and ,a falls1 so that the pins ,p ,p come into the position in fig4 #cc4 ,if1 on the other hand1 the level of the water falls1 ,f falls and ,a rises1 so that the pins ,p ,p assume the position in fig4 #cd4 ,thus1 in general1 the position of the pins ,p ,p becomes an indication of the quantity of water in the boiler4 ,another method is to place a glass tube 7fig4 #ce47 with one end1 ,t1 entering the boiler above the proper level1 and the other end1 ,t1 entering it below the proper level4 ,it must be evident that the water in the tube will always stand at the same level as the water in the boiler2 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 ,this1 and the last-mentioned gauge1 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 ,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 and1 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 7#fg47 ,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 do 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 this1 a method has been invented by which the engine is made to feed its own boiler4 ,the pipe ,g 7fig4 #ae471 which leads from the hot water pump ,h1 terminates in a small cistern1 ,c 7fig4 #cf471 in which the water is received4 ,in the bottom of this cistern a valve1 ,v1 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 weight1 ,f1 dipped in the water in the boiler in a manner similar to that described in fig4 #cb41 and balanced by a counterpoise1 ,a1 in exactly the same way4 ,when the level of the water in the boiler falls1 the float ,f falls with it1 and1 pulling down the arm ,e of the lever1 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 singularly felicitous arrangement1 the boiler is made to replenish itself1 or1 more properly speaking1 it is made to receive such a supply 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 7#dg471 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 ,c is not always required 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 being restored to the cold cistern 7fig4 #ab471 in case water for the supply of that cistern be not sufficiently abundant4 ,in cities and places in which it becomes an object to prevent the waste of water1 the waste-pipes proceeding from the feed-cistern ,c 7fig4 #cf47 and from the cold cistern containing the condenser and air-pump1 may be conducted to a cistern ,a ,b 7fig4 #cg474 ,let ,c be the pipe from the feeding cistern1 and ,d that from the cold cistern2 by these pipes the waste water1 from both these cisterns is deposited in ,a ,b4 ,in the bottom of ,a ,b is a valve ,v1 opening upwards1 connected with a float ,f4 ,when the quantity of water collected in the cistern ,a ,b is such that the level rises considerably1 the float ,f is raised1 and lifts the valve ,v1 and the water flows into the main pipe1 which supplies water for working the engine3 ,g is the cold water-pump for the supply of the cold cistern4 ,this arrangement for saving the water discharged from the feeding and condensing cisterns has been adopted in the printing office of the ,bank of ,ireland1 and a very considerable waste of water is thereby prevented4 7#fh47 ,it is necessary to have a ready method of ascertaining at all times the strength 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 apparatus which has free communication with the steam4 ,it is usually inserted in the jacket of the cylinder 7#dd474 ,let ,a ,b ,c 7fig4 #ch47 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 levels of the mercury in the tubes ,b ,c and ,b ,a2 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 exceed that of the steam1 and the degree or 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 visible3 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 ,c2 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 7#fi47 ,the force with which the piston is pressed depends on two things3 #a1 the actual strength of the steam which presses on it2 and #b1 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 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 #ci471 more than thirty inches long1 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 must1 therefore1 exist in the tube ,a ,b1 above the level of the mercury2 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 barometer 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 engine1 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 ,first ascertain the difference of the levels of the mercury in the steam-gauge4 ,this gives the excess of the steam pressure above the atmospheric pressure4 ,then find the height of the mercury in the barometer-gauge4 ,this gives the excess of the atmospheric pressure above the uncondensed steam4 ,hence1 if these two heights be added together1 we shall obtain the excess of the impelling force of the steam from the boiler on the one side of the piston1 above the resistance of the uncondensed steam on the other side4 ,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 ,then 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 whole effective force with which it moves will be obtained4 ,in the computation of the power of the engine1 however1 all this force1 thus computed1 is not to be allowed as the effective working power4 ,for it requires some force1 and by no means an inconsiderable portion1 to move the engine itself1 even when unloaded2 all this1 therefore1 which is spent in overcoming friction1 c4 is to be left out of account1 and only the balance set down as the effective working power4 ,from what we have stated1 it appears that in order to estimate the effective 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 #ch47 instead of communicating with the atmosphere1 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 will 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#gj47 ,to secure the boiler from accidents arising from the steam becoming too strong1 a safety valve is used1 similar to those described in ,papin's steam engine1 loaded with a weight equal to the strength which the steam is intended to have above the atmospheric pressure2 for it is found expedient1 even in condensing engines1 to use the steam of a pressure somewhat above that of the atmosphere4 ,besides this valve1 another of the very opposite kind is sometimes used4 ,upon stopping the engine1 and extinguishing the fire1 it is found that the steam condensed within the boiler produces a vacuum2 so that the atmosphere1 pressing on the external surface of the boiler1 has a tendency to crush it4 ,to prevent this1 a safety valve is provided1 which opens inwards1 and which being forced open by the atmospheric pressure when a vacuum is produced within1 the air rushes in1 and a balance is obtained between the pressures within and without4 7#ga47 ,we have already explained 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 motion4 ,since1 then1 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 ,for1 otherwise1 one of two effects would ensue3 the boiler would either fail to supply the engine with steam1 or steam would accumulate in the boiler1 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 increase or mitigate the furnace1 as production is to be augmented or diminished4 ,to effect this by any attention on the part of the engine-man would be impossible2 but a most ingenious method has been contrived1 of making the boiler regulate itself in these respects4 ,let ,t 7fig4 #dj47 be a tube inserted in the top of the boiler1 and descending nearly to the bottom4 ,the pressure of the steam on the surface of the water in the boiler forces water up in the tube ,t1 until the difference of the levels is equal to the difference between the pressure of the steam in the boiler and that of the atmosphere4 ,a weight ,f1 half immersed in the water in the tube1 is suspended by a chain which passes over the wheels ,p ,p1 and is balanced by a metal plate ,d1 in the same manner as the float in fig4 #cb4 is balanced by the weight ,a4 ,the plate ,d passes through the mouth of the flue ,e1 as it issues finally from the boiler2 so that when the plate ,d falls1 it stops the flue and thereby suspends the draught of air through the furnace1 mitigates the fire1 and diminishes the production of steam4 ,if1 on the contrary1 the plate ,d be drawn up1 the draught is increased1 the fire rendered more effective1 and the production of steam in the boiler stimulated4 ,now suppose that the boiler is producing steam faster than the engine consumes it1 either because the load on the engine has been diminished1 and therefore its consumption of steam proportionally diminished1 or because the fire has become too intense4 ,the consequence is1 that the steam beginning to accumulate1 will press upon the surface of the water in the boiler with increased force1 and the water will rise in the tube ,t4 ,the weight ,f will therefore be lifted1 and the plate ,d will descend1 stop the draught1 mitigate the fire1 and check the production of steam2 and it will continue so to do1 until the production of steam becomes exactly equal to the demands of the engine4 ,if1 on the other hand1 the production of steam be not equal to the wants of the machine1 either because of the increased load1 or the insufficiency of the fire1 the steam in the boiler losing its elasticity1 the surface of the water rises1 not sustaining a pressure sufficient to keep it at its wonted level4 ,therefore1 the surface in the tube ,t falls1 and the weight ,f falls1 and the plate ,d rises4 ,the draught is thus increased1 by opening the flue1 and the fire rendered more intense2 and thus the production of steam is stimulated1 until it is sufficiently rapid for the purposes of the engine4 ,this apparatus is called the self-acting damper4 7#gb47 ,it has been proposed to connect this damper with the safety-valve invented by the ,chevalier ,edelcrantz4 ,a small brass cylinder is fixed to the boiler1 and is fitted with a piston which moves in it1 without much friction1 and nearly steam-tight4 ,the cylinder is closed at top1 having a hole through which the piston-rod plays2 so that the piston is thus prevented from being blown out of the cylinder by the steam4 ,the side of the cylinder is pierced with small holes opening into the air1 and placed at short distances above each other4 ,let the piston be loaded with a weight proportional to the pressure of the steam intended to be produced4 ,when the steam has acquired a sufficient elasticity1 the piston will be lifted1 and steam will escape through the first hole4 ,if the production of steam be not too rapid1 and that its pressure be not increasing1 the piston will remain suspended in this manner3 but if it increase1 the piston will be raised above the second hole1 and it will continue to rise until the escape of the steam through the holes is sufficient to render the weight of the piston a counterpoise for the steam4 ,this safety valve is particularly well adapted to cases where steam of an exactly uniform pressure is required2 for the pressure must necessarily be always equal to the weight on the piston4 ,thus1 suppose the section of the piston be equal to a square inch2 if it be loaded with #aj lbs41 including its own weight1 the steam which will sustain it in any position in the cylinder1 whether near the bottom or top1 must always be exactly equal in pressure to #aj lbs4 per inch4 ,in this respect it resembles the quality already explained in the governor1 and renders the pressure of the steam uniform1 exactly in the same manner as the governor renders the velocity of the engine uniform4 7#gc47 ,the economy of fuel depends1 in a great degree1 on the construction of the furnace1 independently of the effects of the arrangements we have already described4 ,the grate or fire-place of an ordinary furnace is placed under the boiler2 and the atmospheric air passing through the ignited fuel1 supplies sufficient oxygen to support a large volume of flame1 which is carried by the draught into a flue1 which circulates twice or oftener round the boiler1 and in immediate contact with it1 and finally issues into the chimney4 ,through this flue the flame circulates1 so as to act on every part of the boiler near which the flue passes2 and it is frequently not until it passes into the chimney1 and sometimes not until it leaves the chimney1 that it ceases to exist in the state of flame4 ,the dense black smoke which is observed to issue from the chimneys of furnaces is formed of a quantity of unconsumed fuel1 and may be therefore considered as so much fuel wasted4 ,besides this1 in large manufacturing towns1 where a great number of furnaces are employed1 it is found that the quantity of smoke which thus becomes diffused through the atmosphere1 renders it pernicious to the health1 and destructive to the comforts of the inhabitants4 ,these circumstances have directed the attention of engineers to the discovery of means whereby this smoke or wasted fuel may be consumed for the use of the engine itself1 or for whatever use the furnace may be applied to4 ,the most usual method of accomplishing this is by so arranging matters that fuel in a state of high combustion1 and1 therefore1 producing no smoke1 shall be always kept on that part of the grate which is nearest to the mouth of the flue 7and which we shall call the back72 by this means the smoke which arises from the imperfectly ignited fuel which is nearer to the front of the grate must pass over the surface of the red fuel1 before it enters the flue1 and is thereby ignited1 and passes in a state of flame into the flue4 ,a passage called the feeding-mouth leads to the front of the grate1 and both this passage and the grate are generally inclined at a small angle to the horizon1 in order to facilitate the advance of the fuel according as its combustion proceeds4 ,when fresh fuel for feeding the boiler is first introduced1 it is merely laid in the feeding-mouth4 ,here it is exposed to the action of a part of the heat of the burning fuel on the grate1 and undergoes1 in some degree1 the process of coking4 ,the door of the feeding-mouth is furnished with small apertures for the admission of a stream of air1 which carries the smoke evolved by the coking of the fresh fuel over the burning fuel on the grate1 by which this smoke is ignited1 and becomes flame1 and in this state enters the flue1 and circulates round the boiler4 ,when the furnace is to be fed1 the door of the feeding-mouth is opened1 and the fuel which had been laid in it1 and partially coked1 is forced upon the front part of the grate4 ,at first1 its combustion being imperfect1 but proceeding rapidly1 a dense black smoke arises from it4 ,the current of air from the open door through the feeding-mouth carries this over the vividly burning fuel in the back part of the grate1 by which the smoke being ignited1 passes in a state of flame into the flue4 ,when the furnace again requires feeding1 every part of this fuel will be in a state of active combustion1 and it is forced to the back part of the grate next the flue1 preparatory to the introduction of more fuel from the feeding-mouth4 ,the apertures in the door of the feeding-mouth are furnished with covers1 so that the quantity of air admitted through them can be regulated by the workmen4 ,the efficiency of these furnaces in a great degree depends on the judicious admission of the air through the feeding-mouth3 for if less than the quantity necessary to support the combustion of the fuel be admitted1 a part of the smoke will remain unconsumed2 and if more than the proper quantity be admitted1 it will defeat the effects of the fuel by cooling the boiler4 ,if the process which we have just described be considered1 it will not be difficult to perceive the total impossibility in such a furnace of exactly regulating the draught of air1 so that too much shall not pass at one time1 and too little at another4 ,when the door is open to introduce fresh fuel into the feeding-mouth1 and advance that which occupied it upon the grate1 the workman ceases to have any control whatever over the draught of air2 and even at other times when the door is closed1 his discretion and attention cannot be depended on4 ,the consequence is1 that with these defects the proprietors of steam engines found1 that in the place of economising the fuel1 the use of these furnaces entailed on them such an increased expense that they were generally obliged to lay them aside4 7#gd47 ,mr4 ,brunton of ,birmingham having turned his attention to the subject1 has produced a furnace which seems to be free from the objections against those we have just mentioned4 ,the advantages of his contrivance1 as stated by himself1 are as follow3-- ,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 ,illustration3 ,pl4 ,,viii4 ,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 performing1 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 boiler of course 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 receiver1 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-pit7 is attained without moving the coal upon the grate4 ,the fire-place is a circular grate placed on a vertical shaft in a horizontal position4 ,it is capable of revolving1 and is made to do so by the vertical shaft1 which is turned by wheelwork1 which is worked by the engine itself2 or this shaft or spindle may be turned by a water-wheel1 on which a stream of water is allowed to flow from a reservoir into which it is pumped by the power of the engine2 and by regulating the quantity of water in the stream1 the grate may be made to revolve with a greater or less speed4 ,in that part of the boiler which is over the grate1 there is an aperture1 in which is placed a hopper1 through which fuel is let down upon the grate at the rate of any quantity per minute that may be required4 ,the apparatus which admits the coals through this hopper is worked by the engine also1 and by the same means as the grate is turned so that the grate revolves with a speed proportional to the rapidity with which the fuel is admitted through the hopper1 and by this ingenious arrangement the fuel falls equally thick upon the grate4 ,the supply of water which turns the wheel which works the grate and the machinery in the hopper1 is regulated by a cock connected with the self-regulating damper2 so that when the steam is being produced too fast1 the supply of water will be diminished1 and by that means the supply of fuel to the grate will be diminished1 and the grate will revolve less rapidly3 and when the steam is being produced too slowly for the demands of the engine1 the contrary effects take place4 ,in this way the fuel which is introduced into the furnace is exactly proportioned to the work which the engine has to perform4 ,the hopper may be made large enough to hold coals for a day's work1 so that the furnace requires no other attendance than to deposite coals in the hopper each morning4 ,the coals are let down from the hopper on the grate at that part which is most remote from the flue2 and as they descend in very small quantities at a time1 they are almost immediately ignited4 ,but until their ignition is complete1 a smoke will arise1 which1 passing to the flue over the vividly burning fuel1 will be ignited4 ,air is admitted through proper apertures1 and its quantity regulated by the damper in the same manner as the supply of fuel4 ,the superiority of this beautiful invention over the common smoke-consuming furnaces is very striking4 ,its principle of self-adjustment as to the supply of coals and atmospheric air1 and the proportioning of these to the quantity of work to be performed by the engine1 not only independent of human labour1 but with a greater degree of accuracy than any human skill or attention could possibly effect1 produces saving of expense1 both in fuel and labour4 7#ge47 ,mr4 ,oldham1 engineer to the ,bank of ,ireland1 has proposed another modification of the self-regulating furnace1 which seems to possess several advantages1 and evinces considerable ingenuity4 ,he uses a slightly inclined grate1 at the back or lower end of which is the flue1 and at the front or higher end1 the hopper for admitting the coals4 ,in the bottom or narrow end of the hopper is a moveable shelf1 worked by the engine4 ,upon drawing back this shelf1 a small quantity of fuel is allowed to descend upon a fixed shelf under it2 and upon the return of the moveable shelf1 this fuel is protruded forward upon the grate4 ,every alternate bar of the grate is fixed1 but the intermediate ones are connected with levers1 by which they are moved alternately up and down4#bb ,the effect is1 that the coals upon the bars are continually stirred1 and gradually advanced by their own weight from the front of the grate1 where they fall from the hopper1 to the back1 where they are deposited in the ash-pit4 ,by the shape and construction of the bars1 the air is conducted upwards between them1 and rushes through the burning fuel1 so as to act in the manner of a blowpipe1 and the entire surface of the fire presents a sheet of flame4 ,footnote #bb3 ,mr4 ,brunton used moveable bars in a furnace constructed by him before he adopted the horizontal revolving grate4 ,that plan1 however1 does not appear to have been as successful as the latter1 as he has abandoned it4 ,mr4 ,oldham states that his furnace has been in use for several years without any appearance of derangement in the mechanism1 and with a considerable saving of fuel4 ,we cannot fail to be struck with the beauty of all these contrivances1 by which the engine is made to regulate itself1 and supply its own wants4 ,it is in fact1 all but alive4 ,it was observed by ,belidor1 long before the steam engine reached the perfection which it has now acquired1 that it resembled an animal1 and that no mere work of man ever approached so near to actual life4 ,heat is the principle of its existence4 ,the boiler acts the part of the heart1 from which its vivifying fluid rushes copiously through all the tubes1 where having discharged the various functions of life1 and deposited its heat in the proper places1 it returns again to the source it sprung from1 to be duly prepared for another circulation4 ,the healthfulness of its action is indicated by the regularity of its pulsations2 it procures its own food by its own labour2 it selects those parts which are fit for its support1 both as to quantity and quality2 and has its natural evacuations1 by which all the useless and innutritious parts are discharged4 ,it frequently cures its own diseases1 and corrects the irregularity of its own actions1 exerting something like moral faculties4 ,without designing to carry on the analogy1 ,mr4 ,farey1 in speaking of the variations incident to the work performed by different steam engines1 states some further particulars in which it maybe curiously extended4 ,we must observe1 says he1 that the variation in the performance of different steam engines1 which are constructed on the same principle1 working under the same advantages1 is the same as would be found in the produce of the labour of so many different horses or other animals when compared with their consumption of food2 for the effects of different steam engines will vary as much from small differences in the proportion of their parts1 as the strength of animals from the vigour of their constitutions2 and again1 there will be as great differences in the performance of the same engine when in good and bad order1 from all the parts being tight and well oiled1 so as to move with little friction1 as there is in the labour of an animal from his being in good or bad health1 or excessively fatigued3 but in all these cases there will be a maximum which cannot be exceeded1 and an average which we ought to expect to obtain4 ,,chapter ,,ix4 ,,double-,,cylinder ,,engines4 ,hornblower's ,engine4 -- ,woolf's ,engine4 -- ,cartwright's ,engine4 7#gf47 ,the expansive property of steam1 of which ,watt availed himself in his single engine by cutting off the supply of steam before the descent of the piston was completed1 was applied in a peculiar manner by an engineer named ,hornblower1 about the year #agha1 and at a later period by ,woolf4 ,hornblower was the first who conceived the idea 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 manner which we shall presently describe4 ,the condensing apparatus of ,hornblower1 as well as the other appendages of the engine1 do not differ materially from those of ,watt2 so that it will be sufficient for our present purpose to explain the manner in which the steam is made to act in moving the piston4 ,let ,c1 fig4 #da41 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 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 piston1 ,h is a tube by which a communication may be opened by the valve ,i between the top and bottom of the lesser cylinder ,b4 ,k is a tube communicating1 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 entire 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 #da4 ,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 it as it is urged by the steam above it2 but after a part of the descent has been effected1 the steam below the lesser piston passing into the greater1 expands into an increased space1 and therefore loses its elastic force proportionally4 ,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 it 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 ,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 ,impelled in this way1 let us suppose the pistons to have arrived at the bottoms of the cylinders1 as in fig4 #db41 and let the valves ,g1 ,l1 and ,o 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 communications 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-rods 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 ,o 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 not however appear1 that any adequate advantage was gained by this modification of the principle1 since no engines of this construction are now made4 7#gg47 ,the use of two cylinders was revived by ,arthur ,woolf1 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 under a safety-valve loaded with any given number of pounds upon the square inch1 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 pressure4 ,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 fluids--properties which at that time were perfectly understood--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 place where the barometer would stand at a different height4 ,thus 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#bc ,footnote #bc3 ,it is strange that this absurdity has been repeatedly given as unquestionable fact in various encyclopdias on the article ,steam ,engine1 as well as in by far the greater number of treatises expressly on the subject4 ,the method by which ,mr4 ,woolf proposed to apply the principle which he imagined himself to have discovered was by an arrangement of cylinders similar to those of ,hornblower1 but having their magnitudes proportioned to the greater extent of expansion which he proposed to use4 ,two cylinders1 like those of ,hornblower1 were placed under the working beam1 having their piston-rods at distances from the axis proportioned to the lengths of their respective strokes4 ,the relative magnitudes of the cylinders ,a and ,b must be adjusted according to the extent to which the principle of expansion is intended to be used4 ,the valves ,c ,c were placed at each end of the lesser cylinder in tubes communicating with the boiler1 so as to admit steam on each side of the lesser piston1 and cut it off at pleasure4 ,a tube1 ,d1 formed a communication between the upper end of the lesser and lower end of the greater cylinder1 which communication is opened and closed at pleasure by the valve ,e4 ,in like manner1 the tube ,d forms a communication between the lower end of the lesser cylinder and the upper end of the greater1 which may be opened and closed by the valve ,e4 ,the top and bottom of the greater cylinder communicated with the condenser by valves ,f ,f4 ,let us suppose that the air is blown from the engine in the usual way1 all the valves closed1 and the engine ready to start1 the pistons being at the top of the cylinders4 ,open the valves ,c1 ,e1 and ,f4 ,the steam which occupies the greater cylinder below the piston will now pass into the condenser through ,f1 leaving a vacuum below the piston4 ,the steam which is in the lesser cylinder below the piston will pass through ,d and open the valve ,e1 and will press down the greater piston4 ,the steam from the boiler will flow in at ,c1 and press on the lesser piston4 ,at first the whole motion will proceed from the pressure upon the greater piston1 since the steam1 both above and below the lesser piston1 has the same pressure4 ,but1 as the pistons descend1 the steam below the less passing into the greater cylinder1 expands into a greater space1 and consequently exerts a diminished pressure1 and1 therefore1 the steam on the other side exerting an undiminished pressure1 acquires an impelling force exactly equal to the pressure lost in the expansion of the steam between the two pistons4 ,thus both pistons will be pressed to the bottoms of their respective cylinders4 ,it will be observed that in the descent the greater piston is urged by a continually decreasing force1 while the lesser is urged by continually increasing force4 ,upon the arrival of the pistons at the bottoms of the cylinders1 let the valves1 ,c1 ,e1 ,f be closed1 and ,c1 ,e1 ,f be opened1 as in fig4 #dd4 ,the steam which is above the greater piston now flows through ,f into the condenser1 leaving the space above the piston a vacuum4 ,the steam which is above the lesser piston passes through ,e and ,d below the greater1 while the steam from the boiler is admitted through ,c below the lesser piston4 ,the pressure of the steam entering through ,e below the greater piston1 pressing on it against the vacuum above it1 commences the ascent4 ,in the mean time the steam above the lesser piston passing into the enlarged space of the greater cylinder1 loses gradually its elastic force1 so that the steam entering from the boiler at ,c becomes in part effective1 and the ascent is completed under exactly the same circumstances as the descent1 and in this way the process is continued4 ,it is evident that the valves may be easily worked by the mechanism of the engine itself4 ,in this arrangement the pistons ascend and descend together1 and their rods must consequently be attached to the beam at the same side of the centre4 ,it is sometimes desirable that they should act on different sides of the centre of the beam1 and consequently that one should ascend while the other descends4 ,it is easy to arrange the valves so as to effect this4 ,in fig4 #de41 the lesser piston is at the bottom of the cylinder1 and the greater at the top4 ,on opening the valves ,c1 ,e1 ,f1 a vacuum is produced below the greater piston1 and steam flows from the lesser cylinder1 through ,e1 above the greater piston1 and presses it down4 ,at the same time steam being admitted from the boiler through ,c below the lesser piston1 forces it up against the diminishing force of the steam above it1 which expands into the greater cylinder4 ,thus as the greater piston descends the lesser ascends4 ,when each has traversed its cylinder1 the valves ,c1 ,e1 ,f being closed1 and ,c1 ,e1 ,f opened1 the lesser piston will descend1 and the greater ascend1 and so on4 7#gh47 ,the law according to which the elastic force of steam diminishes as it expands1 of which ,mr4 ,woolf appears to have been entirely ignorant1 is precisely similar to the same property in air and other elastic fluids4 ,if steam expands into twice or thrice its volume1 it will lose its elastic force in precisely the same proportion as it enlarges its bulk2 and therefore will have only a half or a third of its former pressure1 supposing that as it expands its temperature is kept up4 ,although ,mr4 ,woolf's patent contained the erroneous principle which we have noticed1 yet1 so far as his invention suggested the idea of employing steam at a very high-pressure1 and allowing it to expand in a much greater degree than was contemplated either by ,watt or ,hornblower1 it became the means of effecting a considerable saving in fuel2 for engines used for pumping on a large scale1 the steam being produced under a pressure of forty or fifty pounds or more upon the square inch1 might be worked first through a small space with intense force1 and the communication with the boiler being then cut off1 it might be allowed1 with great advantage1 to expand through a very large space4 ,some double-cylinder engines upon this principle have been worked in ,cornwall1 with considerable economy4 ,but the form in which the expansive principle1 combined with high pressure1 is now applied in the engines used for raising water from the mines1 is that in which it was originally proposed by ,watt4 ,a single cylinder of considerable length is employed2 the piston is driven through a small proportion of this length by steam1 admitted from the boiler at a very intense pressure3 the steam being then cut off1 the piston is urged by the expansive force of the steam which has been admitted1 and is by that means brought to the bottom of the cylinder4 ,it is evident1 under such circumstances1 that the pressure of the steam admitted from the boiler must be much greater than the resistance opposed to the piston1 and that the motion of the piston must1 in the first instance1 be accelerated and not uniform4 ,if the piston moved from the commencement with a uniform motion1 the pressure of the steam urging it must necessarily be exactly equal to the resistance opposed to it1 and then cutting off the supply of steam from the boiler1 the piston could only continue its motion by inertia1 the steam immediately becoming of less pressure than the resistance2 and after advancing through a very small space1 the piston would recoil upon the steam1 and come to a state of rest4 ,the steam1 however1 at the moment it is cut off being of much greater pressure than the amount of resistance upon the piston1 will continue to drive the piston forward1 until by its expansion its force is so far diminished as to become equal to the resistance of the piston4 ,from that point the impelling power of the steam will cease1 and the piston will move forward by its inertia only4 ,the point at which the steam is cut off should therefore be so regulated that it shall acquire a pressure equal to the resistance on the piston by its expansion1 just at such a distance from the end of the stroke as the piston may be able to move through by its inertia4 ,it is evident the adjustment of this will require great care and nicety of management4 7#gi47 ,in #agig a patent was granted to the ,rev4 ,mr4 ,cartwright1 a gentleman well known for other mechanical inventions1 for some improvements in the steam-engine4 ,his contrivance is at once so elegant and simple1 that1 although it has not been carried into practice1 we cannot here pass it over without notice4 ,the steam-pipe from the boiler is represented cut off at ,b 7fig4 #df472 ,t is a spindle-valve 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 size 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 ,thus the thin space between the two cylinders formed the condenser4 ,illustration3 ,pl4 ,,ix4 ,illustration3 ,pl4 ,x4 ,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 valve3 ,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 descent1 this is forced through a tube into a hot well1 ,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 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 which was disengaged from it4 ,let us suppose the piston at the top of the cylinder2 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 thus admitted above the piston1 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 moment a projecting spring1 ,k1 attached to the piston-rod1 strikes the stem of the steam-valve ,t1 and presses it into its seat4 ,thus1 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 large 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 wheel1 ,m1 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 a most 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 half the fuel4 ,the inventor even proposed1 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 ,in this engine1 the ordinary method of rendering the piston steam-tight1 by oil or melted wax or tallow poured upon it1 could not be applied1 since the steam above the piston must always have a free passage through the piston-valve ,r4 ,the ingenious inventor therefore contrived a method of making the piston steam-tight in the cylinder1 without oil or stuffing1 and his method has since been adopted with success in other engines4 ,a ring of metal is ground into the cylinder1 so as to fit it perfectly1 and is then cut into four equal segments4 ,the inner surface of this ring being slightly conical1 another ring is ground into it1 so as to fit it perfectly1 and this is also cut into four segments1 and one is placed within the other1 but in such a manner that the joints or divisions do not coincide4 ,the arrangement of the two rings is represented in fig4 #dg4 ,within the inner ring are placed four springs1 which press the pieces outward against the sides of the cylinder1 and are represented in the diagram4 ,four pairs of these rings are placed one over another1 so that their joints do not coincide1 and the whole is screwed together by plates placed at top and bottom4 ,a vertical section of the piston is given in fig4 #dh4 ,one of the advantages of this piston is1 that the longer it is worked1 the more accurately it fits the cylinder1 so that1 as the machine wears it improves4 ,metallic pistons have lately come into very general use1 and such contrivances differ very little from the above4 ,,chapter ,x4 ,,locomotive ,,engines ,,on ,,railways4 ,high-pressure ,engines4 -- ,leupold's ,engine4 -- ,trevithick and ,vivian4 -- ,effects of ,improvement in ,locomotion4 -- ,historical ,account of the ,locomotive ,engine4 -- ,blenkinsop's ,patent4 -- ,chapman's ,improvement4 -- ,walking ,engine4 -- ,stephenson's ,first ,engines4 -- ,his ,improvements4 -- ,liverpool and ,manchester ,railway ,company4 -- ,their ,preliminary ,proceedings4 -- ,the ,great ,competition of #ahbi4 -- ,the ,rocket4 -- ,the ,sanspareil4 -- ,the ,novelty4 -- ,qualities of the ,rocket4 -- ,successive ,improvements4 -- ,experiments4 -- ,defects of the ,present ,engines4 -- ,inclined ,planes4 -- ,methods of surmounting them4 -- ,circumstances of the ,manchester ,railway ,company4 -- ,probable ,improvements in ,locomotives4 -- ,their capabilities with respect to speed4 -- ,probable ,effects of the ,projected ,railroads4 -- ,steam ,power compared with ,horse ,power4 -- ,railroads compared with ,canals4 7#hj47 ,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 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 a 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 high-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 engines1 the whole of the condensing apparatus1 viz4 the cold-water cistern1 condenser1 air-pump1 cold-water pump1 c4 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#ha47 ,high-pressure engines were one of the earliest modifications of the steam engine4 ,the contrivance1 which is obscurely described in the article already quoted 7#bg471 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-- ,a 7fig4 #di47 is the boiler1 with the furnace beneath it2 ,c ,c are two cylinders with two solid pistons1 ,p ,p1 connected with the working-beams ,b ,b1 to which are attached the pump-rods1 ,r ,r1 of two forcing-pumps1 ,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 is issuing 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 ,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 #ej4 ,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 ,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#hb47 ,from the date of the improvement of ,watt until the commencement of the present century1 high-pressure engines were altogether neglected in these countries4 ,in the year #ahjb1 ,messrs4 ,trevithick and ,vivian constructed the first high-pressure engine 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 #ea4 ,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 onwards1 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 upwards1 as represented in the figure4 ,the other mouth is furnished 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 draft 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 ,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 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 and1 through them1 to any machinery which the engine may be applied to move4 ,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 the figure #eb4 ,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 #ea41 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 to the strength of the steam with which it is proposed to work4 ,illustration3 ,pl4 ,,xi4 ,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 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 7e7 ,to the plates of the ,english edition has been added one1 7plate ,a7 representing a high-pressure engine as constructed by the ,west ,point ,foundry in the state of ,new ,york4 ,the principal parts will be readily distinguished from their resemblance to the analogous parts of a condensing engine4 ,the condenser and air-pump of that engine1 it will be observed1 are suppressed4 ,at v x and y z are forcing-pumps by which a supply of water is injected into the boiler at each motion of the engine4 ,for the four-way cock1 used in the ,english high-pressure engines1 a slide valve at r s1 is substituted1 and is found to work to much greater advantage4 ,it is set in motion by an eccentric1 in a manner that will be more obvious from an inspection of the plate than from any description4--,a4 ,e4 7f7 ,a very safe and convenient boiler for a high-pressure engine has been invented in the ,united ,states by ,mr4 ,babcock4 ,the boiler consists of small tubes1 into which water is flashed by a small forcing-pump at every stroke of the engine4 ,the tubes are kept so hot in a furnace1 as to generate steam of the required temperature1 but not hot enough to cause any risk of the decomposition of the water4 ,the strength of the apparatus is such1 and the quantity of water exposed to heat at one time so small1 as to leave hardly any risk of danger4--,a4 ,e4 7#hc47 ,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 turnpike 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 #aj 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#hd47 ,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 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 several 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 about thirty miles1 in little more than an hour8 ,and yet this is a matter of daily and almost hourly occurrence4 ,neither is the road1 on which this wondrous performance is effected1 the most favourable which could be constructed for such machines4 ,it is subject to undulations and acclivities1 which reduce the rate of speed much more than similar inequalities affect the velocity on common roads4 ,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 #ej to #aej tons are transported at the average rate of #ae miles an hour2 but the engines in this case are loaded below their power2 and in one instance we have seen a load--we should rather say a cargo--of wagons1 conveying merchandise to the amount of #bcj tons gross1 transported from ,liverpool to ,manchester at the average rate of #ab 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 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 quarter 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 ,if then travelling steam engines1 with all the imperfections of an incipient invention--with the want of experience1 the great parent of practical improvements--with the want of the common advantage of the full application of the skill and capital of the country--subjected to but one great experiment1 and that experiment limited to one form of engine2 if1 under such disadvantages1 the effects to which we have referred have been produced1 what may we not expect from this extraordinary power1 when the enterprise of the country shall be unfettered1 when greater fields of experience are opened1 when time1 ingenuity1 and capital have removed the existing imperfections1 and have brought to light new and more powerful principles8 ,this is not mere speculation on possibilities1 but refers to what is in a state of actual progression4 ,railways are in progress between the points of greatest intercourse in the ,united ,kingdom1 and travelling steam engines are in preparation for the common turnpike roads2 the practicability and utility of that application of the steam engine having not only been established by experiment to the satisfaction of their projectors1 but proved before the legislature in a committee of inquiry on the subject4 ,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 everything which is necessary for the subsistence of the poor1 or for the enjoyment of the rich1 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 #bjj quarters of corn be necessary to raise #djj1 and #ajj more be required to bring the #djj to market1 then the net surplus will be #ajj4 ,but if by the use of steam carriages the same quantity can be brought to market with an expenditure of #ej quarters1 then the net surplus will be increased from #ajj to #aej 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 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 support 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 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 manufacture 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 civilized 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 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 ,towns1 at present removed some stages from the metropolis1 will become its suburbs2 others1 now 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 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 powers4 ,nor have the terrors of the ,pacific prevented the ,enterprise from doubling the ,cape1 and reaching the shores of ,india4 ,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 material from which at the present moment it derives its powers1 is restricted by local and accidental circumstances4#bd ,footnote #bd3 ,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 ,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#he47 ,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 face of the wheel and the surface of the road were absolutely smooth and free from friction1 so that the face of the wheel 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 wheel would slip or slide upon the road as the wheel is made to revolve4 ,but if1 on the other hand1 the pressure of the face of the wheel 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 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 ,trevithick 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 ,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 railroad2 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 contrivance1 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 #ec4 ,a sketch of these propellers is given in fig4 #ec4 ,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 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 lever1 ,l ,m1 the extremity of which is connected by a cord or chain with a point1 ,s1 placed near the shin of the leg4 ,when the piston is pressed into the cylinder1 the knee1 ,k1 is drawn towards the engine1 and the cord1 ,m ,s1 is made to lift the foot1 ,f1 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 foot1 ,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 thigh1 at ,n1 above the knee1 by a joint1 is a horizontal rod1 ,n ,r1 which works a rack1 ,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-wheel1 acting on the other rack beneath it1 will move the latter in the contrary direction4 ,the rack ,r being then moved in the same direction with the knee1 ,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 leg1 ,l ,f1 immediately above the knee1 at ,n4 ,when the piston is forced inwards1 the knee1 ,k1 will thus be forced backwards2 and when the piston is forced outwards1 the knee1 ,k1 will be drawn forwards4 ,it therefore follows that the two knees1 ,k and ,k1 are pressed alternately backwards and forwards4 ,the foot1 ,f1 when the knee1 ,k1 is drawn forward1 is lifted by the means already described for the foot1 ,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#hf47 ,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 that1 when the road was level1 and the rails clean1 the adhesion of the wheels was sufficient1 in all kind 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 rail2 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 it1 on the railroad1 the requisite number of wagons4#be ,footnote #be3 ,wood on ,railroads1 #b;d edit4 ,in #ahad1 an engine was constructed at ,killingworth1 by ,mr4 ,stephenson1 having two cylinders with a cylindrical 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 #ed4 ,this engine is represented in fig4 #ed41 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 crank1 ,f1 descends to the lowest point1 the crank1 ,g1 rises from the lowest point to the horizontal position1 ,d2 and1 again1 when the crank1 ,f1 rises from the lowest point to the horizontal position1 ,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 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 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#hg47 ,the next stimulus which the progress of this 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 wagons 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 wagons or carriages1 when drawn by any engine to its own station1 or 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 ,lock and ,messrs4 ,walker and ,rastrick1 experienced engineers1 to visit the different railways 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 judgment1 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 engine into which it would be foreign to our subject to enter4 ,the result of the comparison of the two systems was1 that the capital 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-- ---------------------------------------- --------------------------- ,annual ,expense of ,capital4 ,expense4 taking a ,ton of ,goods ,one ,mile4 ---------------------------------------- --------------------------- s4 d4 s4 d4 ,locomotive ,engines #eh1jjj #j #j #be1eag #h #b #jafd of a penny4 ,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 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 #ejjl4 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 #ej lbs4 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 matters1 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 ,sanspariel1 by ,hackworth2 and the ,novelty1 by ,messrs4 ,braithwait 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 #cj miles4 ,the ,rocket performed this journey twice3 the first time in #b hours #ad minutes and #h seconds2 and the second time1 in #b hours #f minutes and #di seconds4 ,its speed at different parts of the journey varied3 its greatest rate of motion was 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 ,sanspariel 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#hh47 ,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 and1 second1 by the current of heated air which is carried by the draft through the fire1 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 #ee4 ,illustration3 ,fig4 #ef4 ,this engine is represented in fig4 #ee4 ,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 #f feet in length1 with flat ends2 the chimney issues from one end1 and to the other end is attached a square box1 ,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 #c inches in breadth2 the magnitude of the box being #c feet in length1 #b feet in width1 and #c 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 freely through the pipe ,c1 into the casing which 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 length is represented at fig4 #ef4 ,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 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 draft 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 draft4 ,the power of this furnace must necessarily depend on the power of draft 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 draft of the furnace4 ,in fig4 #ef4 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 drawing1 fig4 #ee41 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 #bj square feet1 which received heat from the surface of #f 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#hi47 ,the ,sanspareil of ,mr4 ,hackworth is represented in fig4 #eg42 the horizontal section being exhibited in fig4 #eh4 ,illustration3 ,fig4 #eg4 ,illustration3 ,fig4 #eh4 ,the draft of the furnace is produced in the same manner as in the ,rocket1 by ejecting the waste steam coming from 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 ,trevithick and ,vivian4 ,in the horizontal section 7fig4 #eh471 ,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 of the draft 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 #b feet2 and it was gradually reduced1 so that1 at the chimney1 its diameter was only #ae inches4 ,the grate-bars extended #e feet into the tube4 ,the surface of water exposed to the radiant heat of the fire was #af square feet2 and that exposed to the action of the heated air and flame was about #ge square feet4 ,the magnitude of the grate or sheet of burning fuel which radiated heat1 was #aj square feet4 7#ij47 ,the ,novelty1 of ,messrs4 ,braithwait and ,ericson1 is represented in fig4 #ei42 and a section of the generator and boiler is exhibited in fig4 #fj43 the corresponding parts in the two figures are marked by the same letters4 ,illustration3 ,fig4 #ei4 ,a is the generator or receiver1 containing the steam which works the engine2 this communicates with a lower generator1 ,b1 which extends in a horizontal direction the entire length of the carriage4 ,within the generator1 ,a1 is contained the furnace1 ,f1 which communicates in a tube1 ,c2 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 grate1 ,f4 ,below the grate the furnace is not open1 as usual1 to the atmosphere1 but communicates by a tube1 ,e1 with a bellows1 ,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 air1 contained in the furnace1 ,f1 is driven on1 by the same force1 through a small curved tube marked e1 which circulates like a worm 7as represented in fig4 #fj47 through the horizontal generator or receiver2 and1 tapering gradually1 until reduced to very small dimensions1 it finally issues into the chimney1 ,g4 ,the air1 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-crank2 the other pair1 when necessary1 being connected with them4 ,illustration3 ,fig4 #fj4 ,in this engine1 the magnitude of the surface of burning fuel on the grate-bars is less than #b square feet2 the surface exposed to radiant heat is #i-a_/b square feet2 and the surface of water exposed to heated air is about #cc 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 #c to #e1 it exposes a greater surface of water to radiant heat1 in the proportion of #d to #c2 and a greater surface of water to heated air1 in the proportion of more than #c to #b4 ,it was found that the ,rocket1 compared with the ,sanspareil1 consumed fuel1 in the evaporation of a given quantity of water1 in the proportion of #aa to #bh4 ,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 ,company2 and1 certainly1 nothing has been more conducive to the efficiency of the engines since used than this improvement4 ,it is much to be regretted that the ingenious gentleman who suggested this has reaped none of the advantages to which a patentee would be legally entitled4#bf ,footnote #bf3 ,mr4 ,booth received a part of the premium of #ejjl41 but has not participated in any degree in the profits of the manufacture of the engines4 7#ia47 ,the great 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 on 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 passes 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 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 #be tubes1 each #c 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 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 is 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 produce in a given time a certain quantity of steam4 ,each stroke of the piston causes one revolution of the wheels1 and consumes two 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 very obvious1 that it is only surprising that1 in the first instance1 tubes of smaller diameter than #c inches were not used4 ,in engines since constructed1 the number of tubes vary from #ij to #abj1 the diameter being reduced to #b inches or less1 and in some instances tubes have been introduced1 even to the number of #aej1 of #a-a_/b inch diameter4 ,in the ,meteor1 #bj square feet are exposed to radiation1 and #aci to the contact of heated air2 in the ,arrow1 #bj square feet to radiation1 and #ade 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-- ---------------------------------------- ---------- ,average rate of,consumption of ,engines4 speed in miles,coke in pounds per hour4 per ton per mile4 ---------------------------------------- ---------- ,no4 #a4 ,rocket #ad #bda #b4 ,sanspareil #ae #bdg #c4 ,phoenix #ab #adb #d4 ,arrow #ab #abe ---------------------------------------- ---------- 7#ib47 ,since the period at which the 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 ,the consequence of this has been1 that the particular engines to which we have alluded1 and others of the same class1 without having1 as it were1 lived their natural life1 or without having been worn out by work1 have been laid aside to give place to others of improved powers4 ,by the exposure of the cylinders to the atmosphere in the ,rocket1 and engines of a similar form1 a great waste of heat was incurred1 and it was accordingly determined to remove them from the exterior of the boiler1 and to place them within a casing immediately under the chimney3 this chamber was necessarily kept warm by its proximity to the end of the boiler1 but more by the current of heated air which constantly rushed into it from the tubes4 ,this change1 also1 rendered necessary another1 which improved the working of the engine4 ,in the earlier engines the motion of the piston was communicated to the wheel by a connecting rod attached to one of the spokes on the exterior of the wheel1 as represented in fig4 #ee4 ,by the change to which we have just alluded1 the cylinders being placed between the wheels under the chimney1 this mode of working became inapplicable1 and it was considered better to connect the piston-rods with two cranks placed at right angles on the axles of the great wheels4 ,by this means1 it was found that the working of the machine was more even1 and productive of less strain than in the former arrangement4 ,on the other hand1 a serious disadvantage was incurred by the adoption of a cranked axle4 ,the weakness necessarily arising from such a form of axle could only be counterbalanced by great thickness and weight of metal2 and even this precaution does not prevent the occasional fracture of such axles at the angles of the cranks4 ,the advantages1 however1 of this plan1 on the whole1 are considered to predominate4 ,in the most improved engines in present use two safety-valves are provided1 of which only one is in the power of the engine-man4 ,the tubes being smaller and more numerous than in the earlier engines1 the heat is more completely extracted from the air before it enters the chimney4 ,a powerful draft is rendered still more necessary by the smallness of the tubes3 this is effected by forcing the steam which has worked the pistons through a contracted orifice1 presented upwards in the chimney1 by the regulation of which any degree of draft may be obtained4 ,one of the most improved engines at present in use is represented in fig4 #fa4 ,a represents the cylindrical boiler1 the lower half of which is traversed by tubes1 as described in the ,rocket4 ,they are usually from #hj to #ajj in number1 and about #a-a_/b inch in diameter2 the boiler is about #g feet in length2 the fire-chamber is attached to one end of it1 at ,f1 as in the ,rocket1 and similar in construction2 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 any 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-place1 ,f2 and two levers1 ,l1 project from the end1 which communicate with the valves by means of rods1 by which the engine is governed1 so as to stop or reverse the motion4 ,illustration3 ,fig4 #fa4 ,the wheels of these engines have been commonly constructed of wood1 with strong iron tires1 furnished with flanges adapted to the rails4 ,but ,mr4 ,stephenson has recently 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#ic47 ,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 unlimited abstraction of heat from the air passing from the furnace1 by ,mr4 ,booth's ingenious arrangement of tubes traversing the boiler2 and1 #c;d1 ,keeping the cylinders warm1 by immersing them in the chamber under the chimney4#bg ,there are many minor details which might be noticed with approbation1 but these constitute the main features of the improvements1 and should never1 for a moment1 be lost sight of by projectors of locomotive engines4 ,footnote #bg3 ,mr4 ,robert ,stephenson1 whose experience and skill in the construction of locomotives attaches great importance to this condition4 ,it has lately1 however1 been abandoned by some other engine-makers1 for the purpose of getting rid of the cranked axle which must accompany it4 ,the successive introduction of improvements in the engines1 some of which we have mentioned1 has been accompanied by corresponding accessions to their practical power1 and to the economy of fuel2 and they have now arrived at a point which is as far beyond the former expectations of the most sanguine locomotive projectors1 as it assuredly is short of the perfection of which these wonderful machines are still susceptible4 ,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 fuel4 ,since that time ,i am not aware that1 in these respects1 the engine has received any material improvement4 ,the following are the particulars of three experiments thus made3-- ,i4 ,on ,saturday1 the #eth of ,may1 the engine called the ,victory took #bj wagons 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 miles17 in #a h4 #cd min4 #de sec4 ,the train stopped to take in water half-way1 for #aj minutes1 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 ,manchester 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 mile #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 wagons1 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 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 load in this journey 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 stroke2 and the diameter of the drawing wheels is #e feet4 ,,iii4 ,on the #bith of ,may1 the engine called the ,samson1 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 wagons1 laden with merchandise2 net weight about #aej tons2 gross weight1 including wagons1 tender1 c41 #bbc tons #f cwt4 ,the engine with this load travelled from ,liverpool to ,manchester 7#cj miles7 in #b h4 and #dj min41 exclusive of delays upon the road for watering1 c41 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 hour3 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#id47 ,from the above experiments it appears that a locomotive engine1 in good working order1 with its full complement of load1 is capable of transporting weights at an expense in fuel amounting to about #d ounces of coke per ton per mile4 ,the attendance required on the journey is that of an engine-man and a fire-boy2 the former being paid #as4 #f;d4 for each trip of #cj miles1 and the latter #as4 ,in practice1 however1 we are to consider1 that it rarely happens that the full complement of load can be sent with the engines2 and when lesser loads are transported1 the proportionate expense must for obvious reasons1 be greater4 ,the practical expenditure of fuel on the ,liverpool and ,manchester line may1 perhaps1 be fairly estimated at half a pound of coke per ton per mile4 7#ie47 ,having explained the power and efficiency of these locomotive engines1 it is now right to notice some of the defects under which they labour4 ,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 constructed of the later engines costs originally about #hjjl4 ,it may be hoped that1 by the excitement of competition1 the facilities derived from practice1 and from the manufacture of a greater number of engines of the same kind1 some reduction of this cost may be effected4 ,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 ends as to be water-tight4 ,when the boiler is heated1 the tubes are found to expand in a greater degree than the other parts of the boiler2 which frequently causes 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 causes1 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 draught 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 tubing1 which is done at the expense of about #gjl41 allowing for the value of the old tubes4 ,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 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 tubes if they were exposed1 as they are at present1 to the cinders4 ,the next source of expense arises from the wear of the boiler-head1 which is exposed to the action of the fire4 ,these require constant patching and frequent renewal4 ,a considerable improvement has lately been introduced into the method of tubing1 by substituting brass for copper tubes4 ,we are 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 copper4 ,it has been said by some whose opinions are adverse to the advantage of railways1 but more especially to the particular species of locomotive engines now under consideration1 that the repairs of one of these engines cost so great a sum as #aejjl4 per annum1 and that the directors now think of abandoning them1 or adopting either stationary engines or horse-power4 ,as to the first of these statements ,i must observe1 that the expense of repairs of such machines should never be computed in reference to time1 but rather to the work done1 or the distance travelled over4 ,i have ascertained that engines frequently travel a distance of from #be1jjj to #cj1jjj miles before they require new tubing4 ,during that work1 however1 single tubes are1 of course1 occasionally renewed1 and other repairs are made1 the expense of which may safely be stated as under the original cost of the engine4 ,the second statement1 that the company contemplate substituting stationary engines1 or horses1 for locomotives1 is altogether at variance with the truth4 ,whatever improvements may be contemplated in locomotives1 the directors assuredly have not the slightest intention of going back in the progress of improvement1 in the manner just mentioned4 ,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 correctly 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 expense of working the railway by locomotive and by fixed power4 ,these engineers recommended the adoption of locomotive power1 and their estimate was1 that the transport might be effected at the rate of 4#bgh of a penny1 or very little more than a farthing per ton per mile4 ,in the year #ahcc1 five years after this investigation took place1 it was found that the actual cost was 4#fbe of a penny1 or something more than a halfpenny 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 fourfold speed would require an addition of #ej per cent4 to the power1 without taking into account wear and tear4 ,now 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 wagons come back empty1 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 circumstances by stating them at #cc per cent4 in addition to the original estimate4 ,the next point of difference is the fuel4 ,in the original estimate coal is assumed as the fuel1 and it is taken at the price of five shillings and tenpence 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 seventeen shillings and sixpence a ton4 ,taking coke1 then1 to be equivalent to coal1 ton for ton1 this would add 4#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 4#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 ,what 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 and1 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 and your committee conceive1 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 time 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 #ae1eeb ,etna #ag1gfc ,ajax #aa1fgh ,firefly #ae1fjh ------ ,making in all #ie1hea ------ 7#if47 ,the advantages derivable from railroads are greatly abridged by the difficulty arising from those changes of level to which all roads are necessarily liable2 but in the case of railroads1 from causes peculiar to themselves1 these changes of level occasion great inconvenience4 ,to explain the nature of these difficulties1 it will be necessary to consider the relative proportion which must subsist between the power of traction on a level and on an inclined plane4 ,on a level railroad the force of traction necessary to propel any load1 placed on wheel carriages of the construction now commonly used1 may perhaps be estimated at #g-a_/b pounds1#bh for every ton gross in the load2 that is to say1 if a load of one ton gross were placed upon wheel carriages upon a level railroad1 the traces of horses drawing it would be stretched with a force equivalent to #g-a_/b pounds4 ,if the load amounted to two or three tons1 the tension of the traces would be increased to #ae or #bb-a_/b pounds1 and so on4 ,the necessity of this force of traction1 arising from the want of perfect smoothness in the road1 and from the friction of the wheels and axles of the carriages1 must be the same whether the road be level or inclined2 and consequently1 in ascending an inclined plane1 the same force of traction will be necessary in addition to that which arises from the tendency of the load to fall down the plane4 ,this latter tendency is always in the proportion of the elevation of the plane to its length2 that is to say1 a plane which rises #a foot in #ajj will give a weight of #ajj tons a tendency to fall down the plane amounting to #a ton1 and would therefore add #a ton to the force of traction necessary for such a load on a level4 ,footnote #bh3 ,the estimate commonly adopted by engineers at present is #i pounds per ton4 ,i have no doubt1 however1 that this is too high4 ,i am now 7,november1 #ahce17 engaged in an extensive course of experiments on different railways1 with a view to determine with precision this and other points connected with the full developement of their theory2 and ,i have reason to believe1 from the observations ,i have already made1 that even #g-a_/b pounds per ton is above the average force of traction upon the level4 ,now since #g-a_/b pounds is very nearly the #cjjth part of a ton1 it follows that if an inclination upon a railroad rises at the rate of #a foot in #cjj1 or1 what is the same1 #ag-a_/b feet in a mile1 such an acclivity will add #g-a_/b pounds per ton to the force of traction4 ,this acclivity therefore would require a force of traction twice as great as a level4 ,in like manner a rise of #ce feet in a mile would require three times the force of traction of a level1 #eb-a_/b feet in a mile four times that force1 and so on4 ,in fact1 for every #g feet in a mile which an acclivity rises1 #c pounds per ton will be added to the force of traction4 ,if we would then ascertain the power necessary to pull a load up any given acclivity upon a railroad1 we must first take #g-a_/b pounds as the force necessary to overcome the common resistance of the road1 and then add #c pounds for every #g feet which the acclivity rises per mile4 ,for example1 suppose an acclivity to rise at the rate of #gj feet in a mile1 the force of traction necessary to draw a ton up it would be thus calculated3-- ,friction #g-a_/b lbs4 #gj feet #aj times #c lbs4 #cj ------ ,total force #cg-a_/b ,it will be apparent1 therefore1 that if a railroad undulates by inclined planes1 even of the most moderate inclinations1 the propelling power to be used upon it must be of such a nature as to be capable of increasing its intensity in a great degree1 according to the elevation of the planes which it has to encounter4 ,a plane which rises #eb-a_/b feet per mile presents to the eye scarcely the appearance of an ascent1 and yet requires the power of traction to be increased in a fourfold proportion4 ,it is the property of animal power1 that within certain limits its energy can be put forth at will1 according to the exigency of the occasion2 but the intensity of mechanical power1 in the instance now considered1 cannot so conveniently be varied1 except indeed within narrow limits4 ,in the application of locomotive engines upon railways the difficulty arising from inclined planes has been attempted to be surmounted by several methods1 which we shall now explain4 #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 occasions1--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 four parts1 to be successively 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 mode is the cost of keeping such an engine with its boiler continually prepared1 and its steam up4 ,it would be 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 ,this method1 however1 cannot be profitably applied to planes of any considerable length4 #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 ,this expedient is scarcely compatible with a large transit of passengers1 except at the terminus of a line4 #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 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 otherwise 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 discovered1 which is consistent with the expedition necessary for that species of traffic4 ,the objections to this method are1 the necessity of maintaining a much higher pressure in the boiler than is sufficient for the purposes of the load upon more level parts of the line4 ,in the practice of this method considerable aid may be derived also by suspending the supply of feeding water 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 mixes1 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 incline 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 ,this method1 on railroads intended for passengers1 may be successfully applied on inclines which do not exceed #ah feet in a mile2 and1 with a sacrifice of the expense of locomotive power1 inclines so steep as #cf feet in a mile may be worked in this manner4 ,as1 however1 the sacrifice is considerable1 it will1 perhaps1 be always better to work the more steep inclines by assistant engines4 #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 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 #ee feet per mile1 upon the ,liverpool line1 the speed would be diminished to nearly one fourth of its amount upon the level4 ,whatever be the method adopted to surmount inclined planes upon a railway1 inconvenience attends the descent upon them4 ,the motion down the incline by the force of gravity is accelerated2 and if the train be not retarded1 a descent of any considerable length1 even at a small elevation1 would produce a velocity which would be attended with great danger4 ,the shoe used to retard the descent down hills on turnpike roads cannot be used upon railroads1 and the application of brakes to the faces of the wheels is likewise attended with some uncertainty4 ,the friction produced by the rapid motion of the wheel sometimes sets fire to wood1 and iron would be inadmissible4 ,the action of the steam on the piston may be reversed1 so as to oppose the motion of the wheels2 but even this is attended with peculiar difficulty4 ,from all that has been stated1 it will be apparent that1 with our present knowledge1 considerable inclines are fatal to the profitable performance on a railway1 and even small inclinations are attended with great inconvenience4#bi ,footnote #bi3 ,a contrivance might be applied in changes of level in railroads somewhat similar to locks in a canal4 ,the train might be rolled upon a platform which might be raised by machinery2 and thus at the change of level there would be as it were steps from one level to another1 up which the loads would be lifted by any power applied to work the machinery4 ,the advantage in this case would be1 that the trains might be adapted to work always upon a level4 7#ig47 ,to obtain from the locomotive steam engines now used on the railway the most powerful effects1 it is necessary that the load placed on each engine should be very considerable4 ,it is not possible1 with our present knowledge1 to construct and work three locomotive engines of this kind1 each drawing a load of #cj tons1 at the same expense and with the same effect as one locomotive engine drawing #ij tons4 ,hence arises what must appear an inconvenience and difficulty in applying these engines to one of the most profitable species of transport--the transport of passengers4 ,it is impracticable1 even between places of the most considerable intercourse to obtain loads of passengers sufficiently great at each trip to maintain such an engine working on a railway4#cj ,the difficulty of collecting so considerable a number of persons1 at any stated hour1 to perform the journey1 is obvious2 and therefore1 the only method of removing the inconvenience is to cause the same engine which transports passengers also to transport goods1 so that the goods may make up the requisite supplement to the load of passengers4 ,in this way1 provided the traffic in goods be sufficient1 such engines may start with their full complement of load1 whatever be the number of passengers4 ,footnote #cj3 ,on the occasion of races held at ,newton1 a place about #ae miles from ,liverpool1 two engines were sent1 with trains of carriages1 to take back to ,liverpool the visitors to the races4 ,some accident prevented one of the engines from working on the occasion1 and both trains were attached to the same engine3 #hjj persons were on this occasion drawn by the single engine to ,liverpool in the space of about an hour4 7#ih47 ,in comparing the extent of capital1 and the annual expenditure of the ,liverpool and ,manchester line1 and adopting it as a modulus in estimating the expenses of similar undertakings projected elsewhere1 there are several circumstances to which it is important to attend4 ,i have already observed on the large waste of capital in the item of locomotive engines which ought to be regarded as little more than experimental machines1 leading to a rapid succession of improvements4 ,most of these engines are still in good working order1 but have been abandoned for the reasons already assigned4 ,other companies will1 of course1 profit by the experience which has been thus purchased at a high price by the ,liverpool ,company4 ,this advantage in favour of future companies will go on increasing until such companies have their works completed4 ,a large portion of the current expense of a line of railway is independent of its length2 and is little less for the line connecting ,liverpool and ,manchester1 than it would be for a line connecting ,birmingham with ,liverpool or ,london4 ,the establishments of resident engineers1 coach and wagon yards1 c4 at the extremities of the line1 would be little increased by a very great increase in the length of the railway2 and the same observation will apply to other heads of expenditure4 ,it has been the practice of the canal companies between ,liverpool and ,manchester to warehouse the goods transported between these towns1 without any additional charge beyond the price of transport4 ,the ,railway ,company1 in competing with the canals1 were1 of course1 obliged to offer like advantages3 this compelled them to invest a considerable amount of capital in the building of extensive warehouses1 and to incur the annual expense of porterage1 salaries1 c4 connected with the maintenance of such storage4 ,in a longer line of railway such expenses 7if necessary at all7 would not be proportionally increased4 7#ii47 ,the comparison of steam-transport with the transport by horses1 even when working on a railway1 exhibits the advantage of this new power in a most striking point of view4 ,to comprehend these advantages fully1 it will be necessary to consider the manner in which animal power is expended as a means of transport4 ,the portion of the strength of a horse available for the purpose of a load depends on the speed of a horse's motion4 ,to this speed there is a certain limit1 at which the whole power of the horse will be necessary to move his own body1 and at which1 therefore1 he is incapable of carrying any load2 and1 on the other hand1 there is a certain load which the horse is barely able to support1 but incapable of moving with any useful speed4 ,between these two limits there is a certain rate of motion at which the useful effect of the animal is greatest4 ,in horses of the heavier class1 this rate of motion may be taken on the average as that of #b miles an hour2 and in the lighter description of horses1 #b-a_/b miles an hour4 ,beyond this speed1 the load which they are capable of transporting diminishes in a very rapid ratio as the speed increases3 thus1 if #aba express the load which a horse is able to transport a given distance in a day1 working at the rate of four miles an hour1 the same horse will not be able to transport more than the load expressed by #fd1 the same distance1 at #g miles an hour2 and1 at #aj miles an hour1 the load which he can transport will be reduced to #be4 ,the most advantageous speed at which a horse can work being #b miles an hour1 it is found that1 at this rate1 working for #aj hours daily1 he can transport #ab tons1 on a level railway1 a distance of #bj miles2 so that the whole effect of a day's work may be expressed by #bdj tons carried #a mile4 ,but this rate of transport is inapplicable to the purposes of travelling2 and therefore it becomes necessary1 when horses are the moving power1 to have carriages for passengers distinct from those intended for the conveyance of goods2 so that the goods may be conveyed at that rate of speed at which the whole effect of the horse will be the greatest possible2 while the passengers are conveyed at that speed which1 whatever the cost1 is indispensably necessary4 ,the weight of an ordinary mail-coach is about two tons2 and1 on a tolerably level turnpike road1 it travels at the rate of #aj miles an hour4 ,at this rate1 the number of horses necessary to keep it constantly at work1 including the spare horses indispensably necessary to be kept at the several stages1 is computed at the rate of a horse per mile4 ,assuming the distance between ,london and ,birmingham at #ajj miles1 a mail-coach running between these two places would require #ajj horses2 making the journey to and from ,birmingham daily4 ,the performance1 therefore1 of a horse working at this rate may be estimated at #b tons carried #b miles per day1 or #d tons carried #a mile in a day4 ,the force of traction on a good turnpike road is at least #bj times its amount on a level railroad4 ,it therefore follows1 that the performance of a horse on a railroad will be #bj times the amount of its performance on a common road under similar circumstances4 ,we may1 therefore1 take the performance of a horse working at #aj miles an hour1 on a level railroad1 at #hj tons conveyed #a mile daily4 ,the best locomotive engines used on the ,liverpool railway are capable of transporting #aej tons on a level railroad at the same rate2 and1 allowing the same time for stoppage1 its work per day would be #aej tons conveyed #bjj miles1 or #cj1jjj tons conveyed #a mile2 from which it follows1 that the performance of one locomotive engine of this kind is equivalent to that of #gejj horses working on a good turnpike road1 or to #cge horses working on a railway4 ,the consumption of fuel requisite for this performance1 with the most improved engines used at present on the ,manchester and ,liverpool line1 would be at the rate of eight#ca ounces of coke per ton per mile1 including the waste of fuel incurred by the stoppages4 ,thus the daily consumption of fuel1 under such circumstances1 would amount to #aejjj lbs4 of coke2 and #b lbs4 of coke daily would perform the work of one horse on a good turnpike road2 and #dj lbs4 of coke daily would perform the work of one horse on a railway4 ,footnote #ca3 ,in an experimental trip with a heavy train at #ab miles an hour1 ,i found the consumption of coke to be only four ounces per ton per hour4 ,i believe1 however1 the practical consumption in ordinary work to be very nearly eight ounces4 ,in this comparison1 the engine is taken at its most advantageous speed1 while horse-power is taken at its least advantageous speed1 if regard be only had to the total quantity of weight transported to a given distance4 ,but1 in the case above alluded to1 speed is an indispensable element2 and steam1 therefore1 possesses this great advantage over horse power1 that its most advantageous speed is that which is at once adapted to all the purposes of transport1 whether of passengers or of goods4 7#ajj47 ,the effects of steam compared with horse-power1 at lower rates of motion1 will exhibit the advantages of the former1 though in a less striking degree4 ,an eight-horse wagon commonly weighs #h tons1 and travels at the rate of #b-a_/b miles an hour4 ,strong horses working in this way can travel #h hours daily2 thus each horse performs #bj miles a day4 ,the performance1 therefore1 of each horse may be taken as equivalent to #bj tons transported #a mile2 and his performance on a railway being #bj times this amount1 may be taken as equivalent to #djj tons transported #a mile a day4 ,the performance of a horse working in this manner is1 therefore1 #e times the performance of a horse working at #aj miles an hour2 the latter effecting only the performance of #d tons transported #a mile per day on a good turnpike road1 or #hj tons on a railway4 ,we shall hence obtain the proportion of the performance of horses working in wagons to that of a locomotive steam engine4 ,since #b lbs4 of coke are equivalent to the daily performance of a horse in a mail-coach1 and #dj lbs4 on a railway1 at #aj miles an hour1 it follows that #aj lbs4 will be equivalent to the performance of a horse on a turnpike road1 and #bjj lbs4 on a railway1 at #b-a_/b miles an hour4 ,since a locomotive engine can perform the daily work of #gejj mail-coach horses1 it follows that it performs the work of #aejj wagon horses4 ,these results must be understood to be subject to modifications in particular cases1 and to be only average calculations4 ,different steam-engines1 as well as different horses1 varying in their performance to a considerable extent2 and the roads on which horses work being in different states of perfection1 and subject to different declivities1 the performance must vary accordingly4 ,in the practical comparison1 also1 of the results of so powerful an agent as steam applied on railways1 with so slight a power as that of horses on common roads1 it must be considered that the great subdivision of load1 and frequent times of starting1 operate in favour of the performance of horses2 inasmuch as it would oftener occur that engines capable of transporting enormous weights would start with loads inferior to their power1 than would happen in the application of horse-power1 where small loads may start at short intervals4 ,this1 in fact1 constitutes a practical difficulty in the application of steam engines on railroads2 and will1 perhaps1 for the present1 limit their application to lines connecting places of great intercourse4 ,the most striking effect of steam power1 applied on a railroad1 is the extreme speed of transport which is attained by it2 and it is the more remarkable1 as this advantage never was foreseen before experience proved it4 ,when the ,liverpool and ,manchester line was projected1 the transport of heavy goods was the object chiefly contemplated2 and although an intercourse in passengers was expected1 it was not foreseen that this would be the greatest source of revenue to the proprietors4 ,the calculations of future projectors will1 therefore1 be materially altered1 and a great intercourse in passengers will be regarded as a necessary condition for the prosperity of such an undertaking4 ,if this advantage of speed be taken into account1 horse-power can scarcely admit of any comparison whatever with steam-power on a railway4 ,in the experiments which ,i have already detailed1 it appears that a steam engine is capable of drawing #ij tons at the rate of about #bj miles an hour1 and that it could transport that weight twice between ,liverpool and ,manchester in about #c hours4 ,two hundred and seventy horses working in wagons would be necessary to transport the same load the same distance in a day4 ,it may be objected1 that this was an experiment performed under favourable circumstances1 and that assistance was obtained at the difficult point of the inclined plane4 ,in the ordinary performance1 however1 of the engines drawing merchandise1 where great speed is not attempted1 the rate of motion is not less than #ae miles an hour4 ,in the trains which draw passengers1 the chief difficulty of maintaining a great speed arises from the stoppages on the road to take up and let down passengers4 ,there are two classes of carriages at present used3 the first class stops but once1 at a point half-way between ,liverpool and ,manchester1 for the space of a few minutes4 ,this class performs the thirty miles in an hour and a half1 and sometimes in #a hour and #aj minutes4 ,on the level part of the road its common rate of motion is #bg miles an hour2 and ,i have occasionally marked its rate1 and found it above #cj miles an hour4 ,but these1 which are velocities obtained in the regular working of the engines for the transport of passengers and goods1 are considerably inferior to the power of the present locomotives with respect to speed4 ,i have made some experimental trips1 in which more limited loads were placed upon the engines1 by which ,i have ascertained that very considerably increased rates of motion are quite practicable4 ,in one experiment ,i placed a carriage containing #cf persons upon an engine1 with which ,i succeeded in obtaining the velocity of about #dh miles an hour1 and ,i believe that an engine loaded only with its own tender has moved over #ae miles in #ae minutes4 ,it will then perhaps be asked1 if the engines possess these great capabilities of speed1 why they have not been brought into practical operation on the railroad1 where1 on the other hand1 the average speed when actually in motion1 does not exceed #be miles an hour8 ,in answer to this it may be stated1 that the distance of #cj miles between ,liverpool and ,manchester is performed in an hour and a half1 and that #aj trains of passengers pass daily between these places3 the mail1 also1 is transmitted three times a day between them4 ,it is obvious that any greater speed than this1 in so short a distance1 would be quite needless4 ,when1 however1 more extended lines of road shall be completed1 the circumstances will be otherwise1 and the despatch of mails especially will demand attention4 ,full trains of passengers1 commonly transported upon the ,manchester railroad1 weigh about #ej tons gross3 with a lighter load1 a lighter and more expeditious engine might be used4 ,the expense of transport with such an engine would of course be increased2 but for this the increased expedition there would be ample compensation4 ,when1 therefore1 ,london shall have been connected with ,liverpool1 by a line of railroad through ,birmingham1 the commercial interest of these places will naturally direct attention to the greatest possible expedition of intercommunication4 ,for the transmission of mails1 doubtless1 peculiar engines will be built1 adapted to lighter loads and greater speed4 ,with such engines1 the mails1 with a limited number of passengers1 will be despatched2 and1 apart from any possible improvement which the engines may hereafter receive1 and looking only at their present capabilities1 ,i cannot hesitate to express my conviction that such a load may be transported at the rate of above #fj miles an hour4 ,if we may indulge in expectations of what the probable improvements of locomotive steam engines may effect1 ,i do not think that even double that speed is beyond the limits of mechanical probability4 ,on the completion of the line of road from the metropolis to ,liverpool we may1 therefore1 expect to witness the transport of mails and passengers in the short space of three hours4 ,there will probably be about three posts a day between these and intermediate places4 ,the great extension which the application of steam to the purpose of inland transport is about to receive from the numerous railroads which are already in progress1 and from a still greater number of others which are hourly projected1 impart to these subjects of inquiry considerable interest4 ,neither the wisdom of the philosopher1 nor the skill of the statistician1 nor the foresight of the statesman is sufficient to determine the important consequences by which the realization of these schemes must affect the progress of the human race4 ,how much the spread of civilization1 the diffusion of knowledge1 the cultivation of taste1 and the refinement of habits and manners depend upon the easy and rapid inter-mixture of the constituent elements of society1 it is needless to point out4 ,whilst population exists in detached and independent masses1 incapable of transfusion amongst each other1 their dormant affinities are never called into action1 and the most precious qualities of each are never imparted to the other4 ,like solids in physics1 they are slow to form combinations2 but when the quality of fluidity has been imparted to them1 when their constituent atoms are loosened by fusion1 and the particles of each flow freely through and among those of the other1 then the affinities are awakened1 new combinations are formed1 a mutual interchange of qualities takes place1 and compounds of value far exceeding those of the original elements are produced4 ,extreme facility of intercourse is the fluidity and fusion of the social masses1 from whence such an activity of the affinities results1 and from whence such an inestimable interchange of precious qualities must follow4 ,we have1 accordingly1 observed1 that the advancement in civilization and the promotion of intercourse between distant masses of people have ever gone on with contemporaneous progress1 each appearing occasionally to be the cause or the consequence of the other4 ,hence it is that the urban population is ever in advance of the rural in its intellectual character4 ,but1 without sacrificing the peculiar advantages of either1 the benefits of intercourse may be extended to both1 by the extraordinary facilities which must be the consequence of the locomotive projects now in progress4 ,by the great line of railroad which is in progress from ,london to ,birmingham1 the time and expense of passing between these places will probably be halved1 and the quantity of intercourse at least quadrupled1 if we consider only the direct transit between the terminal points of the line2 but if the innumerable tributary streams which will flow from every adjacent point be considered1 we have no analogies on which to build a calculation of the enormous increase of intercommunication which must ensue4 ,perishable vegetable productions necessary for the wants of towns must at present be raised in their immediate suburbs2 these1 however1 where they can be transported with a perfectly smooth motion at the rate of twenty miles an hour1 will be supplied by the agricultural labourer of more distant points4 ,the population engaged in towns1 no longer limited to their narrow streets1 and piled story over story in confined habitations1 will be free to reside at distances which would now place them far beyond reach of their daily occupations4 ,the salubrity of cities and towns will thus be increased by spreading the population over a larger extent of surface1 without incurring the inconvenience of distance4 ,thus the advantages of the country will be conferred upon the town1 and the refinement and civilization of the town will spread their benefits among the rural population4#cb ,footnote #cb3 ,some of the preceding observations appeared in an article contributed by me to the ,british and ,foreign ,review4 7#aja47 ,the quantity of canal property in these countries gives considerable interest to every inquiry which has for its object the relative advantage of this mode of transport1 compared with that of railways1 whether worked by horses or by steam-power2 and this interest has been greatly increased by the recent extension of railway projects4 ,this is a subject which ,i shall have occasion1 in another work1 to examine in all its details2 and1 therefore1 in this place ,i shall advert to it but very briefly4 ,when a floating body is moved on a liquid1 it will suffer a resistance1 which will depend partly upon the transverse section of the part immersed1 and partly on the speed with which it is moved4 ,it is evident that the quantity of the liquid which it must drive before it will depend upon that transverse section1 and the velocity with which it will impel the liquid will depend upon its own speed4 ,now1 so long as the depth of its immersion remains the same1 it is demonstrable that the resistance will increase in proportion to the square of the speed2 that is1 with a double velocity there will be a fourfold resistance1 with a triple velocity a ninefold resistance1 and so on4 ,again1 if the part immersed should be increased or diminished by any cause1 the resistance1 on that account alone1 will be increased or diminished in the same proportion4 ,from these circumstances it will be apparent that a vessel floating on water1 if moved with a certain speed1 will require four times the impelling force to carry it forward with double the speed1 unless the depth of its immersion be diminished as its speed is increased4 ,some experiments which have been made upon canals with boats of a peculiar construction1 drawn by horses1 have led to the unexpected conclusion1 that1 after a certain speed has been attained1 the resistance1 instead of being increased1 has been diminished4 ,this fact is not at variance with the law of resistance already explained4 ,the cause of the phenomenon is found in the fact1 that when the velocity has attained a certain point1 the boat gradually rises out of the water2 so that1 in fact1 the immersed part is diminished4 ,the two conditions1 therefore1 which determine the resistance1 thus modify each other3 while the resistance is1 on the one hand1 increased in proportion to the square of the speed1 it is1 on the other hand1 diminished in proportion to the diminution of the transverse section of the immersed part of the vessel4 ,it would appear that1 at a certain velocity1 these two effects neutralise each other2 and1 probably1 at higher velocities the immersed part may be so much diminished as to diminish the resistance in a greater degree than it is increased by the speed1 and thus actually to diminish the power of traction4 ,it is known that boats are worked on some of the ,scottish canals1 and also on the canal which connects ,kendal with ,preston1 by which passengers are transported1 at the rate of about ten miles an hour1 exclusive of the stoppages at the locks1 c4 ,the power of horses1 exerted in this way1 is1 of course1 exerted more economically than they could be worked at the same speed on common roads2 and1 probably1 it is as economical as they would be worked by railroad4 ,it is1 probably1 more economical than the transport of passengers by steam upon railroads2 but the speed is considerably less1 nor1 from the nature of the impelling power1 is it possible that it can be increased4 ,there is reason to suppose that a like effect takes place with steam vessels4 ,upon increasing the power of the engines in some of the ,post ,office steam packets1 it has been found1 that1 while the time of performing the same voyage is diminished1 the consumption of fuel is also diminished4 ,now1 since the consumption of fuel is in the direct ratio of the moving power1 and the latter in the direct ratio of the resistance1 it follows that the resistance must in this case be likewise diminished4 7#ajb47 ,when a very slow rate of travelling is considered1 the useful effects of horse-power applied on canals is somewhat greater than the effect of the same power applied on railways2 but at all speeds above three miles an hour1 the effect on railways is greater2 and when the speed is considerable1 the canal becomes wholly inapplicable1 while the railway loses none of its advantages4 ,at three miles an hour1 the performance of a horse on a canal and a railway is in the proportion of four to three to the advantage of the canal2 but at four miles an hour his performance on a railway has the advantage in very nearly the same proportion4 ,at six miles an hour1 a horse will perform three times more work on a railway than on a canal4 ,at eight miles an hour1 he will perform nearly five times more work4 ,but the circumstance which1 so far as respects passengers1 must give railways1 as compared with canals1 an advantage which cannot be considered as less than fatal to the latter1 is the fact1 that the great speed and cheapness of transit attainable upon a railway by the aid of steam-power will always secure to such lines not only a monopoly of the travelling1 but will increase the actual amount of that source of profit in an enormous proportion1 as has been already made manifest between ,liverpool and ,manchester4 ,before the opening of the railway there were about twenty-five coaches daily running between ,liverpool and ,manchester4 ,if we assume these coaches on the average to take ten persons at each trip1 it will follow that the number of persons passing daily between these towns was about #ejj4 ,let us1 then1 assume that #cjjj persons passed weekly4 ,this gives in six months #gh1jjj4 ,in the six months which terminated on the #cast of ,december #ahca1 the number of passengers between the same towns1 exclusive of any taken up on the road1 was #bef1cba2 and if some allowance be made for those taken up on the road1 the number may be fairly stated at #cjj1jjj4 ,at present there is but one coach on the road between ,liverpool and ,manchester2 and it follows1 therefore1 that1 besides taking the monopoly of the transit in travellers1 the actual number has been already increased in a fourfold proportion4 ,the monopoly of the transit of passengers thus secured to the line of communication by railroad will always yield so large a profit as to enable merchandise to be carried at a comparatively low rate4 ,in light goods1 which require despatch1 it is obvious that the railroad will always command the preference2 and the question between that mode of communication and canals is circumscribed to the transit of those classes of heavy goods in which even a small saving in the cost of transport is a greater object than despatch4 7#ajc47 ,the first effect which the ,liverpool railroad produced on the ,liverpool and ,manchester canals was a fall in the price of transport2 and at this time1 ,i believe1 the cost of transport per ton on the railroads and on the canals is the same4 ,it will1 therefore1 be naturally asked1 this being the case1 why the greater speed and certainty of the railroad does not in every instance give it the preference1 and altogether deprive the canals of transport8 ,this effect1 however1 is prevented by several local and accidental causes1 as well as by direct influence and individual interest4 ,a large portion of the commercial and manufacturing population of ,liverpool and ,manchester have property invested in the canals1 and are deeply interested to sustain them in opposition to the railway4 ,such persons will give the preference to the canals in their own business1 and will induce those over whom they have influence to do so in every case where speed of transport is not absolutely indispensable4 ,besides these circumstances1 the canal communicates immediately with the shipping at ,liverpool1 and it ramifies in various directions through ,manchester1 washing the walls of many of the warehouses and factories for which the goods transported are destined4 ,the merchandise is thus transferred from the shipping to the boat1 and brought directly to the door of its owner1 or vice vers4 ,if transported by the railway1 on the other hand1 it must be carried to the station at one extremity2 and1 when transported to the station at the other1 it has still to be carried to its destination in different parts of the town4 ,these circumstances will sufficiently explain why the canals still retain1 and may probably continue to retain1 a share of the traffic between these great marts4 ,,chapter ,,xi4 ,,locomotive ,,engines ,,on ,,turnpike ,,roads4 ,railways and ,turnpike ,roads compared4 -- ,mr4 ,gurney's inventions4 -- ,his ,locomotive ,steam ,engine4 -- ,its performances4 -- ,prejudices and errors4 -- ,committee of the ,house of ,commons4 -- ,convenience and safety of ,steam ,carriages4 -- ,hancock's ,steam ,carriage4 -- ,mr4 ,n4 ,ogle4 -- ,trevithick's invention4 -- ,proceedings against ,steam ,carriages4 -- ,turnpike ,bills4 -- ,steam ,carriage between ,gloucester and ,cheltenham4 -- ,its discontinuance4 -- ,report of the ,committee of the ,commons4 -- ,present ,state and ,prospects of ,steam ,carriages4 7#ajd47 ,we have hitherto confined our observations to steam-power as a means of transport applied on railways1 but modern speculation has not stopped here4 ,several attempts have been made1 and some of them attended with considerable success1 to work steam-carriages on turnpike roads4 ,the practicability of this project has been hitherto generally considered to be very questionable2 but if we carry back our view to the various epochs in the history of the invention of the steam engine1 we shall find the same doubt1 and the same difficulty1 started at almost every important step in its progress4 ,in comparing the effect of a turnpike road with that of a railway1 there are two circumstances which obviously give facility and advantage to the railway4 ,one is1 that the obstructions to the rolling motion of the wheels1 produced by the inequalities of the surface1 are very considerably less on a railway than on a road2 less in the proportion of at least #a to #bj4 ,this proportion1 however1 must depend much on the nature of the road with which the railway is compared4 ,it is obvious that a well-constructed road will offer less resistance than one ill constructed2 and it is ascertained that the resistance of a ,macadamised road is considerably more than that of a road well paved with stones3 the decision of this question1 therefore1 must involve the consideration of another1 viz4 whether roads may not be constructed by pavement or otherwise1 smoother and better adapted to carriages moved in the manner of steam-carriages than the roads now used for horse-power8 ,but besides the greater smoothness of railroads compared with turnpike roads1 they have another advantage1 which we suspect to have been considerably exaggerated by those who have opposed the project for steam-carriages on turnpike roads4 ,one of the laws of adhesion1 long since developed by experiment1 and known to scientific men1 is1 that it is greater between the surfaces of bodies of the same nature than between those of a different nature4 ,thus between two metals of the same kind it is greater than between two metals of different kinds4 ,between two metals of any kind it 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 road 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 dragging 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 turnpike road than on a railroad4 ,but1 on the other hand1 the expense of original construction1 and of maintaining the repairs of a railroad1 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 wheels1 as in the engine represented in fig4 #ee4 ,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 water1 as to expose a considerable quantity of surface in contact with it to the action of the fire2 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#aje47 ,first and most prominent in the history of the application of steam to the propelling of carriages on turnpike roads1 stands the name of ,mr4 ,,goldsworthy ,,gurney1 a medical gentleman 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 since #ahbe he has devoted his exertions in perfecting a steam engine capable of attaining the end he had in view4 ,numerous other projectors1 as might have been expected1 have followed in his wake4 ,whether they1 or any of them1 by better fortune1 greater public support1 or more powerful genius1 may outstrip him in the career on which he has ventured1 it would not1 perhaps1 at present1 be easy to predict4 ,but whatever be the event1 to ,mr4 ,gurney is due1 and will be paid1 the honour of first proving the practicability of the project2 and in the history of the adaptation of the locomotive engine to common roads1 his name will stand before all others in point of time1 and the success of his attempts will be recorded as the origin and cause of the success of others in the same race4 ,the incredulity1 opposition1 and even ridicule1 with which the project of ,mr4 ,gurney was met1 are very remarkable4 ,his views were from the first opposed by engineers1 without one exception4 ,the contracted habit of mind1 sometimes produced by an education chiefly1 if not exclusively1 directed to a merely practical object1 subsequently confirmed by exclusively practical pursuits1 may1 perhaps1 in some degree1 account for this4 ,but1 ,i confess1 it has not been without surprise that ,i have observed1 during the last ten years1 the utter incredulity which has prevailed among men of general science on this subject1--an incredulity which the most unequivocal practical proof has scarcely yet dispelled4 ,among scientific men1 says ,mr4 ,gurney1 my opinion had not a single supporter1 with the exception of the late ,dr4 ,wollaston4 ,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 ,it would be foreign to my present object to detail minutely all the steps by which ,mr4 ,gurney gradually improved his contrivance4 ,this1 like other inventions1 has advanced by a series of partial failures2 but it has at length attained that state1 in which1 by practice alone1 on a more extensive scale1 a further degree of perfection can be obtained4 7#ajf47 ,the boiler of this engine is so constructed that there is no part of it1 not even excepting the grate-bars1 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 ,i have seen the bars of a new grate1 never before used1 melted in a single trip between ,liverpool and ,manchester2 and the inventor of another form of locomotive engine has admitted to me that his grate-bars1 though of a considerable thickness1 would not last more than a week4 ,in the boiler of ,mr4 ,gurney1 the grate-bars 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 #fb4 ,the ends of the three cylinders1 just mentioned1 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 #fc4 ,these tubes1 proceeding from the side of the lowest cylinder ,d1 are inclined 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 #fb4 at ,c4 ,the other extremities of these tubes at ,a are connected with the same number of upright tubes1 one of which is expressed 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 #fb4 ,illustration3 ,fig4 #fc4 ,an end view of the boiler is exhibited in fig4 #fd41 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 #fb4 ,from the top of the cylinder ,i proceeds a tube ,n1 by which steam is conducted to the engine4 ,illustration3 ,fig4 #fd4 ,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 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 #fd4 ,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 ,a1 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 bubble 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 in the tubes1 as already explained1 otherwise it might be possible1 notwithstanding the levity of steam compared with water1 that a bubble might remain in a narrow tube without rising4 ,i notice this more particularly1 because the burning of the tubes is a defect which has been erroneously1 in my opinion1 attributed to this boiler4 ,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 ,this ,i conceive to be the chief excellence of ,mr4 ,gurney's boiler4 ,it is impossible that any part of the metal of which it is formed can receive a greater temperature than that of the water which it contains2 and that temperature1 as is obvious1 can be regulated with the most perfect certainty and precision4 ,i have seen the tubes of this boiler1 while exposed to the action of the furnace1 after that action has continued for a long period of time1 and ,i have never observed the soot which covers them to redden1 as it would do if the tube attained a certain temperature4 ,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 water 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 it by occasionally injecting through the tubes such an acid as would combine with the deposite1 and carry it away4 ,this method was perfectly 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 the more simple1 but not less effectual1 method of removing the deposite 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 cleaned these stoppers are removed1 and an iron scraper is introduced through the holes into the tubes1 which being passed backwards and forwards1 removes the deposite4 ,the boiler may be thus cleaned by a common labourer in half a day1 at an expense of about #as4 #f;d4 ,the frequency of the periods at which a boiler of this kind requires cleaning must depend1 in a great degree1 on the nature of the water which is used2 one in daily use with the water of the river ,thames would not require cleaning more than once in a month4 ,mr4 ,gurney states that with water of the most unfavourable description1 once a fortnight would be sufficient4 7#ajg47 ,in the more recent boilers constructed by ,mr4 ,gurney1 he has maintained the draught through the furnace1 by the method of projecting the waste steam into the chimneys2 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 certainly 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 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 because1 on some roads1 a draught is scarcely required1 while on others a powerful blast is indispensable4 ,connected with this blowing box1 is another ingenious apparatus of considerable practical importance4 ,the pipe through which the water which feeds the boiler is conducted to it 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 feeding 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 ,the fuel necessary to accomplish this is1 therefore1 saved1 and the amount of this is calculated at #a_/fth of all that is necessary to evaporate the water4 ,thus1 #a_/fth of the expense of fuel is saved4 ,but1 what is much more important in a locomotive engine1 a portion of the weight of the engine is saved without any sacrifice of its power4 ,there is still another great 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_/fth of the waste steam1 which is thence conducted to the tank1 from which the feeding water is pumped1 saving in this manner #a_/fth in weight and room of the water necessary to be carried in the carriage for feeding the boiler4#cc ,footnote #cc3 ,in boilers constructed for stationary purposes1 or for steam navigation1 the steam-pipe1 after it has passed through the blowing box1 is continued and made to form a series of returned flues over the boiler1 so as to take up the waste heat after it has passed the boiler1 and before it reaches the chimney4 ,but in locomotive engines for common roads1 it has been found by experience1 that the power gained by the waste heat is not sufficient to propel the weight of the material necessary for taking it up4 ,so far as the removal of all inconvenience arising from noise1 this contrivance has been proved by experience to be perfectly effectual4#cd ,footnote #cd3 ,see ,report of the ,commons4 ,in all boilers1 the process of violent ebullition causes a state of agitation in the water1 and a number of counter currents1 by which1 as the steam is disengaged from the surface of the water1 it takes with it a considerable quantity of water in mechanical mixture4 ,if this be carried through the cylinders1 since it possesses none of the qualities of steam1 and adds nothing to the power of the vapour with which it is combined1 it causes an extensive waste of heat and water1 and produces other injurious effects4 ,in every boiler therefore1 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 plate boilers1 the large space which 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 spaces in which the ebullition takes place1 causes the water to be mixed with the steam in a greater quantity than could happen in common plate boilers3 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 overcome by a succession of contrivances of great ingenuity4 ,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 alone has a tendency to diminish the mixture of water with the steam4 ,but in addition to this1 a most effectual 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 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 independent 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 generally 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 simple 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 may be 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 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 a 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 propelled 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 the 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 to 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 in diameter are most advantageous4 ,among the numerous popular prejudices to which this new invention has given rise1 one of the most mischievous in its effects1 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 most clearly and successfully exposed in the evidence taken before the committee of the ,house of ,commons upon steam carriages4 ,it is there fully demonstrated1 not only that carriages thus propelled did 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 wheels1 being fully 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 road is not more than that produced by a carriage drawn by horses 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 ,in that report they will not only find demonstrative evidence that the introduction of steam carriages will materially contribute to the saving in the wear of turnpike roads1 but also that the practicability of working such carriages with a great saving to the public--with great increase of speed and other conveniences to the traveller--is fully established4 ,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 load 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 with the weight of a common stage coach1 with #d horses inclusive4 7#ajh47 ,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 circumstance 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 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 speed2 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 used1 adapted to that speed which at present is generally considered necessary for the purpose 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 reversed 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 very slight indeed1 if any such risk exists1 may be proved from the fact that the boilers used on the ,liverpool and ,manchester railroad being much larger1 and1 in proportion1 inferior in strength to those of ,mr4 ,gurney1 and other steam carriage projectors1 have never yet been productive of any injurious consequences by explosion1 although they have frequently burst4 ,i have stood close to a locomotive on the railroad when the boiler burst4 ,the effect was that the water passed through the tubes into the fire and extinguished it1 but no other consequence ensued4 ,in fig4 #fe4 is represented the appearance of a locomotive of ,mr4 ,gurney's drawing after it a carriage for passengers4 ,illustration3 ,fig4 #fe4 7#aji47 ,one of the greatest difficulties which locomotives upon a turnpike road have to encounter is the ascent of very steep hills1 for it is agreed upon all hands that hills of very moderate inclinations present no difficulty which may not be easily overcome1 even in the present state of our knowledge4 ,the fact of ,mr4 ,gurney having propelled his carriage up ,old ,highgate ,hill1 when the apparatus was in a a much more imperfect state than that to which it has now attained1 establishes the mere question of the possibility of overcoming the difficulty2 but it remains still to be decided whether the inconvenience caused by providing means of meeting the exigency of very steep hills may not be greater than the advantage of being able to surmount them can compensate for3 and ,mr4 ,farey1 whose authority upon subjects of this kind is entitled to the highest respect1 thinks that it is upon the whole more advantageous to provide1 at very steep hills1 post horses to assist the steam carriage up them1 than to incur the inconvenience of providing the necessary power and strength of machinery for occasions which at best but rarely occur4 ,if the question merely referred to the command of motive power1 it appears to me that ,mr4 ,gurney's boiler would be amply sufficient to supply all that could be required for any hills which occur upon turnpike roads2 but it is not to be forgotten1 that not merely an ample supply of motive power1 but also a strength and weight in the machinery proportionate to the power to be exerted1 is indispensably necessary4 ,the strength and weight necessary to ascend a very steep hill will be considerably greater than that which is necessary for a level road1 or for hills of moderate inclinations2 and it follows that if we ascend those steep hills by the unaided power of the locomotive1 we must load the engine with all the weight of machinery requisite for such emergencies1 such additional weight being altogether unnecessary1 and therefore a serious impediment upon all other parts of the road1 inasmuch as it must exclude an equivalent weight of goods or passengers1 which might otherwise be transported1 and thereby in fact diminish proportionally the efficiency of the machine4 ,it is right1 however1 to observe1 that this is a point upon which a difference of opinion is entertained by persons equally competent to form a judgment1 and that some consider that it is practicable to construct an engine without inconvenient weight which will ascend all the hills which occur upon turnpike roads4 ,however this may be1 the difficulty is one which the improved system of roads in ,england renders of a comparatively trifling nature4 ,if horses were resorted to as the means of assistance up such hills as the engine would be incapable of surmounting1 such aid would not be requisite more than twice or thrice upon the mail-coach road between ,london and ,holyhead2 and the same may be said of the roads connecting the greatest points of intercourse in the kingdom4 ,such hills as the ascent at ,pentonville upon the ,new ,road1 the ascent in ,st4 ,james's ,street1 the ascent from ,waterloo ,place to the ,county ,fire ,office1 the ascent at ,highgate ,archway1 present no difficulty whatever4 ,it is only ,old ,highgate ,hill1 and hills of a similar kind1 which would ever require a supply of horses in aid of the engine4 ,i therefore incline to agree with ,mr4 ,farey1 that1 at least for the present1 it will be more expedient to construct carriages adapted to surmount moderate hills only1 and to provide post horses in aid of the extreme emergencies to which ,i have just alluded4 7#aaj47 ,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 thin plates of metal like a galvanic battery1 the water being allowed to flow between every alternate pair of plates1 at ,e1 fig4 #ff41 and the intermediate spaces ,h forming the flue through which the flame and hot air are propelled4 ,illustration3 ,fig4 #ff4 ,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 grate2 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 this1--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 who are placed on the fore part of the vehicle2 so that all the machinery is behind them4 ,the carriages are adapted to carry #ad 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 #i miles an hour1 and working with a pressure of about #ajj lbs4 on the square inch1 loaded with #ac 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 there were several large holes in the plates of the water-chamber1 through which the water had flowed on the fire2 but neither noise nor explosion1 nor any dangerous consequences ensued4 ,this boiler has some obvious defects4 ,it is evident that thin flat plates are the form which1 mechanically considered1 is least favourable to strength2 nor does it appear that any material advantage is gained to compensate for this by the magnitude of the surface exposed to the action of the fire4 ,it is a great defect that a part of the surface of each of the plates is exposed to the action of the fire while it is out of contact with the water2 in fact1 in the upper part of the spaces marked ,e1 fig4 #ff41 steam only is contained4 ,it has been observed by engineers1 and usually shown by experiment1 that if steam be heated on the surface of water it will be decomposed1 and its elasticity destroyed2 this is not the only evil connected with the arrangement1 for on this part of the metal1 nevertheless1 the fire acts1--with less intensity1 it is true1 than on that part which contains the water1--but still with sufficient intensity to destroy the metal4 ,mr4 ,hancock appears to have attempted to remedy this defect by occasionally inverting the position of the flat chambers1 placing that which at one time was at the bottom at the top1 and vice vers4 ,this may equalise the wear produced by the action of the fire upon the metal out of contact with water1 but still the wear on the whole will not be less rapid4 ,there appears to be no provision or space for separating the steam from the water with which it is charged2 in fact1 there are no means in this engine of discharging the function of ,mr4 ,gurney's separator4 ,this will be found to produce considerable waste and loss of power in practice4 ,the bars upon which the fire rests are of solid metal2 and such is the intense heat to which they are subject1 that1 in an engine constantly at work1 it is unlikely that they will last1 without being renewed1 more than about a week1 if so much4 ,the draft is maintained in this engine by means of a revolving fan worked by the engine4 ,this1 perhaps1 is one of the greatest defects as compared with other locomotives4 ,the quantity of power requisite to work this bellows1 and of which the engine is robbed1 is very great4 ,this defect is so fatal1 that ,i consider it is quite impossible that the ingenious inventor can persevere in the use of it4 ,mr4 ,hancock has abandoned the use of the cranks upon his working axle1 and has substituted an endless chain and rag-wheels4 ,this also appears to me defective1 and a source by which considerable power is lost4 ,on the other hand1 however1 the weakness of the axle which is always produced by cranks is avoided4 7#aaa47 ,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 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 affixed1 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 six1 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 7#aab47 ,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 ,birmingham 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 padded1 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 ,an obvious defect which such a boiler presents is the difficulty of removing from it any deposite or incrustation1 which may collect between the sheets of copper so closely and intricately connected4 ,dr4 ,church proposes to effect this1 when it is required1 by the use of an acid1 which will combine readily with the incrustation1 and by which the boiler may therefore be washed4 ,this method of cleansing boilers was recommended by ,dr4 ,wollaston to ,mr4 ,gurney1 who informed me1 however1 that he found that it was not practicable in the way in which boilers must commonly be used4 ,i apprehend1 also1 that the spaces between the sheets of copper1 in ,dr4 ,church's boiler just described1 will hardly permit the steam bubbles which will be formed to escape with sufficient facility into the steam-chest2 and being retained in that part of the boiler which is exposed to the action of the fire1 the metal will be liable to receive an undue temperature4 ,i have1 however1 seen this engine working1 and its performance was very satisfactory4 7#aac47 ,various other projects for steam carriages on common roads are in various degrees of advancement1 among which may be mentioned those of ,messrs4 ,maudslay and ,field1 ,col4 ,macerone1 and ,mr4 ,russell of ,edinburgh2 but our limits compel us to omit any detailed account of them4 ,,chapter ,,xii4 ,,steam ,,navigation4 ,propulsion by paddle-wheels4 -- ,manner of driving them4 -- ,marine ,engine4 -- ,its form and arrangement4 -- ,proportion of its cylinder4 -- ,injury to boilers by deposites and incrustation4 -- ,not effectually removed by blowing out4 -- ,mr4 ,samuel ,hall's condenser4 -- ,its advantages4 -- ,originally suggested by ,watt4 -- ,hall's steam saver4 -- ,howard's vapour engine4 -- ,morgan's paddle-wheels4 -- ,limits of steam navigation4 -- ,proportion of tonnage to power4 -- ,average speed4 -- ,consumption of fuel4 -- ,iron steamers4 -- ,american steam raft4 -- ,steam navigation to ,india4 -- ,by ,egypt and the ,red ,sea to ,bombay4 -- ,by same route to ,calcutta4 -- ,by ,syria and the ,euphrates to ,bombay4 -- ,steam communication with the ,united ,states from the west coast of ,ireland to ,st4 ,john's1 ,halifax1 and ,new ,york4 7#aad47 ,among the various ways in which the steam engine has ministered to the social progress of our race1 none is more important and interesting than the aid it has afforded to navigation4 ,before it lent its giant powers to that art1 locomotion over the waters of the deep was attended with a degree of danger and uncertainty1 which seemed so necessary and so inevitable1 that1 as a common proverb1 it became the type and representative of everything else which was precarious and perilous4 ,the application1 however1 of steam to navigation has rescued the mariner from much of the perils of the winds and waves2 and even in its actual state1 apart from the improvements which it is still likely to receive1 it has rendered all voyages of moderate length as safe and as regular as journeys over land4 ,we are even now upon the brink of such improvements as will probably so extend the powers of the steam engine1 as to render it available as the means of connecting the most distant points of the earth4 ,the manner in which the steam engine is commonly applied to propel vessels must be so familiar as to require but short explanation4 ,a pair of wheels1 like common under-shot water-wheels1 bearing on their rims a number of flat boards called paddle boards1 are placed one at each side of the vessel1 in such a position that when the vessel is immersed to her ordinary depth the lowest paddle boards shall be submerged4 ,these wheels are fixed upon a shaft1 which is made to revolve by cranks placed upon it1 in the same manner as the fly-wheel of a common steam engine is turned4 ,it is now the invariable custom to place in steam vessels two engines1 each of which works a crank3 these two cranks are placed at right angles to each other1 in the same manner as the cranks already described upon the working axles of locomotive engines4 ,when either crank is at its dead point1 the other is in full activity1 so that the necessity for a fly wheel is superseded4 ,the engines may be either condensing or high-pressure engines2 but in ,europe the low-pressure condensing engine has been invariably used for nautical purposes4 ,in the ,united ,states1 where steam navigation had its origin1 and where it was1 until a recent period1 much more extensively practised than in ,europe1 less objection was felt to the use of high-pressure engines2 and their limited bulk1 their small original cost1 and simplicity of structure1 strongly recommended them1 more especially for the purposes of river navigation4 7g47 ,the original type of nearly all the engines used in steam navigation was that constructed at ,soho by ,watt and ,bolton for ,mr4 ,fulton1 and first used by him upon the ,hudson river4 ,this had the beam below the piston-rod as in the ,english boat-engines1 but the cylinder above deck1 as in the ,american4 ,from this primitive form1 the two nations have diverged in opposite directions4 ,the ,americans1 navigating rivers1 and having speed for their principal object1 have not hesitated to keep the cylinder above deck1 and have lengthened the stroke of the piston in order to make the power cut on a more advantageous point of the wheel4 ,compactness has been gained by the suppression of the working beam4 ,on the other hand1 the ,english1 having the safe navigation of stormy seas as their more important object1 have shortened the cylinder in order that the piston-rod may work wholly under the deck1 and the arrangement of ,fulton's working beam has been retained by them4 ,in this way there can be no doubt1 that they have lost the power of obtaining equal speed from a given expenditure of power1 and those conversant in the practice and theory of stowing ships may well doubt whether security is not also sacrificed4--,a4 ,e4 ,the arrangement of the parts of the maritime engine differs in some respects1 from that of the land engine4 ,want of room renders greater compactness necessary2 and in order to diminish the height of the machine1 the working beam is transferred from above the cylinder to below it4 ,in fact1 there are two beams1 one at each side of the engine1 which are connected by a parallel motion with the piston1 the rods of the parallel motion extending from the lower part of the engine to the top of the piston-rod4 ,the working end of the beam is connected with the crank by a connecting rod1 presented upwards instead of downwards1 as in the land engine4 ,the proportion of the length and diameters of the cylinders differ from those of land engines for a like reason3 to save height1 short cylinders with large diameters are used4 ,thus1 in an engine of #bjj horse-power1 the length of the cylinder is sometimes #fj inches1 and its diameter #ec inches3 the valves and the gearing which work them1 the air-pump1 condenser1 and other parts of the machine1 do not differ materially from those already described in the land engines4 7h47 ,the action of machinery may be rendered more equable by using two engines1 each of half the power1 instead of a single one4 ,if one of these be working with its maximum force when the other is changing the direction of its motion1 the result of their joint action will be a force nearly constant4 ,such a combination was invented by ,mr4 ,francis ,ogden1 and has been used in several steam boats constructed under his directions4 ,it would however be far more valuable in other cases1 particularly where great uniformity in the velocity is indispensable4 ,this method has now become almost universal in the engines used in the ,english steam boats1 each of which has usually two1 both applied to the same shaft1 and therefore capable of being used singly or together to turn the paddle wheels4 ,in the ,american steam boats1 although two engines have been often applied1 each usually acts upon no more than one of the wheels4 ,we can see no other good reason for this1 than that our engineers do not wish to be thought to copy ,mr4 ,ogden4--,a4 ,e4 ,the nature of the work which the marine engine has to perform1 is such1 that great regularity of action is neither necessary nor possible4 ,the agitation of the surface of the sea will cause the immersion of the paddle-wheels to vary very much1 and the resistance to the engine will undergo a corresponding change3 the governor1 and other parts of the apparatus already described1 contrived for imparting to the engine that extreme regularity which is indispensable in its application to manufactures1 are therefore here omitted2 and nothing is introduced except what is necessary to maintain the engine in its full working power4 ,it is evident that it must be a matter of considerable importance to reduce the space occupied by the machinery on board a vessel to the least possible dimensions4 ,the marine boilers1 therefore1 are constructed so as to yield the necessary quantity of steam with the smallest practical dimensions4 ,with this view a much more extensive surface in proportion to the size of the boiler is exposed to the action of the fire4 ,in fact1 the flues which carry off the heated air to the chimney are conducted through the boiler1 so as to act upon the water on every side in thin oblong shells1 which traverse the boiler backward and forward repeatedly1 until finally they terminate in the chimney4 ,by this arrangement the original expense of the boilers is very considerably increased2 but1 on the other hand1 their steam-producing power is also greatly augmented2 and from experiments lately made by ,mr4 ,watt at ,birmingham1 it appears that they work with an economy of fuel compared with common land boilers in the proportion of about two to three4 ,thus they have the additional advantage of saving the tonnage as well as the expense of one third of the fuel4 ,one of the most formidable difficulties which has been encountered in applying the steam engine to the purposes of navigation has arisen from the necessity of supplying the boiler with sea water1 instead of pure fresh water4 ,this water 7also used for the purpose of condensation7 being injected into the condenser and mixed with the condensed steam1 is conducted as feeding water into the boiler4 ,the salt contained in the sea water1 not being evaporated1 remains in the boiler4 ,in fact1 it is separated from the water in the same manner as by the process of distillation4 ,as the evaporation in the boiler is continued1 the proportion of salt contained in the water is1 therefore1 constantly increased1 until a greater proportion is accumulated than the water is capable of holding in solution2 a deposition of salt then commences1 and is lodged in the cavities at the bottom of the boiler4 ,the continuance of this process1 it is evident1 would at length fill the boiler with salt4 ,but besides this1 under some circumstances1 a deposition of lime#ce is made1 and a hard incrustation is formed on the inner surface of the boiler4 ,in some situations1 also1 sand and mud are received into the boiler1 being suspended in the water pumped in for feeding it4 ,all these substances1 whether deposited in a loose form in the lower parts of the boiler or collected in a crust on its inner surface1 form obstructions to the passage of heat from the fire to the water4 ,the crust thus formed is not unfrequently an inch or more in thickness1 and so hard that good chisels are broken in removing it4 ,the heat more or less intercepted by these substances collects in the metal of the boiler1 and raises it to a temperature far exceeding that of the water within4 ,it may even1 if the incrustation be great1 be sufficient to render the boiler red-hot4 ,these circumstances occasion the rapid wear of the boiler1 and endanger its safety by softening it4 ,footnote #ce3 ,ten thousand grains of pure sea water contain muriate of soda #bbj grs41 sulphate of soda #cc grs41 muriate of magnesia #db grs41 and muriate of lime #h grs4 ,the remedy which has generally been adopted to remove or diminish these injurious effects consists in allowing a stream of hot water continually to flow from the boiler1 and supplying from the feed-pipe a corresponding portion of cold water4 ,while the hot water which flows from the boiler in this case contains1 besides its just proportion of salt1 that portion which has been liberated from the water converted into vapour1 the cold water which is supplied through the feed-pipe contains less than its just proportion of salt1 since it is composed of the natural sea water1 mixed with the condensed steam1 which latter contains no salt4 ,in this manner1 the proportion of the salt in the boiler may be prevented from accumulating2 but this is attended with considerable inconvenience and loss4 ,it is evident that the discharge of the hot water1 and the introduction of so considerable a quantity of cold water1 entails upon the machine a great waste of fuel1 and1 consequently1 renders it necessary that the vessel should be supplied with a much larger quantity of coals than are merely necessary for propelling it4 ,in long voyages1 where this inconvenience is most felt1 this is a circumstance of obvious importance4 ,but besides the waste of fuel1 the speed of the vessel is diminished by the rate of evaporation in the boiler being checked by the constant stream of cold water flowing into it4 ,this process of discharging the water1 which is called blowing out1 is only practised occasionally4 ,in the ,admiralty steamers1 the engineers are ordered to blow out every two hours4 ,but it is more usual to do so only once a day4 ,this method1 however1 of blowing out furnishes but a partial remedy for the evils we have alluded to3 a loose deposite will perhaps be removed by such means1 but an incrustation1 more or less according to the circumstances and quality of the water1 will be formed2 besides which1 the temptation to work the vessel with efficiency for the moment influences the engine men to neglect blowing out2 and it is found that this class of persons can rarely be relied upon to resort to this remedy with that constancy and regularity which are essential for the due preservation of the boilers4 ,the class of steam vessels which1 at present1 are exposed to the greatest injury from these causes are the sea-going steamers employed by the ,admiralty2 and we find1 by a report made by ,messrs4 ,lloyd and ,kingston to the ,admiralty1 in ,august1 #ahcd1 that it is admitted that the method of blowing out is1 even when daily attended to1 ineffectual4 ,the water in the boiler1 these gentlemen observe1 is kept from exceeding a certain degree of saltness1 by periodically blowing a portion of it into the sea2 but whatever care is taken1 in long voyages especially1 salt will accumulate1 and sometimes in great quantities and of great hardness1 so that it is with difficulty it can be removed4 ,boilers are thus often injured as much in a few months as they would otherwise be in as many years4 ,the other evil necessarily resulting from this state of things is1 besides the rapid destruction of the boilers1 a great waste of fuel1 occasioned by the difficulty with which the heat passes through the incrustation on the inside1 by the leaks which are thereby caused1 and by the practice of blowing out periodically1 as before mentioned1 a considerable portion of the boiling water4 ,it would be impracticable to carry on board the vessel a sufficient quantity of pure fresh water to work the engine exclusively by its means4 ,to accomplish this1 it would be necessary to have a sufficient supply of cold water to keep the condensing cistern cold1 to supply the jet in the condenser1 and to have a reservoir in which the warm water coming from the waste pipe of the cold cistern might be allowed to cool4 ,engineers have therefore directed their attention to some method by which the steam may be condensed without a jet1 and after condensation be preserved for the purpose of feeding the boiler4 ,if this could be accomplished1 it would not be necessary to provide a greater quantity of pure water than would be sufficient to make up the small portion of waste which might proceed from leakage and from other causes2 and it is evident that this portion might always be readily obtained by the distillation of sea water1 which might be effected by a small vessel exposed to the same fire which acts upon the boiler4 7#aae47 ,mr4 ,samuel ,hall of ,basford1 near ,nottingham1 has taken out patents for a new form of condenser1 contrived for the attainment of these ends1 besides some other improvements in the engine4 ,the condenser of ,mr4 ,hall consists of a great number of narrow tubes immersed in a cistern of cold water3 the steam as it passes from the cylinder1 after having worked the piston1 enters these tubes1 and is immediately condensed by their cold surfaces4 ,it flows in the form of water from their remote extremities1 and is drawn off by the air-pump1 and conducted in the usual way to a cistern from which the boiler is fed4 ,in the marine engines constructed under ,mr4 ,hall's patents1 the tubes of the condenser being in an upright or vertical position1 the steam flows from the cylinder into the upper part of the condenser1 which is a low flat chamber1 in the bottom of which is inserted the upper extremities of the tubes1 through which the steam passes downwards1 and as it passes is condensed4 ,it flows thence into a similar chamber below1 from whence it is drawn off by the air-pump4 ,it is evident that at sea an unlimited supply of cold water may be obtained to keep the condensing cistern cold1 so that a perfect condensation may always be effected by these tubes1 if they be made sufficiently small4 ,the water formed by the condensed steam will be pure distilled water2 and if the boiler be originally filled with water which does not hold in solution any earthy or other matter which might be deposited or encrusted1 it may be worked for any length of time without injury4 ,the small quantity of waste from leakage is supplied in ,mr4 ,hall's engine by a simple apparatus in which a sufficient quantity of sea water may be distilled4 ,the following are the advantages1 as stated by ,mr4 ,hall1 to be gained by his condenser3-- #a4 ,a saving of fuel1 amounting in some cases to so much as a third of the ordinary consumption4 #b4 ,the preservation of the boilers from the destruction produced in common engines by the corrosive action of sea or other impure water1 and by encrustations of earthy matter4 #c4 ,the saving of the time spent in cleaning the boilers4 #d4 ,a considerable increase of power1 owing to the cleanness of the boilers2 the absence of injected water to be pumped out of a vacuum2 the greater perfection of the vacuum2 the better preservation of the piston and valves of the air-pump2 and 7by another contrivance of his7 the more perfect lubrication of the parts of the engine4 #e4 ,the water in the boiler being constantly maintained at the same height by self-acting arrangement4 #f4 ,the size of a boiler exerting a given power1 being much smaller than the common kind1 owing to its more perfect action4 ,messrs4 ,lloyd and ,kingston were employed by government to examine and report the effects of ,mr4 ,hall's boilers1 and they stated in their report1 already referred to1 that the result is so successful as to leave nothing to be wished for4 ,among the advantages which they enumerate are the increased durability of the engines2 the prevention of accidents through carelessness1 or otherwise1 arising from the condenser and air-pump becoming choked with injection water2 and the additional security against the boilers being burnt in consequence of the water being suffered to get too low4 ,but the greatest advantages1 compared with which they consider all others to be of secondary importance1 are the increased durability of the boilers and the saving of fuel4 ,about #af engines1 built either wholly upon ,mr4 ,hall's principle or having his condenser attached to them1 have now 7,october1 #ahce7 been working in different parts of ,england1 and on board different vessels for various periods1 from three years to three months2 and it appears from the concurrent testimony of the proprietors and managers of them1 that they are attended with all the advantages which the patentee engaged for4 ,the part of the contrivance the performance of which would have appeared most doubtful would have been the maintenance of a sufficiently good vacuum in the condenser1 in the absence of the usual method of condensation by the injection of cold water2 nevertheless it appears that a better vacuum is sustained in these engines than in the ordinary engines which condense by jet4 ,the barometer-gauge varies from #bi to #bi-a_/b inches1 and in some cases comes up to #cj inches1 according to the state of the barometer3 this is a vacuum very nearly perfect1 and indeed may be said to be so for all practical purposes4 ,the ,prince ,llewellyn and the ,air steam packets1 belonging to the ,st4 ,george ,steam ,packet ,company1 have worked such a pair of these engines for about a year4 ,the ,city of ,london steam packet1 the property of the ,general ,steam ,navigation ,company1 has been furnished with two fifty-horse engines1 and has worked them during the same period4 ,in all cases the boilers have been found perfectly free from scale or incrustation2 and the deposite is either absolutely nothing or very trifling1 requiring the boiler to be swept about once in half a year1 and sometimes not so often4 ,the trial which has been made of these engines in the navy has proved satisfactory1 so far as it has been carried4 ,the ,lords of the ,admiralty have lately ordered a pair of seventy-horse engines to be constructed on this principle for a vessel now 7,october1 #ahce7 in process of construction2#cf and another vessel in all respects similar1 except having copper boilers1 is likewise ordered2 so that a just comparison may be made4 ,it would1 however1 have been more fair if both vessels had been provided with iron boilers1 since copper does not receive incrustation as readily as iron4 ,footnote #cf3 ,this order has1 as ,mr4 ,hall informs me1 been given without requiring any guarantee as to the performance of the engines4 ,it would seem that the advantages of these boilers in the vessels of the ,st4 ,george ,steam ,packet ,company were regarded by the directors as sufficiently evident1 since1 after more than a year's experience1 they are about to place a pair of ninety-horse engines of this kind in a new and powerful steamer called the ,hercules4 ,engines furnished with ,mr4 ,hall's apparatus have not yet1 so far as ,i am informed1 been tried with reference to the power exerted by the consumption of a given quantity of fuel4 ,the mere fact of a good vacuum being sustained in the condenser cannot by itself be regarded as a conclusive proof of the efficiency of the engine1 without the water or air introduced by a condensing jet4 ,mr4 ,hall1 nevertheless1 uses as large an air-pump as that of an ordinary condensing engine1 and recommends even a larger one4 ,for what purpose1 it may be asked1 is such an appendage introduced8 ,if there be nothing to be removed but the condensed steam1 a very small pump ought to be sufficient4 ,it is not wonderful that a good vacuum is sustained in the condenser1 if the power expended on the air-pump is employed in pumping away uncondensed steam4 ,such a contrivance would be merely a deception1 giving an apparent but no real advantage to the engine4 ,having mentioned these advantages1 which are said to arise from ,mr4 ,hall's condenser1 it is right to state that it is in fact a reproduction of an early invention of ,mr4 ,watt4 ,there is in possession of ,james ,watt1 esquire1 a drawing of a condenser laid before parliament in #aggf1 in which the same method of condensing without a jet is proposed4 ,mr4 ,watt1 however1 finding that he could not procure by that means so sudden or so perfect a vacuum as by injection1 abandoned it4 ,i believe he also found that the tubes of the condenser became furred with a deposite which impeded the process of condensation4 ,it would seem1 however1 that ,mr4 ,hall has found means to obviate these effects4 ,it is right to add1 that ,mr4 ,hall1 in his specification1 distinctly disclaims all claim to the method of condensing by tubes without jet4 ,there is another part of ,mr4 ,hall's contrivance which merits notice4 ,in all engines1 a considerable quantity of steam is allowed to escape from the safety valve4 ,whenever the vessel stops1 the steam1 which would otherwise be taken from the boiler by the cylinders1 passes out through this valve into the atmosphere4 ,also1 whenever the cylinders work at under-power1 and do not consume the steam as fast as it is produced by the boiler1 the surplus steam escapes through the valve4 ,now1 according to the principle of ,mr4 ,hall's method1 it is necessary to save the water which thus escapes in vapour1 since otherwise the pure water of the boiler would be more rapidly wasted4 ,mr4 ,hall accordingly places a safety valve of peculiar construction in communication with a tube which leads to the condenser1 so that whenever1 either by stopping the engine or diminishing its working power1 steam accumulates in the boiler1 its increased pressure opens the safety valve1 and it passes through this pipe to the condenser1 where it is reconverted into water1 and pumped off by the air-pump into the cistern from which the boiler is fed4 ,the attainment of an object so advantageous as to extend the powers of steam navigation1 and to render the performance of voyages of any length practicable1 so far as the efficiency of the machinery is concerned1 has naturally stimulated the inventive genius of the country4 ,the preservation of the boiler by the prevention of deposite and incrustation is an object of paramount importance2 and its attainment necessarily involves1 to a certain degree1 another condition on which the extension of steam voyages must depend1 viz4 the economy of fuel4 ,in proportion as the economy of fuel is increased1 in the same proportion will the limit to which steam navigation may be carried be extended4 7#aaf47 ,a patent has been obtained by ,mr4 ,thomas ,howard of ,london for a form of engine possessing much novelty and ingenuity1 and having pretensions to the attainment of a very extraordinary economy of fuel1 in addition to those advantages which have been already explained as attending ,mr4 ,hall's engines4 ,in these engines1 as in ,mr4 ,hall's1 the steam is constantly reproduced from the same water1 so that pure or distilled water may be used2 but ,mr4 ,howard dispenses with the use of a boiler altogether4 ,the steam also with which he works is in a state essentially different from the steam used in ordinary engines4 ,in these1 the vapour is raised directly from the water in a boiling state1 and it contains as much water as it is capable of holding at its temperature4 ,thus1 at the temperature of #bab1 a cubic foot of steam used in common engines will contain about a cubic inch of water2 but in the contrivance of ,mr4 ,howard1 a considerable quantity of heat is imparted to the steam before it passes into the cylinder in addition to what is necessary to maintain it in the vaporous form4 ,a quantity of mercury is placed in a shallow wrought-iron vessel over a coke fire1 by which it is maintained at the temperature of from #djj to #ejj4 ,the surface exposed to the fire is three fourths of a square foot for each horse-power4 ,the upper surface of the mercury is covered by a very thin plate of iron1 which rests in contact with it1 and which is so contrived as to present about four times as much surface as that exposed beneath to the fire4 ,adjacent to this a vessel of water is placed1 kept heated nearly to the boiling-point1 which communicates by a nozzle and valve with the chamber or vessel immediately above the mercury4 ,at intervals corresponding to the motion of the piston1 a small quantity of water is injected from this vessel1 and thrown upon the plate of iron which rests upon the hot mercury3 from this it receives the heat necessary not only to convert it into steam1 but to expand that steam1 and raise it to a temperature above the temperature it would receive if raised in immediate contact with water4 ,in fact1 the steam thus produced will have a temperature not corresponding to its pressure1 but considerably above that point1 and it will therefore be in circumstances under which it will part with more or less of its heat1 and allow its temperature to be lowered without being even partially condensed1 whereas steam used in the ordinary steam engines must be more or less condensed by the slightest diminution of its temperature4 ,the quantity of liquid injected into the steam chamber must be regulated by the power at which the engine is intended to work4 ,the fire is supplied with air by a blowing machine1 which is subject to exact regulation4 ,the steam1 produced in the manner already explained1 passes into a chamber which surrounds the working cylinder2 and this chamber itself is enclosed by another space1 through which the air from the furnace must pass before it reaches the flue4 ,in this way it imparts its redundant heat to the steam which is about to work the cylinder1 and raises it to a temperature of about #djj2 the pressure1 however1 not exceeding #be lbs4 per square inch4 ,the arrangement of valves for the admission of the steam to the cylinder is such as to cause the steam to act expansively4 ,the vacuum on the opposite side of the piston is maintained by condensation in the following manner3--,the condenser is a copper vessel placed in a cistern constantly supplied with cold water1 and the steam flows to it from the cylinder by an eduction pipe in the usual way3 a jet is admitted to it from an adjacent vessel1 which1 before the engine commences work1 is filled with distilled water2 the condensing water and condensed steam are pumped from the condenser by air-pumps of the usual construction1 but smaller1 inasmuch as there is no air to be withdrawn1 as in common engines4 ,the warm water thus pumped out of the condenser is driven into a copper pipe or worm1 which is carried with many coils through a cistern of cold water1 so that when it arrives at the end of this pipe it is reduced to the common temperature of the atmosphere4 ,the pipe is then conducted into the vessel of distilled water already mentioned1 and the water flowing from it continually replaces the water which flows into the condenser through the condensing jet4 ,the condensing water being purged of air1 a very small air-pump is sufficient2 since it has only to exhaust the condenser and tubes at starting1 and to remove whatever air may enter by casual leakage4 ,the patentee states that the condensation takes place as rapidly and as perfectly as in the best steam engine1 and it is evident that this method of condensation is applicable even where the mercurial generator already described may not be employed4 ,the vessel from which the water is injected into the mercurial generator is likewise fed by the air-pump connected with the condenser4 ,there is another pipe besides the copper worm already described1 which is carried from the hot well to this vessel1 and the water is of course returned through it without being cooled4 ,this vessel is likewise sufficiently exposed to the action of the fire to maintain it at a temperature somewhat below the boiling point4 ,an apparatus of this construction was in the spring of the present year 7#ahce7 placed in the ,admiralty steamer called the ,,comet1 in connexion with a pair of #dj-;horse engines4 ,the patentee states that these engines were ill adapted to the contrivance2 nevertheless1 the vessel was successfully worked in the ,thames for #hjj miles3 she also performed a voyage from ,falmouth to ,lisbon1 but was prevented from returning by an accident which occurred to the machinery near the latter port4 ,in this experimental voyage1 the consumption of fuel is stated never to have exceeded a third of her former consumption1 when worked by ,bolton and ,watt's engines2 the former consumption of coals being about #hjj lbs4 per hour1 and the consumption with ,mr4 ,howard's engine being under #bej lbs4 of coke per hour4 ,after this failure 7which1 however1 was admitted to be one of accident and not of principle7 the government did not consider itself justified in bestowing further time or incurring greater expense in trying this engine4 ,mr4 ,howard1 however1 has himself built a new vessel1 in which he is about to place a pair of forty-horse engines4 ,this vessel is now 7,december1 #ahce7 nearly ready1 and will bring the question to issue by a fair experiment4 ,the advantages of the contrivance as enumerated by the patentee are3-- ,first1 ,the small space and weight occupied by the machinery1 arising from the absence of a boiler4 ,secondly1 ,the diminished consumption of fuel4 ,thirdly1 ,the reduced size of the flues4 ,fourthly1 ,the removal of the injurious effects arising from deposite and incrustation4 ,fifthly1 ,the absence of smoke4 ,some of these improvements1 if realized1 will be attended with important advantages in steam navigation4 ,steamers of a given tonnage and power will have more disposable space for lading and fuel1 and in short voyages may carry greater freight1 or an increased number of passengers2 or by taking a larger quantity of fuel1#cg may make greater runs than are now attainable2 or1 finally1 with the same tonnage and the same lading1 they may be supplied with more powerful machinery4 ,footnote #cg3 ,the fuel used in this form of engine is coke1 and not coal4 ,a ton of coke occupies the same space as two tons of coal2 the saving of tonnage1 therefore1 by the increased economy of fuel will not be in so great a proportion as the saving of fuel4 ,a quantity of fuel of equivalent power will occupy about half the present space1 but the displacement or immersion which it produces will be only one fourth of its present effect4 7#aag47 ,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 attaining this end4 ,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 these1 however1 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 such simplicity of construction as is compatible with those repairs which are possible on such emergencies is quite essential for safe practical use4 ,illustration3 ,fig4 #fg4 ,the ordinary paddle-wheel1 as ,i have 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 or braces in a fixed position2 and that position is such that the planes 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 figure #fg4 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 but1 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 reaction 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 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 immersed the greater will be the proportion of the propelling power thus wasted in elevating and depressing the water2 and1 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 takes 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 cargo3 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 lightened2 and it does not appear that it is practicable to use sea water as ballast to restore the proper degree of immersion4 7#aah47 ,among the contrivances which have been proposed for remedying these defects of the common paddle wheel by introducing paddle boards capable of shifting their position as they revolve with the circumference of the wheel1 the only one which has been adopted to any considerable extent in practice is that which is commonly known as ,morgan's ,paddle ,wheel4 ,the original patent for this contrivance was granted to ,elijah ,galloway1 and sold by him to ,mr4 ,william ,morgan4 ,subsequently to the purchase some improvements in its structure and arrangements were introduced1 and it is now extensively adopted by ,government in the ,admiralty steamers4 ,it was first tried on board ,his ,majesty's steamer the ,,confiance2 and after several successful experiments was ordered by the ,lords of the ,admiralty to be introduced on board the ,,flamer1 the ,,firebrand1 the ,,columbia1 the ,,spitfire1 the ,,lightning1 a large war steamer called the ,,medea1#ch the ,,tartarus1 the ,,blazer1 c4 ,it has been tried by ,government in several well-conducted experiments1 where two vessels of precisely the same model1 supplied with similar engines of equal power1 and propelled1 one by ,morgan's paddle-wheels1 and the other by the common paddle-wheels2 when it was found that the advantage of the former1 whether in smooth or in rough water1 was quite apparent4 ,one of the commanders in these experiments 7,lieutenant ,belson7 states that the improvement in the speed of the ,,confiance1 after being supplied with these wheels1 was proportionately greater in a sea way than in smooth water2 that their action was not impeded by the waves1 since the variation of the velocity of the engine did not exceed one or two revolutions per minute3 the vessel's way was never stopped1 and there was no sensible increase of vibration on the paddle boxes during the gale4 ,another commander reported that on a comparison of the ,,confiance and a similar and equally powerful vessel1 the ,,carron1 the ,,confiance performed in fifty-four hours the voyage which occupied the ,,carron eighty-four hours in running4 ,independently of the great saving of fuel effected 7namely1 ten bushels per hour#ci71 or the time saved in running the same distance1 other advantages have been secured by the modification in question4 ,on a comparison of the respective logs of the two vessels1 it appeared that the ,,confiance had gained by the alteration in her wheels an increase of speed amounting to #b knots on #g in smooth water1 and #b-a_/b knots on #d to #d-a_/b knots in rough weather2 that the action of the paddles did not bring up the engine or retard their velocity in a head sea2 that in rolling their action assisted in righting the vessel2 and that the wear and strain1 as well on the vessel as on the engines1 were materially reduced4 ,with respect to the durability of these wheels1 the commander of the ,,flamer reported in ,january1 #ahcd1 that in six weeks of the most tempestuous weather they found them to act remarkably well1 without even a single float being shifted4#dj ,footnote #ch3 ,this splendid ship is #hfj tons burden1 with engines of #bbj horse power4 ,footnote #ci3 ,see ,report quoted in ,mechanic's ,magazine1 vol4 xxii4 p4 #bge4 ,this saving cannot amount to less than #dj per cent4 upon the whole consumption of fuel2 it certainly is considerably beyond what ,i should have conceived to be possible2 but ,i have no reason to doubt the accuracy of the ,report4 ,i estimate the former consumption at #aj pounds per horse power per hour1 which on #bbj horse-power would be #bbjj pounds1 of which #hdj pounds #aj bushels1 would be about #d-ajths4 ,footnote #dj3 ,see a more detailed account of these reports in the ,mechanic's ,magazine1 vol4 xxii4 p4 #bgd41 from which ,i have taken the drawing of this paddle-wheel2 and also see ,report of the ,committee of the ,house of ,commons on ,steam ,navigation to ,india1 ,evidence of ,william ,morgan1 p4 #ie4 ,this paddle-wheel is represented in figure #fh4 ,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 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 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 ,l are connected at the other end with a centre ,p1 round which they are capable of revolving4 ,now 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 ,p lies precisely between it and the centre ,o1 its distance from ,p is less than in any other position4 ,as it departs from that point1 its distance from the centre ,p gradually increases until it arrives at the opposite point of its revolution1 where the centre ,o is exactly between it and the centre ,p2 then the distance of the paddle board from the centre ,p is greatest4 ,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 from ,p 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 ,f it increases to a right angle2 at ,g it becomes obtuse2 and at ,k1 where it is most distant from the centre ,p1 it becomes most obtuse4 ,it again diminishes at ,i1 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#da ,footnote #da3 ,a paddle-wheel resembling this has lately been constructed by ,messrs4 ,seawards4 ,it has been charged by ,mr4 ,morgan as being a colourable invasion of his patent1 and the dispute has been brought into the courts of law4 7i7 ,the relative value of the two wheels1 namely1 the common paddle-wheel1 and that of ,morgan has been investigated by ,professor ,barlow of the ,military ,school1 at ,woolwich1 and the results published in a paper of much ability in the ,philosophical ,transactions for #ahcd4 ,by this paper it appears1 that1 when the paddles are not wholly immersed1 the wheel of ,morgan has no important advantage over the other1 and only acquires one when the wheel wallows4 ,but the most important of his inferences is that the common paddle is least efficient when in a vertical position1 contrary to the usual opinion4 ,from this we have a right to infer that the search for a form of wheel which shall always keep the paddle vertical is one whose success need not be attended with any important consequence4 ,the superior qualities of ,morgan's wheel when the paddles are deeply immersed is ascribed by ,barlow to the lessening of the shock sustained by the common paddle-wheel when it strikes the water4 ,this being the case1 the triple wheel of ,stevens is probably superior to that of ,morgan in its efficiency1 while it has the advantage of being far simpler and less liable to be put out of order4--,a4 ,e4 7#aai47 ,to form an approximate estimate of the limit of the present powers of steam navigation1 it will be necessary to consider the mutual relation of the capacity or tonnage of the vessel2 the magnitude1 weight1 and power of the machinery2 the available stowage for fuel2 and the average speed attainable in all weathers1 as well as the general purposes to which the vessel is to be appropriated1 whether for the transport of goods and merchandise1 or merely of despatches and passengers4 ,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 space occupied by the fuel2 the magnitude of the latter will necessarily depend upon the length of the voyage which the vessel must make without receiving a fresh supply of coals4 ,if the voyage be short1 this space may be proportionally limited1 and a greater portion of room will be left for the machinery4 ,if1 on the contrary1 the voyage be longer1 a greater stock of coals will be necessary1 and a less space will remain for the machinery4 ,more powerful vessels1 therefore1 in proportion to their tonnage1 may be used for short than for long voyages4 ,illustration3 ,pl4 ,,xii4 ,taking an average of fifty-one voyages made by the ,admiralty steamers1 from ,falmouth to ,corfu and back during four years ending ,june1 #ahcd1 it was found that the average rate of steaming1 exclusive of stoppages1 was #g-a_/d miles per hour1 taken in a direct line between the places1 and without allowing for the necessary deviations in the course of the vessel4 ,the vessels which performed this voyage varied from #cej to #gjj tons burthen by measurement1 and were provided with engines varying from #ajj horse to #bjj horse-power1 with stowage for coals varying from #hj to #bdj tons4 ,the proportion of the power to the tonnage varied from #a horse to #c tons to #a horse to #d tons2 thus1 the ,,messenger had a power of #bjj horses1 and measured #gcj tons2 the ,,flamer had a power of #abj horses1 and measured #ejj tons2 the ,,columbia had #abj horses1 and measured #cfj tons4 ,in general1 it may be assumed that for the shortest class of trips1 such as those of the ,margate steamers1 and the packets between ,liverpool or ,holyhead and ,dublin1 the proportion of the power to the tonnage should be that of #a horse-power to every #b tons by measure2 while for the longest voyages the proportion would be reduced to #a horse to #d tons1 voyages of intermediate lengths having every variety of intermediate proportion4 ,steamers thus proportioned in their power and tonnage may then1 on an average of weathers1 be expected to make #g-a_/d miles an hour while steaming1 which is equivalent to #agd miles per day of twenty-four hours4 ,but1 in very long voyages1 it rarely happens that a steamer can work constantly without interruption4 ,besides stress of weather1 in which she must sometimes lie-to1 she is liable to occasional derangements of her machinery1 and more especially of her paddles4 ,in almost every long voyage hitherto attempted1 some time has been lost in occasional repairs of this nature while at sea4 ,we shall perhaps1 therefore1 for long voyages1 arrive at a more correct estimate of the daily run of a steamer by taking it at #afj miles4#db ,footnote #db3 ,the ,american reader will hardly be able to refrain from a smile at this estimate of ,dr4 ,lardner of the speed of steamboats1 founded upon the most improved practice of ,europe at the close of the year #ahce4 ,the boats on the ,hudson ,river have for years past averaged a speed of #ae miles per hour1 and the ,lexington1 which was constructed for a navigation part of which is performed in the open ocean1 could probably keep up a speed of the same amount1 except in severe storms4 ,with boats1 constructed on the principles of those which navigate ,long ,island ,sound and the ,chesapeake1 we should not fear to assume #ab miles per hour1 or1 upwards of #bhj miles per day as their average rate of crossing the ocean4--,a4 ,e4 ,by a series of carefully conducted experiments on the consumption of coals1 under marine boilers and common land boilers1 which have been lately made at the works of ,mr4 ,watt1 near ,birmingham1 it has been proved that the consumption of fuel under marine boilers is less than under land boilers1 in the proportion of #b to #c very nearly4 ,on the other hand1 ,i have ascertained from general observation throughout the manufacturing districts in the ,north of ,england1 that the average consumption of coals under land boilers of all powers above the very smallest class is at the rate of #ae pounds of coals per horse-power per hour4 ,from this result1 the accuracy of which may be fully relied upon1 combined with the result of the experiments just mentioned at ,soho1 we may conclude that the average consumption of marine boilers will be at the rate of #aj lbs4 of coal per horse power per hour4 ,mr4 ,field1 of the firm of ,maudslay and ,field1 in his evidence before a ,select ,committee of the ,house of ,commons on ,steam ,navigation to ,india1 has stated from his observation1 and from experiments made at different periods1 that the consumption is only #h lbs4 per horse-power per hour4 ,in the evidence of ,mr4 ,william ,morgan1 however1 before the same committee1 the actual consumption of fuel on board the ,mediterranean packets is estimated at #af cwt4 per hour for engines of #bjj horse power1 and #h-a_/d cwt4 for engines of #ajj horse-power4 ,from my own observation1 which has been rather extensive both with respect to land and marine boilers1 ,i feel assured that #aj lbs4 per hour more nearly represents the practical consumption than the lower estimate of ,mr4 ,field4 ,we may then assume the daily consumption of coal by marine boilers1 allowing them to work upon an average for #bb hours1 the remainder of the time being left for casual stoppages1 at #bbj lbs4 of coal per horse-power1 or very nearly #a ton for every ten horses' power4 ,in short voyages1 where there will be no stoppage1 the daily consumption will a little exceed this2 but the distance traversed will be proportionally greater4 ,when the proportion of the power to the tonnage remains unaltered1 the speed of the vessel does not materially change4 ,we may therefore assume that #aj pounds of coal per horse power will carry a sea-going steamer adapted for long voyages #g-a_/d miles direct distance2 and therefore to carry her #ajj miles will require #ach pounds1 or the #a_/afth part of a ton nearly4 ,now1 the ,mediterranean steamers are capable of taking a quantity of fuel at the rate of #a-a_/d tons per horse power2 but the proportion of their power to their tonnage is greater than that which would probably be adapted for longer runs4 ,we shall1 therefore1 perhaps be warranted in assuming that it is practicable to construct a steamer capable of taking #a-a_/b tons of fuel per horse-power4 ,at the rate of consumption just mentioned1 this would be sufficient to carry her #bdjj miles in average weather2 but as an allowance of fuel must always be made for emergencies1 we cannot suppose it possible for her to encounter this extreme run4 ,allowing1 then1 spare fuel to the extent of a quarter of a ton per horse-power1 we should have as an extreme limit of a steamer's practicable voyage1 without receiving a relay of coals1 a run of about #bjjj miles4 7#abj47 ,this computation is founded upon results obtained from the use chiefly of the ,north of ,england coal4 ,it has1 however1 been stated in evidence before the select committee above mentioned1 that the ,llangennech coal of ,wales is considerably more powerful4 ,captain ,wilson1 who commanded the ,,hugh ,,lindsay steamer in ,india1 has stated that this coal is more powerful than ,newcastle1 in the proportion of #i to #f-a_/b4dc ,some of the commanders of the ,mediterranean packets have likewise stated that the strength of this coal is greater than that of ,newcastle in the proportion of #af to #aa4dd ,so far then as relates to this coal1 the above estimate must be modified1 by reducing the consumption nearly in the proportion of #c to #b4 ,footnote #dc3 ,vide ,report of ,select ,committee on ,steam ,navigation1 p4 #aeb4 ,footnote #dd3 ,ibid4 p4 #g4 ,the class of vessels best fitted for undertaking long voyages1 without relays of coal1 would be one from about #hjj to #ajjj tons measurement furnished with engines from #bjj to #bej horse-power4#de ,such vessels could take a supply of from #cjj to #djj tons of coals1 which being consumed at the rate of from #bj to #be tons per day1 would last about fifteen days4 ,footnote #de3 ,engines in steam vessels generally work considerably above their nominal power4 ,the power1 however1 to which we uniformly refer is the nominal power1 or that power at which they would work with steam of the ordinary pressure4 ,applying these results1 however1 to particular cases1 it will be necessary to remember that they are average calculations1 and must be subject to such modifications as the circumstances may suggest in the particular instances3 thus1 if a voyage is contemplated under circumstances in which an adverse wind generally prevails1 less than the average speed must be allowed1 or1 what is the same1 a greater consumption of fuel for a given distance4 ,against a strong head wind1 in which a sailing vessel would double-reef her top-sails1 even a powerful steamer cannot make more than from #b to #c miles an hour1 especially if she has a head sea to encounter4 7#aba47 ,in considering the general economy of fuel1 it may be right to state1 that the results of experience obtained in the steam navigation of our channels1 and particularly in the case of the ,post ,office packets on the ,liverpool station1 have clearly established the fact1 that by increasing the ratio of the power to the tonnage1 an actual saving of fuel in a given distance is effected1 while at the same time the speed of the vessel is increased4 ,in the case of the ,post ,office steamers called the ,,dolphin and the ,,thetis 7,liverpool station17 the power has been successively increased1 and the speed proportionably augmented2 but the consumption of fuel per voyage between ,liverpool and ,dublin has been diminished4 ,this1 at first view1 appears inconsistent with the known theory of the resistance of solids moving through fluids2 since this resistance increases in the same proportion as the square of the speed4 ,but this physical principle is founded on the supposition that the immersed part of the floating body remains the same4 ,now ,i have myself proved by experiments on canals1 that when the speed of the boat is increased beyond a certain limit1 its draught of water is rapidly diminished2 and in the case of a large steam raft constructed upon the river ,hudson1 it was found that when the speed was raised to #bj miles an hour1 the draught of water was diminished by #g inches4 ,i have therefore no doubt that the increased speed of steamers is attended with a like effect2 that1 in fact1 they rise out of the water2 so that1 although the resistance is increased by reason of their increased speed1 it is diminished in a still greater proportion by reason of their diminished immersion4 ,meanwhile1 whatever be the cause1 it is quite certain that the resistance in moving through the water must be diminished1 because the moving power is always in proportion to the quantity of coals consumed1 and at the same time in the proportion to the resistance overcome4 ,since1 then1 the quantity of coals consumed in a given distance is diminished while the speed is increased1 the resistance encountered throughout the same distance must be proportionally diminished4 7#abb47 ,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 strike 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 was 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 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 7#abc47 ,the greatest speed which has yet been attained upon water by the application of steam has been accomplished in the case of a river steamer of peculiar form1 which has been constructed upon the river ,hudson4 ,this boat1 or rather raft1 consisted of two hollow vessels formed of thin sheet iron1 somewhat in the shape of spindles or cigars 7from whence it was called the cigar boat47 ,in the thickest part these floats were eight feet in diameter1 tapering towards the ends1 and about #cjj feet long3 these floats or buoys1 being placed parallel to each other1 having a distance of more than #af feet between them1 supported a deck or raft #cjj feet long1 and #cb feet wide4 ,a paddle-wheel #cj feet in diameter and #af feet broad revolved between the spindles1 impelled by a steam engine placed upon the deck4 ,this vessel drew about #cj inches of water1 and attained a speed of from #bj to #be miles an hour3 she ran upon a bank in the river ,hudson1 and was lost4 ,the projector is now employed in constructing another vessel of still larger dimensions4 ,it is evident that such a structure is altogether unfitted for sea navigation4 ,in the case of a wide navigable river1 however1 such as the ,hudson1 it will no doubt be attended with the advantage of greater expedition4 7#abd47 ,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 ,sea1 it is proposed to establish steamers between ,malta and ,alexandria 7#hfj miles74 ,a steamer of #djj tons burthen and #ajj horse-power would perform this voyage1 upon an average of all weathers incident to the situation1 in from #e to #f days1 consuming #aj 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 ,alexandria1 the transit might be effected by land across the ,isthmus to ,suez--a journey of from #d to #e days--by caravan and camels2 or the transit might be made either by land or water from ,alexandria to ,cairo1 a distance of #agc miles2 and from ,cairo to ,suez1 #ic miles1 across the desert1 in about #e days4 ,at ,suez would be a station for steamers1 and the ,red ,sea would be traversed in #c runs or more4 ,if necessary1 stations for coals might be established at ,cosseir1 ,judda1 ,mocha1 and finally at ,socatra--an island immediately beyond the mouth of the ,red ,sea1 in the ,indian ,ocean3 the run from ,suez to ,cosseir would be #cjj miles--somewhat more than twice the distance from ,liverpool to ,dublin4 ,from ,cosseir to ,judda1 #dej miles2 from ,judda to ,mocha1 #eag miles2 and from ,mocha to ,socatra1 #fcb 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 #abjj miles1 which would be1 upon an average of weather1 about #h days' steaming4 ,the whole passage from ,alexandria to ,bombay1 allowing #c days for delay between ,suez and ,bombay1 would be #bf days3 the time from ,bombay to ,malta would therefore be about #cc days2 and adding #ad days to this for the transit from ,malta to ,england1 we should have a total of #dg days from ,london to ,bombay1 or about #g weeks4 ,if the terminus proposed were ,calcutta1 the course from ,socatra would be #abej 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 #djj 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 #fjj miles will reach ,madras2 and from ,madras to ,calcutta would be a run of about #fjj miles4 ,the voyage from ,london to ,calcutta would be performed in about #fj days4 ,at a certain season of the year there exists a powerful physical opponent to the transit from ,india to ,suez3 from 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 months--if indeed it would be practicable at all for any continuance in that season4 ,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 #hdj 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 #bee miles2 from ,bassidore to ,bushire1 another point on the eastern coast of the ,persian ,gulf1 would be a run of #cjj miles2 and from ,bushire to the mouth of the ,euphrates1 would be #abj miles4 ,it is evident that the longest of these runs would offer no more difficulty than the passage from ,malta to ,alexandria4 ,from ,bussora near the mouth of the ,euphrates1 to ,bir1 a town upon its left bank near ,aleppo1 would be #aadc 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 difficulty but not of great length2 and from ,scandaroon 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 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 ,even the run from ,malta to ,alexandria or ,scandaroon is liable to objection1 from the liability of the boiler to deposite and incrustation1 unless some effectual method be taken to remove this source of injury4 ,if1 however1 the contrivance of ,mr4 ,hall1 or of ,mr4 ,howard1 or any other expedient for a like object1 be successful1 the difficulty will then be limited to the necessary supply of coals for so long a voyage4 ,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 ,socatra but to ,aden1 a point on the coast of ,arabia near the ,straits of ,babel ,mandeb1 being a run of #afda miles1 which she performed in #aj days and #ai hours4 ,the entire distance from ,bombay to ,suez was in one case performed in #af days and #af hours2 and under the most unfavourable circumstances1 in #bc days4 ,the average was #ba days for each trip4 7#abe47 ,another projected line of steam communication1 which offers circumstances of equal interest to the people of these countries and the ,united ,states1 is that which is proposed to be established between ,london and ,new ,york4 ,on the completion of the ,london and ,liverpool railroad1 ,dublin will be connected with ,london1 by a continuous line of steam transport4 ,it is proposed to continue this line by a railroad from ,dublin to some point on the western coast of ,ireland2 among others1 the harbour of ,,valentia has been mentioned4 ,the nearest point of the western continent is ,st4 ,john's1 ,newfoundland1 the distance of which from ,valentia is #aijj miles2 the distance from ,st4 ,john's to ,new ,york is about #abjj miles1 ,halifax 7,nova ,scotia7 being a convenient intermediate station4 ,the distance from ,valentia to ,st4 ,john's comes very near the point which we have already assigned as the probable present limit of steam navigation4 ,the ,atlantic ,ocean also offers a formidable opponent in the westerly winds which almost constantly prevail in it4 ,these winds are1 in fact1 the reaction of the trades1 which blow near the equator in a contrary direction1 and are produced by those portions of the equatorial atmosphere which1 rushing down the northern latitudes1 carry with them the velocity from west to east proper to the equator4 ,besides this difficulty1 ,st4 ,john's and ,halifax are both inaccessible1 by reason of the climate1 during certain months of the year4 ,should these causes prevent this project from being realized1 another course may be adopted4 ,we may proceed from the southern point of ,ireland or ,england to the ,azores1 a distance of about #ahjj miles3 from the ,azores to ,new ,york would be a distance of about #bjjj miles1 or from the ,azores to ,st4 ,john's would be #afjj miles4#df ,footnote #df3 ,a treatise on the ,steam ,engine is not the place to enter into discussion on the causes of the several constant1 periodic1 and prevailing winds1 otherwise we should feel it our duty to correct the opinion adopted by ,dr4 ,lardner from the older authorities1 in relation to the course of the westerly winds4 ,these winds are1 in the ,south ,atlantic1 and in both ,south and ,north ,pacific1 constant winds4 ,in the ,north ,atlantic between the latitudes1 of #ce and #de1 and1 therefore1 in the track of the vessels which navigate between the ,united ,states and ,great ,britain1 they are the most frequent prevailing winds1 except in the months of ,april and ,october4 ,they are certainly not the reaction of the trade winds1 which is in a well known zone1 to the south of the region in which these westerly winds prevail1 under the name of the ,horse latitudes of our navigations1 and the ,grassy sea of the ,spaniards4 ,those who wish to study the true theory of these winds will find it in ,daniell's learned and ingenious work1 ,on ,atmospheric ,phenomena1 or in the analysis of that work in the ,american ,quarterly ,review4 7k7 ,while the inhabitants of ,great ,britain are discussing the project of the communication with ,new ,york1 by means of the stations described by ,dr4 ,lardner1 those of the ,united ,states appear to be seriously occupied in carrying into effect a direct communication from ,new ,york to ,liverpool4 ,at the speed which has been given to the ,american steam boats1 this presents no greater difficulties than the voyage from the ,azores to ,new ,york1 would1 to one having the speed of no more than #g-a_/d miles per hour4 ,as this attempt is beyond the limit of individual enterprise1 there is1 at the present moment1 an application before the ,legislature of the ,state of ,new ,york for a charter to carry this project into effect4 ,it will be difficult to estimate the results of this enterprise1 which will bring the old and new world within #ab or #ae days voyage of each other4--,a4 ,e4#dg ,footnote #dg3 ,dr4 ,lardner appears purposely to have omitted any detail of the history of ,steam ,navigation4 ,it would be an invidious task on the part of a mere editor to attempt to supply what he has thought proper to avoid4 ,we therefore merely refer to this subject for the purpose of expressing the hope1 that this silence is an earnest that the writers of ,europe are about to abandon the claims they have set up for their countrymen to the merit of introducing the successful practice of ,steam navigation1 and that the respective services of ,fitch1 ,evans1 ,fulton1 and the elder ,stevens will soon be universally acknowledged4--,a4 ,e4 ,,chapter ,,xii4 ,,general ,,economy ,,of ,,steam ,,power4 ,mechanical efficacy of steam -- proportional to the quantity of water evaporated1 and to the fuel consumed -- ,independent of the pressure4 -- ,its mechanical efficacy by condensation alone4 -- ,by condensation and expansion combined -- by direct pressure and expansion -- by direct pressure and condensation -- by direct pressure1 condensation1 and expansion4 -- ,the power of engines4 -- ,the duty of engines4 -- ,meaning of horse power4 -- ,to compute the power of an engine4 -- ,of the power of boilers4 -- ,the structure of the grate-bars4 -- ,quantity of water and steam room4 -- ,fire surface and flue surface4 -- ,dimensions of steam pipes4 -- ,velocity of piston4 -- ,economy of fuel4 -- ,cornish duty reports4 7#acj47 ,having explained in the preceding chapters the most important circumstances connected with the principal varieties of steam engines1 it remains now to explain some matters of detail connected with the power1 efficiency1 and economy of these machines1 which1 though perhaps less striking and attractive than the subjects which have hitherto engaged us1 are still not undeserving of attention4 ,it has been shown in the first chapter1 that water exposed to the ordinary atmospheric pressure 7the amount of which may be expressed by a column of #cj inches of mercury7 will pass from the liquid into the vaporous state when it arrives at the temperature of #bab2 and the vapour thus produced from it will have an elastic force equal to that of the atmosphere4 ,if the water1 however1 to which heat is applied1 be submitted to a greater or less pressure than that of the atmosphere1 it will boil at a greater or less temperature1 and will always produce steam of an elastic force equal to the pressure under which it boils4 ,now it is a fact as remarkable as it is important1 that to convert a given weight of water into vapour will require the same quantity of heat1 under whatever pressure1 and at whatever temperature the water may boil4 ,let us suppose a tube1 the base of which is equal to a square foot1 in which a piston fits air-tight and steam-tight4 ,immediately under the piston1 let a cubic inch of water be placed1 which will be spread in a thin layer over the bottom of the tube4 ,let the piston be counterbalanced by a weight 7acting over a pulley7 which will be equivalent to the weight of the piston1 so that it shall be free to ascend by the application of any pressure below it4 ,now let the flame of a lamp be applied at the bottom of the tube3 the water under the piston being affected by no pressure from above1 except that of the atmosphere acting upon the piston1 will boil at the temperature of #bab1 and by the continued application of the lamp it will at length be converted into steam4 ,the steam into which the cubic inch of water is converted will expand into the magnitude of a cubic foot1 exerting an elastic force equal to the atmospheric pressure2 consequently the piston will be raised one foot above its first position in the tube1 and the cubic foot beneath it will be completely filled with steam4 ,let us suppose1 that to produce this effect required the lamp to be applied to the tube for the space of fifteen minutes4 ,the water being again supposed at its original temperature1 and the piston in its first position1 let a weight be placed upon the piston equal to the pressure of the atmosphere1 so that the water beneath the piston will be pressed down by double the atmospheric pressure4 ,if the lamp be once more applied1 the water will1 as before1 be converted into vapour2 but the piston will now be raised to the height of only six inches#dh from the bottom1 the steam expanding into only half its former bulk4 ,the temperature at which the water would commence to be converted into vapour1 instead of being #bab1 would be #bej2 but the time elapsed between the moment of the first application of the lamp1 and the complete conversion of the water into steam1 will still be fifteen minutes4 ,footnote #dh3 ,strictly speaking1 the height to which the piston would be raised would not diminish in so great a proportion as the pressure is increased1 because the increase of pressure being necessarily accompanied by an increase of temperature1 a corresponding expansion would be produced4 ,therefore there will be a slight increase in the total mechanical effect of the steam4 ,the difference1 however1 is not very important in practice1 and it is usual to consider the density of steam as proportional to the pressure4 ,again1 if the piston be loaded with a weight equal to double the atmospheric pressure1 the water will be pressed down by the force of three atmospheres4 ,if the lamp be applied as before1 the water would be converted into steam in the same time2 but the piston will now be raised only four inches above its first position1 and the steam will consequently be three times as dense as when the piston was pressed down only by the atmosphere4 ,from these and similar experiments we infer3-- ,first1 ,that the elastic pressure of steam is equal to the mechanical pressure under which the water producing the steam has been boiled4 ,secondly1 ,that the bulk which steam fills is diminished in the same proportion as the pressure of the steam is increased2 or1 in other words1 that the density of steam is always in the same proportion as its pressure4 ,thirdly1 ,that the same quantity of heat is sufficient to convert the same weight of water into steam1 whatever be the pressure under which the water is boiled1 or whatever be the density and pressure of the steam produced4 ,fourthly1 ,that the same quantity of water being converted into steam1 produces the same mechanical effect1 whatever be the pressure or the density of the steam4 ,thus1 in the first case1 the weight of one atmosphere was raised a foot high2 in the second case1 the weight of two atmospheres was raised through half a foot2 and1 in the third case1 the weight of three atmospheres was raised through the third of a foot2 the weight raised being in every case increased in the same proportion as the height through which it is elevated is diminished4 ,every increase of the weight is1 therefore1 compensated by a proportionate diminution of the height through which it is raised1 and the mechanical effect is consequently the same4 ,fifthly1 ,that the same quantity of heat or fuel is necessary and sufficient to produce the same mechanical effect1 whatever be the pressure of the steam which it produces4 ,if steam be used to raise a piston against the atmospheric pressure only1 although a definite physical force will be exerted by it1 and a mechanical effect produced1 yet under such circumstances it will exert no directly useful efficiency2 but after the piston has been raised1 and the tube beneath it filled with steam balancing the atmosphere above it1 a useful effect to the same amount may be obtained by cooling the tube1 and thereby reconverting the steam into water4 ,the piston will thus be urged downwards by the unresisted force of the atmosphere1 and any chain or rod attached to it will be drawn downwards with a corresponding force4 ,if the area of the piston be1 as already supposed1 equal to the magnitude of one square foot1 the atmospheric pressure upon it1 being #ae pounds for each square inch1 will amount to #add times #ae pounds1 or #bafj pounds4 ,by drawing down a chain or rope acting over a pulley1 the piston would in its descent 7omitting the consideration of friction1 c47 raise a weight of #bafj pounds a foot high4 ,since #bafj pounds are nearly equal to one ton1 it may1 for the sake of round numbers be stated thus3-- ,a cubic inch of water1 being converted into steam1 will1 by the condensation of that steam1 raise a ton weight a foot high4 ,such is the way in which the force of steam is rendered practically available in the atmospheric engine4 7#aca47 ,the method by which steam is used in the single-acting steam engine of ,watt is1 in all respects1 similar1 except that the piston1 instead of being urged downwards by the force of the atmosphere1 is pressed by steam of a force equal to the atmospheric pressure4 ,it is evident1 however1 that this does not alter the mechanical result4 ,we have stated that a considerable increase of power1 from a given quantity of steam1 was produced by cutting off the steam after the piston had made a part of its descent1 and allowing the remainder of the descent to be produced by the expansive force of the steam already admitted4 ,we shall now more fully explain the principle on which this increase of power depends4 ,let ,a ,b 7fig4 #fi417 as before1 represent a tube1 the bottom of which is equal to a square foot1 and let ,p be a piston in it1 resting upon a cubic inch of water spread over the bottom2 and let w be an empty vessel1 the weight of which exactly counterpoises the piston4 ,by the application of the lamp1 the water will be converted into steam of the atmospheric pressure1 and the piston will be raised from ,p to ,p1 through the height of one foot1 the space in the tube beneath it being filled with steam1 and the vessel w will have descended through one foot4 ,let half a ton of water be now poured into the vessel ,w2 its weight will draw the piston ,p upwards1 so that the steam below it will expand into a larger space4 ,when the piston ,p was only balanced by the empty vessel ,w1 it was pressed downwards by the whole weight of the atmosphere above1 which amounts to about one ton3 now1 however1 half of this pressure is balanced by the half ton of water poured into the vessel ,w2 consequently the effective downward pressure on the piston ,p will be only half a ton1 or half its former amount4 ,the piston will therefore rise1 until the pressure of the steam below it is diminished to the same extent4 ,by what has been already explained1 this will take place when the steam is allowed to expand into double its former bulk2 consequently1 when the piston has risen to ,p1 one foot higher1 or two feet from the bottom of the tube1 the steam will then exactly balance the downward pressure on the piston1 and the latter will remain stationary2 the vessel ,w1 with the half ton of water it contains1 will have descended one foot lower1 or two feet below its first position4 ,let the steam now be cooled and reconverted into water1 and at the same time let another half ton of water be supplied to the vessel ,w2 the pressure below the piston being entirely removed1 the atmospheric pressure will act above it with undiminished force2 and this force1 amounting to one ton1 will draw up the vessel ,w1 with its contents4 ,when the piston descends1 as it will do1 to the bottom of the tube1 the ton of water contained in the vessel ,w will be raised through two perpendicular feet4#di ,footnote #di3 ,strictly speaking1 the quantity of water supposed in these cases to be placed in the vessel ,w would just balance the atmospheric pressure4 ,a slight preponderance must therefore be given to the piston1 to produce the motion4 ,now1 in this process it will be observed that the quantity of steam consumed is not more than in the former case1 viz4 the vapour produced by boiling one cubic inch of water4 ,let us consider1 however1 the mechanical effect which has resulted from it2 half a ton of water has been allowed to descend through one foot1 while a ton has been raised through two feet3 deducting the force lost by the descent of half a ton through one foot from the force obtained by the ascent of one ton through the two feet1 we obtain for the whole mechanical effect one ton and a half raised through one foot2 for it is evident that half a ton has been raised from the lowest point to which the vessel ,w descended one foot above that point1 and one ton has been raised through the other foot1 which is equivalent to one ton and a half through one foot4 ,comparing this with the effect produced in the first case1 where the steam was condensed without causing its expansion1 it will be evident that there is an increase of #ej per cent4 upon the whole mechanical effect produced4 ,but this is not the limit of the increase of power by expansion4 ,instead of condensing the steam when the piston had arrived at ,p1 let a further quantity of water amounting to one sixth of a ton be poured into the vessel ,w1 in addition to the half ton which it previously contained2 the effective pressure on the piston ,p1 being only half a ton1 will be overbalanced by the preponderating weight in the vessel w1 and the piston will consequently ascend4 ,it will become stationary when the steam by expansion loses a quantity of force equal to the additional weight which the vessel ,w has received3 now1 that vessel1 having successively received a half and a sixth of a ton will contain two thirds of a ton2 consequently the effective downward pressure on the piston will be only a third of a ton1 and the steam to balance this must expand into three times the space it occupied when equal1 to the atmospheric pressure4 ,it must therefore ascend to ,p1 three feet above the bottom of the tube4 ,if the steam in the tube be now condensed1 and at the same time one third of a ton of water be supplied to the vessel ,w1 so as to make its total contents amount to one ton1 the piston will descend1 being urged downwards by the unresisted atmospheric pressure1 and the ton of water contained in the vessel ,w will be raised through three perpendicular feet4 ,in this case1 as in the former1 the total quantity of steam consumed is that of one cubic inch of water2 but the mechanical effect it produces is still further increased4 ,to calculate its amount1 we must consider that half a ton of water has fallen through two feet1 which is equivalent to a ton falling through one foot1 besides which the sixth part of a ton has fallen through one foot4 ,the total loss1 therefore1 by the fall of water has been one ton and one sixth through one foot1 while the force gained by the ascent of water has been one ton raised through three feet1 which is equivalent to three tons through one foot4 ,if1 then1 from three tons we deduct one and one sixth1 the remainder will be one ton and five sixths raised through one foot2 this effect being above #hj per cent4 more than that which is produced in the first case1 where the steam was not allowed to expand4 ,to carry the inquiry one step further3 ,let us suppose that1 upon the arrival of the piston at ,p1 a further addition of water to the amount of one twelfth of a ton be added to it3 this1 with the water it already contained1 would make the total contents three fourths of a ton2 consequently1 the effective pressure upon the piston would now be reduced to one fourth of the atmospheric pressure4 ,the atmospheric steam would balance this when expanded into four times its original volume3 consequently1 the piston would come to a state of rest at ,p1 four feet above the bottom of the tube1 and the vessel ,w would consequently have descended through four perpendicular feet4 ,if the steam in the tube be now condensed as in the former cases1 and at the same time a quarter of a ton of water be added to the vessel ,w1 the piston will descend to the bottom of the tube1 and the ton of water in the vessel ,w will be raised through four perpendicular feet4 ,to estimate the mechanical effect thus produced1 we have1 as before1 to deduct the total force lost by the fall of water from the force gained by its elevation3 the water has fallen in three distinct portions3 first1 half a ton has fallen through three perpendicular feet1 which is equivalent to one ton and a half through one foot2 secondly1 one sixth of a ton has fallen through two perpendicular feet1 which is equivalent to one third of a ton through one foot2 and thirdly1 one twelfth of a ton has fallen through one foot3 these added together will be equivalent to one ton and eleven twelfths through one foot4 ,one ton has been raised through four feet1 which is equivalent to four tons through one foot3 deducting from this the force lost by the descent1 the surplus gained will be two tons and one twelfth through one foot1 being about #ajh per cent4 more than the force resulting from the condensation of steam without expansion4 ,to the increase of mechanical effect to be produced in this way1 there is no theoretical limit4 ,according to the manner in which we have here explained it1 to produce the greatest possible effect by a given extent of expansion1 it would be necessary to supply the water or other counterpoise to the vessel ,w1 not in separate masses1 as we have here supposed1 but continuously1 so as to produce a regular motion of the piston upwards4 ,such is the principle on which the advantages of the expansive engine of ,watt and ,hornblower depend1 explained so far as it can be without the aid of the language and reasoning of analysis4#ej ,footnote #ej3 ,a strict investigation of this important property1 as well as of the other consequences of the quality of expansion1 would require more abstruse mathematical processes than would be consistent with the nature of this work4 7#acb47 ,we have here1 however1 only considered the mechanical effect produced by the condensation of steam4 ,let us now examine its direct action4 ,let the piston ,p be supposed to be connected by a rod with a load or resistance which it is intended to raise1 and let the load placed upon it be supposed to amount to one ton1 the total pressure on the piston will then be two tons2 one due to the atmospheric pressure1 and the other to the amount of the load4 ,upon applying heat to the water1 steam will be produced2 and when the water has been completely evaporated1 the piston will rise to the height of six inches from the bottom of the tube4 ,the total mechanical effect thus produced will be one ton weight raised through six perpendicular inches1 which is equivalent to half a ton raised through one foot4 ,again1 let the load upon the piston be two tons2 this will produce a total pressure upon the water below it amounting to three tons1 including the atmospheric pressure4 ,the water1 when converted into vapour under this pressure1 will raise the piston and its load through four perpendicular inches3 the useful mechanical effect will then be two tons raised through the third of a foot1 which is equivalent to two thirds of a ton raised one foot4 ,in the same manner1 if the piston were loaded with three tons1 the mechanical effect would be equivalent to three fourths of a ton raised through one foot1 and so on4 ,it appears therefore from this reasoning1 that when the direct force of steam of greater pressure than the atmosphere is used without condensation1 the total mechanical effect is always less than that produced by the condensation of atmospheric steam without expansion2 but that the greater the pressure under which the steam is produced1 the less will be the difference between these effects4 ,in general1 the proportion of the mechanical effect of high-pressure steam to the effect produced by the condensation of atmospheric steam1 will be as the number of atmospheres expressing the pressure of the steam to the same number increased by one4 ,thus1 if steam be produced under the pressure of six atmospheres1 the proportion of its effect to that of the condensation of atmospheric steam will be as six to seven4 7#acc47 ,another method of applying the power of steam mechanically is1 to combine its direct action with condensation but without expansion4 ,the piston being1 as before1 loaded with one ton1 the evaporation of the water will raise it through six perpendicular inches1 and the result so far will be equivalent to a ton raised half a foot2 but if the piston-rod be supposed also to act by a chain or cord over a wheel1 so as to pull a weight up1 the steam which has just raised the ton weight through six inches1 may be condensed1 and the piston will descend with a force of one ton into the vacuum thus produced1 and another ton may be thus raised through half a foot4 ,the total mechanical power thus yielded by the steam1 adding to its direct action its effect by condensation1 will then be one ton raised through one foot1 being an effect exactly equal to that obtained by the condensation of atmospheric steam4 ,if the piston be loaded with two tons1 its direct action will1 as we have shown1 raise these two tons through four inches1 which is equivalent to two thirds of a ton raised a foot4 ,by condensing this steam a ton weight may be raised in the same manner1 by the descent of the piston through a third of a foot1 which is equivalent to the third of a ton raised through one foot4 ,by pursuing like reasoning1 it will appear that1 if the direct force of high-pressure steam be combined with the indirect force produced by its condensation1 the total mechanical effect will be precisely equal to the mechanical effect by the mere condensation of atmospheric steam4 7#acd47 ,in applying the principle of expansion to the direct action of high-pressure steam1 advantages are gained analogous to those already explained with reference to the method of condensation4 ,let the piston be supposed to be loaded with three tons3 the evaporation of the water beneath it will raise this weight1 including the atmospheric pressure1 through three perpendicular inches4 ,let one ton be now removed1 and the remaining two tons will be raised1 by the expansion of the steam1 through another perpendicular inch4 ,let the second ton be now removed1 and the piston loaded with the remaining ton will rise1 by the expansion of the steam1 to the height of six inches from the bottom4 ,these consequences follow immediately from the principle that steam will expand in proportion as the pressure upon it is diminished1 observing that in this case the atmospheric pressure1 amounting to one ton1 must always be added to the load4 ,in this process three separate effects are produced3 one ton is raised through three inches1 which is equivalent to a quarter of a ton raised through one foot2 another ton is raised through four inches1 which is equivalent to a third of a ton through a foot1 and the third ton is raised through six inches1 which is equivalent to half a ton raised through a foot4 ,the total of these effects amounts to one and one-twelfth of a ton raised through one foot1 while the same load1 raised by the high-pressure steam without expansion1 would be equivalent to only half a ton raised through one foot4 ,again1 let the load placed upon the piston be five tons3 the evaporation of the water will raise this through the sixth part of a foot2 if one ton be now removed1 the other four tons will be raised to a height above the bottom of the tube equal to a fifth part of a foot2 another ton being removed1 the remaining three will be raised to a height from the bottom equal to a fourth of a foot2 and so on1 the last ton being raised through half a foot4 ,to estimate the total mechanical effect thus produced1 we are to consider that the several tons raised from their first position are raised through the sixth1 fifth1 fourth1 third1 and half of a perpendicular foot1 giving a total effect equal to the sixth1 fifth1 fourth1 third1 and half of a ton severally raised through one foot2 these1 therefore1 added together1 will give a total of nineteen twentieths of a ton raised through one foot4 ,in general1 the expansive force applied to the direct action of high-pressure steam1 therefore1 will increase its effect according to the same law1 and subject to the same principles as were shown with respect to the method of condensation accompanied with expansion4 ,the expansive action of high-pressure steam may be accompanied with condensation1 so as considerably to increase the mechanical effect produced2 for1 after the weights with which the piston is loaded have been successively raised to the extent permitted by the elastic force of the steam1 and are removed from the piston1 the steam will expand until it balances the atmospheric pressure4 ,it may afterwards be made further to expand1 by adding weights to the counterpoise ,w in the manner already explained2 and1 the steam being subsequently condensed1 all the effects will be produced upon the descent of the piston which we have before noticed4 ,it is evident that by this means the mechanical effect admits of very considerable increase4 7#ace47 ,we have hitherto considered the piston to be resisted by the atmospheric pressure above it2 but1 as is shown in the preceding chapters1 in the modern steam engines1 the atmosphere is expelled from the interior of the machine by allowing the steam to pass freely through all its cavities in the first instance1 and to escape at some convenient aperture1 which1 opening outwards1 will effectually prevent the subsequent re-admission of air4 ,the piston-rod and other parts which pass from the external atmosphere to the interior of the machine1 are likewise so constructed and so supplied with oil or other lubricating matter that neither the escape of steam nor the entrance of air is permitted4 ,we are therefore now to consider the effect of the action of steam against the piston ,p1 when subjected to a resistance which may be less in amount1 to any extent1 than the atmospheric pressure4 ,in such machines the steam always acts both directly by its power1 and indirectly by its condensation4 ,in calculating its effects1 excluding friction1 c41 we have therefore only to estimate its total force upon the piston1 and to deduct the force of the uncondensed vapour which will resist the motion of the piston4 ,supposing1 then1 the total force exerted upon the piston1 after deducting the resistance from the uncondensed vapour1 to be one ton1 and the length of the cylinder to be one foot1 each motion of the piston from end to end of the cylinder will produce a mechanical force equivalent to a ton weight raised one foot high4 ,if in this case the magnitude of the piston be equivalent to one square foot1 the pressure of the steam will be equal to that of the atmosphere1 and the quantity of water in the form of steam which the cylinder will contain will be a cubic inch1 while the quantity of steam in it will be a cubic foot4 ,in proportion as the area of the piston is enlarged the pressure of the steam will be diminished1 if the moving force is required to remain the same2 but with every diminution of pressure the density of the steam will be diminished in the same proportion1 and the cylinder will still contain the same quantity of water in the form of vapour4 ,in this way steam may be used1 as a mechanical agent1 with a pressure to almost any extent less than that of the atmosphere1 and at temperatures considerably lower than #bab4 ,to obtain the same mechanical force1 it is only necessary to enlarge the piston in the same proportion as the pressure of the steam is diminished4 ,by a due attention to this circumstance1 the expansive power of steam1 both in its direct action and by condensation1 may be used with very much increased advantage2 and such is the principle on which the benefits derived from ,woolf's contrivances depend4 ,if steam of a high-pressure1 say of three or four atmospheres1 be admitted to the piston1 and allowed to impel it through a very small portion of the descent1 it may then be cut off and its expansion may be allowed to act upon the piston until the pressure of the steam is diminished considerably below the atmospheric pressure2 the steam may then be condensed and a vacuum produced1 and the process repeated4 ,in the double-acting engines1 commonly used in manufactures and in navigation1 and still more in the high-pressure engines used for locomotion1 the advantageous application of the principle of expansion appears to have been hitherto attended with difficulties2 for1 notwithstanding the benefits which unquestionably attend it in the economy of fuel1 it has not been generally resorted to4 ,to derive from this principle full advantage1 it would be necessary that the varying power of the expanding steam should encounter a corresponding1 or a nearly corresponding1 variation in the resistance3 this requisite may be attained1 in engines applied to the purpose of raising water1 by many obvious expedients2 but when they have1 as in manufactures1 to encounter a nearly uniform resistance1 or1 in navigation and locomotion1 a very irregular resistance1 the due application of expansion is difficult1 if indeed it be practicable4 ,we have seen that the mechanical effect produced by steam when the principle of expansion is not used1 is always proportional to the quantity of water contained in the steam1 and is likewise in the same proportion so long as a given degree of expansion is used4 ,it is apparent1 therefore1 that the mechanical power which is or ought to be exerted by an engine is in the direct proportion of the quantity of water evaporated4 ,it has also been shown that the quantity of water evaporated1 whatever be the pressure of the steam1 will be in the direct proportion of the quantity of heat received from the fuel1 and therefore in the direct proportion of the quantity of fuel itself1 so long as the same proportion of its heat is imparted to the water4 7#acf47 ,the ,,power of an engine is a term which has been used to express the rate at which it is able to raise a given load1 or overcome a given resistance4 ,the ,,duty of an engine is another term1 which has been adopted to express the load which may be raised a given perpendicular height1 by the combustion of a given quantity of fuel4 ,when steam engines were first introduced1 they were commonly applied to work pumps or mills which had been previously wrought by horses4 ,it was1 therefore1 convenient1 and indeed necessary1 in the first instance1 to be able to express the performance of these machines by reference to the effects of animal power1 to which manufacturers1 miners1 and others1 had been long accustomed4 ,when an engine1 therefore1 was capable of performing the same work in a given time1 as any given number of horses of average strength usually performed1 it was said to be an engine of so many horses' power4 ,this term was long used with much vagueness and uncertainty3 at length1 as the use of steam engines became more extended1 it was apparent that confusion and inconvenience would ensue1 if some fixed and definite meaning were not assigned to it1 so that the engineers and others should clearly understand each other in expressing the powers of these machines4 ,the term horse-power had so long been in use1 that it was obviously convenient to retain it4 ,it was only necessary to agree upon some standard by which it might be defined4 ,the performance of a horse of average strength1 working for eight hours a day1 was1 therefore1 selected as a standard or unit of steam-engine power4 ,smeaton estimated the amount of mechanical effect which the animal could produce at #bb1iaf pounds1 raised one foot per minute2 ,desaguiliers makes it #bg1ejj pounds1 raised through the same height4 ,messrs4 ,bolton and ,watt caused experiments to be made with the strong horses used in the breweries in ,london2 and from the result of these they assigned #cc1jjj pounds raised one foot per minute1 as the value of a horse's power3 this is1 accordingly1 the estimate now generally adopted2 and1 when an engine is said to be of so many horses' power1 it is meant that1 when in good working order and properly managed1 it is capable of overcoming a resistance equivalent to so many times #cc1jjj pounds raised one foot per minute4 ,thus1 an engine of ten-horse-power would be capable of raising #ccj1jjj pounds one foot per minute4 ,as the same quantity of water converted into steam will always produce the same mechanical effect1 whatever be the density of the steam produced from it1 and at whatever rate the evaporation may proceed1 it is evident that the power of a steam engine will depend on two circumstances3 first1 the rate at which the boiler with its appendages is capable of evaporating water2 and1 secondly1 the rate at which the engine is capable of consuming the steam by its work4 ,we shall consider these two circumstances separately4 ,the rate at which the boiler produces steam will depend upon the rate at which heat can be transmitted from the fire to the water which it contains4 ,now this heat is transmitted in two ways3 either by the direct action of the fire radiating heat against the surface of the boiler2 or by the flame1 and heated air which escapes from the fire1 passing through the flues1 as already explained4 ,the surface of the boiler exposed to the direct radiation of the fire is technically called fire surface2 and that which takes heat from the flame and air1 on its way to the chimney1 is called flue surface4 ,of these the most efficient in the generation of steam is the former4 ,in stationary boilers1 used for condensing engines1 where magnitude and weight are matters of little importance1 it has been found that the greatest effect has been produced in general by allowing four and a half square feet of fire surface1 and four and a half square feet of flue surface1 for every horse-power4 ,by means of this quantity of fire and flue surface1 a cubic foot of water per hour may be evaporated4 ,it has been already shown that the total power exerted by a cubic inch of water1 converted into steam1 will be equivalent to #bafj pounds raised one foot4 ,a cubic foot of water consists of #agbh cubic inches1 and the power produced by its evaporation will therefore be found by multiplying #bafj by #agbh2 the product1 #c1gcb1dhj1 expresses the number of pounds' weight which the evaporation of a cubic foot of water would raise one foot high1 supposing that its entire mechanical force were rendered available3 but to suppose this in practice1 would be to suppose the machine1 through the medium of which it is worked1 moved without any power being expended upon its own parts4 ,it would be1 in fact1 supposing all its moving parts to be free from friction and other causes of resistance4 ,to form a practical estimate1 then1 of the real quantity of available mechanical power obtained from the evaporation of a given quantity of water1 it will be necessary to inquire what quantity of this power is intercepted by the engine through which it is transmitted4 ,in different forms of steam engine--indeed1 we may say in every individual steam engine--the amount thus lost is different2 nevertheless1 an approximate estimate may be obtained1 sufficiently exact to form the basis of a general conclusion4 ,let us consider1 then1 severally1 the means by which mechanical power is intercepted by the engine4 ,first1 ,the steam must flow from the boiler into the cylinder to work the piston2 it passes necessarily through pipes more or less contracted1 and is1 therefore1 subject to friction as well as cooling in its passage4 ,second1 ,force is lost by the radiation of heat from the cylinder and its appendages4 ,third1 ,the friction of the piston in the cylinder must be overcome4 ,fourth1 ,loss of steam takes place by leakage4 ,fifth1 ,force is expended in expelling the steam after having worked the piston4 ,sixth1 ,force is required to open and close the several valves1 to pump up the water for condensation1 and to overcome the friction of the various axes4 ,seventh1 ,force is expended upon working the air-pump4 ,in engines which do not condense the steam1 and which1 therefore1 work with steam of high-pressure1 some of these sources of waste are absent1 but others are of increased amount4 ,if we suppose the total effective force of the water evaporated per hour in the boiler to be expressed by #ajjj1 it is calculated that the waste in a high-pressure engine will be expressed by the number #cib2 or1 in other words1 taking the whole undiminished force obtained by evaporation as expressed by #aj1 very nearly #d of these parts will be consumed in moving the engine1 and the other #f only will be available4 ,in a single-acting engine which condenses the steam1 taking1 as before1 #ajjj to express the total mechanical power of the water evaporated in the boiler1 #djb will express the part of this consumed in moving the engine1 and #eih1 therefore1 will express the portion of the power practically available2 or1 taking round numbers1 we shall have the same result as in the non-condensing engine1 viz4 the whole force of the water evaporated being expressed by #aj1 #d will express the waste1 and #f the available part4 ,in a double-acting engine the available part of the power bears a somewhat greater proportion to the whole4 ,taking1 as before1 #ajjj to express the whole force of the water evaporated1 #cfh will express the proportion of that force expended on the engine1 and #fcb the proportion which is available for work4 ,in general1 then1 taking round numbers1 we may consider that the mechanical force of four tenths of the water evaporated in the boiler is intercepted by the engine1 and the other six tenths are available as a moving force4 ,in this calculation1 however1 the resistance produced in the condensing engine by the uncondensed steam is not taken into account3 the amount of this force will depend upon the temperature at which the water is maintained in the condenser4 ,if this water be kept at the temperature of #abj1 the vapour arising from it will have a pressure expressed by three inches seven tenths of mercury2 if we suppose the pressure of steam in the boiler to be measured by #cg inches of mercury1 then the resistance from the uncondensed steam will amount to one tenth of the whole power of the boiler2 this1 added to the four tenths already accounted for1 would show a waste amounting to half the whole power of the boiler1 and consequently only half the water evaporated would be available as a moving power4 ,if the temperature of the condenser be kept down to #ajj1 then the pressure of uncondensed steam will be expressed by two inches of mercury1 and the loss of power consequent upon it would amount to a proportionally less fraction of the whole power4 ,the following example will illustrate the method of estimating the effective power of an engine4 ,in a double-acting engine1 in good working condition1 the total power of steam in the boiler being expressed by #ajjj1 the proportion intercepted by the engine1 exclusive of the resistance of the uncondensed steam1 will be #cfh1 and the effective part #fcb4 ,now1 suppose the pressure of steam in the boiler to be measured by a column of #ce inches of mercury2 the thousandth part of this will be seven two hundredths of an inch of mercury1 and #fcb of these parts will express the effective portion of the power4 ,by multiplying seven two hundredths by #fcb1 we obtain #bb nearly4 ,now1 suppose the temperature in the condenser is #abjj1 the pressure of steam corresponding to that temperature will be measured by #c-g_/aj inches of mercury4 ,subtracting this from #bb1 there will remain #ah-c_/aj inches of mercury1 as the effective moving force upon the piston2 this will be equivalent to about #g lbs4 on each circular inch4 ,if the diameter of the piston then be #bd inches1 its surface will consist of a number of circular inches expressed by the square of #bd1 or #bd #bd #egf2 and1 as upon each of these circular inches there is an effective pressure of #g lbs41 we shall find the total pressure in pounds by multiplying #egf by #g1 which gives #djcb lbs4 ,we shall find the space through which this force works per minute1 by knowing the length of the cylinder and the number of strokes per minute4 ,suppose the length of the cylinder to be #e feet1 and the number of strokes per minute #ba-a_/b4 ,in each stroke#ea the piston will1 therefore1 move through #aj feet1 and in one minute it will move through #bae feet4 ,the moving force1 therefore1 is #djcb lbs4 moved through #bae feet per minute1 which is equivalent to #bae times #djcb lbs41 or #hff1hhj lbs41 raised one foot per minute4 ,footnote #ea3 ,by a stroke of the piston is meant its motion from one end of the cylinder and back again4 ,for every #cc1jjj lbs4 contained in this1 the engine has a horse-power4 ,to find the horse-power1 then1 of the engine1 we have only to divide #hff1hhj by #cc1jjj2 the quotient is #bf nearly1 and1 therefore1 the engine is one of #bf horse power4 ,let it be required to determine the quantity of water which a boiler must evaporate per hour1 for each horse-power of the engine which it works4 ,it has been already explained that one horse-power expresses #cc1jjj lbs4 raised one foot high per minute1 or1 #a1ihj1jjj lbs4 raised one foot high per hour4 ,the quantity of water necessary to produce this mechanical effect by evaporation1 will be found by considering that a cubic inch of water1 being evaporated1 will produce a mechanical force equivalent to #bafj lbs4 raised a foot high4 ,if we divide #a1ihj1jjj1 therefore1 by #bafj1 we shall find the number of cubic inches of water which must be evaporated per hour1 in order to produce the mechanical effect expressed by one horse-power2 the result of this division will be #iaf1f1 which is therefore the number of cubic inches of water per hour1 whose evaporation is equivalent to one horse-power4 ,but it has been shown that1 for every #f cubic inches of water evaporated in the boiler which are available as a moving power1 there will be #d cubic inches intercepted by the engine4 ,to find1 then1 the quantity of waste corresponding to #iaf cubic inches of water1 it will be necessary to divide that number by #f1 and to multiply the result by #d3 this process will give #faj as the number of cubic inches of water wasted4 ,the total quantity of water1 therefore1 which must be evaporated per hour1 to produce the effect of one horse-power1 will be found by adding #faj to #iaf1 which gives #aebf4 ,this result1 however1 being calculated upon a supposition of a degree of efficiency in the engines which is1 perhaps1 somewhat above their average state1 it has been customary with engineers to allow a cubic foot of water per hour for each horse-power1 a cubic foot being #agbh cubic inches1 or above #aa per cent4 more than the above estimate4 7#acg47 ,it has been stated1 that to evaporate a cubic foot of water per hour requires #i square feet of surface exposed to the action of the fire and heated air4 ,this1 therefore1 is the quantity of surface necessary for each horse-power1 and we shall find the total quantity of fire and flue surface necessary for a boiler of a given power1 by multiplying the number of horses in the power by #i2 the product will express1 in square feet1 the quantity of boiler surface which must be exposed to the fire1 one half of this being fire surface and the other half flue surface4 ,since the supply of heat to the boiler must be proportionate to the quantity of fuel maintained in combustion1 and the quantity of that fuel must depend on the extent of grate surface1 it is clear that a determinate proportion must exist between the power of the boiler1 and the extent of grating in the fire place4 ,the quantity of oxygen which combines with the fuel varies with the quality of that fuel2 for different kinds of coal it varies from two to three pounds for each pound of coal4 ,we shall take it an average of #b-a_/b pounds4 ,now #b-a_/b pounds of oxygen will measure #cj cubic feet2 also #e cubic feet of atmospheric air contain #a cubic foot of oxygen2 and consequently #aej cubic feet of atmospheric air will be necessary for the combustion of #a pound of average coals4 ,at least one third of the air1 which passes through a fire1 escapes uncombined into the chimney4 ,we must1 therefore1 allow #bbj cubic feet of atmospheric air to pass through the grate-bars for every pound of fuel which is consumed4 ,now since land boilers will consume #ae pounds1 and marine boilers #aj pounds1 per hour per horse-power1 it follows that the spaces between the grate-bars1 and the extent of grate surface1 must be sufficient to allow #cjjj cubic feet of air per hour in land boilers1 and #bjjj cubic feet in marine boilers1 to pass through them for each horse-power1 or1 what is the same1 for each foot of water converted into steam per hour4 ,the quantity of grate surface necessary for this does not seem to be ascertained with precision2 but1 perhaps1 we may take as an approximate estimate for land boilers one square foot of grate surface per horse-power1 and for marine boilers two thirds of a square foot1 the spaces between the grate-bars being equal to their breadth4 ,it is evident that the capacity of a boiler for water and steam must have a determinate relation to the power of the engine it is intended to supply4 ,for each horse-power of the engine1 it has been shown that a cubic foot of water must pass from the boiler in the form of steam per hour4 ,now1 it is evident that the steam could not be supplied of a uniform force1 if the quantity of steam contained at any moment in the boiler were not considerably greater than the contents of the cylinder4 ,for example1 if the volume of steam in the boiler were precisely equal to the capacity of the cylinder1 then one measure of the cylinder would for the moment cause the steam to expand into double its bulk and to lose half its force1 supposing it to pass freely from the boiler to the cylinder4 ,in the same manner1 if the volume of steam contained in the boiler were twice the contents of the cylinder1 the steam would for a moment lose a third of its force1 and so on4 ,it is clear1 therefore1 that the space allotted to steam in the boiler must be so many times greater than the magnitude of the cylinder1 that the abstraction of a cylinder full of steam from it shall cause a very trifling diminution of its force4 ,in the same manner1 we may perceive the necessity of maintaining a large proportion between the total quantity of water in the boiler1 and the quantity supplied in the form of steam to the cylinder4 ,if1 for example 7taking as before an extreme case17 the quantity of water in the boiler were only equal to the quantity supplied in the form of steam to the cylinder in a minute1 it would be necessary that the contents of the boiler should be replaced by cold water once in each minute3 and1 under such circumstances1 it is evident that the action of the heat upon the water would be quite unmanageable4 ,but1 independent of this1 the quantity of water must be sufficient to fill the boiler above the point at which the flue surface terminates1 otherwise the heat of the fuel would act upon the part of the boiler containing steam and not water2 and1 steam receiving heat sluggishly1 the metal of the boiler would be gradually destroyed by undue temperature4 ,the total quantity of space for water and steam in boilers is subject to considerable variation in proportion to their power4 ,small boilers require a greater proportion of steam and water-room1 or a greater capacity of boiler1 in proportion1 than large ones2 and the same applies to their fire surface and flue surface4 ,the general experience of engineers has led to the conclusion1 that a low-pressure boiler of the common kind requires ten cubic feet of water-room1 and ten cubic feet of steam-room in the boiler1 for every cubic foot which the engine consumes per hour1 or1 what is the same1 for each horse-power of the engine4 ,thus1 an engine of ten-horse-power1 according to this rule1 would require a boiler having the capacity of #bjj cubic feet which should be constantly kept half filled with water4 ,there are1 however1 different estimates of this4 ,some engineers hold that a boiler should have twenty-five cubic feet of capacity for each horse-power of the engine1 while others reduce the steam so low as eight cubic feet4 ,in a table of the capacities of boilers of different powers1 and the feed of water necessary to be maintained in them1 ,mr4 ,tredgold assigns to a boiler of five-horse-power fourteen cubic feet of water per horse-power2 for one of ten-horse power1 twelve and a half cubic feet2 and1 for one of forty-horse1 eleven cubic feet4 ,for engines of greater power it is generally found advantageous to have two or more boilers of small power1 instead of one of large power4 ,this method is almost invariably adopted on board steam boats1 and has the advantage of securing the continuance of the working of the engine1 in case of one of the boilers being deranged4 ,it is also found convenient to keep an excess of power in the boilers1 above the wants of the engine4 ,thus1 an engine of sixty-horse-power may be advantageously supplied with two forty-horse boilers1 and an engine of eighty-horse-power with two fifty-horse boilers1 and so on4 7#ach47 ,the pressure of steam in the cylinder of an engine is always less than the pressure of steam in the boiler1 owing to the obstructions which it encounters in its passage through the steam pipes and valves4 ,the difference between these pressures will depend upon the form and magnitude of the passages3 the straighter and wider they are1 the less the difference will be2 if they are contracted and subject to bends1 especially to angular inflexions1 the steam will be considerably diminished in its pressure before it reaches the cylinder4 ,the throttle valve placed in the steam pipe may also be so managed as to diminish the pressure of steam in the cylinder to any extent3 this effect1 which is well understood by practical engineers1 is called wire-drawing the steam4 ,by such means it is evidently possible for the steam in the boiler to have any degree of high-pressure while the engine is worked at any degree of low pressure4 ,since1 however1 the pressure of the steam in the cylinder is a material element in the performance of the engine1 the magnitude1 position1 and shape of the steam pipe and of the valves are a matter of considerable practical importance4 ,but theory furnishes us with little more than very general principles to guide us4 ,one practical rule which has been adopted is1 to make the diameter of the steam pipe about one fifth of that of the cylinder3 by this means the area of the transverse action of the pipe will be one twenty-fifth part of the superficial magnitude of the piston2 and1 since the same quantity of steam per minute must flow through this pipe as through the cylinder1 it follows that the velocity of the steam1 in passing through the steam pipe1 will be twenty-five times the velocity of the piston4 7#aci47 ,another rule which has been adopted is1 to allow a square inch of magnitude1 in the section of the steam pipe1 for each horse-power of the engine4 ,the result of this and all similar rules is1 that the steam should always pass through the steam pipe with the same velocity1 whatever be the power of the engine4 ,in engines of the same power1 the piston will have very different velocities in the cylinder1 according to the effective pressure of the steam1 and the proportions and capacity of the cylinder4 ,it is clear from what has been already explained1 that1 when the power is the same1 the same actual quantity of water1 in the form of steam1 must pass through the cylinder per minute3 but1 if the steam be used with a considerable pressure1 being in a condensed state1 the same weight of it will occupy a less space2 and consequently the cylinders of high-pressure engines are smaller than those of the same power in low-pressure engines3 the magnitude of the cylinder and the piston therefore1 as well as the velocity of the latter1 will depend first upon the pressure of the steam4 ,but with steam of a given pressure1 the velocity of the piston will be different3 with a given capacity of cylinder1 and a given pressure of steam1 the power of the engine will determine the number of strokes per minute4 ,but the actual velocity of the piston will depend1 in that case1 on the proportion which the diameter of the cylinder bears to its length2 the greater the diameter of the piston is with respect to its length1 the less will be its velocity4 ,in case of stationary engines used on land1 that proportion of the diameter of the cylinder to its length is selected1 which is thought to contribute to the most efficient performance of the machine4 ,according to some engineers1 the length of the cylinder should be twice its diameter2#eb others make the length equal to two diameters and a half2 but there are circumstances in which considerations of practical convenience render it necessary to depart from these proportions4 ,in marine engines1 where great length of cylinder would be inadmissible1 and where1 on the other hand1 considerable power is required1 cylinders of short stroke and great diameter are used4 ,in these engines the length of the stroke is often not greater than the diameter of the piston1 and sometimes even less4 ,footnote #eb3 ,this is the proportion under which the cylinder with a given capacity will present the least possible surface to the cooling effect of the atmosphere4 ,the actual velocity which has been found to have the best practical effect1 for the piston in low-pressure engines1 is about #bjj feet per minute4 ,this1 however1 is subject to some variation4 7#adj47 ,a given weight or measure of fuel burnt under the boiler of an engine is capable of producing a mechanical effect through the means of that engine1 which1 when expressed in an equivalent number of pounds' weight lifted a foot high1 is called the duty of the engine4 ,if all the heat developed in the combustion of the fuel could be imparted to the water in the boiler1 and could be rendered instrumental in producing its evaporation2 and if1 besides1 the steam thus produced could be all rendered mechanically available at the working point2 then the duty of the engine would be the entire undiminished effect of the heat of combustion2 but it is evident that this can never practically be the case4 ,in the first place1 the heat developed by the combustion can never be wholly imparted to the water in the boiler3 some part of it will necessarily escape without reaching the boiler at all2 another portion will be consumed in heating the metal of the boiler1 and in supplying the loss by radiation from its surface2 another portion will be abstracted by the various sources of the waste and leakage of steam2 another portion will be abstracted by the reaction of the condensed steam2 and another portion of the power will be consumed in overcoming the friction and resistance of the engine itself4 ,it is apparent that all these sources of waste will vary according to the circumstances and conditions of the machine1 and according to the form and construction of the furnace1 flues1 boilers1 c4 ,the duty1 therefore1 of different engines will be different2 and when such machines are compared1 with a view to ascertain their economy of fuel1 it has been found necessary carefully to register and to compare the fuel consumed with the weight or resistance overcome4 ,in engines applied to manufactures generally or navigation1 it is not easy to measure the amount of resistance which the engine encounters1 but when the engine is applied to the pumping of water1 its performance is more easily determined4 ,in the year #ahaa1 several of the proprietors of the mines in ,cornwall1 suspecting that some of their engines might not be doing a duty adequate to their consumption of fuel1 came to a determination to establish a uniform method of testing the performance of their engines4 ,for this purpose a counter was attached to each engine1 to register the number of strokes of the piston4 ,all the engines were put under the superintendence of ,messrs4 ,thomas and ,john ,lean1 engineers2 and the different proprietors of the mines1 as well as their directing engineers1 respectively pledged themselves to give every facility and assistance in their power for the attainment of so desirable an end4 ,messrs4 ,lean were directed to publish a monthly report of the performance of each engine1 specifying the name of the mine1 the size of the cylinder1 the load upon the engine1 the length of the stroke1 the number of pump lifts1 the depth of the lift1 the diameter of the pumps1 the time worked1 the consumption of coals1 the load on the pump1 and1 finally1 the duty of the engine1 or the number of pounds lifted one foot high by a bushel of coals4 ,the publication of these monthly reports commenced in ,august1 #ahaa1 and have been regularly continued to the present time4 ,the favourable effect which these reports have produced upon the vigilance of the several engineers1 and the emulation they have excited1 both among engine-makers and those to whom the working of the machines are intrusted1 are rendered conspicuous in the improvement which has gradually taken place in the performance of the engines1 up to the present time4 ,in a report published in ,december1 #ahbf1 the highest duty was that of an engine at ,wheal ,hope mine in ,cornwall4 ,by the consumption of one bushel of coals1 this engine raised #df1hch1bdf pounds a foot high1 or1 in round numbers1 forty-seven millions of pounds4 ,in a report published in the course of the present year 7#ahce7 it was announced that a steam engine1 erected at a copper mine near ,st4 ,anstell1 in ,cornwall1 had raised by its average work #ie millions of pounds #a foot high1 with a bushel of coals4 ,this enormous mechanical effect having given rise to some doubts as to the correctness of the experiments on which the report was founded1 it was agreed that another trial should be made in the presence of a number of competent and disinterested witnesses4 ,this trial accordingly took place a short time since1 and was witnessed by a number of the most experienced mining engineers and agents3 the result was1 that for every bushel of coal consumed under the boiler the engine raised #abe-a_/b millions of pounds weight one foot high4 7#ada47 ,it may not be uninteresting to illustrate the amount of mechanical virtue1 which is thus proved to reside in coals1 in a more familiar manner4 ,since a bushel of coal weighs #hd lbs4 and can lift #ef1jbg tons a foot high1 it follows that a pound of coal would raise #ffg tons the same height2 and that an ounce of coal would raise #db tons one foot high1 or it would raise #ah lbs4 a mile high4 ,since a force of #ah lbs4 is capable of drawing #b tons upon a railway1 it follows that an ounce of coal possesses mechanical virtue sufficient to draw #b tons a mile1 or #a ton #b miles1 upon a level railway4#ec ,footnote #ec3 ,the actual consumption of coal upon railways is in practice about eight ounces per ton per mile4 ,it is1 therefore1 worked with sixteen times less effect than in the engine above mentioned4 ,the circumference of the earth measures #be1jjj miles4 ,if it were begirt by an iron railway1 a load of one ton would be drawn round it in six weeks by the amount of mechanical power which resides in the third part of a ton of coals4 ,the great pyramid of ,egypt stands upon a base measuring #gjj feet each way1 and is #ejj feet high2 its weight being #ab1gfj1jjj1jjj lbs4 ,to construct it1 cost the labour of #ajj1jjj men for #bj years4 ,its materials would be raised from the ground to their present position by the combustion of #dgi tons of coals4 ,the weight of metal in the ,menai bridge is #d1jjj1jjj lbs41 and its height above the level of the water is #abj feet3 its mass might be lifted from the level of the water to its present position by the combustion of #d bushels of coals4#ed ,footnote #ed3 ,some of these examples were given by ,sir ,john ,herschel1 in his ,preliminary ,discourse on ,natural ,philosophy2 but since that work was written an increased power has been obtained from coals1 in the proportion of #g to #ab-a_/b4 ,the enormous consumption of coals in the arts and manufactures1 and in steam navigation1 has of late years excited the fears of some persons as to the possibility of the exhaustion of our mines4 ,these apprehensions1 however1 may be allayed by the assurance received from the highest mining and geological authorities1 that1 estimating the present demand from our coal mines at #af millions of tons annually1 the coal fields of ,northumberland and ,durham alone are sufficient to supply it for #agjj years1 and after the expiration of that time the great coal basin of ,south ,wales will be sufficient to supply the same demand for #bjjj years longer4 ,but1 in speculations like these1 the probable1 if not certain1 progress of improvement and discovery ought not to be overlooked2 and we may safely pronounce that1 long before a minute fraction of such a period of time shall have rolled over1 other and more powerful mechanical agents will altogether 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 science1 at the present moment1 the vigour1 activity1 and sagacity with which researches in it are prosecuted in every civilized 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 hidden powers of nature 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 ,,chapter ,,xix4 ,,plain ,,rules ,,for ,,railway ,,speculators4 7#adb47 ,for some time after the completion of the ,liverpool and ,manchester railway1 doubts were entertained of its ultimate success as a commercial speculation2 and1 even still1 after several years' continuance1 some persons are found1 sceptical by temperament1 who have not acquired full confidence in the permanency of its advantages4 ,the possibility of sustaining a system of regular transport upon it1 with the unheard of speed effected at the commencement of the undertaking1 was1 for a long period1 questioned by a considerable portion even of the scientific world2 and1 after that possibility was established1 by the regular performance of some years1 the practicability of permanently profitable work1 at that rate of speed1 was still doubted by many1 and altogether denied by some4 ,the numerous difficulties to be encountered1 and the enormous expense of locomotive power1 have been fully admitted by the directors in their semi-annual reports4 ,persons interested in canals and other rival establishments1 and others constitutionally doubtful of everything1 attributed the dividends to the indirect proceedings of the managers1 and asserted that when they appeared to be sharing their profit's1 they1 in reality1 were sharing their capital4 ,this delusion1 however1 could not long continue1 and the payment of a steady semi-annual dividend of #d-a_/b per cent4 since the opening of the railway1 together with the commencement of a reserved fund of a considerable amount1 with a premium of above #ajj per cent4 on the original shares1 has brought conviction to understandings impenetrable to general reasoning2 and the tide of opinion1 which1 for a time1 had turned against railways1 has now1 by the usual reaction1 set in so violently in their favour1 that it becomes the duty of those who professionally devote themselves to such inquiries1 to restrain and keep within moderate bounds the public ardour1 rather than to stimulate it4 ,the projects for the construction of great lines of internal communication which have been announced would require1 if realized1 a very large amount of capital4 ,considering that the estimated capital is invariably less than the amount actually required1 we shall not1 perhaps1 overrate the extent of the projected investments if we estimate them at fifty millions4 ,the magnitude of this amount has created alarm in the minds of some persons1 lest a change of investment so extensive should produce a serious commercial shock4 ,it should1 however1 be considered that1 even if all the projected undertakings should be ultimately carried into execution1 a long period must elapse1 perhaps not less than fifteen or twenty years1 before they can be all completed3 the capital will be required1 not suddenly1 but by small instalments1 at distant intervals of time4 ,even if it were true1 therefore1 that1 to sustain their enterprises1 an equivalent amount of capital must be withdrawn from other investments1 the transfer would lake place by such slow degrees as to create no serious inconvenience4 ,but1 in fact1 it is not probable that any transfer of capital whatever will be necessary4 ,trade and manufacturers are at the present moment in a highly flourishing condition2 and the annual accumulation of capital in the country is so great1 that the difficulty will probably be1 not to find capital to meet investments1 but to find suitable investments for the increasing capital4 ,in ,manchester alone1 it is said that the annual increment on capital is no less than three millions4 ,in fifteen years1 therefore1 this mart alone would be sufficient to supply all the funds necessary for the completion of all the proposed railroads1 without withdrawing capital from any other investment4 ,the facilities which these ,joint ,stock ,companies offer for the investment of capital1 even of the smallest amount1 the temptations which the prospect of large profits hold out1 and the low interest obtained on national stock of every description1 have attracted a vast body of capitalists1 small and great1 who have subscribed to these undertakings with the real intention of investment4 ,but1 on the other hand1 there is a very extensive body of speculators who engage in them upon a large scale1 without the most distant intention1 and1 indeed1 without the ability1 of paying up the amount of their shares4 ,the loss which the latter class of persons may sustain would1 probably1 excite little commiseration1 were it not for the consequences which must result to the former1 should a revolution take place1 and the market be inundated with the shares of these gambling speculators1 who buy only to sell again4 ,effects would be produced which must be ruinous to a large proportion of the bon fide subscribers4 ,it may1 therefore1 be attended with some advantage to persons who really intend to make permanent investments of this nature1 to state1 in succinct and intelligible terms1 the principal circumstances on which the efficiency and economy of railroads depend1 so as to enable them1 in some measure1 to form a probable conjecture of the prospective advantages which the various projects hold out4 ,in doing this1 we shall endeavour1 as much as possible1 to confine our statements to simple facts and results1 which can neither be denied nor disputed1 leaving1 for the most part1 the inferences to which they lead to be deduced from them by others4 ,it may be premised1 that persons proposing to engage in any railroad speculation should obtain first a table of gradients2 that is1 an account of all the acclivities upon the line from terminus to terminus1 stating how many feet in a mile each incline rises or falls1 and its length4 ,secondly1 it would also be advantageous to have a statement of the lengths of the radii of the different curves as well as the lengths of the curves themselves4 ,thirdly1 an account of the actual intercourse which has taken place1 for a given time1 upon the turnpike road connecting the proposed termini1 stating the number of coaches licensed1 and the average number of passengers they carry2 also as near an account of the transport of merchandise as may be obtained4 ,the latter1 however1 is of less moment4 ,an approximate estimate may be made of the intercourse in passengers1 by allowing for each coach1 upon each trip1 half its licensed complement of load4 ,fourthly1 the water communication by canal or otherwise between the places2 and the amount of tonnage transported by it4 ,with the information thus obtained1 the following succinct maxims will be found useful3-- ,i4 ,no railroad can be profitably worked without a large intercourse of passengers4 ,goods1 merchandise1 agricultural produce1 c41 ought to be regarded as of secondary importance4 ,,ii4 ,a probable estimate of the number of passengers to be expected upon a projected line of railroad may be made by increasing the average number of passengers for the last three years1 by the common road1 in a twofold proportion4 ,the average number of passengers daily between ,liverpool and ,manchester1 before the formation of the railway1 was about #dej2 the present average number is above #acjj4 ,a short railroad of about five miles is constructed between ,dublin and ,kingstown3 on which the average number of passengers daily between those places has increased in nearly the same proportion4 ,,iii4 ,passengers can be profitably transported by canal1 at a speed not exceeding nine miles an hour1 exclusive of delays at locks1 at the rate of one penny per head per mile4 ,the average fares charged upon the ,manchester railway are at the rate of #a-hd_/ajj;d4 per head per mile1 the average speed being twenty miles an hour4 ,to transport passengers at the rate of ten miles an hour on a railway1 would cost very little less than the greater speed of twenty miles an hour1 so that a railroad could not enter into competition on equal terms with a canal by equalising the speed4 ,the canal between ,kendal and ,preston measures #eg miles3 passengers are transported upon it between these places at the average speed of a mile in #f-a_/b minutes1 or #i-a_/d miles an hour nearly1 exclusive of delays at locks4 ,the fare charged is at the average rate of a penny a mile4 ,there are eight locks1 rising #i feet each1 and a tunnel #djj yards long1 through which the boat is tracked by hand2 the tunnel requires #e minutes1 and the locks from #be to #bh minutes1 in descending1 and #de to #dh minutes in ascending4 ,similar boats are worked on the ,forth and ,clyde1 and the ,union canals in ,scotland1 and on the ,paisley and ,johnstone canal at nearly the same fares4 ,,iv4 ,at the fare of #a-hd_/ajj;d4 per head per mile1 the profit on the ,manchester railroad is #ajj per cent4 on the disbursements for passengers4 ,v4 ,goods can be profitably transported by canal at a lower tonnage than by railroads2 the speed on the canal 7for goods7 being1 however1 but one-fifth of the speed on the railroad4 ,,vi4 ,goods are transported on the ,liverpool and ,manchester railroad at three-pence three farthings per ton per mile1 with a profit of about #dj per cent4 upon the disbursement1 having the competition of a canal between its termini4 ,,vii4 ,a long railroad can be worked with greater relative economy than a short one4 ,,viii4 ,steam engines work with the greatest efficiency and economy1 when the resistance they have to overcome is perfectly uniform and invariable4 ,,ix4 ,the variation of resistance on railroads depends1 first1 on acclivities1 secondly1 on curves4 ,by curves are meant the changes of direction of the road to the right or to the left4 ,the direction of a railroad cannot be changed suddenly by an angle1 but must be effected gradually by a curve4 ,supposing the curve to be 7as it generally is7 the arc of a circle1 the radius of the curve is the distance of the centre of the circle from the curve4 ,this radius is an important element in the estimate of the road4 ,x4 ,the more nearly a railroad approaches to an absolute level1 and perfect straightness1 the more profitably will it be worked4 ,,xi4 ,the total amount of mechanical power necessary to transfer a given load from one extremity of a railroad to another is a matter of easy and exact calculation1 when the gradients and curves are known2 and the merits of different lines may be compared together in this respect3 but it is not the only test of their efficiency which must be applied4 ,,xii4 ,a railroad having gradients exceeding seventeen feet in a mile will require more mechanical power to work it than it would were it level2 and the more of these excessive gradients there are upon it1 and the more steep they are1 the greater will be this disadvantage4 ,,xiii4 ,although a railroad having no gradients exceeding seventeen feet in a mile does not require more mechanical power than a level1 yet the mechanical power which it requires will not be so advantageously expended1 and1 therefore1 it will not be so economical4 ,,xiv4 ,a railroad which has gradients above thirty feet in a mile will require such gradients to be worked by assistant locomotive engines1 which will be attended with a waste of power1 and an increase of expenditure1 more or less1 according to the number and length of such gradients4 ,,xv4 ,a very long inclined plane cannot be worked by an assistant locomotive without a wasteful expense4 ,gradients exceeding seventeen feet per mile must1 therefore1 be short4 ,,xvi4 ,gradients exceeding fifty feet in a mile cannot be profitably worked except by stationary engines and ropes1 an expedient attended with so many objections as to be scarcely compatible with a large intercourse of passengers4 ,,xvii4 ,steep gradients1 provided they descend from the extremities of a line1 are admissible provided they be short4 ,it is evident that in this case the inclined planes will help at starting to put the trains in motion1 at the time when1 in general1 there would be the greatest strain upon the moving power2 and1 in approaching the terminus1 the momentum would be sufficient to carry the train to the top of the plane1 if its length were not great1 since it must1 at all events1 come to a stop at the extremity4 ,,xviii4 ,the effect of gradients in increasing the resistance during the ascent may be estimated by considering that a gradient of seventeen feet in a mile doubles the resistance of the level1 thirty-four feet in a mile triples it1 and eight and a half feet in a mile adds one half its amount1 and so on4 ,,xix4 ,with the speed now attainable on railways1 curves should be avoided with radii shorter than a mile4 ,expedients may diminish the resistance1 but1 through the negligence of engine drivers1 they must always be attended with danger4 ,curves are not objectionable near the extremities of a line4 ,,xx4 ,the worst position for a curve is the foot of an inclined plane1 because of the velocity which the trains acquire in the descent1 and the occasional impracticability of checking them4 ,,xxi4 ,in proportion as the speed of locomotives is increased by the improvements they are likely to receive1 the objections and dangers incident to curves will be increased4 ,,xxii4 ,the difficulty which attends the use of long tunnels arises from the destruction of the vital air which is produced by the combustion in the furnaces of the engines4 ,tunnels on a level should1 therefore1 be from twenty-five to thirty feet high1 and should be ventilated by shafts or other contrivances4 ,,xxiii4 ,the transition from light to darkness1 the sensation of humidity1 and the change in summer from a warm atmosphere to a cold one1 will always form an objection to long tunnels on lines of railroad intended for a large intercourse of passengers4 ,,xxiv4 ,all the objections to a tunnel are aggravated when it happens to be upon an acclivity4 ,the destruction of vital air in ascending it will be increased in exactly the same proportion as the moving power is increased4 ,thus1 if it ascend #ag feet in a mile1 the destruction of vital air will be twice as great as on a level2 if it ascend #cd feet in a mile1 it will be three times as great2 #ea feet in a mile1 four times as great1 and so on4 ,,xxv4 ,if by an overruling necessity a tunnel is constructed on an acclivity1 its magnitude and means of ventilation should be greater than on a level1 in the same proportion as the resistance produced by the acclivity is greater than the resistance upon a level4 ,,xxvi4 ,tunnels should be ventilated by shafts at intervals of not more than #bjj yards4 ,,xxvii4 ,while a train is passing through a tunnel1 no beneficial ventilation can be obtained from shafts4 ,the engine will leave behind it the impure air which it produces1 and the passengers will be enveloped in it before it has time to ascend the shafts4 ,sufficient magnitude1 however1 may be given to the tunnel to prevent any injurious consequences from this cause4 ,a disagreeable and inconvenient odour will be experienced4 ,,xxviii4 ,tunnels on a level1 the length of which do not exceed a third of a mile1 will probably not be objectionable4 ,tunnels of equal length upon acclivities would be more objectionable4 ,i may observe generally that we have as yet little or no experience of the effect of tunnels on lines of railroad worked by locomotive engines1 where there is a large intercourse of passengers4 ,on the ,leicester and ,swannington railroad1 there is a tunnel of about a mile long1 on a part of the road which is nearly level2 it is ventilated by eight shafts1 and ,i have frequently passed through it with a locomotive engine4 ,even when shut up in a close carriage the annoyance is very great1 and such as would never be tolerated on a line of road having a large intercourse in passengers4 ,this railroad is chiefly used to take coals from some collieries near ,swannington1 and there is no intercourse in passengers upon it1 except of the labouring classes from the adjacent villages3 the engines burn coal1 and not coke2 and they consequently produce smoke1 which is more disagreeable than the gases which result from the combustion of coke4 ,this tunnel also is of small calibre4 ,on the ,leeds and ,selby railroad there is a tunnel1 on a part which is nearly level1 the length of which is #gjj yards1 width #bb feet1 height #ag4 ,it is ventilated by three shafts of about #aj feet diameter and #fj feet high4 ,there is an intercourse of passengers amounting to four hundred per day1 upon this road1 and1 generally speaking1 they do not object to go through the tunnel with a locomotive engine4 ,the fuel is coke4 7l7 ,in order to show the present state of railroad transportation in the ,united ,states1 and enable our readers to compare it with the opinions and facts adduced by ,dr4 ,lardner1 we take the latest accounts from the ,charleston and ,hamburgh ,railroad4 ,the engines drag a train of cars which carry a load of #acj tons1 and perform the distance 7#bdj miles7 in three days1 travelling only by day-light4 ,with these loads they mount planes having inclinations of #cg feet per mile4 ,the same engines are capable of carrying passengers at the rate of #dj miles per hour1 and often perform #cj1 but their average speed is limited by regulation to #bj miles per hour4 ,this railroad is remarkable for being the largest which has yet been constructed1 and is besides an object of just pride1 in as much as it was commenced at a time1 when according to ,dr4 ,lardner1 the subject was but imperfectly understood even in ,europe1 and all its arrangements are due to native talent and skill1 unassisted by previous discoveries in ,europe4--,a4 ,e4 ,,index4 ,a4 ,atmospheric air1 elastic force of1 #bc ,atmospheric pressure rendered available as a mechanic agent by ,denis ,papin1 #dh ,atmospheric engine1 first conception of by ,newcomen1 #fa4 ,description of1 #fc4 ,advantage of over that of ,savery1 #fi ,b4 ,barometer1 the1 #ba ,barometer gauge1 the1 #abc ,belidor1 #acc ,birmingham and ,london railroad1 probable advantages to be derived from1 #bjf ,black1 ,dr41 his doctrine of latent heat1 #gf ,blasco de ,garay1 his contrivance to propel vessels1 #db ,blinkensop1 ,mr41 constructs a locomotive engine1 #afa ,boiler1 methods for showing the level of water in the1 #aah4 ,its power and proportions1 #big ,bolton1 ,matthew1 his connexion with ,watt1 #hh ---- and ,watt1 ,messrs41 immense expenditure of1 in bringing their engines into use1 #ia ,booth1 ,mr41 his method of using tubes to conduct heated air through locomotive boilers1 #agf4 ,his report to the directors of the ,liverpool and ,manchester railway on the apparent discrepancies of ,messrs4 ,walker and ,rastrick's estimate of locomotive power1 #ahi ,braithwaite and ,ericsson1 ,messrs41 their ,novelty described1 #age ,branca1 ,giovanni1 his machine for propelling a wheel by a blast of steam1 #de ,brewster1 ,dr41 #gi ,brunton1 ,mr41 his improved furnace described1 #acj ,c4 ,canals1 transport on1 #bjh4 ,experiments with boats on1 #bji1 ,comparison of with railroads1 #baj ,cartwright1 ,rev4 ,mr41 description of his improvements in the steam engine1 #adb ,cawley1 ,john1 #fa ,century of ,inventions by the ,marquis of ,worcester1 #df ,chapman1 ,messrs41 obtain a patent for working a locomotive by means of a chain1 #afb ,church1 ,dr41 his steam carriage1 #bci ,cohesion1 attraction of1 #cb ,condensation of solids1 #bh ,condensation by jet1 accidental discovery of1 #fe ,cornwall1 reports of duty of steam engines in1 #cjc ,cotton1 processes in the culture of1 #ah ,cylinder1 its proportions1 #cjj ,d4 ,d valve1 description of the1 #aac ,damper1 the1 #abf ,duty of a steam engine1 #bia ,duty1 reports of1 in ,cornwall1 #cjc ,e4 ,eccentric2 description of the1 #aaa ,edelcrantz1 the ,chevalier1 #abg ,f4 ,farey1 ,mr41 his statement respecting the variations in the work of different steam engines1 #acc ,fluids1 property of1 #ba ,fly-wheel1 introduction of the1 #ajd ,four-way cock1 description of the1 #aae ,fuel1 table of the consumption of1 in different locomotives1 #ahj ,g4 ,governor1 description of the1 #aje ,guericke1 ,otto1 inventor of the air-pump1 #gj ,gurney1 ,mr41 his steam carriage1 #baf ,h4 ,hackworth1 ,mr41 description of his engine1 the ,sanspareil1 #agc ,hall1 ,mr4 ,samuel1 his patent steam engine1 #bdh4 ,its advantages for navigation1 #bdi4 ,its successful application1 #bej ,hamilton1 ,duke of1 #hh ,hancock1 ,mr4 ,walter1 his steam carriage1 #bce ,heat1 phenomena of1 #bi ,hero of ,alexandria1 description of his machine1 #da ,hopper1 the1 or apparatus for supplying the fire-place with coals1 #aca ,hornblower1 ,mr41 his double-cylinder engine1 #acd ,horse power and steam power1 comparison between1 #bjb ,horse power of an engine1 #bia4 ,method of calculating it1 #bic ,howard1 ,mr4 ,thomas1 his patent steam engine1 #bec4 ,its advantages in navigation1 #bef ,huskisson1 ,mr41 #aed ,i4 ,inclined planes1 their injurious effects on railroads1 #aid4 ,methods proposed to remedy these1 #aid ,india1 steam communication with1 #bga ,k4 ,kendal and ,preston canal1 speed of boats on1 #bji ,l4 ,leeds and ,selby railroad1 #cag ,leicester and ,swannington railroad1 #cag ,leupold1 his ,theatrum ,machinarum1 #aaf4 ,his engine described1 #adg ,liquids converted into vapour by the application of heat1 #bg4 ,difference of temperatures of1 #ce ,liverpool and ,manchester railroad1 effects of the introduction of steam transport on1 #aeb4 ,want of experience in the construction of the engines1 #aed4 ,proceedings of the directors1 #afg4 ,premium offered by them for the best engine1 #afi4 ,experiments made on1 #ahc4 ,passengers the chief source of profit to the proprietors1 #bjd ,liverpool and ,london1 supposed advantages from the connexion of these places by railroad1 #bjf ,llangennech coal1 its economy1 #bfg ,locomotive engines1 description of the ,rocket1 #aga4 ,the ,sanspareil1 #agc4 ,the ,novelty1 #age4 ,mr4 ,booth's method of using tubes to conduct heated air through boilers1 #agg4 ,mr4 ,stephenson's method of subdividing the flue1 #agi4 ,amount of fuel consumed in1 #ahj4 ,progressive improvement of1 #ahj4 ,description of an improved form of engine1 #aha4 ,circumstances on which their efficiency depends1 #ahc4 ,experiments with1 on ,liverpool and ,manchester railroad1 #ahd4 ,defects of1 #ahf4 ,improvement in the method of tubing1 #ahh4 ,proposed methods for working them on levels and inclined planes1 #aid4 ,extraordinary speed and power of1 #bjd4 ,their introduction on turnpike roads1 #bac ,locomotive power1 expense of1 #ahh ,locomotive boilers1 improved form of1 #agg ,m4 ,machines1 definition of1 #ai ,manufactures1 motions required in1 #ai ,morgan1 ,mr41 his patent paddle-wheel1 #bei ,morland1 ,sir ,samuel1 his application of steam to raise water1 #dg ,motion1 a primary agent in the cultivation of cotton1 #ah4 ,variety of1 #ai ,murray1 ,mr41 description of his suggested slide valve1 #aac ,n4 ,newcomen1 ,thomas1 and ,john ,cawley1 turn their attention to the practicability of applying steam engines to the drainage of mines1 #fa ,newcomen1 ,thomas1 his construction of the atmospheric engine1 #fc ,novelty1 description of the1 #age ,o4 ,ogle1 ,mr41 his steam carriage1 #bci ,oldham1 ,mr41 his modification of the self-regulating furnace1 #acb ,p4 ,paddle-wheel1 the common one1 #beg4 ,mr4 ,morgan's patent one1 #bei ,papin1 ,denis1 his contrivance1 by which atmospheric pressure is rendered available as a mechanical agent1 #dh4 ,description of his steam engine1 #ga ,parallel motion1 description of the1 #ie ,piston1 its velocity1 #cjb ,post-office steam packets1 their speed1 #bfh ,potter1 ,humphrey1 his contrivance for working the valves1 #fg ,power of a steam engine1 how estimated1 #bia ,r4 ,railroads1 first introduction of locomotives on1 #aea4 ,important effects to be expected from their adoption1 #aee4 ,imaginary difficulty respecting the progression of carriages on1 #afj4 ,various methods resorted to1 to remedy this supposed difficulty1 #afa4 ,one of these methods described1 #afb4 ,comparative estimate of the expenses of locomotive and stationary engines1 #afh4 ,difficulties arising from changes of level1 #aib4 ,their great extension1 #bjf4 ,comparison of1 with turnpike roads1 #bac4 ,inclined planes on1 #aid ,railway speculators1 plain rules for1 #cjg ,roads1 their resistance to draft1 #bac4 ,compared with railroads1 #bac ,robinson1 ,dr41 #gc ,roebuck1 ,dr41 assistance rendered by him to ,watt1 #hg4 ,his embarrassments1 #hh ,rocket1 description of the1 #aga ,s4 ,savery1 ,thomas1 obtains a patent for an engine to raise water1 #di4 ,his discovery of the principle of condensation1 #di4 ,constructs the first engine brought into operation1 #ej4 ,description of1 #ea4 ,inefficiency of1 #eg4 ,great consumption of fuel necessary in his engines1 #fj4 ,different purposes to which he proposed to apply the steam engine1 #fa4 ,limited power of his engine1 #fi ,sanspareil1 description of the1 #agc ,smeaton turns his attention to the details of the atmospheric engines1 #gc ,solids converted into liquids by the application of heat1 #bg ,solomon ,de ,caus1 description of the apparatus of1 #dc ,somerset1 ,edward1 ,marquis of ,worcester1 invention of the steam engine ascribed to him1 #de4 ,description of his contrivance1 #de4 ,similar to ,savery's1 #df4 ,his ,century of ,inventions1 #df ,steam carriages1 ,mr4 ,gurney's1 #baf4 ,mr4 ,hancock's1 #bce4 ,mr4 ,ogle's1 #bch4 ,dr4 ,church's1 #bci ,steam1 its properties described1 #cj4 ,its mechanical power in proportion to the water evaporated1 #bgg4 ,its volume1 #bgi4 ,its quantity of heat1 #bgi4 ,its power in respect of fuel1 #bhj4 ,its expansive action1 how advantageous1 #bhj4 ,combination of expansion with condensation1 #bhe4 ,high-pressure1 its expansive action1 #bhh4 ,examples illustrative of its mechanical force1 #cje ,steam engine1 first mover in1 #ai4 ,physical effects connected with1 #bj4 ,claims to the invention of1 #ch4 ,efficacy of1 as a mechanical agent1 #ci4 ,first brought into operation by ,savery1 #ej4 ,its inefficiency1 #eh4 ,first proposed to be applied to the drainage of mines1 #fa4 ,accidental discovery of condensation by jet1 #fe4 ,further improvements by ,humphrey ,potter and ,beighton1 #fg1 #fh4 ,description of ,papin's engine1 #ga4 ,first experiments of ,watt and subsequent improvements1 #gc4 ,dr4 ,black's theory of latent heat1 #gf4 ,watt's method of condensation1 #gf4 ,further improvements of ,watt1 #gg4 ,description of ,watt's single-acting engine1 #hj4 ,the cold water pump1 #hf4 ,the hot water pump1 #hf4 ,erection of a specimen engine at ,soho1 and gradual demand for them1 #hi4 ,the single-acting engine inapplicable to manufactures1 #ia4 ,the double-acting engine1 #ib4 ,invention of the parallel motion1 #ie4 ,introduction of the rotatory motion1 #ajj4 ,the fly-wheel1 #ajd4 ,the governor1 #aje4 ,the throttle valve1 #aje4 ,the eccentric1 #aaa4 ,the ,d valve1 #aac4 ,the four-way cock1 #aae4 ,methods for ascertaining the level of water in the boiler1 #aah4 ,the engine made to feed its own boiler1 #abj4 ,waste of water prevented1 #aba4 ,the steam gauge1 #abb4 ,barometer gauge1 #abc4 ,the damper1 #abe4 ,methods proposed for preventing the waste of fuel1 #abh4 ,mr4 ,brunton's furnace described1 #acj4 ,mr4 ,oldham's modification of the self-regulating furnace1 #acb4 ,improvements by ,hornblower and ,woolf1 #acd4 ,description of the improvements of ,mr4 ,cartwright1 #adb4 ,high-pressure engines1 #ade4 ,leupold's engine described1 #adg4 ,construction of the first high-pressure engine by ,messrs4 ,trevithick and ,vivian1 #adh4 ,first application of the steam engine to propel carriages on railroads1 #aea4 ,how applied to navigation1 #bdb4 ,marine engine2 its form and arrangement1 #bdc4 ,mr4 ,howard's patent engine described1 #bec4 ,mr4 ,hall's engine described1 #bdh ,steam gauge1 the1 #abb ,steam navigation1 incredulity which existed respecting1 #aei4 ,the limit of its present powers1 #bfd ,steam vessels1 their average speed1 #bfe4 ,their average consumption of fuel1 #bfe4 ,proportion of their power to their tonnage1 #bff4 ,speed of post-office packets1 #bfh4 ,iron steam vessels1 #bfi4 ,american vessel called the ,cigar ,boat1 its great speed1 #bgj ,stephenson's1 ,mr41 description of an engine constructed by him1 #afd4 ,premium awarded to this engine by the ,liverpool and ,manchester ,railway ,directors1 #agj4 ,his method of dividing the flues1 #agi ,stephenson and ,lock1 ,messrs41 appointed by the ,directors of the ,liverpool and ,manchester ,railroad to make reports on the merits of various railroads1 #afg ,sun and planet wheels1 #aja ,t4 ,thermometer1 description of1 #bd ,throttle valve1 use of1 #ajd ,traction1 force of1 on a railroad1 #aib ,tredgold1#gj ,trevithick and ,vivian1 ,messrs41 construct the first high-pressure engine used in this country1 #adh ,u4 ,united ,states1 steam communication with1 #bgd ,v4 ,vacuum1 production of1 by experiment1 #cg ,vapour1 elastic1 force of1 #ce ,valves1 ,watt's method of working the1 #aji ,w4 ,walker and ,rastrick1 ,messrs41 apparent discrepancy of their estimated expense of locomotive power1 #ahi ,washborough takes out a patent for ,watt's invention of the rotatory motion1 #ajj ,water1 sea1 injurious to marine boilers1 #bde4 ,how remedied by blowing out1 #bdf ,watt1 ,james1 important discoveries of1 #ci4 ,his acquaintance with ,dr4 ,robinson and first experiments on the steam engine1 #gc4 ,his subsequent improvements1 #ge4 ,his method of condensation1 #gf4 ,his first introduction of the air-pump into the steam engine1 #gg4 ,further improvements1 #gh4 ,his difficulties1 #gh4 ,description of his single-acting engine1 #hj4 ,his introduction to ,dr4 ,roebuck1 #hh4 ,erects his first engine on the estate of the ,duke of ,hamilton1 #hh4 ,after further improvements1 obtains a patent for this engine1 in conjunction with ,roebuck1 #hh4 ,his difficulties owing to ,dr4 ,roebuck's failure1 and subsequent connexion with ,bolton1 #hh4 ,obtains an extension of his patent1 #hi4 ,ingenious invention of1 to determine the rate of remuneration he should receive1 #hi4 ,his invention of the parallel motion1 #ie4 ,his method for producing a rotatory motion anticipated by ,washborough1 who takes out a patent for it1 #aja4 ,his contrivance of the governor1 #ajd4 ,his method of working the valves1 #aji4 ,his suggestion of the ,d valve1 #aac ,wood1 ,mr4 ,nicholas1 #afh ,woolf1 ,mr41 his improvements in the steam engine1 #acd4 ,obtains a patent for the double-cylinder engine1 #acg 99 99 99 99 99 ,,just ,,published1 ,,in ,,one ,,volume1 #h,,vo4 ,,mathematics ,,for ,,practical ,,men2 ,,being ,a ,,common-,,place ,,book ,,of ,,principles1 ,,theorems1 ,,rules ,,and ,,tables1 ,,in ,,various ,,departments ,,of ,,pure ,,and ,,mixed ,,mathematics1 ,with their applications2 especially to the pursuits of ,surveyors1 ,architects1 ,mechanics1 and ,civil ,engineers4 ,with numerous engravings4 ,,by ,,olinthus ,,gregory1 ,,ll4 ,d41 ,f4 ,r4 ,a4 ,s4 ,only let men awake1 and fix their eyes1 one while on the nature of things1 another while on the application of them to the use and service of mankind4--,lord ,bacon4 ,,second ,,edition1 ,,corrected ,,and ,,improved4 ,extract of a ,letter from ,,walter ,r4 ,,johnson1 ,professor of ,mechanics and ,natural ,philosophy in the ,franklin ,institute4 ,this treatise is intended and admirably calculated to supply the deficiency in the means of mathematical instruction to those who have neither time nor inclination to peruse numerous abstract treatises in the same departments4 ,it has1 besides the claims of a good elementary manual1 the merit of embracing several of the most interesting and important departments of ,mechanics1 applying to these the rules and principles embraced in the earlier sections of the work4 ,questions in ,statics1 ,dynamics1 ,hydrostatics1 ,hydrodynamics1 c41 are treated with a clearness and precision which must increase the powers of the student over his own intellectual resources by the methodical habits which a perusal of such works cannot fail to impart4 ,with respect to ,engineering1 and the various incidents of that important profession1 much valuable matter is contained1 in this volume2 and the results of many laborious series of experiments are presented with conciseness and accuracy4 ,letter from ,,albert ,b4 ,,dod1 ,professor of ,mathematics in the ,college of ,new ,jersey4 ,,messrs4 ,,carey ,,hart1 ,gentlemen1--,i am glad to learn that you have published an ,american edition of ,dr4 ,gregory's ',mathematics for ,practical ,men4' ,i have for some time been acquainted with this work1 and ,i esteem it highly4 ,it contains the best digest1 within my knowledge1 of such scientific facts and principles1 involved in the subjects of which it treats1 as are susceptible of direct practical application4 ,while it avoids such details of investigation and processes of mathematical reasoning as would render it unintelligible to the general reader1 it equally avoids the sacrifice of precision in its statement of scientific results1 which is too often made in popular treatises upon the ,mathematics and ,natural ,philosophy4 ,the author has succeeded to a remarkable degree in collecting such truths as will be found generally useful1 and in presenting them1 in an available form1 to the practical mechanic4 ,to such1 the work cannot be too strongly recommended2 and to the student1 too1 it will often be found highly useful as a book of reference4 ,with much respect1 ,your obedient servant1 ,,albert ,b4 ,,dod1 ,professor of ,mathematics in the ,college of ,new ,jersey4 ,princeton1 ,nov4 #aa1 #ahcd4 ,extract of a ,letter from ,,edward ,h4 ,,courtenay1 ,professor of ,mathematics in the ,university of ,pennsylvania4 ,the design of the author--that of furnishing a valuable collection of rules and theorems for the use of such as are unable1 from the want of time and previous preparation1 to investigate mathematical principles--appears to have been very successfully attained in the present volume4 ,the information which it affords in various branches of the pure and mixed ,mathematics embraces a great variety of subjects1 is arranged conveniently1 and is in general conveyed in accurate and concise terms4 ,to ,,the ,,engineer1 ,,the ,,architect1 ,,the ,,mechanic--indeed to all for whom results are chiefly necessary--the work will doubtless form a very valuable acquisition4 ,letter from ,,charles ,,davies1 ,professor of ,mathematics in the ,military ,academy1 ,west ,point4 ,,military ,,academy1 ,west ,point1 ,may #adth1 #ahce4 ,to ,messrs4 ,e4 ,l4 ,carey ,a4 ,hart1-- ,the ',mathematics for ,practical ,men1' by ,dr4 ,gregory1 which you have recently published1 is a work that cannot fail to be extensively useful4 ,it embraces1 within a comparatively small compass1 all the rules and formulas for mathematical computation1 and all the practical results of mechanical philosophy4 ,it is1 indeed1 a collection of the useful results of science and the interesting facts which have been developed by experience4 ,it may safely be said1 that no work1 of the same extent1 contains so much information1 with the rules for applying it to practical purposes4 ,i have the honour to be1 ,with great respect1 ,your obedient servant1 ,,charles ,,davies1 ,professor of ,mathematics4 ,extract from a ,letter from ,j4 ,a4 ,,miller1 ,professor of ,mathematics in ,mount ,st4 ,mary's ,college1 ,emmettsburg1 ,md4 ,since the ,london edition of ,gregory's ,mathematics for ,practical ,men appeared in this country1 it has been much used in this institution4 ,the accuracy of its definitions1 its beautiful systematic arrangement1 the many simplified and facilitated methods which it proposes1 and its highly practical character1 must recommend it strongly to public patronage1 as one of the very best works which have lately issued from the press4 ,i have examined your edition of this valuable work sufficiently to say with confidence that it is very accurately printed4 99 99 99 99 99 ,transcriber's note3 ,only obvious printer's errors have been corrected 7e4g43 #c s instead of #b1 etc474 ,the author's spelling has been maintained and inconsistencies have not been standardised4 ,the advertisement page has been move from the front to the end of the book4 ,other corrections made3 --,page x3 the wealth of rations has been replaced by the wealth of nations4 --,page #ag3 ,pressure of ,rarified ,air4 has been replaced by ,pressure of ,rarefied ,air4 --,page #ih3 ,this beautiful contrivance1 which is incontestibly has been replaced by ,this beautiful contrivance1 which is incontestably4 --,page #ajj3 the working beam no longer used has been replaced by the working beam is no longer used4 --,page #bbc3 is attended with peliar difficulty has been replaced by is attended with peculiar difficulty4 --,page #bga3 ,the projecter is now employed in has been replaced by ,the projector is now employed in4