,,evolution999999        ,!             
,int]national ,sci5tific ,s]ies  ,,!    
,,new ,,physics ,,& ,,its ,,evolution   
by  ,,luci5 ,,po9c> ,inspctur-,g5]al de 
l',in/ruction ,publique  ,be+ !         
,au?oriz$ ,translation ( ,,la ,,physique
 ,,mod]ne1 ,,son ,,volution  ,new ,york 
,d4 ,appleton & ,company  #aiji         
,prefatory ,note  ,m4 ,luci5 ,po9c> is  
"o ( ! di/+ui%$ family ( ma!maticians   
:i* has dur+ ! la/ few ye>s giv5 a      
,m9i/] ( ,f9ance to ! ,republic & a     
,presid5t to ! ,acadmie des ,sci5ces4   
,he is also "o ( ! n9ete5               
,inspectors-,g5]al ( ,public ,in/ruction
 :o are *>g$ ) ! duty ( visit+ ! diff]5t
 univ]sities & lyces 9 ,france & (      
report+ ^u ! /ate ( ! /udies !re pursu$4
 ,h5ce he is 9 an excell5t position to  
appreciate at its prop] value !         
extraord9>y *ange :i* has lately        
revolutioniz$ physical sci5ce1 :ile 8   
(ficial position has kept him alo( f !  
controv]sies ar\s$ by ! discov]y (      
radium & by rec5t speculations on !     

con/itution ( matt]4  ,m4 ,po9c>'s      
object & me?od 9 writ+ ! book are       
suffici5tly expla9$ 9 ! preface :i*     
foll[s2 b x may be rem>k$ t ! be/ (     
me?ods has its defects1 & ! excessive   
cond5sation :i* has alone made x        
possible to include ! la/ decade's      
discov]ies 9 physical sci5ce )9 a       
compass ( "s #cjj pages has1 p]haps1    
made ! facts "h not$ assimilable )      
difficulty by ! untra9$ read]4 ,to rem$y
 ?is z f> z possible1 ,i h prefix$ to ! 
pres5t translation a table ( cont5ts s  
ext5d$ z to =m a fairly complete dige/ (
 ! book1 :ile full indexes ( au?ors &   
subjects h also be5 add$4 ,! few notes  
necess>y ei!r = bett] elucidation ( !   
t]ms employ$1 or = giv+ acc\nt (        
discov]ies made :ile ^! pages 7 pass+   
?r\gh ! press1 may be di/+ui%$ f !      
au?or's own by ! signature ,,ed4  ,,!   
,,editor4  ,,royal ,,in/itution ,,(     
,,great ,,brita91 ,april #aijg4         
,au?or's ,preface  ,dur+ ! la/ t5 ye>s s
 _m works h accumulat$ 9 ! doma9 (      

,physics1 & s _m new !ories h be5       
prop\nd$1 t ^? :o foll[ ) int]e/ !      
progress ( sci5ce1 & ev5 "s pr(ess$     
s*ol>s1 absorb$ z !y are 9 _! own       
special /udies1 f9d !mselves at sea 9 a 
confusion m app>5t ?an real4  ,x has    
!re=e occurr$ to me t x might be useful 
to write a book :i*1 :ile avoid+ too    
great insi/5ce on purely te*nical       
details1 %\ld try to make kn[n ! g5]al  
results at :i* physici/s h lately       
arriv$1 & to indicate ! direction &     
import :i* %\ld be ascrib$ to ^?        
speculations on ! con/itution ( matt]1 &
 ! discussions on ! nature ( fir/       
pr9ciples1 to :i* x has become1 s to    
speak1 ! fa%ion ( ! pres5t day to devote
 oneself4  ,i h endeav\r$ ?r\gh\t to    
rely only on ! exp]im5ts 9 :i* we c     
place ! mo/ confid5ce1 &1 above all1 to 
%[ h[ ! ideas prevail+ at ! pres5t day h
 be5 =m$1 by trac+ _! evolution1 &      
rapidly exam9+ ! successive             
trans=mations :i* h br\ght !m to _!     
pres5t condition4  ,9 ord] to und]/& !  

text1 ! read] w h no ne$ to consult any 
treatise on physics1 = ,i h ?r\gh\t giv5
 ! necess>y def9itions & set =? !       
fundam5tal facts4 ,moreov]1 :ile /rictly
 employ+ exact expressions1 ,i h avoid$ 
! use ( ma!matical language4 ,algebra is
 an admirable tongue1 b !re are _m      
occasions :]e x c only be us$ ) mu*     
discretion4  ,no?+ w\ld be easi] ?an to 
po9t out _m great omissions f ?is little
 volume2 b "s1 at all ev5ts1 are n      
involunt>y4  ,c]ta9 que/ions :i* are    
/ill too confus$ h be5 put on "o side1 z
 h a few o!rs :i* =m an important       
collection = a special /udy to be       
possibly made lat]4 ,?us1 z reg>ds      
electrical ph5om5a1 ! relations betwe5  
electricity & optics1 z also ! !ories ( 
ionization1 ! electronic hypo!sis1 etc41
 h be5 treat$ at "s l5g?2 b x has n be5 
?\ght necess>y to dilate ^u ! modes (   
production & utilization ( ! curr5t1 ^u 
! ph5om5a ( magnetism1 or ^u all !      
applications :i* belong to ! doma9 (    
,electrote*nics4  ,l4 ,,po9c>4          

,cont5ts   ,,editor',s ,,prefatory      
,,note  ,,au?or',s ,,preface  ,,table   
,,( ,,cont5ts   ,,*apt] ,i  ,,!         
,,evolution ,,( ,,physics  ,revolution>y
 *ange 9 mod]n ,physics only app>5t3    
evolution n revolution ! rule 9         
,physical ,!ory-- ,revival (            
metaphysical speculation & influ5ce (   
,desc>tes3 all ph5om5a r$uc$ to matt] & 
movem5t-- ,mod]n physici/s *all5ge ?is3 
physical1 unlike me*anical1 ph5om5a     
seldom rev]sible--,two s*ools1 "o       
consid]+ exp]im5tal laws imp]ative1 !   
o!r m]ely /udy+ relations ( magnitudes3 
bo? tea* some?+ ( tru?--,?ird or        
eclectic s*ool-- ,is me*anics a bran* ( 
electrical sci5ce8   ,,*apt] ,,ii       
,,measurem5ts   #a4 ,metrology3 ,"l     
,kelv9's view ( its necessity-- ,its    
def9ition   #b4 ,! ,measure ( ,l5g?3    
,necessity = unit-- ,absolute           
l5g?--,hi/ory ( ,/&>d--,description (   
,/&>d ,metre--,unit ( wave-l5g?s        
pref]able--,! ,int]national ,metre   #c4
 ,! ,measure ( ,mass3 ,di/9ction betwe5 

mass & weight--,objections to legal     
kilogramme & its precision--,possible   
improvem5t   #d4 ,! ,measure ( ,"t3     
,unit ( "t ! second--,alt]native units  
propos$--,improvem5ts 9 *ronometry &    
inv>   #e4 ,! ,measure ( ,temp]ature3   
,fundam5tal & d]iv$ units--,ord9>y unit 
( temp]ature purely arbitr>y--,absolute 
unit mass ( ,h at pressure ( #a m4 ( ,hg
 at #j ,c4--,div]g5ce ( !rmometric &    
!rmodynamic scales--,helium !rmomet] =  
l[1 !rmo-electric c\ple = high1         
temp]atures--,lumm] & ,pr+%eim's        
improvem5ts 9 !rmometry4   #f4 ,d]iv$   
,units & ,measure ( ,en]gy3 ,importance 
( erg z unit--,calorimet] usual means ( 
det]m9ation--,photometric units4   #g4  
,measure ( ,physical ,con/ants3 ,con/ant
 ( gravitation--,discov]ies ( ,cav5di%1 
,v]non ,boys1 ,etvs1 ,ri*>z &           
,krig>-,m5zel--,mi*elson's improvem5ts  
on ,fizeau & ,f\cault's exp]im5ts--     
,measure ( spe$ ( light4   ,,*apt] ,,iii
  ,,pr9ciples   #a4 ,! ,pr9ciples (     
,physics3 ,! ,pr9ciples ( ,me*anics     

affect$ by rec5t discov]ies--,is mass   
inde/ructible8--,l&olt & ,heydweill]'s  
exp]im5ts --,lavoisi]'s law only        
approximately true--,curie's pr9ciple ( 
symmetry4   #b4 ,! ,pr9ciple ( !        
,cons]vation ( ,en]gy3 ,its evolution3  
,b]n\lli1 ,lavoisi] & ,laplace1 ,"y1    
,rum=d1 ,davy1 ,sadi ,c>not1 & ,rob]t   
,may]--,may]'s drawbacks--,error ( ^? :o
 w\ld make me*anics "p (                
en]getics--,v]det's pr$ictions--,rank9e 
inv5tor ( en]getics--,usefulness ( ,"w z
 /&>d =m ( en]gy--,physici/s :o ?9k     
matt] =m ( en]gy-- ,objections to       
?is--,philosophical value ( cons]vation 
doctr9e4   #c4 ,! ,pr9ciple ( ,c>not &  
,clausius3 ,orig9ality ( ,c>not's       
pr9ciple t fall ( temp]ature necess>y = 
production ( "w by heat-- ,clausius'    
po/ulate t heat _c pass f cold to hot   
body )\t accessory ph5om5a--,entropy    
result ( ?is--,def9ition (              
entropy--,entropy t5ds to increase      
incessantly--,a magnitude :i* measures  
evolution ( sy/em--,clausius' & ,kelv9's

 d$uction t heat end ( all en]gy 9      
,univ]se--,objection to ?is-- ,c>not's  
pr9ciple n necess>ily ref]able to       
me*anics --,br[nian                     
movem5ts--,lippmann's objection to      
k9etic hypo!sis4   #d4 ,!rmodynamics3   
,hi/orical "w ( ,massieu1 ,will>d       
,gibbs1 ,helmholtz1 & ,duhem--,will>d   
,gibbs f\nd] ( !rmodynamic /atics1 ,van 
t',h(f its reviv]--,! ,phase            
,law--,raveau expla9s x )\t             
!rmodynamics4   #e4 ,atomism3           
,connection ( subject ) prec$+          
,hannequ9's essay on ! atomic           
hypo!sis--,molecul> physics 9           
disfav\r--,surface-t5sion1 etc41 vani%es
 :5 molecule rea*$--,size (             
molecule--,k9etic !ory ( gases--,will>d 
,gibbs & ,boltzmann introduce into x law
 ( probabilities--,mean free pa? (      
gase\s molecules--,application to       
optics--,f9al division ( matt]4         
,,*apt] ,,iv  ,,! ,,v>i\s ,,/ates ,,(   
,,matt]   #a4 ,! ,/atics ( ,fluids3     
,rese>*es ( ,&rews1 ,cailletet1 & o!rs  

on liquid & gase\s /ates-- ,amagat's    
exp]im5ts--,van d] ,waals'              
equation--,discov]y ( correspond+       
/ates--,amagat's sup]pos$               
diagrams--,exceptions to law--,/atics ( 
mix$ fluids-- ,kam]l+h ,onnes'          
rese>*es--,critical ,con/ants--         
,*>act]i/ic equation ( fluid n yet      
asc]ta9able4   #b4 ,! ,liquefaction (   
,gases & ,l[ ,temp]atures3 ,l9de's1     
,siem5s'1 & ,claude's me?ods ( liquefy+ 
gases--,app>atus ( ,claude              
describ$--,dew>'s                       
exp]im5ts--,modification ( electrical   
prop]ties ( matt] by extreme cold3 (    
magnetic & *emical-- ,vitality ( bact]ia
 unalt]$--,ramsay's discov]y ( r>e gases
 ( atmosph]e--,_! di/ribution 9         
nature--,liquid hydrog5--,helium4   #c4 
,solids & ,liquids3 ,cont9uity ( ,solid 
& ,liquid ,/ates--,viscosity common to  
bo?--,also ,rigidity-- ,spr+'s analogies
 ( solids & liquids--,cry/allization    
--,lehmann's liquid cry/als--,_! exi/5ce
 d\bt$ --,tamman's view ( discont9uity  

betwe5 cry/all9e & liquid /ates4   #d4  
,! ,de=mation ( ,solids3 ,ela/icity--   
,hoocke's1 ,ba*'s1 & ,b\asse's          
rese>*es--,voigt on ! ela/icity (       
cry/als--,ela/ic & p]man5t              
de=mations--,brill\9's /ates ( un/able  
equilibria--,duhem & ! !rmodynamic      
po/ulates-- ,exp]im5tal                 
confirmation--,guillaume's rese>*es on  
nickel /eel--,alloys4   ,,*apt] ,v      
,,solutions ,,& ,,electrolytic          
,,dissociation   #a4 ,solution3         
,kir*h(f's1 ,gibb's1 ,duhem's & ,van    
t',h(f's rese>*es4   #b4 ,osmosis3      
,hi/ory ( ph5om5on--,traube & biologi/s 
e/abli% exi/5ce ( semi-p]meable         
walls--,vill>d's exp]im5ts )            
gases--,pfeff] %[s osmotic pressure     
proportional to conc5tration--          
,disagreem5t z to cause ( ph5om5on4     
#c4 ,osmosis appli$ to ,solution3 ,van  
t',h(f's discov]ies--,analogy betwe5    
dissolv$ body & p]fect gas--,faults 9   
analogy4   #d4 ,electrolytic            
,dissociation3 ,van t',h(f's &          

,arrh5ius' rese>*es--,ionic hypo!sis    
(--,fi]ce opposition to at              
fir/--,arrh5ius' ideas n[ triumphant    
--,advantages ( ,arrh5ius' hypo!sis--,! 
ions :i* react--,o/wald's conclusions f 
?is--,n]n/'s !ory (                     
,electrolysis--,electrolysis ( gases    
makes electronic !ory                   
probable--,f>aday's two laws--,val5cy-- 
,helmholtz's consequ5ces f ,f>aday's    
laws4   ,,*apt] ,,vi  ,,! ,,e!r   #a4 ,!
 ,lum9if]\s ,e!r3 ,fir/ idea ( ,e!r due 
to ,desc>tes--,e!r mu/ be               
impond]able--,fresnel %[s light         
vibrations to be transv]se--,transv]se  
vibrations _c exi/ 9 fluid--,e!r mu/ be 
discont9u\s4   #b4 ,radiations3         
,wave-l5g?s & _! measurem5ts--,rub5s' & 
,l5>d's rese>*es-- ,/ation>y waves &    
col\r-photography--,fresnel's hypo!sis  
oppos$ by ,neumann--,wi5]'s & ,cotton's 
exp]im5ts4   #c4 ,! ,electromagnetic    
,e!r3 ,ampre's advocacy ( ma!matical    
expression--,f>aday fir/ %[s influ5ce ( 
m$ium 9 electricity--,maxwell's pro( t  

light-waves electromagnetic--,8         
un9telligibility--,requir$ confirmation 
( !ory by ,h]tz4   #d4 ,electrical      
,oscillations3 ,h]tz's exp]im5ts--      
,blondlot proves electromagnetic        
di/urbance propagat$ ) spe$ (           
light--,discov]y ( e!r waves int]m$iate 
betwe5 ,h]tzian & visible ones--,rub5s' 
& ,ni*ols' exp]im5ts--,h]tzian & light  
rays contra/$--,pressure ( light4   #e4 
,! ,x-,rays3 ,rntg5's                   
discov]y--,prop]ties ( ,x-rays--,n      
homog5e\s--,ru!r=d & ,m',clung's        
exp]im5ts on en]gy correspond+          
to--,b>kla's exp]im5ts on pol>isation   
(--,_! spe$ t ( light--,are !y m]ely    
ultra-violet8--,/okes & ,wie*]t's !ory (
 indep5d5t pulsations g5]ally           
pref]r$--,j4,j4 ,?omson's idea ( _!     
=mation-- ,su!rl&'s & ,le ,bon's        
!ories--,! ,n-,rays-- ,blondlot's       
discov]y--,exp]im5ts _c be repeat$      
outside ,france--,gutton & ,masc>t's    
confirmation-- ,negative exp]im5ts prove
 no?+--,suppos$ wave-l5g? ( ,n-rays4    

#f4 ,! ,e!r & ,gravitation3 ,desc>tes' &
 ,newton's ideas on gravitation--,its   
spe$ & o!r extraord9>y                  
*>act]i/ics--,lesage's                  
hypo!sis--,crmieux' exp]im5ts ) drops ( 
liquids--,hypo!sis ( e!r insuffici5t4   
,,*apt] ,,vii  ,,wireless ,,telegraphy  
#a4 ,hi/ories ( wireless telegraphy     
already writt51 & difficulties ( !      
subject4   #b4 ,two sy/ems3 t :i* uses !
 mat]ial m$ia 7e>?1 air1 or wat]71 & t  
:i* employs e!r only4   #c4 ,use ( e>? z
 return wire by ,/e9heil --,morse's     
exp]im5ts ) wat] ( canal--,se9e us$ z   
return wire dur+ siege ( ,p>is--,johnson
 & ,melhui%'s ,indian                   
exp]im5ts--,preece's telegraph ov]      
,bri/ol ,*annel--,he welcomes ,m>coni4  
#d4 ,e>ly attempts at transmission (    
messages ?r\gh e!r--,exp]im5ts ( ,ra!nau
 & o!rs4   #e4 ,=]unn]s ( e!r           
telegraphy3 ,cl]k ,maxwell &            
,h]tz--,dolbe>1 ,hughes1 & ,graham      
,bell4   #f4 ,telegraphy by ,h]tzian    
waves fir/ sugge/$ by                   

,?relfall--,crookes'1 ,tesla's1         
,lodge's1 ,ru!r=d's1 & ,pop(f's         
contributions--,m>coni fir/ makes x     
practicable4   #g4 ,! receiv] 9 wireless
 telegraphy--,v>ley's1                  
,calzec*i--,one/i's1 & ,branly's        
rese>*es-- ,explanation ( coh]] /ill    
obscure4   #h4 ,wireless telegraphy     
ent]s ! comm]cial /age-- ,defect (      
,m>coni's sy/em--,braun's1 ,arm/rong's1 
,lee de ,=e/'s1 & ,fess5d5's sy/ems make
 use ( e>?-- ,h]tz & ,m>coni entitl$ to 
=emo/ place among discov]]s4   ,,*apt]  
,,viii  ,,! ,,conductivity ,,( ,,gases  
,,& ,,! ,,ions   #a4 ,! ,conductivity ( 
,gases3 ,relations ( matt] to e!r c>d9al
 problem--,conductivity ( gases at fir/ 
misappreh5d$--,erman's =gott5           
rese>*es--,giese fir/ notices           
ph5om5on--,exp]im5t ) ,x-rays-- ,j4,j4  
,?omson's int]pretation--,ioniz$ gas n  
ob$i5t to ,ohm's law--,dis*>ge ( *>g$   
conductors by ioniz$ gas4   #b4 ,!      
,cond5sation ( wat]-vap\r by ,ions3     
,vap\r w n cond5se )\t                  

nucleus--,wilson's exp]im5ts on         
electrical cond5sation--,wilson &       
,?omson's c\nt+ exp]im5t--,tw5ty million
 ions p] c4cm4 ( gas--,e/imate ( *>ge   
borne by ion-- ,spe$ ( *>ges--,zel5y's &
 ,langev9's exp]im5ts--,negative ions   
#a_/ajjj ( size ( atoms--,natural unit (
 electricity or electrons4   #c4 ,h[    
,ions are ,produc$3 ,v>i\s causes (     
ionization--,moreau's exp]im5ts )       
alkal9e salts--,b>us & ,blo* on         
ionization by phosphorus                
vap\rs--,ionization always result (     
%ock4   #d4 ,electrons 9 ,metals3       
,movem5t ( electrons 9 metals =e%ad[$ by
 ,web]--,giese's1 ,riecke's1 ,drude's1 &
 ,j4,j4 ,?omson's rese>*es--,pa? ( ions 
9 metals & conduction ( heat--,!ory (   
,lor5tz--,hesehus' explanation (        
electrification by contact--,emission ( 
electrons by *>g$ body-- ,?omson's      
measurem5t ( positive ions4   ,,*apt]   
,,ix  ,,ca?ode ,,rays ,,& ,,radioactive 
,,bodies   #a4 ,! ,ca?ode ,rays3 ,hi/ory
 ( discov]y--,crookes' !ory--,l5>d      

rays--,p]r9's pro( ( negative           
*>ge--,ca?ode rays give rise to         
,x-rays--,! canal rays--,vill>d's       
rese>*es & magneto-ca?ode rays--        
,ionopla/y--,?omson's measurem5ts ( spe$
 ( rays-- ,all atoms c be dissociat$4   
#b4 ,radioactive ,sub/ances3 ,uranic    
rays ( ,niepce de ,/ ,victor &          
,becqu]el--,g5]al radioactivity (       
matt]--,le ,bon's & ,ru!r=d's comp>ison 
( uranic ) ,x rays--,pi]re & ,mme4      
,curie's discov]y ( polonium &          
radium--,_! *>act]i/ics--,debi]ne       
discov]s act9ium4   #c4 ,radiations &   
,emanations ( ,radioactive ,bodies3     
,giesel's1 ,becqu]el's1 & ,ru!r=d's     
,rese>*es--,alpha1 beta1 & gamma        
rays--,sagnac's second>y rays--,crookes'
 sp9?>iscope--,! emanation --,ramsay &  
,soddy's rese>*es ^u x--,trans=mations (
 radioactive bodies--,_! ord]4   #d4    
,disaggregation ( ,matt] & ,atomic      
,en]gy3 ,actual trans=mations ( matt] 9 
radioactive bodies --,helium or lead    
f9al product--,ultimate disappe>ance (  

radium f e>?--,en]gy lib]at$ by radium3 
its am\nt & s\rce--,sugge/$ models (    
radioactive atoms--,g5]alization f      
radioactive ph5om5a -,le ,bon's         
!ories--,balli/ic hypo!sis g5]ally      
admitt$--,does en]gy come f             
)\t--,sagnac's exp]im5ts--,el/] &       
,geitel's contra4   ,,*apt] ,x  ,,!     
,,e!r ,,& ,,matt]   #a4 ,! ,relations   
betwe5 ! ,e!r & ,matt]3 ,attempts to    
r$uce all matt] to =ms ( e!r--,emission 
& absorption ph5om5a %[ reciprocal      
action-- ,laws ( radiation--,radiation (
 gases--,production (                   
spectrum--,diff]5ces betwe5 light & s\nd
 v>iations %[ diff]5ce ( m$ia--,cau*y's1
 ,briot's1 ,c>vallo's & ,b\ss9esq's     
rese>*es--,helmholtz's & ,po9c>'s       
electromagnetic !ories ( disp]sion4     
#b4 ,! ,!ory ( ,lor5tz3--,me*anics fails
 to expla9 relations betwe5 e!r &       
matt]--,lor5tz pr$icts action ( magnet  
on spectrum--,zeeman's exp]im5t --,lat] 
rese>*es ^u ,zeeman effect--            
,multiplicity ( electrons--,lor5tz's    

explanation ( !rmoelectric ph5om5a by   
electrons--,maxwell's & ,lor5tz's !ories
 d n agree--,lor5tz's probably m        
correct--,e>?'s movem5t 9 relation to   
e!r4   #c4 ,! ,mass ( ,electrons3       
,?omson's & ,max ,abraham's view t      
in]tia ( *>g$ body due to               
*>ge--,longitud9al & transv]sal         
mass--,spe$ ( electrons _c exce$ t (    
light--,ratio ( *>ge to mass & its      
v>iation--,electron simple electric     
*>ge--,ph5om5a produc$ by its           
accel]ation4   #d4 ,new ,views on ,e!r &
 ,matt]3 ,insuffici5cy ( ,l>mor's       
view--,e!r def9able by electric &       
magnetic fields--,is matt] all          
electrons8 ,atom probably positive c5tre
 surr\nd$ by negative                   
electrons--,ignorance conc]n+ positive  
p>ticles--,successive trans=mations (   
matt] probable --,gravitation /ill      
unacc\nt$ =4   ,,*apt] ,,xi  ,,!        
,,future ,,( ,,physics  ,p]si/5ce (     
ambition to discov] supreme pr9ciple 9  
physics--,supremacy ( electron !ory at  

pres5t "t--,d\btless de/9$ to disappe> l
 o!rs-- ,con/ant progress ( sci5ce      
pr$ict$--,imm5se field op5 be=e x4      
,,index ,,( ,,names  ,,index ,,(        
,,subjects     ,,*apt] ,i  ,,!          
,,evolution ,,( ,,physics   ,! n[ num]\s
 public :i* tries ) "s success to keep  
abrea/ ( ! movem5t 9 sci5ce1 f see+ its 
m5tal habits e day upset1 & f           
occasionally witness+ unexpect$         
discov]ies t produce a m lively s5sation
 f _! reaction on social life1 is l$ to 
suppose t we live 9 a really exceptional
 epo*1 scor$ by pr(\nd crises &         
illu/rat$ by extraord9>y discov]ies1 ^: 
s+ul>ity surpasses ev]y?+ kn[n 9 ! pa/4 
,?us we (t5 he> x said t physics1 9     
p>ticul>1 has ( late ye>s und]gone a    
v]itable revolution2 t all its pr9ciples
 h be5 made new1 t all ! edifices       
con/ruct$ by our fa!rs h be5 ov]?r[n1 & 
t on ! field ?us cle>$ has sprung up !  
mo/ abundant h>ve/ t has ev] enri*$ !   
doma9 ( sci5ce4  ,x is 9 fact true t !  
crop becomes ri*] & m fruitful1 ?anks to

 ! developm5t ( our laboratories1 & t ! 
quantity ( seek]s has consid]ably       
increas$ 9 all c\ntries1 :ile _! quality
 has n dim9i%$4 ,we %\ld be su/a9+ an   
absolute p>adox1 & at ! same "t committ+
 a cry+ inju/ice1 7 we to conte/ ! high 
importance ( rec5t progress1 & to seek  
to dim9i% ! glory ( contempor>y         
physici/s4 ,yet x may be z well n to    
give way to exagg]ations1 h[ev]         
p>donable1 & to gu>d aga9/ facile       
illusions4 ,on clos] exam9ation x w be  
se5 t our pr$ecessors might at sev]al   
p]iods 9 hi/ory h conceiv$1 z           
legitimately z ourselves1 simil>        
s5tim5ts ( sci5tific pride1 & h felt t !
 _w 0 ab\t to appe> to !m trans=m$ & "u 
an aspect until !n absolutely unkn[n4   
,let u take an example :i* is sali5t    
en\gh2 =1 h[ev] arbitr>y ! conv5tional  
division ( "t may appe> to a physici/'s 
eyes1 x is natural1 :5 in/itut+ a       
comp>ison betwe5 two epo*s1 to *oose ^? 
:i* ext5d ov] a space ( half a score (  
ye>s1 & are sep>at$ f ea* o!r by ! gap (

 a c5tury4 ,let u1 !n1 g back a hundr$  
ye>s & exam9e :at w\ld h be5 ! /ate (   
m9d ( an erudite amateur :o _h read &   
und]/ood ! *ief publications on physical
 rese>* betwe5 #ahjj & #ahaj4  ,let u   
suppose t ?is intellig5t & att5tive     
spectator witness$ 9 #ahjj ! discov]y ( 
! galvanic batt]y by ,volta4 ,he might f
 t mom5t h felt a pres5tim5t t a        
prodigi\s trans=mation 0 ab\t to occur 9
 our mode ( reg>d+ electrical ph5om5a4  
,br\ght up 9 ! ideas ( ,c\lomb &        
,frankl91 he might till !n h imag9$ t   
electricity _h unveil$ ne>ly all its    
my/]ies1 :5 an entirely orig9al app>atus
 sudd5ly gave bir? to applications ( !  
highe/ int]e/1 & excit$ ! blossom+ (    
!ories ( imm5se philosophical ext5t4  ,9
 ! treatises on physics publi%$ a little
 lat]1 we f9d traces ( ! a/oni%m5t      
produc$ by ?is sudd5 revelation ( a new 
_w4 ,electricity1 wrote ! ,abb ,hay1    
enri*$ by ! lab\r ( s _m di/+ui%$       
physici/s1 seem$ to h rea*$ ! t]m :5 a  
sci5ce has no fur!r important /eps be=e 

x1 & only leaves to ^? :o cultivate x ! 
hope ( confirm+ ! discov]ies ( _!       
pr$ecessors1 & ( ca/+ a bright] light on
 ! tru?s reveal$4 ,"o w\ld h ?\ght t all
 rese>*es = div]sify+ ! results (       
exp]im5t 7 exhau/$1 & t !ory itself c\ld
 only be augm5t$ by ! addition ( a      
great] degree ( precision to !          
applications ( pr9ciples already kn[n4  
,:ile sci5ce ?us appe>$ to be mak+ =    
repose1 ! ph5om5a ( ! convulsive        
movem5ts obs]v$ by ,galvani 9 ! muscles 
( a frog :5 connect$ by metal 7 br\ght  
to ! att5tion & a/oni%m5t (             
physici/s4444 ,volta1 9 t ,italy :i* _h 
be5 ! cradle ( ! new k1 discov]$ !      
pr9ciple ( its true !ory 9 a fact :i*   
r$uces ! explanation ( all ! ph5om5a 9  
"q to ! simple contact ( two sub/ances (
 diff]5t nature4 ,?is fact became 9 8   
h&s ! g]m ( ! admirable app>atus to :i* 
its mann] ( be+ & its fecundity assign  
"o ( ! *ief places among ^? ) :i* !     
g5ius ( mank9d has enri*$ physics4      
,%ortly aft]w>ds1 our amateur w\ld le>n 

t ,c>lisle & ,ni*olson _h decompos$ wat]
 by ! aid ( a batt]y2 !n1 t ,davy1 9    
#ahjc1 _h produc$1 by ! help ( ! same   
batt]y1 a q unexpect$ ph5om5on1 & _h    
succe$$ 9 prep>+ metals end[$ ) m>vell\s
 prop]ties1 beg9n+ ) sub/ances ( an e>?y
 appe>ance :i* _h be5 kn[n = a long "t1 
b ^: real nature _h n be5 discov]$4  ,9 
ano!r ord] ( ideas1 surprises z         
prodigi\s w\ld wait = our amateur4      
,comm5c+ ) #ahjb1 he might h read !     
admirable s]ies ( memoirs :i* ,"y !n    
publi%$1 & might !reby h le>n$ h[ ! /udy
 ( ! ph5om5a ( diffraction l$ to !      
belief t ! undulation !ory1 :i*1 s9ce ! 
works ( ,newton seem$ irretrievably     
condemn$1 01 on ! contr>y1 beg9n+ q a   
new life4 ,a little lat]--9 #ahjh--;he  
might h witness$ ! discov]y made by     
,malus ( pol>ization by reflexion1 &    
w\ld h be5 able to note1 no d\bt )      
/upefaction1 t "u c]ta9 conditions a ray
 ( light loses ! prop]ty ( be+ reflect$4
  ,he might also h he>d ( "o ,rum=d1 :o 
0 !n promulgat+ v s+ul> ideas on !      

nature ( heat1 :o ?\ght t ! !n classical
 notions might be false1 t caloric does 
n exi/ z a fluid1 & :o1 9 #ahjd1 ev5    
demon/rat$ t heat is creat$ by friction4
 ,a few ye>s lat] he w\ld le>n t ,*>les 
_h enunciat$ a capital law on !         
dilatation ( gases2 t ,pi]re ,prevo/1 9 
#ahji1 0 mak+ a /udy1 full ( orig9al    
ideas1 on radiant heat4 ,9 ! meantime he
 w\ld n h fail$ to read volumes iii4 &  
iv4 ( ! ,mecanique cele/e ( ,laplace1   
publi%$ 9 #ahjd & #ahje1 & he might1 no 
d\bt1 h ?\ght t be=e long ma!matics w\ld
 enable physical sci5ce to develop )    
un=ese5 safety4  ,all ^! results may    
d\btless be comp>$ 9 importance ) !     
pres5t discov]ies4 ,:5 /range metals l  
potassium & sodium 7 isolat$ by an      
entirely new me?od1 ! a/oni%m5t mu/ h   
be5 on a p> ) t caus$ 9 our "t by !     
magnific5t discov]y ( radium4 ,!        
pol>ization ( light is a ph5om5on z     
und\bt$ly s+ul> z ! exi/5ce ( ! ,x rays2
 & ! upheaval produc$ 9 natural         
philosophy by ! !ories ( ! dis9tegration

 ( matt] & ! ideas conc]n+ electrons is 
probably n m consid]able ?an t produc$ 9
 ! !ories ( light & heat by ! works (   
,"y & ,rum=d4  ,if we n[ dis5tangle     
ourselves f cont+5cies1 x w be und]/ood 
t 9 reality physical sci5ce progresses  
by evolution r ?an by revolution4 ,its  
m>* is cont9u\s4 ,! facts :i* our !ories
 enable u to discov]1 subsi/ & are l9k$ 
toge!r long aft] ^! !ories h disappe>$4 
,out ( ! mat]ials ( =m] edifices        
ov]?r[n1 new dwell+s are con/antly be+  
recon/ruct$4  ,! lab\r ( our =]unn]s    
nev] :olly p]i%es4 ,! ideas ( ye/]day   
prep>e = ^? ( to-morr[2 !y conta9 !m1 s 
to speak1 9 pot5tia4 ,sci5ce is 9 "s    
sort a liv+ organism1 :i* gives bir? to 
an indef9ite s]ies ( new be+s tak+ !    
places ( ! old1 & :i* evolves accord+ to
 ! nature ( its environm5t1 adapt+      
itself to ext]nal conditions1 & heal+ at
 e /ep ! w\nds :i* contact ) reality may
 h occasion$4  ,sometimes ?is evolution 
is rapid1 sometimes x is sl[ en\gh2 b x 
obeys ! ord9>y laws4 ,! wants impos$ by 

its surr\nd+s create c]ta9 organs 9     
sci5ce4 ,! problems set to physici/s by 
! eng9e] :o wi%es to facilitate         
transport or to produce bett]           
illum9ation1 or by ! doctor :o seeks to 
"k h[ su* & su* a rem$y acts1 or1 aga91 
by ! physiologi/ desir\s ( und]/&+ !    
me*anism ( ! gase\s & liquid ex*anges   
betwe5 ! cell & ! out] m$ium1 cause new 
*apt]s 9 physics to appe>1 & sugge/     
rese>*es adapt$ to ! necessities (      
actual life4  ,! evolution ( ! diff]5t  
p>ts ( physics does n1 h[ev]1 take place
 ) equal spe$1 because ! circum/ances 9 
:i* !y are plac$ are n equally          
fav\rable4 ,sometimes a :ole s]ies (    
que/ions w appe> =gott51 & w live only )
 a langui%+ exi/5ce2 & !n "s accid5tal  
circum/ance sudd5ly br+s !m new life1 & 
!y become ! object ( manifold lab\rs1   
engross public att5tion1 & invade ne>ly 
! :ole doma9 ( sci5ce4  ,we h 9 our own 
day witness$ su* a spectacle4 ,!        
discov]y ( ! ,x rays--a discov]y :i*    
physici/s no d\bt consid] z ! logical   

outcome ( rese>*es long pursu$ by a few 
s*ol>s work+ 9 sil5ce & obscurity on an 
o!rwise mu* neglect$ subject-- seem$ to 
! public eye to h inaugurat$ a new era 9
 ! hi/ory ( physics4 ,if1 z is ! case1  
h[ev]1 ! extraord9>y sci5tific movem5t  
provok$ by ,rntg5's s5sational exp]im5ts
 has a v remote orig91 x has1 at lea/1  
be5 s+ul>ly quick5$ by ! fav\rable      
conditions creat$ by ! int]e/ ar\s$ 9   
its a/oni%+ applications to radiography4
  ,a lucky *ance has ?us ha/5$ an       
evolution already tak+ place1 & !ories  
previ\sly outl9$ h receiv$ a s+ul>      
developm5t4 ,)\t wi%+ to yield too mu*  
to :at may be consid]$ a :im ( fa%ion1  
we _c1 if we are to note 9 ?is book !   
/age actually rea*$ 9 ! cont9u\s m>* (  
physics1 refra9 f giv+ a cle>ly         
prepond]ant place to ! que/ions sugge/$ 
by ! /udy ( ! new radiations4 ,at !     
pres5t "t x is ^! que/ions :i* move u ! 
mo/2 !y h %[n u unkn[n horizons1 & t[>ds
 ! fields rec5tly op5$ to sci5tific     
activity ! daily increas+ cr[d ( se>*]s 

ru%es 9 r disord]ly fa%ion4  ,"o ( ! mo/
 int]e/+ consequ5ces ( ! rec5t          
discov]ies has be5 to rehabilitate 9 !  
eyes ( s*ol>s1 speculations relat+ to ! 
con/itution ( matt]1 &1 9 a m g5]al way1
 metaphysical problems4 ,philosophy has1
 ( c\rse1 nev] be5 completely sep>at$ f 
sci5ce2 b 9 times pa/ _m physici/s      
dissociat$ !mselves f /udies :i* !y     
look$ ^u z unreal ^w-squabbles1 &       
sometimes n unreasonably ab/a9$ f jo9+ 9
 discussions :i* seem$ to !m idle & ( r 
pu]ile subtlety4 ,!y _h se5 ! ru9 ( mo/ 
( ! sy/ems built up a priori by d>+     
philosoph]s1 & deem$ x m prud5t to li/5 
to ! advice giv5 by ,kir*h(f & to       
sub/itute ! description ( facts = a %am 
explanation ( nature4  ,x %\ld h[ev] be 
rem>k$ t ^! physici/s some:at deceiv$   
!mselves z to ! value ( _! caution1 & t 
! mi/ru/ !y manife/$ t[>ds philosophical
 speculations did n preclude _! admitt+1
 unkn[n to !mselves1 c]ta9 axioms :i* !y
 did n discuss1 b :i* are1 prop]ly      
speak+1 metaphysical conceptions4 ,!y 7 

unconsci\sly speak+ a language taught !m
 by _! pr$ecessors1 ( :i* !y made no    
attempt to discov] ! orig94 ,x is ?us t 
x 0 readily consid]$ evid5t t physics   
mu/ necess>ily "s day re-ent] ! doma9 ( 
me*anics1 & !nce x 0 po/ulat$ t ev]y?+ 9
 nature is due to movem5t4 ,we1 fur!r1  
accept$ ! pr9ciples ( ! classical       
me*anics )\t discuss+ _! legitimacy4    
,?is /ate ( m9d 01 ev5 ( late ye>s1 t ( 
! mo/ illu/ri\s physici/s4 ,x is        
manife/$1 q s9c]ely & )\t ! slighte/    
res]ve1 9 all ! classical works devot$  
to physics4 ,?us ,v]det1 an illu/ri\s   
pr(essor :o has _h ! greate/ & mo/ happy
 influ5ce on ! intellectual =mation ( a 
:ole g5]ation ( s*ol>s1 & ^: works are  
ev5 at ! pres5t day v (t5 consult$1     
wrote3 ,! true problem ( ! physici/ is  
always to r$uce all ph5om5a to t :i*    
seems to u ! simple/ & cle>e/1 t is to  
say1 to movem5t4 ,9 8 celebrat$ c\rse ( 
lectures at l'cole ,polyte*nique1 ,jam9 
likewise said3 ,physics w "o day =m a   
*apt] ( g5]al me*anics2 & 9 ! preface to

 8 excell5t c\rse ( lectures on physics1
 ,m4 ,violle1 9 #ahhd1 ?us expresses    
himself3 ,! sci5ce ( nature t5ds t[>ds  
me*anics by a necess>y evolution1 !     
physici/ be+ able to e/abli% solid      
!ories only on ! laws ( movem5t4 ,! same
 idea is aga9 met ) 9 ! words ( ,cornu 9
 #ahif3 ,! g5]al t5d5cy %\ld be to %[ h[
 ! facts obs]v$ & ! ph5om5a measur$1    
?\gh fir/ br\ght toge!r by empirical    
laws1 end1 by ! impulse ( successive    
progressions1 9 com+ "u ! g5]al laws (  
rational me*anics2 & ! same physici/ %[$
 cle>ly t 9 8 m9d ?is connexion (       
ph5om5a ) me*anics _h a deep &          
philosophical reason1 :51 9 ! f9e       
disc\rse pron\nc$ by him at ! op5+      
c]emony ( ! ,congrs de ,physique 9      
#aijj1 he exclaim$3 ,! m9d ( ,desc>tes  
so>s ov] mod]n physics1 or r1 ,i %\ld   
say1 he is _! lum9>y4 ,! fur!r we       
p5etrate into ! k ( natural ph5om5a1 !  
cle>] & ! m develop$ becomes ! bold     
,c>tesian conception reg>d+ ! me*anism (
 ! univ]se4 ,!re is no?+ 9 ! physical _w

 b matt] & movem5t4  ,if we adopt ?is   
conception1 we are l$ to con/ruct       
me*anical repres5tations ( ! mat]ial _w1
 & to imag9e movem5ts 9 ! diff]5t p>ts (
 bodies capable ( reproduc+ all !       
manife/ations ( nature4 ,! k9ematic k ( 
^! movem5ts1 t is to say1 ! det]m9ation 
( ! position1 spe$1 & accel]ation at a  
giv5 mom5t ( all ! p>ts ( ! sy/em1 or1  
on ! o!r h&1 _! dynamical /udy1 enabl+ u
 to "k :at is ! action ( ^! p>ts on ea* 
o!r1 w\ld !n be suffici5t to enable u to
 =etell all t c occur 9 ! doma9 (       
nature4  ,?is 0 ! great ?\ght cle>ly    
express$ by ! ,encyclopdi/s ( ! eighte5?
 c5tury2 & if ! necessity ( int]pret+ ! 
ph5om5a ( electricity or light l$ !     
physici/s ( la/ c5tury to imag9e        
p>ticul> fluids :i* seem$ to obey ) "s  
difficulty ! ord9>y rules ( me*anics1 ^!
 physici/s /ill cont9u$ to reta9 _! hope
 9 ! future1 & to treat ! idea (        
,desc>tes z an ideal to be rea*$ soon]  
or lat]4  ,c]ta9 s*ol>s--p>ticul>ly ^? (
 ! ,engli% ,s*ool--outrunn+ exp]im5t1 & 

pu%+ ?+s to extremes1 took pleasure 9   
propos+ v curi\s me*anical models :i* 7 
(t5 /range images ( reality4 ,! mo/     
illu/ri\s ( !m1 ,"l ,kelv91 may be      
consid]$ z _! repres5tative type1 & he  
has himself said3 ,x seems to me t !    
true s5se ( ! "q1 ,d we or d we n und]/&
 a p>ticul> subject 9 physics8 is--,c we
 make a me*anical model :i* corresponds 
to x8 ,i am nev] satisfi$ s long z ,i h 
be5 unable to make a me*anical model ( !
 object4 ,if ,i am able to d s1 ,i      
und]/& x4 ,if ,i _c make su* a model1 ,i
 d n und]/& x4 ,b x mu/ be ackn[l$g$ t  
"s ( ! models ?us devis$ h become       
excessively complicat$1 & ?is           
complication has = a long "t disc\rag$  
all b v bold m9ds4 ,9 addition1 :5 x    
became a "q ( p5etrat+ into ! me*anism (
 molecules1 & we 7 no long] satisfi$ to 
look at matt] z a mass1 ! me*anical     
solutions seem$ undet]m9$ & ! /ability (
 ! edifices ?us con/ruct$ 0             
insuffici5tly demon/rat$4  ,return+ !n  
to our />t+-po9t1 _m contempor>y        

physici/s wi% to subject ,desc>tes' idea
 to /rict criticism4 ,f ! philosophical 
po9t ( view1 !y fir/ enquire :e!r x is  
really demon/rat$ t !re exi/s no?+ else 
9 ! kn[able ?an matt] & movem5t4 ,!y ask
 !mselves :e!r x is n habit & tradition 
9 p>ticul> :i* lead u to ascribe to     
me*anics ! orig9 ( ph5om5a4 ,p]haps also
 a "q ( s5se "h comes 94 ,our s5ses1 :i*
 are1 aft] all1 ! only w9d[s op5 t[>ds  
ext]nal reality1 give u a view ( "o side
 ( ! _w only2 evid5tly we only "k !     
univ]se by ! relations :i* exi/ betwe5 x
 & our organisms1 & ^! organisms are    
peculi>ly s5sitive to movem5t4  ,no?+1  
h[ev]1 proves t ^? acquisitions :i* are 
! mo/ anci5t 9 hi/orical ord] ought1 9 !
 developm5t ( sci5ce1 to rema9 ! basis (
 our k4 ,nor does any !ory prove t our  
p]ceptions are an exact indication (    
reality4 ,_m reasons1 on ! contr>y1     
might be invok$ :i* t5d to compel u to  
see 9 nature ph5om5a :i* _c be r$uc$ to 
movem5t4  ,me*anics z ord9>ily und]/ood 
is ! /udy ( rev]sible ph5om5a4 ,if !re  

be giv5 to ! p>amet] :i* repres5ts "t1#a
 & :i* has assum$ increas+ values dur+ !
 duration ( ! ph5om5a1 decreas+ values  
:i* make x g ! opposite way1 ! :ole     
sy/em w aga9 pass ?r\gh exactly ! same  
/ages z be=e1 & all ! ph5om5a w unfold  
!mselves 9 rev]s$ ord]4 ,9 physics1 !   
contr>y rule appe>s v g5]al1 &          
rev]sibility g5]ally does n exi/4 ,x is 
an ideal & limit$ case1 :i* may be      
sometimes approa*$1 b c nev]1 /rictly   
speak+1 be met ) 9 its entirety4 ,no    
physical ph5om5on ev] recomm5ces 9 an   
id5tical mann] if its direction be      
alt]$4 ,x is true t c]ta9 ma!maticians  
w>n u t a me*anics c be devis$ 9 :i*    
rev]sibility w\ld no long] be ! rule1 b 
! bold attempts made 9 ?is direction are
 n :olly satisfactory4  ,footnote #a3   
,i4e41 ! "t-curve4--,,ed4  ,on ! o!r h&1
 x is e/abli%$ t if a me*anical         
explanation ( a ph5om5on c be giv51 we c
 f9d an inf9ity ( o!rs :i* likewise     
acc\nt = all ! peculi>ities reveal$ by  
exp]im5t4 ,b1 z a matt] ( fact1 no "o   

has ev] succe$$ 9 giv+ an indisputable  
me*anical repres5tation ( ! :ole        
physical _w4 ,ev5 7 we dispos$ to admit 
! /range/ solutions ( ! problem2 to     
cons5t1 = example1 to be satisfi$ ) !   
hidd5 sy/ems devis$ by ,helmholtz1 :]eby
 we ought to divide v>iable ?+s into two
 classes1 "s accessible1 & ! o!rs n[ & =
 ev] unkn[n1 we %\ld nev] manage to     
con/ruct an edifice to conta9 all ! kn[n
 facts4 ,ev5 ! v compreh5sive me*anics (
 a ,h]tz fails :]e ! classical me*anics 
has n succe$$4  ,deem+ ?is *eck         
irrem$iable1 _m contempor>y physici/s   
give up attempts :i* !y look ^u z       
condemn$ be=eh&1 & adopt1 to guide !m 9 
_! rese>*es1 a me?od :i* at fir/ sight  
appe>s mu* m mode/1 & also mu* m sure4  
,!y make up _! m9ds n to see at once to 
! bottom ( ?+s2 !y no long] seek to     
sudd5ly /rip ! la/ veils f nature1 & to 
div9e h] supreme secrets2 b !y "w       
prud5tly & advance b sl[ly1 :ile on !   
gr\nd ?us conqu]$ foot by foot !y       
endeav\r to e/abli% !mselves firmly4 ,!y

 /udy ! v>i\s magnitudes directly       
accessible to _! obs]vation )\t busy+   
!mselves z to _! ess5ce4 ,!y measure    
quantities ( heat & ( temp]ature1       
diff]5ces ( pot5tial1 curr5ts1 &        
magnetic fields2 & !n1 v>y+ !           
conditions1 apply ! rules ( exp]im5tal  
me?od1 & discov] betwe5 ^! magnitudes   
mutual relations1 :ile !y ?us succe$ 9  
enunciat+ laws :i* translate & sum up _!
 lab\rs4  ,^! empirical laws1 h[ev]1    
!mselves br+ ab\t by induction !        
promulgation ( m g5]al laws1 :i* are    
t]m$ pr9ciples4 ,^! pr9ciples are       
orig9ally only ! results ( exp]im5ts1 & 
exp]im5t all[s !m besides to be *eck$1 &
 _! m or less high degree ( g5]ality to 
be v]ifi$4 ,:5 !y h be5 ?us def9itely   
e/abli%$1 !y may s]ve z fre% />t+-po9ts1
 &1 by d$uction1 lead to v v>i$         
discov]ies4  ,! pr9ciples :i* gov]n     
physical sci5ce are few 9 numb]1 & _! v 
g5]al =m gives !m a philosophical       
appe>ance1 :ile we _c long resi/ !      
temptation ( reg>d+ !m z metaphysical   

dogmas4 ,x ?us happ5s t ! lea/ bold     
physici/s1 ^? :o h want$ to %[ !mselves 
! mo/ res]v$1 are !mselves l$ to =get ! 
exp]im5tal "* ( ! laws !y h prop\nd$1 & 
to see 9 !m imp]i\s be+s ^: au?ority1   
plac$ above all v]ification1 c no long] 
be discuss$4  ,o!rs1 on ! contr>y1 c>ry 
prud5ce to ! ext5t ( timidity4 ,!y      
desire to griev\sly limit ! field (     
sci5tific inve/igation1 & !y assign to  
sci5ce a too re/rict$ doma94 ,!y cont5t 
!mselves ) repres5t+ ph5om5a by         
equations1 & ?9k t !y ought to submit to
 calculation magnitudes exp]im5tally    
det]m9$1 )\t ask+ !mselves :e!r ^!      
calculations reta9 a physical mean+4 ,!y
 are ?us l$ to recon/ruct a physics 9   
:i* !re aga9 appe>s ! idea ( quality1   
und]/ood1 ( c\rse1 n 9 ! s*ola/ic s5se1 
s9ce f ?is quality we c argue ) "s      
precision by repres5t+ x "u num]ical    
symbols1 b /ill con/itut+ an elem5t (   
diff]5tiation & ( het]og5eity4  ,not)/&+
 ! errors !y may lead to if c>ri$ to    
excess1 bo? ^! doctr9es r5d]1 z a :ole1 

mo/ important s]vice4 ,x is no bad ?+ t 
^! contradictory t5d5cies %\ld subsi/1 =
 ?is v>iety 9 ! conception ( ph5om5a    
gives to actual sci5ce a "* ( int5se    
life & ( v]itable y\?1 capable (        
impassion$ ef=ts t[>ds ! tru?4          
,spectators :o see su* mov+ & v>i$      
pictures pass+ be=e !m1 exp]i5ce ! feel+
 t !re no long] exi/ sy/ems fix$ 9 an   
immobility :i* seems t ( dea?4 ,!y feel 
t no?+ is un*angeable2 t ceaseless      
trans=mations are tak+ place be=e _!    
eyes2 & t ?is cont9u\s evolution &      
p]petual *ange are ! necess>y conditions
 ( progress4  ,a great numb] ( seek]s1  
moreov]1 %[ !mselves on _! own acc\nt   
p]fectly eclectic4 ,!y adopt1 accord+ to
 _! ne$s1 su* or su* a mann] ( look+ at 
nature1 & d n hesitate to utilize v     
diff]5t images :5 !y appe> to !m useful 
& conv5i5t4 ,&1 )\t d\bt1 !y are n      
wrong1 s9ce ^! images are only symbols  
conv5i5t = language4 ,!y all[ facts to  
be gr\p$ & associat$1 b only pres5t a   
fairly di/ant resemblance ) ! objective 

reality4 ,h5ce x is n =bidd5 to multiply
 & to modify !m accord+ to circum/ances4
 ,! really ess5tial ?+ is to h1 z a     
guide ?r\gh ! unkn[n1 a map :i* c]ta9ly 
does n claim to repres5t all ! aspects (
 nature1 b :i*1 hav+ be5 drawn up       
accord+ to pr$et]m9$ rules1 all[s u to  
foll[ an asc]ta9$ road 9 ! et]nal j\rney
 t[>ds ! tru?4  ,among ! provisional    
!ories :i* are ?us will+ly con/ruct$ by 
s*ol>s on _! j\rney1 l edifices ha/ily  
run up to receive an un=ese5 h>ve/1 "s  
/ill appe> v bold & v s+ul>4 ,ab&on+ !  
se>* aft] me*anical models = all        
electrical ph5om5a1 c]ta9 physici/s     
rev]se1 s to speak1 ! conditions ( !    
problem1 & ask !mselves :e!r1 in/ead (  
giv+ a me*anical int]pretation to       
electricity1 !y may n1 on ! contr>y1    
give an electrical int]pretation to !   
ph5om5a ( matt] & motion1 & ?us m]ge    
me*anics itself 9 electricity4 ,"o ?us  
sees dawn+ afre% ! et]nal hope (        
co-ord9at+ all natural ph5om5a 9 "o     
gr&iose & impos+ syn!sis4 ,:atev] may be

 ! fate res]v$ = su* attempts1 !y des]ve
 att5tion 9 ! highe/ degree2 & x is     
desirable to exam9e !m c>efully if we   
wi% to h an exact idea ( ! t5d5cies (   
mod]n physics4     ,,*apt] ,,ii         
,,measurem5ts    #a4 ,,metrology  ,n s v
 long ago1 ! s*ol> 0 (t5 cont5t )       
qualitative obs]vations4 ,_m ph5om5a 7  
/udi$ )\t mu* tr\ble be+ tak5 to obta9  
actual measurem5ts4 ,b x is n[ becom+ m 
& m und]/ood t to e/abli% ! relations   
:i* exi/ betwe5 physical magnitudes1 &  
to repres5t ! v>iations ( ^! magnitudes 
by functions :i* all[ u to use ! p[] (  
ma!matical analysis1 x is mo/ necess>y  
to express ea* magnitude by a def9ite   
numb]4  ,"u ^! conditions alone c a     
magnitude be consid]$ z effectively     
kn[n4 ,i (t5 say1 ,"l ,kelv9 has said1 t
 if y c measure t ( :i* y are speak+ &  
express x by a numb] y "k some?+ ( y\r  
subject2 b if y _c measure x nor express
 x by a numb]1 y\r k is ( a sorry k9d & 
h>dly satisfactory4 ,x may be ! beg9n+ (
 ! acqua9tance1 b y are h>dly1 9 y\r    

?\ghts1 advanc$ t[>ds sci5ce1 :atev] !  
subject may be4  ,x has n[ become       
possible to measure exactly ! elem5ts   
:i* ent] into ne>ly all physical        
ph5om5a1 & ^! measurem5ts are tak5 ) ev]
 increas+ precision4 ,e "t a *apt] 9    
sci5ce progresses1 sci5ce %[s itself m  
exact+2 x p]fects its means (           
inve/igation1 x dem&s m & m exactitude1 
& "o ( ! mo/ /rik+ features ( mod]n     
physics is ?is con/ant c>e = /rictness &
 cle>ness 9 exp]im5tation4  ,a v]itable 
sci5ce ( measurem5t has ?us be5         
con/itut$ :i* ext5ds ov] all p>ts ( !   
doma9 ( physics4 ,?is sci5ce has its    
rules & its me?ods2 x po9ts out ! be/   
processes ( calculation1 & tea*es !     
me?od ( correctly e/imat+ errors & tak+ 
acc\nt ( !m4 ,x has p]fect$ ! processes 
( exp]im5t1 co-ord9at$ a l>ge numb] (   
results1 & made possible ! unification (
 /&>ds4 ,x is ?anks to x t ! sy/em (    
measurem5ts unanim\sly adopt$ by        
physici/s has be5 =m$4  ,at ! pres5t day
 we designate m peculi>ly by ! "n (     

metrology t "p ( ! sci5ce ( measurem5ts 
:i* devotes itself specially to !       
det]m9+ ( ! prototypes repres5t+ !      
fundam5tal units ( dim5sion & mass1 & ( 
! /&>ds ( ! fir/ ord] :i* are d]iv$ f   
!m4 ,if all measurable quantities1 z 0  
long ?\ght possible1 c\ld be r$uc$ to ! 
magnitudes ( me*anics1 metrology w\ld   
?us be occupi$ ) ! ess5tial elem5ts     
ent]+ into all ph5om5a1 & might         
legitimately claim ! highe/ rank 9      
sci5ce4 ,b ev5 :5 we suppose t "s       
magnitudes c nev] be connect$ ) mass1   
l5g?1 & "t1 x /ill holds a prepond]at+  
place1 & its progress f9ds an e*o       
?r\gh\t ! :ole doma9 ( ! natural        
sci5ces4 ,x is !re=e well1 9 ord] to    
give an acc\nt ( ! g5]al progress (     
physics1 to exam9e at ! outset !        
improvem5ts :i* h be5 effect$ 9 ^!      
fundam5tal measurem5ts1 & to see :at    
precision ^! improvem5ts h all[$ u to   
atta94    #b4 ,,! ,,measure ,,( ,,l5g?  
,to measure a l5g? is to comp>e x )     
ano!r l5g? tak5 z unity4 ,measurem5t is 

!re=e a relative op]ation1 & c only     
enable u to "k ratios4 ,did bo? ! l5g?  
to be measur$ & ! unit *os5 happ5 to v>y
 simultane\sly & 9 ! same degree1 we    
%\ld p]ceive no *ange4 ,moreov]1 ! unit 
be+1 by def9ition1 ! t]m ( comp>ison1 & 
n be+ itself comp>able ) any?+1 we h    
!oretically no means ( asc]ta9+ :e!r its
 l5g? v>ies4  ,if1 h[ev]1 we 7 to note  
t1 sudd5ly & 9 ! same proportions1 !    
di/ance betwe5 two po9ts on ?is e>? _h  
increas$1 t all ! planets _h mov$ fur!r 
f ea* o!r1 t all objects ar\nd u _h     
become l>g]1 t we ourselves _h become   
tall]1 & t ! di/ance travell$ by light 9
 ! duration ( a vibration _h become     
great]1 we %\ld n hesitate to ?9k       
ourselves ! victims ( an illusion1 t 9  
reality all ^! di/ances _h rema9$ fix$1 
& t all ^! appe>ances 7 due to a %ort5+ 
( ! rule :i* we _h us$ z ! /&>d =       
measur+ ! l5g?s4  ,f ! ma!matical po9t (
 view1 x may be consid]$ t ! two        
hypo!ses are equival5t2 all has l5g!n$  
ar\nd u1 or else our /&>d has become    

less4 ,b x is no simple "q ( conv5i5ce &
 simplicity :i* leads u to reject ! "o  
supposition & to accept ! o!r2 x is "r 9
 ?is case to li/5 to ! voice ( common   
s5se1 & ^? physici/s :o h an in/9ctive  
tru/ 9 ! notion ( an absolute l5g? are  
p]haps n wrong4 ,x is only by *oos+ our 
unit f ^? :i* at all times h seem$ to   
all m5 ! mo/ inv>iable1 t we are able 9 
our exp]im5ts to note t ! same causes   
act+ "u id5tical conditions always      
produce ! same effects4 ,! idea (       
absolute l5g? is d]iv$ f ! pr9ciple (   
causality2 & our *oice is =c$ ^u u by ! 
necessity ( obey+ ?is pr9ciple1 :i* we  
_c reject )\t decl>+ by t v act all     
sci5ce to be impossible4  ,simil> rem>ks
 might be made ) reg>d to ! notions (   
absolute "t & absolute movem5t4 ,!y h   
be5 put 9 evid5ce & set =? v =cibly by a
 le>n$ & pr(\nd ma!matician1 ,m4        
,pa9lev4  ,on ! p>ticul>ly cle> example 
( ! measure ( l5g?1 x is int]e/+ to     
foll[ ! evolution ( ! me?ods employ$1 & 
to run ?r\gh ! hi/ory ( ! progress 9    

precision f ! "t t we h possess$ au!ntic
 docum5ts relat+ to ?is "q4 ,?is hi/ory 
has be5 writt5 9 a ma/]ly way by "o ( ! 
physici/s :o h 9 our days done ! mo/ by 
_! p]sonal lab\rs to add to x glori\s   
pages4 ,m4 ,b5oit1 ! le>n$ ,director ( !
 ,int]national ,bureau ( ,weights &     
,measures1 has furni%$ 9 v>i\s reports v
 complete details on ! subject1 f :i* ,i
 "h borr[ ! mo/ int]e/+4  ,we "k t 9    
,france ! fundam5tal /&>d = measures (  
l5g? 0 = a long "t ! ,toise du ,*telet1 
a k9d ( callip]s =m$ ( a b> ( iron :i* 9
 #affh 0 emb$d$ 9 ! outside wall ( !    
,*telet1 at ! foot ( ! /aircase4 ,?is b>
 _h at its extremities two projections )
 squ>e faces1 & all ! toises ( comm]ce  
_h to fit exactly betwe5 !m4 ,su* a     
/&>d1 r\ghly con/ruct$1 & expos$ to all 
! injuries ( wea!r & "t1 (f]$ v slight  
gu>antees ei!r z to ! p]man5ce or !     
correctness ( its copies4 ,no?+1 p]haps1
 c bett] convey an idea ( ! importance (
 ! modifications made 9 ! me?ods (      
exp]im5tal physics ?an ! easy comp>ison 

betwe5 s rudim5t>y a process & ! actual 
measurem5ts effect$ at ! pres5t "t4  ,! 
,toise du ,*telet1 not)/&+ its evid5t   
faults1 0 employ$ = ne>ly a hundr$ ye>s2
 9 #agff x 0 replac$ by ! ,toise du     
,pr\1 s call$ because x _h s]v$ = !     
measurem5ts ( ! t]re/rial arc effect$ 9 
,p]u f #agce to #agci by ,b\gu]1 ,la    
,condam9e1 & ,god94 ,at t "t1 accord+ to
 ! comp>isons made betwe5 ?is new toise 
& ! ,toise du ,nord1 :i* _h also be5 us$
 = ! measurem5t ( an arc ( ! m]idian1 an
 error ( ! t5? "p ( a millimetre 9      
measur+ l5g?s ( ! ord] ( a metre 0      
consid]$ q unimportant4 ,at ! end ( !   
eighte5? c5tury1 ,delambre1 9 8 "w ,sur 
la ,base du ,sy/me mtrique dcimal1      
cle>ly gives u to und]/& t magnitudes ( 
! ord] ( ! hundr$? ( a millimetre appe> 
to him incapable ( obs]vation1 ev5 9    
sci5tific rese>*es ( ! highe/ precision4
 ,at ! pres5t date ! ,int]national      
,bureau ( ,weights & ,measures          
gu>antees1 9 ! det]m9ation ( a /&>d (   
l5g? comp>$ ) ! metre1 an approximation 

( two or ?ree t5-?\s&?s ( a millimetre1 
& ev5 a little m "u c]ta9 circum/ances4 
,?is v rem>kable progress is due to !   
improvem5ts 9 ! me?od ( comp>ison on !  
"o h&1 & 9 ! manufacture ( ! /&>d on !  
o!r4 ,m4 ,b5oit rightly po9ts out t a   
k9d ( competition has be5 set up betwe5 
! /&>d de/9$ to repres5t ! unit ) its   
subdivisions & multiples & ! in/rum5t   
*>g$ ) obs]v+ x1 comp>able1 up to a     
c]ta9 po9t1 ) t :i* 9 ano!r ord] ( ideas
 goes on betwe5 ! gun & ! arm\r-plate4  
,! measur+ in/rum5t ( to-day is an      
in/rum5t ( comp>ison con/ruct$ )        
meticul\s c>e1 :i* enables u to d away )
 causes ( error =m]ly ignor$1 to        
elim9ate ! action ( ext]nal ph5om5a1 &  
to )draw ! exp]im5t f ! influ5ce ( ev5 !
 p]sonality ( ! obs]v]4 ,?is /&>d is no 
long]1 z =m]ly1 a flat rule1 weak &     
fragile1 b a rigid b>1 incapable (      
de=mation1 9 :i* ! mat]ial is utilis$ 9 
! be/ conditions ( resi/ance4 ,= a /&>d 
) ends has be5 sub/itut$ a /&>d ) m>ks1 
:i* p]mits mu* m precise def9ition & c  

be employ$ 9 optical processes (        
obs]vation alone2 t is1 9 processes :i* 
c produce 9 x no de=mation & no         
alt]ation4 ,moreov]1 ! m>ks are trac$ on
 ! plane ( ! neutral fibres#b expos$1 & 
! inv>iability ( _! di/ance ap>t is ?us 
assur$1 ev5 :5 a *ange is made 9 ! way !
 rule is support$4  ,footnote #b3 ,!    
au?or seems to ref] to ! fact t 9 ! /&>d
 metre1 ! measurem5t is tak5 f ! c5tral 
"o ( ?ree m>ks at ea* end ( ! b>4 ,!    
transv]se section ( ! b> is an ,x1 & !  
read+ is made by a microscope4--,,ed4   
,?anks to /udies ?us sy/ematically      
pursu$1 we h succe$$ 9 ! c\rse ( a      
hundr$ ye>s 9 increas+ ! precision (    
measures 9 ! proportion ( a ?\s& to "o1 
& we may ask ourselves :e!r su* an      
increase w cont9ue 9 ! future4 ,no d\bt 
progress w n be /ay$2 b if we keep to ! 
def9ition ( l5g? by a mat]ial /&>d1 x   
w\ld seem t its precision _c be         
consid]ably increas$4 ,we h ne>ly rea*$ 
! limit impos$ by ! necessity ( mak+    
/rokes ( su* a ?ickness z to be         

obs]vable "u ! microscope4  ,x may      
happ51 h[ev]1 t we %all be br\ght "o (  
^! days to a new conception ( ! measure 
( l5g?1 & t v diff]5t processes (       
det]m9ation w be ?\ght (4 ,if we took z 
unit1 = in/ance1 ! di/ance cov]$ by a   
giv5 radiation dur+ a vibration1 !      
optical processes w\ld at once admit (  
mu* great] precision4  ,?us ,fizeau1 !  
fir/ to h ?is idea1 says3 ,a ray (      
light1 ) its s]ies ( undulations (      
extreme t5uity b p]fect regul>ity1 may  
be consid]$ z a micromet] ( ! greate/   
p]fection1 & p>ticul>ly suitable =      
det]m9+ l5g?4 ,b 9 ! pres5t /ate ( ?+s1 
s9ce ! legal & cu/om>y def9ition ( !    
unit rema9s a mat]ial /&>d1 x is n en\gh
 to measure l5g? 9 t]ms ( wave-l5g?s1 & 
we mu/ also "k ! value ( ^! wave-l5g?s 9
 t]ms ( ! /&>d prototype ( ! metre4     
,?is 0 det]m9$ 9 #ahid by ,m4 ,mi*elson 
& ,m4 ,b5oit 9 an exp]im5t :i* w rema9  
classic4 ,! two physici/s measur$ a /&>d
 l5g? ( ab\t t5 c5timetres1 fir/ 9 t]ms 
( ! wave-l5g?s ( ! r$1 gre51 & blue     

radiations ( cadmium1 & !n 9 t]ms ( !   
/&>d metre4 ,! great difficulty ( !     
exp]im5t proce$s f ! va/ diff]5ce :i*   
exi/s betwe5 ! l5g?s to be comp>$1 !    
wave-l5g?s b>ely am\nt+ to half a       
micron2#c ! process employ$ consi/$ 9   
not+1 in/ead ( ?is l5g?1 a l5g? easily  
made ab\t a ?\s& times great]1 namely1 !
 di/ance betwe5 ! fr+es ( int]f]5ce4    
,footnote #c3 ,i4e4 #a_/bjjj ( a        
millimetre4--,,ed4  ,9 all measurem5t1 t
 is to say 9 e det]m9ation ( ! relation 
( a magnitude to ! unit1 !re has to be  
det]m9$ on ! "o h& ! :ole1 & on ! o!r ! 
fractional "p ( ?is ratio1 & naturally !
 mo/ delicate det]m9ation is g5]ally t (
 ?is fractional "p4 ,9 optical processes
 ! difficulty is rev]s$4 ,! fractional  
"p is easily kn[n1 :ile x is ! high     
figure ( ! numb] repres5t+ ! :ole :i*   
becomes a v s]i\s ob/acle4 ,x is ?is    
ob/acle :i* ,,mm4 ,mi*elson & ,b5oit    
ov]came ) admirable +5uity4 ,by mak+ use
 ( a some:at simil> idea1 ,m4 ,mac de   
,lp9ay & ,,mm4 ,p]ot & ,fabry1 h lately 

effect$ by optical me?ods1 measurem5ts (
 ! greate/ precision1 & no d\bt fur!r   
progress may /ill be made4 ,a day may   
p]haps come :5 a mat]ial /&>d w be giv5 
up1 & x may p]haps ev5 be recognis$ t   
su* a /&>d 9 "t *anges its l5g? by      
molecul> /ra91 & by we> & te>3 & x w be 
fur!r not$ t1 9 accordance ) c]ta9      
!ories :i* w be notic$ lat] on1 x is n  
inv>iable :5 its ori5tation is *ang$4   
,= ! mom5t1 h[ev]1 ! ne$ ( any *ange 9 !
 def9ition ( ! unit is 9 no way felt2 we
 mu/1 on ! contr>y1 hope t ! use ( !    
unit adopt$ by ! physici/s ( ! :ole _w w
 spread m & m4 ,x is "r to rem>k t a few
 errors /ill occur ) reg>d to ?is unit1 
& t ^! errors h be5 facilitat$ by       
incoh]5t legislation4 ,france h]self1   
?\gh %e 0 ! admirable initiator ( !     
metrical sy/em1 has = too long all[$ a v
 regrettable confusion to exi/2 & x _c  
be not$ )\t a c]ta9 sadness t x 0 n     
until ! #aa? ,july #aijc t a law 0      
promulgat$ re-e/abli%+ ! agreem5t betwe5
 ! legal & ! sci5tific def9ition ( !    

metre4  ,p]haps x may n be useless to   
briefly indicate "h ! reasons ( !       
disagreem5t :i* _h tak5 place4 ,two     
def9itions ( ! metre c be1 & 9 fact 7   
giv54 ,"o _h = its basis ! dim5sions ( !
 e>?1 ! o!r ! l5g? ( ! mat]ial /&>d4 ,9 
! m9ds ( ! f\nd]s ( ! metrical sy/em1 ! 
fir/ ( ^! 0 ! true def9ition ( ! unit ( 
l5g?1 ! second m]ely a simple           
repres5tation4 ,x 0 admitt$1 h[ev]1 t   
?is repres5tation _h be5 con/ruct$ 9 a  
mann] p]fect en\gh = x to be ne>ly      
impossible to p]ceive any diff]5ce      
betwe5 ! unit & its repres5tation1 & = !
 practical id5tity ( ! two def9itions to
 be ?us assur$4 ,! creators ( ! metrical
 sy/em 7 p]suad$ t ! measurem5ts ( !    
m]idian effect$ 9 _! day c\ld nev] be   
surpass$ 9 precision2 & on ! o!r h&1 by 
borr[+ f nature a def9ite basis1 !y     
?\ght to take f ! def9ition ( ! unit "s 
( its arbitr>y "*1 & to ensure ! means (
 aga9 f9d+ ! same unit if by any accid5t
 ! /&>d became alt]$4 ,_! confid5ce 9 ! 
value ( ! processes !y _h se5 employ$ 0 

exagg]at$1 & _! mi/ru/ ( ! future       
unju/ifi$4 ,?is example %[s h[ imprud5t 
x is to endeav\r to fix limits to       
progress4 ,x is an error to ?9k ! m>* ( 
sci5ce c be /ay$2 & 9 reality x is n[   
kn[n t ! t5-million? "p ( ! qu>t] ( !   
t]re/rial m]idian is long] ?an ! metre  
by #j4ahg millimetres4 ,b contempor>y   
physici/s d n fall into ! same error z  
_! =]unn]s1 & !y reg>d ! pres5t result z
 m]ely provisional4 ,!y guess1 9 fact1 t
 new improvem5ts w be effect$ 9 ! art ( 
measurem5t2 !y "k t geodesical          
processes1 ?\gh mu* improv$ 9 our days1 
h /ill mu* to d to atta9 ! precision    
display$ 9 ! con/ruction & det]m9ation (
 /&>ds ( ! fir/ ord]2 & consequ5tly !y d
 n propose to keep ! anci5t def9ition1  
:i* w\ld lead to hav+ = unit a magnitude
 possess+ ! grave defect f a practical  
po9t ( view ( be+ con/antly v>iable4    
,we may ev5 consid] t1 look$ at         
!oretically1 its p]man5ce w\ld n be     
assur$4 ,no?+1 9 fact1 proves t s5sible 
v>iations may n 9 "t be produc$ 9 !     

value ( an arc ( ! m]idian1 & s]i\s     
difficulties may arise reg>d+ ! probable
 inequality ( ! v>i\s m]idians4  ,= all 
^! reasons1 ! idea ( f9d+ a natural unit
 has be5 gradually ab&on$1 & we h become
 resign$ to accept+ z a fundam5tal unit 
an arbitr>y & conv5tional l5g? hav+ a   
mat]ial repres5tation recognis$ by      
univ]sal cons5t2 & x 0 ?is unit :i* 0   
consecrat$ by ! foll[+ law ( ! #aa?     
,july #aijc3--  ,! /&>d prototype ( !   
metrical sy/em is ! int]national metre1 
:i* has be5 sanction$ by ! ,g5]al       
,conf]5ce on ,weights & ,measures4      
#c4 ,,! ,,measure ,,( ,,mass  ,on !     
subject ( measures ( mass1 simil> rem>ks
 to ^? on measures ( l5g? might be made4
 ,! confusion "h 0 p]haps /ill great]1  
because1 to ! unc]ta9ty relat+ to ! fix+
 ( ! unit1 0 add$ "s indecision on ! v  
nature ( ! magnitude def9$4 ,9 law1 z 9 
ord9>y practice1 ! notions ( weight & ( 
mass 7 n1 9 fact1 sep>at$ ) suffici5t   
cle>ness4  ,!y repres5t1 h[ev]1 two     
ess5tially diff]5t ?+s4 ,mass is !      

*>act]i/ic ( a quantity ( matt]2 x      
dep5ds nei!r on ! geographical position 
"o occupies nor on ! altitude to :i* "o 
may rise2 x rema9s inv>iable s long z   
no?+ mat]ial is add$ or tak5 away4      
,weight is ! action :i* gravity has ^u !
 body "u consid]ation2 ?is action does n
 dep5d solely on ! body1 b on ! e>? z   
well2 & :5 x is *ang$ f "o spot to      
ano!r1 ! weight *anges1 because gravity 
v>ies ) latitude & altitude4  ,^!       
elem5t>y notions1 to-day und]/ood ev5 by
 "y beg9n]s1 appe> to h be5 = a long "t 
indi/9ctly grasp$4 ,! di/9ction rema9$  
confus$ 9 _m m9ds1 because1 = ! mo/ "p1 
masses 7 comp>atively e/imat$ by !      
int]m$i>y ( weights4 ,! e/imations (    
weight made ) ! balance utilize ! action
 ( ! weight on ! beam1 b 9 su*          
conditions t ! influ5ce ( ! v>iations ( 
gravity becomes elim9at$4 ,! two weights
 :i* are be+ comp>$ may bo? ( !m *ange  
if ! weigh+ is effect$ 9 diff]5t places1
 b !y are attract$ 9 ! same proportion4 
,if once equal1 !y rema9 equal ev5 :5 9 

reality !y may bo? h v>i$4  ,! curr5t   
law def9es ! kilogramme z ! /&>d ( mass1
 & ! law is c]ta9ly 9 con=mity ) ! r    
obscurely express$ int5tions ( ! f\nd]s 
( ! metrical sy/em4 ,_! t]m9ology 0     
vague1 b !y c]ta9ly _h 9 view ! supply (
 a /&>d = comm]cial transactions1 & x is
 q evid5t t 9 b>t] :at is important to !
 buy] z well z to ! sell] is n !        
attraction ! e>? may ex]cise on ! goods1
 b ! quantity t may be suppli$ = a giv5 
price4 ,besides1 ! fact t ! f\nd]s      
ab/a9$ f indicat+ any specifi$ spot 9 ! 
def9ition ( ! kilogramme1 :5 !y 7       
p]fectly acqua9t$ ) ! consid]able       
v>iations 9 ! int5sity ( gravity1 leaves
 no d\bt z to _! real desire4  ,! same  
objections h be5 made to ! def9ition ( !
 kilogramme1 at fir/ consid]$ z ! mass (
 a cubic decimetre ( wat] at #d ,c41 z  
to ! fir/ def9ition ( ! metre4 ,we mu/  
admire ! incr$ible precision atta9$ at !
 outset by ! physici/s :o made ! initial
 det]m9ations1 b we "k at ! pres5t day t
 ! kilogramme !y con/ruct$ is slightly  

too heavy 7by ab\t #a_/be1jjj74 ,v      
rem>kable rese>*es h be5 c>ri$ out )    
reg>d to ?is det]m9ation by !           
,int]national ,bureau1 & by ,,mm4 ,mac  
de ,lp9ay & ,buisson4 ,! law ( ! #aa?   
,july #aijc has def9itely regul>iz$ !   
cu/om :i* physici/s _h adopt$ "s ye>s   
be=e2 & ! /&>d ( mass1 ! legal prototype
 ( ! metrical sy/em1 is n[ !            
int]national kilogramme sanction$ by !  
,conf]5ce ( ,weights & ,measures4  ,!   
comp>ison ( a mass ) ! /&>d is effect$ )
 a precision to :i* no o!r measurem5t c 
atta94 ,metrology v\*es = ! hundr$? ( a 
milligramme 9 a kilogramme2 t is to say1
 t x e/imates ! hundr$-million? "p ( !  
magnitude /udi$4  ,we may--z 9 ! case ( 
! l5g?s--ask ourselves :e!r ?is already 
admirable precision c be surpass$2 &    
progress w\ld seem likely to be sl[1 =  
difficulties s+ul>ly increase :5 we get 
to su* small quantities4 ,b x is p]mitt$
 to hope t ! physici/s ( ! future w d   
/ill bett] ?an ^? ( to-day2 & p]haps we 
may cat* a glimpse ( ! "t :5 we %all    

beg9 to obs]ve t ! /&>d1 :i* is         
con/ruct$ f a heavy metal1 namely1      
iridium-plat9um1 itself obeys an        
app>5tly g5]al law1 & little by little  
loses "s p>ticles ( its mass by         
emanation4    #d4 ,,! ,,measure ,,( ,,"t
  ,! ?ird fundam5tal magnitude (        
me*anics is "t4 ,!re is1 s to speak1 no 
physical ph5om5on 9 :i* ! notion ( "t   
l9k$ to ! sequ5ce ( our /ates (         
consci\sness does n play a consid]able  
"p4  ,ance/ral habits & a v e>ly        
tradition h l$ u to pres]ve1 z ! unit ( 
"t1 a unit connect$ ) ! e>?'s movem5t2 &
 ! unit to-day adopt$ is1 z we "k1 !    
sexagesimal second ( mean "t4 ,?is      
magnitude1 ?us def9$ by ! conditions ( a
 natural motion :i* may itself be       
modifi$1 does n seem to (f] all !       
gu>antees desirable f ! po9t ( view (   
inv>iability4 ,x is c]ta9 t all !       
friction ex]cis$ on ! e>?--by ! tides1 =
 in/ance--mu/ sl[ly l5g!n ! duration ( !
 day1 & mu/ influ5ce ! movem5t ( ! e>?  
r\nd ! sun4 ,su* influ5ce is c]ta9ly v  

slight1 b x nev]!less gives an          
un=tunately arbitr>y "* to ! unit       
adopt$4  ,we might h tak5 z ! /&>d ( "t 
! duration ( ano!r natural ph5om5on1 :i*
 appe>s to be always reproduc$ "u       
id5tical conditions2 ! duration1 =      
in/ance1 ( a giv5 lum9\s vibration4 ,b !
 exp]im5tal difficulties ( evaluation ) 
su* a unit ( ! times :i* ord9>ily h to  
be consid]$1 w\ld be s great t su* a    
re=m 9 practice _c be hop$ =4 ,x %\ld1  
moreov]1 be rem>k$ t ! duration ( a     
vibration may itself be influ5c$ by     
ext]nal circum/ances1 among :i* are !   
v>iations ( ! magnetic field 9 :i* its  
s\rce is plac$4 ,x c\ld n1 !re=e1 be    
/rictly consid]$ z indep5d5t ( ! e>?2 & 
! !oretical advantage :i* might be      
expect$ f ?is alt]ation w\ld be some:at 
illusory4  ,p]haps 9 ! future rec\rse   
may be _h to v diff]5t ph5om5a4 ,?us    
,curie po9t$ out t if ! air inside a    
glass tube has be5 r5d]$ radioactive by 
a solution ( radium1 ! tube may be seal$
 up1 & x w !n be not$ t ! radiation (   

its walls dim9i%es ) "t1 9 accordance ) 
an expon5tial law4 ,! con/ant ( "t d]iv$
 by ?is ph5om5on rema9s ! same :atev] ! 
nature & dim5sions ( ! walls ( ! tube or
 ! temp]ature may be1 & "t might ?us be 
d5n$ indep5d5tly ( all ! o!r units4  ,we
 might also1 z ,m4 ,lippmann has sugge/$
 9 an extremely +5i\s way1 decide to    
obta9 measures ( "t :i* c be consid]$ z 
absolute because !y are det]m9$ by      
p>amet]s ( ano!r nature ?an t ( !       
magnitude to be measur$4 ,su* exp]im5ts 
are made possible by ! ph5om5a (        
gravitation4 ,we c\ld employ1 = in/ance1
 ! p5dulum by adopt+1 z ! unit ( =ce1 ! 
=ce :i* r5d]s ! con/ant ( gravitation   
equal to unity4 ,! unit ( "t ?us def9$  
w\ld be indep5d5t ( ! unit ( l5g?1 &    
w\ld dep5d only on ! sub/ance :i* w\ld  
give u ! unit ( mass "u ! unit ( volume4
  ,x w\ld be equally possible to utilize
 electrical ph5om5a1 & "o might devise  
exp]im5ts p]fectly easy ( execution4    
,?us1 by *>g+ a cond5s] by means ( a    
batt]y1 & dis*>g+ x a giv5 numb] ( times

 9 a giv5 int]val ( "t1 s t ! effect ( !
 curr5t ( dis*>ge %\ld be ! same z !    
effect ( ! output ( ! batt]y ?r\gh a    
giv5 resi/ance1 we c\ld e/imate1 by !   
measurem5t ( ! electrical magnitudes1 ! 
duration ( ! int]val not$4 ,a sy/em (   
?is k9d mu/ n be look$ ^u z a simple jeu
 d'esprit1 s9ce ?is v practicable       
exp]im5t w\ld easily p]mit u to *eck1 ) 
a precision :i* c\ld be c>ri$ v f>1 !   
con/ancy ( an int]val ( "t4  ,f !       
practical po9t ( view1 *ronometry has   
made 9 ^! la/ few ye>s v s5sible        
progress4 ,! errors 9 ! movem5ts (      
*ronomet]s are correct$ 9 a mu* m       
sy/ematic way ?an =m]ly1 & c]ta9        
inv5tions h enabl$ important improvem5ts
 to be effect$ 9 ! con/ruction ( ^!     
in/rum5ts4 ,?us ! curi\s prop]ties :i*  
/eel comb9$ ) nickel--s admirably /udi$ 
by ,m4,*4,ed4 ,guillaume--exhibits 9 !  
matt] ( dilatation are n[ utiliz$ s z to
 almo/ completely annihilate ! influ5ce 
( v>iations ( temp]ature4    #e4 ,,!    
,,measure ,,( ,,temp]ature  ,f ! ?ree   

me*anical units we d]ive second>y units2
 z1 = in/ance1 ! unit ( "w or me*anical 
en]gy4 ,! k9etic !ory takes temp]ature1 
z well z heat itself1 to be a quantity (
 en]gy1 & ?us seems to connect ?is      
notion ) ! magnitudes ( me*anics4 ,b !  
legitimacy ( ?is !ory _c be admitt$1 & !
 calorific movem5t %\ld also be a       
ph5om5on s /rictly conf9$ 9 space t our 
mo/ delicate means ( inve/igation w\ld n
 enable u to p]ceive x4 ,x is bett]1 !n1
 to cont9ue to reg>d ! unit ( diff]5ce (
 temp]ature z a di/9ct unit1 to be add$ 
to ! fundam5tal units4  ,to def9e !     
measure ( a c]ta9 temp]ature1 we take1 9
 practice1 "s arbitr>y prop]ty ( a body4
 ,! only necess>y condition ( ?is       
prop]ty is1 t x %\ld con/antly v>y 9 !  
same direction :5 ! temp]ature rises1 & 
t x %\ld possess1 at any temp]ature1 a  
well-m>k$ value4 ,we measure ?is value  
by melt+ ice & by ! vap\r ( boil+ wat]  
"u normal pressure1 & ! successive      
hundr$?s ( its v>iation1 beg9n+ ) !     
melt+ ice1 def9es ! p]c5tage4           

,!rmodynamics1 h[ev]1 has made x pla9 t 
we c set up a !rmometric scale )\t rely+
 ^u any det]m9$ prop]ty ( a real body4  
,su* a scale has an absolute value      
indep5d5tly ( ! prop]ties ( matt]4 ,n[ x
 happ5s t if we make use = ! e/imation (
 temp]atures1 ( ! ph5om5a ( dilatation  
"u a con/ant pressure1 or ( ! increase (
 pressure 9 a con/ant volume ( a gase\s 
body1 we obta9 a scale v ne> ! absolute1
 :i* almo/ co9cides ) x :5 ! gas        
possesses c]ta9 qualities :i* make x    
ne>ly :at is call$ a p]fect gas4 ,?is   
mo/ lucky co9cid5ce has decid$ ! *oice (
 ! conv5tion adopt$ by physici/s4 ,!y   
def9e normal temp]ature by means ( !    
v>iations ( pressure 9 a mass ( hydrog5 
beg9n+ ) ! initial pressure ( a metre ( 
m]cury at #j ,c4  ,m4,p4 ,*appuis1 9 "s 
v precise exp]im5ts conduct$ ) mu*      
me?od1 has prov$ t at ord9>y temp]atures
 ! indications ( su* a !rmomet] are s   
close to ! degrees ( ! !oretical scale t
 x is almo/ impossible to asc]ta9 !     
value ( ! div]g5ces1 or ev5 ! direction 

t !y take4 ,! div]g5ce becomes1 h[ev]1  
manife/ :5 we "w ) extreme temp]atures4 
,x results f ! useful rese>*es ( ,m4    
,daniel ,b]!lot t we mu/ subtract #j4ah 
f ! indications ( ! hydrog5 !rmomet]    
t[>ds ! temp]ature -#bdj ,c1 & add #j4je
 to #ajjj to equate !m ) ! !rmodynamic  
scale4 ,( c\rse1 ! diff]5ce w\ld also   
become /ill m noticeable on gett+ ne>]  
to ! absolute z]o2 = z hydrog5 gets m & 
m cool$1 x gradually exhibits 9 a less] 
degree ! *>act]i/ics ( a p]fect gas4    
,to /udy ! l[] regions :i* bord] on t   
k9d ( pole ( cold t[>ds :i* are /ra9+ ! 
ef=ts ( ! _m physici/s :o h ( late ye>s 
succe$$ 9 gett+ a few degrees fur!r     
=w>d1 we may turn to a gas /ill m       
difficult to liquefy ?an hydrog54 ,?us1 
!rmomet]s h be5 made ( helium2 & f !    
temp]ature ( -#bfj ,c4 d[nw>d ! div]g5ce
 ( su* a !rmomet] f "o ( hydrog5 is v   
m>k$4  ,! measurem5t ( v high           
temp]atures is n op5 to ! same !oretical
 objections z t ( v l[ temp]atures2 b1 f
 a practical po9t ( view1 x is z        

difficult to effect ) an ord9>y gas     
!rmomet]4 ,x becomes impossible to      
gu>antee ! res]voir rema9+ suffici5tly  
imp]meable1 & all security disappe>s1   
not)/&+ ! use ( recipi5ts v sup]ior to  
^? ( =m] times1 su* z ^? lately devis$  
by ! physici/s ( ! ,rei*ansalt4 ,?is    
difficulty is obviat$ by us+ o!r me?ods1
 su* z ! employm5t ( !rmo-electric      
c\ples1 su* z ! v conv5i5t c\ple ( ,m4  
le ,*ateli]2 b ! graduation ( ^!        
in/rum5ts c only be effect$ at ! co/ ( a
 r bold extrapolation4  ,m4,d4 ,b]!lot  
has po9t$ out & exp]im5t$ ) a v int]e/+ 
process1 f\nd$ on ! measurem5t by !     
ph5om5a ( int]f]5ce ( ! refractive index
 ( a column ( air subject$ to !         
temp]ature x is desir$ to measure4 ,x   
appe>s admissible t ev5 at ! highe/     
temp]atures ! v>iation ( ! p[] (        
refraction is /rictly proportional to t 
( ! d5sity1 = ?is proportion is exactly 
v]ifi$ s long z x is possible to *eck x 
precisely4 ,we c ?us1 by a me?od :i*    
(f]s ! great advantage ( be+ indep5d5t (

 ! p[] & dim5sion ( ! envelopes         
employ$--s9ce ! l5g? ( ! column ( air   
consid]$ alone ent]s into !             
calculation--obta9 results equival5t to 
^? giv5 by ! ord9>y air !rmomet]4       
,ano!r me?od1 v old 9 pr9ciple1 has also
 lately acquir$ great importance4 ,= a  
long "t we s\ght to e/imate ! temp]ature
 ( a body by /udy+ its radiation1 b we  
did n "k any positive relation betwe5   
?is radiation & ! temp]ature1 & we _h no
 good exp]im5tal me?od ( e/imation1 b _h
 rec\rse to purely empirical =mulas & ! 
use ( app>atus ( little precision4 ,n[1 
h[ev]1 _m physici/s1 cont9u+ ! classic  
rese>*es ( ,kir*h(f1 ,boltzmann1        
,pr(essors ,wi5 & ,planck1 & tak+ _!    
/>t+-po9t f ! laws ( !rmodynamics1 h    
giv5 =mulas :i* e/abli% ! radiat+ p[] ( 
a d>k body z a function ( ! temp]ature &
 ! wave-l5g?1 or1 bett] /ill1 ( ! total 
p[] z a function ( ! temp]ature &       
wave-l5g? correspond+ to ! maximum value
 ( ! p[] ( radiation4 ,we see1 !re=e1 ! 
possibility ( appeal+ = ! measurem5t (  

temp]ature to a ph5om5on :i* is no long]
 ! v>iation ( ! ela/ic =ce ( a gas1 &   
yet is also connect$ ) ! pr9ciples (    
!rmodynamics4  ,?is is :at ,pr(essors   
,lumm] & ,pr+%eim h %[n 9 a s]ies (     
/udies :i* may c]ta9ly be reckon$ among 
! greate/ exp]im5tal rese>*es ( ! la/   
few ye>s4 ,!y h con/ruct$ a radiator    
closely resembl+ ! !oretically integral 
radiator :i* a clos$ iso!rmal vessel    
w\ld be1 & ) only a v small op5+1 :i*   
all[s u to collect f outside !          
radiations :i* are 9 equilibrium ) !    
int]ior4 ,?is vessel is =m$ ( a holl[   
c>bon cyl9d]1 heat$ by a curr5t ( high  
int5sity2 ! radiations are /udi$ by     
means ( a bolomet]1 ! disposition ( :i* 
v>ies ) ! nature ( ! exp]im5ts4  ,x is  
h>dly possible to ent] into ! details ( 
! me?od1 b ! result suffici5tly         
indicates its importance4 ,x is n[      
possible1 ?anks to _! rese>*es1 to      
e/imate a temp]ature ( #bjjj ,c4 to )9  
ab\t #e4 ,t5 ye>s ago a simil>          
approximation c\ld h>dly h be5 arriv$ at

 = a temp]ature ( #ajjj ,c4    #f4      
,,d]iv$ ,,units ,,& ,,! ,,measure ,,( ,a
 ,,quantity ,,( ,,en]gy  ,x mu/ be      
und]/ood t x is only by arbitr>y        
conv5tion t a dep5d5cy is e/abli%$      
betwe5 a d]iv$ unit & ! fundam5tal      
units4 ,! laws ( numb]s 9 physics are   
(t5 only laws ( proportion4 ,we trans=m 
!m into laws ( equation1 because we     
introduce num]ical coeffici5ts & *oose !
 units on :i* !y dep5d s z to simplify z
 mu* z possible ! =mulas mo/ 9 use4 ,a  
p>ticul> spe$1 = in/ance1 is 9 reality  
no?+ else b a spe$1 & x is only by !    
peculi> *oice ( unit t we c say t x is !
 space cov]$ dur+ ! unit ( "t4 ,9 ! same
 way1 a quantity ( electricity is a     
quantity ( electricity2 & !re is no?+ to
 prove t1 9 its ess5ce1 x is really     
r$ucible to a function ( mass1 ( l5g?1 &
 ( "t4  ,p]sons are /ill to be met ) :o 
seem to h "s illusions on ?is po9t1 & :o
 see 9 ! doctr9e ( ! dim5sions ( ! units
 a doctr9e ( g5]al physics1 :ile x is1  
to say tru?1 only a doctr9e ( metrology4

 ,! k ( dim5sions is valuable1 s9ce x   
all[s u1 = in/ance1 to easily v]ify !   
homog5eity ( a =mula1 b x c 9 no way    
give u any in=mation on ! actual nature 
( ! quantity measur$4  ,magnitudes to   
:i* we attribute l dim5sions may be     
qualitatively irr$ucible "o to ! o!r4   
,?us ! diff]5t =ms ( en]gy are measur$  
by ! same unit1 & yet x seems t "s ( !m1
 su* z k9etic en]gy1 really dep5d on "t2
 :ile = o!rs1 su* z pot5tial en]gy1 !   
dep5d5cy e/abli%$ by ! sy/em (          
measurem5t seems some:at fictiti\s4  ,! 
num]ical value ( a quantity ( en]gy (   
any nature %\ld1 9 ! sy/em ,c4,g4,s41 be
 express$ 9 t]ms ( ! unit call$ ! erg2  
b1 z a matt] ( fact1 :5 we wi% to comp>e
 & measure diff]5t quantities ( en]gy ( 
v>y+ =ms1 su* z electrical1 *emical1 &  
o!r quantities1 etc41 we ne>ly always   
employ a me?od by :i* all ^! en]gies are
 f9ally trans=m$ & us$ to heat ! wat] ( 
a calorimet]4 ,x is !re=e v important to
 /udy well ! calorific ph5om5on *os5 z !
 unit ( heat1 & to det]m9e ) precision  

its me*anical equival5t1 t is to say1 ! 
numb] ( ergs necess>y to produce ?is    
unit4 ,?is is a numb] :i*1 on ! pr9ciple
 ( equival5ce1 dep5ds nei!r on ! me?od  
employ$1 nor ! "t1 nor any o!r ext]nal  
circum/ance4  ,z ! result ( ! brilliant 
rese>*es ( ,r[l& & ( ,mr ,griffi?s on ! 
v>iations ( ! specific heat ( wat]1     
physici/s h decid$ to take z calorific  
/&>d ! quantity ( heat necess>y to raise
 a gramme ( wat] f #ae to #af ,c41 !    
temp]ature be+ measur$ by ! scale ( !   
hydrog5 !rmomet] ( ! ,int]national      
,bureau4  ,on ! o!r h&1 new det]m9ations
 ( ! me*anical equival5t1 among :i* x is
 "r to m5tion t ( ,mr4 ,ames1 & a full  
discussion z to ! be/ results1 h l$ to !
 adoption ( ! numb] #d4ahg to repres5t !
 numb] ( ergs capable ( produc+ ! unit (
 heat4  ,9 practice1 ! measurem5t ( a   
quantity ( heat is v (t5 effect$ by     
means ( ! ice calorimet]1 ! use ( :i* is
 p>ticul>ly simple & conv5i5t4 ,!re is1 
!re=e1 a v special int]e/ 9 kn[+ exactly
 ! melt+-po9t ( ice4 ,m4 ,l$uc1 :o =    

sev]al ye>s has measur$ a great numb] ( 
physical con/ants ) m9ute precautions & 
a rem>kable s5se ( precision1 concludes1
 aft] a close discussion ( ! v>i\s      
results obta9$1 t ?is heat is equal to  
#gi4a calories4 ,an error ( almo/ a     
calorie _h be5 committ$ by sev]al r5[n$ 
exp]im5t]s1 & x w be se5 t 9 c]ta9 po9ts
 ! art ( measurem5t may /ill be l>gely  
p]fect$4  ,to ! unit ( en]gy might be   
imm$iately atta*$ o!r units4 ,= in/ance1
 radiation be+ no?+ b a flux ( en]gy1 we
 c\ld1 9 ord] to e/abli% photometric    
units1 divide ! normal spectrum into b&s
 ( a giv5 wid?1 & measure ! p[] ( ea* = 
! unit ( radiat+ surface4  ,b1 not)/&+  
"s rec5t rese>*es on ?is "q1 we _c yet  
consid] ! di/ribution ( en]gy 9 !       
spectrum z p]fectly kn[n4 ,if we adopt !
 excell5t habit :i* exi/s 9 "s rese>*es 
( express+ radiat+ en]gy 9 ergs1 x is   
/ill cu/om>y to br+ ! radiations to a   
/&>d giv+1 by its con/itution alone1 !  
unit ( "o p>ticul> radiation4 ,9        
p>ticul>1 ! def9itions are /ill adh]$ to

 :i* 7 adopt$ z ! result ( ! rese>*es ( 
,m4 ,violle on ! radiation ( fus$       
plat9um at ! temp]ature (               
solidification2 & mo/ physici/s utilize 
9 ! ord9>y me?ods ( photometry ! cle>ly 
def9$ notions ( ,m4 ,blondel z to !     
lum9\s int5sity ( flux1 illum9ation     
7clairem5t71 light 7clat71 & light+     
7clairage71 ) ! correspond+ units1      
decimal c&le1 lum51 lux1 c>cel lamp1    
c&le p] squ>e c5timetre1 & lum5-h\r4#d  
,footnote #d3 ,^! are ! magnitudes &    
units adopt$ at ! ,int]national         
,congress ( ,electricians 9 #aijd4 ,= _!
 def9ition & explanation1 see ,demanet1 
,notes de ,physique ,exprim5tale        
7,l\va91 #aije71 t4 iv4 p4 #h4--;,,ed4  
#g4 ,,measure ,,( ,,c]ta9 ,,physical    
,,con/ants  ,! progress ( metrology has 
l$1 z a consequ5ce1 to correspond+      
progress 9 ne>ly all physical           
measurem5ts1 & p>ticul>ly 9 ! measure ( 
natural con/ants4 ,among ^!1 ! con/ant (
 gravitation occupies a position q ap>t 
f ! importance & simplicity ( ! physical

 law :i* def9es x1 z well z by its      
g5]ality4 ,two mat]ial p>ticles are     
mutually attract$ to ea* o!r by a =ce   
directly proportional to ! product ( _! 
mass1 & inv]sely proportional to ! squ>e
 ( ! di/ance betwe5 !m4 ,! coeffici5t ( 
proportion is det]m9$ :5 once ! units   
are *os51 & z soon z we "k ! num]ical   
values ( ?is =ce1 ( ! two masses1 & ( _!
 di/ance4 ,b :5 we wi% to make          
laboratory exp]im5ts s]i\s difficulties 
appe>1 ow+ to ! weakness ( ! attraction 
betwe5 masses ( ord9>y dim5sions4       
,microscopic =ces1 s to speak1 h to be  
obs]v$1 & !re=e all ! causes ( errors h 
to be avoid$ :i* w\ld be unimportant 9  
mo/ o!r physical rese>*es4 ,x is kn[n t 
,cav5di% 0 ! fir/ :o succe$$ by means ( 
! torsion balance 9 effect+ fairly      
precise measurem5ts4 ,?is me?od has be5 
aga9 tak5 9 h& by diff]5t exp]im5t]s1 & 
! mo/ rec5t results are due to ,mr      
,v]non ,boys4 ,?is le>n$ physici/ is    
also ! au?or ( a mo/ useful practical   
inv5tion1 & has succe$$ 9 mak+ qu>tz    

?reads z f9e z c be desir$ & extremely  
uni=m4 ,he f9ds t ^! ?reads possess     
valuable prop]ties1 su* z p]fect        
ela/icity & great t5acity4 ,he has be5  
able1 ) ?reads n m ?an #a_/ejj ( a      
millimetre 9 diamet]1 to measure )      
precision c\ples ( an ord] =m]ly        
consid]$ outside ! range ( exp]im5t1 &  
to r$uce ! dim5sions ( ! app>atus (     
,cav5di% 9 ! proportion ( #aej to #a4 ,!
 great advantage f\nd 9 ! use ( ^! small
 in/rum5ts is ! bett] avoidance ( !     
p]turbations aris+ f draughts ( air1 & (
 ! v s]i\s influ5ce ( ! slighte/        
inequality 9 temp]ature4  ,o!r me?ods h 
be5 employ$ 9 late ye>s by o!r          
exp]im5t]s1 su* z ! me?od ( ,b>on ,etvs1
 f\nd$ on ! use ( a torsion lev]1 !     
me?od ( ! ord9>y balance1 us$ especially
 by ,pr(essors ,ri*>z & ,krig>-,m5zel & 
also by ,pr(essor ,poynt+1 & ! me?od (  
,m4 ,wils+1 :o uses a balance ) a       
v]tical beam4 ,! results fairly agree1 &
 lead to attribut+ to ! e>? a d5sity    
equal to #e4ebg4  ,! mo/ famili>        

manife/ation ( gravitation is gravity4  
,! action ( ! e>? on ! unit ( mass plac$
 9 "o po9t1 & ! int5sity ( gravity1 is  
measur$1 z we "k1 by ! aid ( a p5dulum4 
,! me?ods ( measurem5t1 :e!r by absolute
 or by relative det]m9ations1 s greatly 
improv$ by ,borda & ,bessel1 h be5 /ill 
fur!r improv$ by v>i\s geodesians1 among
 :om %\ld be m5tion$ ,m4 von ,/]neek &  
,g5]al ,def=ges4 ,num]\s obs]vations h  
be5 made 9 all p>ts ( ! _w by v>i\s     
explor]s1 & h l$ to a fairly complete k 
( ! di/ribution ( gravity ov] ! surface 
( ! globe4 ,?us we h succe$$ 9 mak+     
evid5t anomalies :i* w\ld n easily f9d  
_! place 9 ! =mula ( ,clairaut4  ,ano!r 
con/ant1 ! det]m9ation ( :i* is ( !     
greate/ utility 9 a/ronomy ( position1 &
 ! value ( :i* ent]s into               
electromagnetic !ory1 has to-day assum$1
 ) ! new ideas on ! con/itution ( matt]1
 a /ill m consid]able importance4 ,i    
ref] to ! spe$ ( light1 :i* appe>s to u1
 z we %all see fur!r on1 ! maximum value
 ( spe$ :i* c be giv5 to a mat]ial body4

  ,aft] ! hi/orical exp]im5ts ( ,fizeau 
& ,f\cault1 tak5 up afre%1 z we "k1     
p>tly by ,cornu1 & p>tly by ,mi*elson & 
,newcomb1 x rema9$ /ill possible to     
increase ! precision ( ! measurem5ts4   
,pr(essor ,mi*elson has und]tak5 "s new 
rese>*es by a me?od :i* is a comb9ation 
( ! pr9ciple ( ! too!d :eel ( ,fizeau ) 
! revolv+ mirror ( ,f\cault4 ,! too!d   
:eel is "h replac$1 h[ev]1 by a grat+1 9
 :i* ! l9es & ! spaces betwe5 !m take ! 
place ( ! tee? & ! gaps1 ! reflect$     
light only be+ return$ :5 x /rikes on ! 
space betwe5 two l9es4 ,! illu/ri\s     
,am]ican physici/ e/imates t he c ?us   
evaluate to ne>ly five kilometres ! pa? 
trav]s$ by light 9 "o second4 ,?is      
approximation corresponds to a relative 
value ( a few hundr$-?\s&?s1 & x f>     
exce$s ^? hi!rto atta9$ by ! be/        
exp]im5t]s4 ,:5 all ! exp]im5ts are     
complet$1 !y w p]haps solve c]ta9       
que/ions /ill 9 susp5se2 = in/ance1 ! "q
 :e!r ! spe$ ( propagation dep5ds on    
int5sity4 ,if ?is turns out to be !     

case1 we %\ld be br\ght to ! important  
conclusion t ! amplitude ( !            
oscillations1 :i* is c]ta9ly v small 9  
relation to ! already t9y wave-l5g?s1 _c
 be consid]$ z unimportant 9 reg>d to ^!
 l5g?s4 ,su* w\ld seem to h be5 ! result
 ( ! curi\s exp]im5ts ( ,m4 ,mull] & (  
,m4 ,eb]t1 b ^! results h be5 rec5tly   
disput$ by ,m4 ,d\bt4  ,9 ! case ( s\nd 
vibrations1 on ! o!r h&1 x %\ld be not$ 
t exp]im5t1 consi/5tly ) ! !ory1 proves 
t ! spe$ increases ) ! amplitude1 or1 if
 y w1 ) ! int5sity4 ,m4 ,violle has     
publi%$ an important s]ies ( exp]im5ts  
on ! spe$ ( propagation ( v cond5s$     
waves1 on ! de=mations ( ^! waves1 & on 
! relations ( ! spe$ & ! pressure1 :i*  
v]ify 9 a rem>kable mann] ! results     
=e%ad[$ by ! already old calculations ( 
,riemann1 repeat$ lat] by ,hugoniot4    
,if1 on ! contr>y1 ! amplitude is       
suffici5tly small1 !re exi/s a spe$     
limit :i* is ! same 9 a l>ge pipe & 9   
free air4 ,by "s beautiful exp]im5ts1   
,,mm4 ,violle & ,vauti] h cle>ly %[n t  

any di/urbance 9 ! air melts some:at    
quickly into a s+le wave ( giv5 =m1 :i* 
is propagat$ to a di/ance1 :ile         
gradually becom+ weak] & %[+ a con/ant  
spe$ :i* diff]s little 9 dry air at #j  
,c4 f #cca4cf metres p] second4 ,9 a    
n>r[ pipe ! influ5ce ( ! walls makes    
itself felt & produces v>i\s effects1 9 
p>ticul> a k9d ( disp]sion 9 space ( !  
h>monics ( ! s\nd4 ,?is ph5om5on1       
accord+ to ,m4 ,brill\91 is p]fectly    
explicable by a !ory simil> to ! !ory ( 
grat+s4     ,,*apt] ,,iii  ,,pr9ciples  
#a4 ,,! ,,pr9ciples ,,( ,,physics       
,facts consci5ti\sly obs]v$ lead by     
induction to ! enunciation ( a c]ta9    
numb] ( laws or g5]al hypo!ses :i* are !
 pr9ciples already ref]r$ to4 ,^!       
pr9cipal hypo!ses are1 9 ! eyes ( a     
physici/1 legitimate g5]alizations1 !   
consequ5ces ( :i* we %all be able at    
once to *eck by ! exp]im5ts f :i* !y    
issue4  ,among ! pr9ciples almo/        
univ]sally adopt$ until lately figure   
prom95tly ^? ( me*anics--su* z !        

pr9ciple ( relativity1 & ! pr9ciple ( ! 
equality ( action & reaction4 ,we w n   
detail nor discuss !m "h1 b lat] on we  
%all h an opportunity ( po9t+ out h[    
rec5t !ories on ! ph5om5a ( electricity 
h %ak5 ! confid5ce ( physici/s 9 !m & h 
l$ c]ta9 s*ol>s to d\bt _! absolute     
value4  ,! pr9ciple ( ,lavoisi]1 or     
pr9ciple ( ! cons]vation ( mass1 pres5ts
 itself "u two diff]5t aspects accord+  
to :e!r mass is look$ ^u z ! coeffici5t 
( ! in]tia ( matt] or z ! factor :i*    
int]v5es 9 ! ph5om5a ( univ]sal         
attraction1 & p>ticul>ly 9 gravitation4 
,we %all see :5 we treat ( ^! !ories1 h[
 we h be5 l$ to suppose t in]tia dep5d$ 
on velocity & ev5 on direction4 ,if ?is 
conception 7 exact1 ! pr9ciple ( !      
inv>iability ( mass w\ld naturally be   
de/roy$4 ,consid]$ z a factor (         
attraction1 is mass really              
inde/ructible8  ,a few ye>s ago su* a "q
 w\ld h seem$ s+ul>ly audaci\s4 ,& yet !
 law ( ,lavoisi] is s f> f self-evid5t t
 = c5turies x escap$ ! notice (         

physici/s & *emi/s4 ,b its great app>5t 
simplicity & its high "* ( g5]ality1 :5 
enunciat$ at ! end ( ! eighte5? c5tury1 
rapidly gave x su* an au?ority t no "o 0
 able to any long] dispute x unless he  
desir$ ! reputation ( an oddity incl9$  
to p>adoxical ideas4  ,x is important1  
h[ev]1 to rem>k t1 "u fallaci\s         
metaphysical appe>ances1 we are 9       
reality us+ empty words :5 we repeat !  
aphorism1 ,no?+ c be lo/1 no?+ c be     
creat$1 & d$uce f x ! inde/ructibility (
 matt]4 ,?is inde/ructibility1 9 tru?1  
is an exp]im5tal fact1 & ! pr9ciple     
dep5ds on exp]im5t4 ,x may ev5 seem1 at 
fir/ sight1 m s+ul> ?an n t ! weight ( a
 bodily sy/em 9 a giv5 place1 or !      
quoti5t ( ?is weight by t ( ! /&>d      
mass--t is to say1 ! mass ( ^!          
bodies--rema9s inv>iable1 bo? :5 !      
temp]ature *anges & :5 *emical reag5ts  
cause ! orig9al mat]ials to disappe> &  
to be replac$ by new ones4 ,we may      
c]ta9ly consid] t 9 a *emical ph5om5on  
annihilations & creations ( matt] are   

really produc$2 b ! exp]im5tal law      
tea*es u t !re is comp5sation 9 c]ta9   
respects4  ,! discov]y ( ! radioactive  
bodies has1 9 "s sort1 r5d]$ popul> !   
speculations ( physici/s on ! ph5om5a ( 
! disaggregation ( matt]4 ,we %all h to 
seek ! exact mean+ :i* ought to be giv5 
to ! exp]im5ts on ! emanation ( ^!      
bodies1 & to discov] :e!r ^! exp]im5ts  
really imp]il ! law ( ,lavoisi]4  ,= "s 
ye>s diff]5t exp]im5t]s h also effect$  
_m v precise measurem5ts ( ! weight (   
div]s bodies bo? be=e & aft] *emical    
reactions betwe5 ^! bodies4 ,two highly 
exp]i5c$ & cauti\s physici/s1 ,pr(essors
 ,l&olt & ,heydweill]1 h n hesitat$ to  
ann\nce ! s5sational result t 9 c]ta9   
circum/ances ! weight is no long] ! same
 aft] z be=e ! reaction4 ,9 p>ticul>1 ! 
weight ( a solution ( salts ( copp] 9   
wat] is n ! exact sum ( ! jo9t weights (
 ! salt & ! wat]4 ,su* exp]im5ts are    
evid5tly v delicate2 !y h be5 disput$1 &
 !y _c be consid]$ z suffici5t =        
conviction4 ,x foll[s nev]!less t x is  

no long] =bidd5 to reg>d ! law (        
,lavoisi] z only an approximate law2    
accord+ to ,s&=d & ,ray1 ?is            
approximation w\ld be ab\t              
#a_/b1djj1jjj4 ,?is is also ! result    
rea*$ by ,pr(essor ,poynt+ 9 exp]im5ts  
reg>d+ ! possible action ( temp]ature on
 ! weight ( a body2 & if ?is be really  
s1 we may reassure ourselves1 & f ! po9t
 ( view ( practical application may     
cont9ue to look ^u matt] z              
inde/ructible4  ,! pr9ciples ( physics1 
by impos+ c]ta9 conditions on ph5om5a1  
limit aft] a fa%ion ! field ( !         
possible4 ,among ^! pr9ciples is "o :i*1
 not)/&+ its importance :5 comp>$ ) t ( 
univ]sally kn[n pr9ciples1 is less      
famili> to "s p4 ,?is is ! pr9ciple (   
symmetry1 m or less consci\s            
applications ( :i* c1 no d\bt1 be f\nd 9
 v>i\s works & ev5 9 ! conceptions (    
,cop]nican a/ronom]s1 b :i* 0 g5]aliz$ &
 cle>ly enunciat$ = ! fir/ "t by ! late 
,m4 ,curie4 ,?is illu/ri\s physici/     
po9t$ out ! advantage ( introduc+ into !

 /udy ( physical ph5om5a ! consid]ations
 on symmetry famili> to cry/allograph]s2
 = a ph5om5on to take place1 x is       
necess>y t a c]ta9 dissymmetry %\ld     
previ\sly exi/ 9 ! m$ium 9 :i* ?is      
ph5om5on occurs4 ,a body1 = in/ance1 may
 be animat$ ) a c]ta9 l9e> velocity or a
 spe$ ( rotation2 x may be compress$1 or
 twi/$2 x may be plac$ 9 an electric or 
9 a magnetic field2 x may be affect$ by 
an electric curr5t or by "o ( heat2 x   
may be trav]s$ by a ray ( light ei!r    
ord9>y or pol>iz$ rectil9eally or       
circul>ly1 etc43--9 ea* case a c]ta9    
m9imum & *>act]i/ic dissymmetry is      
necess>y at e po9t ( ! body 9 "q4  ,?is 
consid]ation enables u to =esee t c]ta9 
ph5om5a :i* might be imag9$ a priori _c 
exi/4 ,?us1 = in/ance1 x is impossible t
 an electric field1 a magnitude direct$ 
& n sup]posable on its image 9 a mirror 
p]p5dicul> to its direction1 c\ld be    
creat$ at "r angles to ! plane (        
symmetry ( ! m$ium2 :ile x w\ld be      
possible to create a magnetic field "u !

 same conditions4  ,?is consid]ation ?us
 leads u to ! discov]y ( new ph5om5a2 b 
x mu/ be und]/ood t x _c ( itself give u
 absolutely precise notions z to !      
nature ( ^! ph5om5a1 nor disclose _!    
ord] ( magnitude4    #b4 ,,! ,,pr9ciple 
,,( ,,! ,,cons]vation ,,( ,,en]gy       
,dom9at+ n physics alone1 b ne>ly e o!r 
sci5ce1 ! pr9ciple ( ! cons]vation (    
en]gy is ju/ly consid]$ z ! gr&e/       
conque/ ( contempor>y ?\ght4 ,x %[s u 9 
a p[]ful light ! mo/ div]se que/ions2 x 
introduces ord] into ! mo/ v>i$ /udies2 
x leads to a cle> & coh]5t int]pretation
 ( ph5om5a :i*1 )\t x1 appe> to h no    
connexion ) ea* o!r2 & x supplies       
precise & exact num]ical relations      
betwe5 ! magnitudes :i* ent] into ^!    
ph5om5a4  ,! bolde/ m9ds h an in/9ctive 
confid5ce 9 x1 & x is ! pr9ciple :i* has
 mo/ /\tly resi/$ t assault :i* ! d>+ ( 
a few !ori/s has lately direct$ to !    
ov]?r[ ( ! g5]al pr9ciples ( physics4   
,at e new discov]y1 ! fir/ ?\ght (      
physici/s is to f9d out h[ x accords ) !

 pr9ciple ( ! cons]vation ( en]gy4 ,!   
application ( ! pr9ciple1 moreov]1 nev] 
fails to give valuable h9ts on ! new    
ph5om5on1 & (t5 ev5 sugge/s a           
complem5t>y discov]y4 ,up till n[ x     
seems nev] to h receiv$ a *eck1 ev5 !   
extraord9>y prop]ties ( radium n s]i\sly
 contradict+ x2 also ! g5]al =m 9 :i* x 
is enunciat$ gives x su* a suppl5ess t x
 is no d\bt v difficult to ov]?r[4  ,i d
 n claim to set =? "h ! complete hi/ory 
( ?is pr9ciple1 b ,i w endeav\r to %[ ) 
:at pa9s x 0 born1 h[ x 0 kept back 9   
its e>ly days & !n ob/ruct$ 9 its       
developm5t by ! unfav\rable conditions (
 ! surr\nd+s 9 :i* x appe>$4 ,x fir/ (  
all came1 9 fact1 to oppose itself to ! 
reign+ !ories2 b1 little by little1 x   
act$ on ^! !ories1 & !y 7 modifi$ "u its
 pressure2 !n1 9 _! turn1 ^! !ories     
react$ on x & *ang$ its primitive =m4   
,x _h to be made less wide 9 ord] to fit
 into ! classic frame1 & 0 absorb$ by   
me*anics2 & if x ?us became less g5]al1 
x ga9$ 9 precision :at x lo/ 9 ext5t4   

,:5 once def9itely admitt$ & class$1 z x
 71 9 ! (ficial doma9 ( sci5ce1 x       
endeav\r$ to bur/ its bonds & return to 
a m indep5d5t & l>g] life4 ,! hi/ory (  
?is pr9ciple is simil> to t ( all       
evolutions4  ,x is well kn[n t !        
cons]vation ( en]gy 01 at fir/1 reg>d$ f
 ! po9t ( view ( ! reciprocal           
trans=mations betwe5 heat & "w1 & t !   
pr9ciple receiv$ its fir/ cle>          
enunciation 9 ! p>ticul> case ( !       
pr9ciple ( equival5ce4 ,x is1 !re=e1    
rightly consid]$ t ! s*ol>s :o 7 ! fir/ 
to d\bt ! mat]ial nature ( caloric 7 !  
precursors ( ,r4 ,may]2 _! ideas1 h[ev]1
 7 ! same z ^? ( ! celebrat$ ,g]man     
doctor1 = !y s\ght especially to        
demon/rate t heat 0 a mode ( motion4    
,)\t go+ back to e>ly & isolat$ attempts
 l ^? ( ,daniel ,b]n\lli1 :o1 9 8       
hydrodynamics1 prop\nd$ ! basis ( !     
k9etic !ory ( gases1 or ! rese>*es (    
,boyle on friction1 we may recall1 to %[
 h[ x 0 prop\nd$ 9 =m] times1 a r =gott5
 page ( ! ,mmoire sur la ,*aleur1       

publi%$ 9 #aghj by ,lavoisi] & ,laplace3
 ,o!r physici/s1 !y wrote1 aft] sett+   
out ! !ory ( caloric1 ?9k t heat is no?+
 b ! result ( ! ins5sible vibrations (  
matt]4444 ,9 ! sy/em we are n[ exam9+1  
heat is ! vis viva result+ f ! ins5sible
 movem5ts ( ! molecules ( a body2 x is !
 sum ( ! products ( ! mass ( ea*        
molecule by ! squ>e ( its velocity4444  
,we %all n decide betwe5 ! two prec$+   
hypo!ses2 sev]al ph5om5a seem to support
 ! la/ m5tion$--= in/ance1 t ( ! heat   
produc$ by ! friction ( two solid       
bodies4 ,b !re are o!rs :i* are m simply
 expla9$ by ! fir/1 & p]haps !y bo?     
op]ate at once4 ,mo/ ( ! physici/s ( t  
p]iod1 h[ev]1 did n %>e ! prud5t d\bts (
 ,lavoisi] & ,laplace4 ,!y admitt$1 )\t 
hesitation1 ! fir/ hypo!sis2 &1 f\r ye>s
 aft] ! appe>ance ( ! ,mmoire sur la    
,*aleur1 ,sigaud de ,lafond1 a pr(essor 
( physics ( great reputation1 wrote3    
,pure ,fire1 free f all /ate (          
comb9ation1 seems to be an assembly (   
p>ticles ( a simple1 homog5e\s1 &       

absolutely unalt]able matt]1 & all !    
prop]ties ( ?is elem5t indicate t ^!    
p>ticles are inf9itely small & free1 t  
!y h no s5sible cohesion1 & t !y are    
mov$ 9 e possible direction by a        
cont9ual & rapid motion :i* is ess5tial 
to !m4444 ,! extreme t5acity & !        
surpris+ mobility ( its molecules are   
manife/ly %[n by ! ease ) :i* x         
p5etrates into ! mo/ compact bodies & by
 its t5d5cy to put itself 9 equilibrium 
?r\gh\t all bodies ne> to x4  ,x mu/ be 
ackn[l$g$1 h[ev]1 t ! idea ( ,lavoisi] &
 ,laplace 0 r vague & ev5 inexact on "o 
important po9t4 ,!y admitt$ x to be     
evid5t t all v>iations ( heat1 :e!r real
 or app>5t1 und]gone by a bodily sy/em  
:5 *ang+ its /ate1 are produc$ 9 inv]se 
ord] :5 ! sy/em passes back to its      
orig9al /ate4 ,?is phrase is ! v d5ial (
 equival5ce :]e ^! *anges ( /ate are    
accompani$ by ext]nal "w4  ,laplace1    
moreov]1 himself became lat] a v conv9c$
 p>tisan ( ! hypo!sis ( ! mat]ial nature
 ( caloric1 & 8 imm5se au?ority1 s      

=tunate 9 o!r respects = ! developm5t ( 
sci5ce1 0 c]ta9ly 9 ?is case ! cause ( !
 ret>dation ( progress4  ,! names ( ,"y1
 ,rum=d1 ,davy1 are (t5 quot$ among ^?  
physici/s :o1 at ! comm5cem5t ( !       
n9ete5? c5tury1 caught sight ( ! new    
tru?s z to ! nature ( heat4 ,to ^! names
 is v prop]ly add$ t ( ,sadi ,c>not4 ,a 
note f\nd among 8 pap]s unque/ionably   
proves t1 be=e #ahcj1 ideas _h occurr$  
to him f :i* x result$ t 9 produc+ "w an
 equival5t am\nt ( heat 0 de/roy$4 ,b ! 
ye> #ahdb is p>ticul>ly memorable 9 !   
hi/ory ( sci5ce z ! ye> 9 :i* ,jules    
,rob]t ,may] succe$$1 by an entirely    
p]sonal ef=t1 9 really enunciat+ !      
pr9ciple ( ! cons]vation ( en]gy4       
,*emi/s recall ) j pride t ! ,rem>ques  
sur les =ces de la nature anime1        
contemptu\sly reject$ by all ! j\rnals (
 physics1 7 receiv$ & publi%$ 9 !       
,annal5 ( ,liebig4 ,we ought nev] to    
=get ?is example1 :i* %[s ) :at         
difficulty a new idea contr>y to !      
classic !ories ( ! p]iod succe$s 9 com+ 

to ! front2 b ext5uat+ circum/ances may 
be urg$ on behalf ( ! physici/s4  ,rob]t
 ,may] _h a r insuffici5t ma!matical    
education1 & 8 ,memoirs1 ! ,rem>ques1 z 
well z ! ult]ior publications1 ,mmoire  
sur le m\vem5t organique et la nutrition
 & ! ,matriaux p\r la dynamique du ciel1
 conta91 side by side ) v pr(\nd ideas1 
evid5t errors 9 me*anics4 ,?us x (t5    
happ5s t discov]ies put =w>d 9 a some:at
 vague mann] by adv5tur\s m9ds n        
ov]burd5$ by ! heavy baggage ( sci5tific
 erudition1 :o audaci\sly press =w>d 9  
advance ( _! "t1 fall into q            
intelligible oblivion until r$iscov]$1  
cl>ifi$1 & put into %ape by sl[] b sur] 
seek]s4 ,?is 0 ! case ) ! ideas ( ,may]4
 ,!y 7 n und]/ood at fir/ sight1 n only 
on acc\nt ( _! orig9ality1 b also       
because !y 7 c\*$ 9 incorrect language4 
,may] 01 h[ev]1 end[$ ) a s+ul> /r5g? ( 
?\ght2 he express$ 9 a r confus$ mann] a
 pr9ciple :i*1 = him1 _h a g5]ality     
great] ?an me*anics itself1 & s 8       
discov]y 0 9 advance n only ( 8 own "t b

 ( half ! c5tury4 ,he may ju/ly be      
consid]$ ! f\nd] ( mod]n en]getics4     
,fre$ f ! obscurities :i* prev5t$ its   
be+ cle>ly p]ceiv$1 8 idea /&s out      
to-day 9 all its impos+ simplicity4 ,yet
 x mu/ be ackn[l$g$ t if x 0 some:at    
d5aturalis$ by ^? :o endeav\r$ to adapt 
x to ! !ories ( me*anics1 & if x at fir/
 lo/ its sublime /amp ( g5]ality1 x ?us 
became firmly fix$ & consolidat$ on a m 
/able basis4  ,! ef=ts ( ,helmholtz1    
,clausius1 & ,"l ,kelv9 to introduce !  
pr9ciple ( ! cons]vation ( en]gy into   
me*anics1 7 f> f useless4 ,^! illu/ri\s 
physici/s succe$$ 9 giv+ a m precise =m 
to its num]\s applications2 & _!        
attempts ?us contribut$1 by reaction1 to
 give a fre% impulse to me*anics1 &     
all[$ x to be l9k$ to a m g5]al ord] (  
facts4 ,if en]getics has n be5 able to  
be includ$ 9 me*anics1 x seems inde$ t !
 attempt to include me*anics 9 en]getics
 0 n 9 va94  ,9 ! middle ( ! la/ c5tury1
 ! explanation ( all natural ph5om5a    
seem$ m & m ref]able to ! case ( c5tral 

=ces4 ,ev]y:]e x 0 ?\ght t reciprocal   
actions betwe5 mat]ial po9ts c\ld be    
p]ceiv$1 ^! po9ts be+ attract$ or       
repell$ by ea* o!r ) an int5sity dep5d+ 
only on _! di/ance or _! mass4 ,if1 to a
 sy/em ?us compos$1 ! laws ( ! classical
 me*anics are appli$1 x is %[n t half ! 
sum ( ! product ( ! masses by ! squ>e ( 
! velocities1 to :i* is add$ ! "w :i*   
might be accompli%$ by ! =ces to :i* !  
sy/em w\ld be subject if x return$ f its
 actual to its initial position1 is a   
sum con/ant 9 quantity4  ,?is sum1 :i*  
is ! me*anical en]gy ( ! sy/em1 is !re=e
 an inv>iable quantity 9 all ! /ates to 
:i* x may be br\ght by ! int]action (   
its v>i\s p>ts1 & ! ^w en]gy well       
expresses a capital prop]ty ( ?is       
quantity4 ,= if two sy/ems are connect$ 
9 su* a way t any *ange produc$ 9 ! "o  
necess>ily br+s ab\t a *ange 9 ! o!r1   
!re c be no v>iation 9 ! *>act]i/ic     
quantity ( ! second except s f> z !     
*>act]i/ic quantity ( ! fir/ itself     
v>ies--on condition1 ( c\rse1 t !       

connexions are made 9 su* a mann] z to  
introduce no new =ce4 ,x w ?us be se5 t 
?is quantity well expresses ! capacity  
possess$ by a sy/em = modify+ ! /ate ( a
 neighb\r+ sy/em to :i* we may suppose x
 connect$4  ,n[ ?is !orem ( pure        
me*anics 0 f\nd want+ e "t friction took
 place--t is to say1 9 all really       
obs]vable cases4 ,! m p]ceptible !      
friction1 ! m consid]able ! diff]5ce2 b1
 9 addition1 a new ph5om5on always      
appe>$ & heat 0 produc$4 ,by exp]im5ts  
:i* are n[ classic1 x became e/abli%$ t 
! quantity ( heat ?us creat$ indep5d5tly
 ( ! nature ( ! bodies is always        
7provid$ no o!r ph5om5a int]v5e7        
proportional to ! en]gy :i* has         
disappe>$4 ,reciprocally1 also1 heat may
 disappe>1 & we always f9d a con/ant    
relation betwe5 ! quantities ( heat & "w
 :i* mutually replace ea* o!r4  ,x is q 
cle> t su* exp]im5ts d n prove t heat is
 "w4 ,we might j z well say t "w is     
heat4 ,x is mak+ a gratuit\s hypo!sis to
 admit ?is r$uction ( heat to me*anism2 

b ?is hypo!sis 0 s s$uctive1 & s mu* 9  
con=mity ) ! desire ( ne>ly all         
physici/s to arrive at "s sort ( unity 9
 nature1 t !y made x ) eag]ness & became
 unres]v$ly conv9c$ t heat 0 an active  
int]nal =ce4  ,_! error 0 n 9 admitt+   
?is hypo!sis2 x 0 a legitimate "o s9ce x
 has prov$ v fruitful4 ,b "s ( !m       
committ$ ! fault ( =gett+ t x 0 an      
hypo!sis1 & consid]$ x a demon/rat$     
tru?4 ,moreov]1 !y 7 ?us br\ght to see 9
 ph5om5a no?+ b ^! two p>ticul> =ms (   
en]gy :i* 9 _! m9ds 7 easily id5tifi$ ) 
ea* o!r4  ,f ! outset1 h[ev]1 x became  
manife/ t ! pr9ciple is applicable to   
cases :]e heat plays only a p>asitical  
"p4 ,!re 7 ?us discov]$1 by translat+ ! 
pr9ciple ( equival5ce1 num]ical         
relations betwe5 ! magnitudes (         
electricity1 = in/ance1 & ! magnitudes (
 me*anics4 ,heat 0 a sort ( v>iable     
int]m$i>y conv5i5t = calculation1 b     
introduc$ 9 a r\ndab\t way & de/9$ to   
disappe> 9 ! f9al result4  ,v]det1 :o1 9
 lectures :i* h rightly rema9$          

celebrat$1 def9$ ) rem>kable cle>ness ! 
new !ories1 said1 9 #ahfb3 ,electrical  
ph5om5a are always accompani$ by        
calorific manife/ations1 ( :i* ! /udy   
belongs to ! me*anical !ory ( heat4 ,?is
 /udy1 moreov]1 w n only h ! effect (   
mak+ kn[n to u int]e/+ facts 9          
electricity1 b w ?r[ "s light on !      
ph5om5a ( electricity !mselves4  ,!     
em95t pr(essor 0 ?us express+ ! g5]al   
op9ion ( 8 contempor>ies1 b he c]ta9ly  
seem$ to h felt 9 advance t ! new !ory 0
 ab\t to p5etrate m deeply into ! inmo/ 
nature ( ?+s4 ,?ree ye>s previ\sly1     
,rank9e also _h put =? "s v rem>kable   
ideas ! full mean+ ( :i* 0 n at fir/    
well und]/ood4 ,he x 0 :o compreh5d$ !  
utility ( employ+ a m inclusive t]m1 &  
inv5t$ ! phrase en]getics4 ,he also     
endeav\r$ to create a new doctr9e ( :i* 
rational me*anics %\ld be only a        
p>ticul> case2 & he %[$ t x 0 possible  
to ab&on ! ideas ( atoms & c5tral =ces1 
& to con/ruct a m g5]al sy/em by        
sub/itut+ = ! ord9>y consid]ation ( =ces

 t ( ! en]gy :i* exi/s 9 all bodies1    
p>tly 9 an actual1 p>tly 9 a pot5tial   
/ate4  ,by giv+ m precision to !        
conceptions ( ,rank9e1 ! physici/s ( !  
end ( ! n9ete5? c5tury 7 br\ght to      
consid] t 9 all physical ph5om5a !re    
occur app>itions & disappe>ances :i* are
 balanc$ by v>i\s en]gies4 ,x is        
natural1 h[ev]1 to suppose t ^!         
equival5t app>itions & disappe>ances    
correspond to trans=mations & n to      
simultane\s creations & de/ructions4 ,we
 ?us repres5t en]gy to ourselves z tak+ 
diff]5t =ms--me*anical1 electrical1     
calorific1 & *emical-- capable ( *ang+  
"o into ! o!r1 b 9 su* a way t !        
quantitative value always rema9s ! same4
 ,9 l mann] a bank draft may be         
repres5t$ by notes1 gold1 silv]1 or     
bullion4 ,! e>lie/ kn[n =m ( en]gy1 i4e4
 "w1 w s]ve z ! /&>d z gold s]ves z !   
monet>y /&>d1 & en]gy 9 all its =ms w be
 e/imat$ by ! correspond+ "w4 ,9 ea*    
p>ticul> case we c /rictly def9e &      
measure1 by ! correct application ( !   

pr9ciple ( ! cons]vation ( en]gy1 !     
quantity ( en]gy evolv$ "u a giv5 =m4   
,we c ?us arrange a ma*9e compris+ a    
body capable ( evolv+ ?is en]gy2 !n we c
 =ce all ! organs ( ?is ma*9e to        
complete an entirely clos$ cycle1 ) !   
exception ( ! body itself1 :i*1 h[ev]1  
has to return to su* a /ate t all !     
v>iables f :i* ?is /ate dep5ds resume _!
 initial values except ! p>ticul>       
v>iable to :i* ! evolution ( ! en]gy "u 
consid]ation is l9k$4 ,! diff]5ce betwe5
 ! "w ?us accompli%$ & t :i* w\ld h be5 
obta9$ if ?is v>iable also _h return$ to
 its orig9al value1 is ! measure ( !    
en]gy evolv$4  ,9 ! same way t1 9 ! m9ds
 ( me*anicians1 all =ces ( :atev] orig91
 :i* are capable ( comp\nd+ ) ea* o!r & 
( balanc+ ea* o!r1 belong to ! same     
category ( be+s1 s = _m physici/s en]gy 
is a sort ( entity :i* we f9d "u v>i\s  
aspects4 ,!re ?us exi/s = !m a _w1 :i*  
comes 9 "s way to sup]pose itself ^u !  
_w ( matt]--t is to say1 ! _w ( en]gy1  
dom9at$ 9 its turn by a fundam5tal law  

simil> to t ( ,lavoisi]4#e ,?is         
conception1 z we h already se51 passes !
 limit ( exp]i5ce2 b o!rs g fur!r /ill4 
,absorb$ 9 ! contemplation ( ?is new _w1
 !y succe$ 9 p]suad+ !mselves t ! old _w
 ( matt] has no real exi/5ce & t en]gy  
is suffici5t by itself to give u a      
complete compreh5sion ( ! ,univ]se & (  
all ! ph5om5a produc$ 9 x4 ,!y po9t out 
t all our s5sations correspond to *anges
 ( en]gy1 & t ev]y?+ app>5t to our s5ses
 is1 9 tru?1 en]gy4 ,! fam\s exp]im5t ( 
! bl[s ) a /ick by :i* x 0 demon/rat$ to
 a sceptical philosoph] t an out] _w    
exi/$1 only proves1 9 reality1 ! exi/5ce
 ( en]gy1 & n t ( matt]4 ,! /ick 9      
itself is in(f5sive1 z ,pr(essor ,o/wald
 rem>ks1 & x is its vis viva1 its k9etic
 en]gy1 :i* is pa9ful to u2 :ile if we  
possess$ a spe$ equal to its own1 mov+ 9
 ! same direction1 x w\ld no long] exi/ 
s f> z our s5se ( t\* is conc]n$4       
,footnote #e3 ,no?+ is creat$2 no?+ is  
lo/--,,ed4  ,on ?is hypo!sis1 matt] w\ld
 only be ! capacity = k9etic en]gy1 its 

pret5d$ imp5etrability en]gy ( volume1 &
 its weight en]gy ( position 9 !        
p>ticul> =m :i* pres5ts itself 9        
univ]sal gravitation2 nay1 space itself 
w\ld only be kn[n to u by ! exp5diture (
 en]gy necess>y to p5etrate x4 ,?us 9   
all physical ph5om5a we %\ld only h to  
reg>d ! quantities ( en]gy br\ght into  
play1 & all ! equations :i* l9k !       
ph5om5a to "o ano!r w\ld h no mean+ b :5
 !y apply to ex*anges ( en]gy4 ,= en]gy 
alone c be common to all ph5om5a4  ,?is 
extreme mann] ( reg>d+ ?+s is s$uctive  
by its orig9ality1 b appe>s some:at     
insuffici5t if1 aft] enunciat+          
g5]alities1 we look m closely into ! "q4
 ,f ! philosophical po9t ( view x may1  
moreov]1 seem difficult n to conclude1 f
 ! qualities :i* reveal1 if y w1 ! v>i$ 
=ms ( en]gy1 t !re exi/s a sub/ance     
possess+ ^! qualities4 ,?is en]gy1 :i*  
resides 9 "o region1 & :i* transports   
itself f "o spot to ano!r1 =cibly br+s  
to m9d1 :atev] view we may take ( x1 !  
idea ( matt]4  ,helmholtz endeav\r$ to  

con/ruct a me*anics bas$ on ! idea (    
en]gy & its cons]vation1 b he _h to     
invoke a second law1 ! pr9ciple ( lea/  
action4 ,if he ?us succe$$ 9 disp5s+ ) !
 hypo!sis ( atoms1 & 9 %[+ t ! new      
me*anics gave u to und]/& !             
impossibility ( c]ta9 movem5ts :i*1     
accord+ to ! old1 ought to h be5 b nev] 
7 exp]im5tally produc$1 he 0 only able  
to d s because ! pr9ciple ( lea/ action 
necess>y = 8 !ory became evid5t 9 ! case
 ( ^? irrev]sible ph5om5a :i* alone     
really exi/ 9 ,nature4 ,! en]geti/s h   
?us n succe$$ 9 =m+ a ?or\ghly s\nd     
sy/em1 b _! ef=ts h at all ev5ts be5    
p>tly successful4 ,mo/ physici/s are (  
_! op9ion1 t k9etic en]gy is only a     
p>ticul> v>iety ( en]gy to :i* we h no  
"r to wi% to connect all its o!r =ms4   
,if ^! =ms %[$ !mselves to be innum]able
 ?r\gh\t ! ,univ]se1 ! pr9ciple ( !     
cons]vation ( en]gy w\ld1 9 fact1 lose a
 great "p ( its importance4 ,e "t t a   
c]ta9 quantity ( en]gy seem$ to appe> or
 disappe>1 x w\ld always be p]missible  

to suppose t an equival5t quantity _h   
appe>$ or disappe>$ some:]e else "u a   
new =m2 & ?us ! pr9ciple w\ld 9 a way   
vani%4 ,b ! kn[n =ms ( en]gy are fairly 
re/rict$ 9 numb]1 & ! necessity (       
recognis+ new ones seldom makes itself  
felt4 ,we %all see1 h[ev]1 t to expla91 
= in/ance1 ! p>adoxical prop]ties (     
radium & to re-e/abli% concord betwe5 ^!
 prop]ties & ! pr9ciple ( ! cons]vation 
( en]gy1 c]ta9 physici/s h rec\rse to ! 
hypo!sis t radium borr[s an unkn[n en]gy
 f ! m$ium 9 :i* x is plung$4 ,?is      
hypo!sis1 h[ev]1 is 9 no way necess>y2 &
 9 a few o!r r>e cases 9 :i* simil>     
hypo!ses h _h to be set up1 exp]im5t has
 always 9 ! long run enabl$ u to discov]
 "s ph5om5on :i* _h escap$ ! fir/       
obs]v]s & :i* corresponds exactly to !  
v>iation ( en]gy fir/ made evid5t4  ,"o 
difficulty1 h[ev]1 arises f ! fact t !  
pr9ciple ought only to be appli$ to an  
isolat$ sy/em4 ,:e!r we imag9e actions  
at a di/ance or believe 9 int]m$iate    
m$ia1 we mu/ always recognise t !re exi/

 no bodies 9 ! _w incapable ( act+ on   
ea* o!r1 & we c nev] affirm t "s        
modification 9 ! en]gy ( a giv5 place   
may n h its e*o 9 "s unkn[n spot af> (f4
 ,?is difficulty may sometimes r5d] !   
value ( ! pr9ciple r illusory4          
,simil>ly1 x behoves u n to receive )\t 
a c]ta9 di/ru/ ! ext5sion by c]ta9      
philosoph]s to ! :ole ,univ]se1 ( a     
prop]ty demon/rat$ = ^? re/rict$ sy/ems 
:i* obs]vation c alone rea*4 ,we "k no?+
 ( ! ,univ]se z a :ole1 & e g5]alization
 ( ?is k9d outruns 9 a s+ul> fa%ion !   
limit ( exp]im5t4  ,ev5 r$uc$ to ! mo/  
mode/ proportions1 ! pr9ciple ( !       
cons]vation ( en]gy reta9s1 nev]!less1 a
 p>am\nt importance2 & x /ill pres]ves1 
if y w1 a high philosophical value4     
,m4,j4 ,p]r9 ju/ly po9ts out t x gives u
 a =m "u :i* we are exp]im5tally able to
 grasp causality1 & t x tea*es u t a    
result has to be pur*as$ at ! co/ ( a   
det]m9$ ef=t4  ,we c1 9 fact1 ) ,m4     
,p]r9 & ,m4 ,langev91 repres5t ?is 9 a  
way :i* puts ?is *>act]i/ic 9 evid5ce by

 enunciat+ x z foll[s3 ,if at ! co/ ( a 
*ange ,c we c obta9 a *ange ,k1 !re w   
nev] be acquir$ at ! same co/1 :atev] ! 
me*anism employ$1 fir/ ! *ange ,k & 9   
addition "s o!r *ange1 unless ?is latt] 
be "o t is o!rwise kn[n to co/ no?+ to  
produce or to de/roy4 ,if1 = in/ance1 ! 
fall ( a weight c be accompani$1 )\t    
any?+ else be+ produc$1 by ano!r        
trans=mation--! melt+ ( a c]ta9 mass (  
ice1 = example--x w be impossible1 no   
matt] h[ y set ab\t x or :atev] !       
me*anism us$1 to associate ?is same     
trans=mation ) ! melt+ ( ano!r weight ( 
ice4  ,we c ?us1 9 ! trans=mation 9 "q1 
obta9 an appropriate numb] :i* w sum up 
t :i* may be expect$ f ! ext]nal effect1
 & c give1 s to speak1 ! price at :i*   
?is trans=mation is b\ght1 measure its  
inv>iable value by a common measure 7=  
in/ance1 ! melt+ ( ! ice71 &1 )\t any   
ambiguity1 def9e ! en]gy lo/ dur+ !     
trans=mation z proportional to ! mass ( 
ice :i* c be associat$ ) x4 ,?is measure
 is1 moreov]1 indep5d5t ( ! p>ticul>    

ph5om5on tak5 z ! common measure4    #c4
 ,,! ,,pr9ciple ,,( ,,c>not ,,&         
,,clausius  ,! pr9ciple ( ,c>not1 ( a   
nature analog\s to ! pr9ciple ( !       
cons]vation ( en]gy1 has also a simil>  
orig94 ,x 0 fir/ enunciat$1 l ! la/     
nam$1 al?\gh prior to x 9 "t1 9         
consequ5ce ( consid]ations :i* deal only
 ) heat & me*anical "w4 ,l x1 too1 x has
 evolv$1 gr[n1 & invad$ ! entire doma9 (
 physics4 ,x may be int]e/+ to exam9e   
rapidly ! v>i\s phases ( ?is evolution4 
,! orig9 ( ! pr9ciple ( ,c>not is cle>ly
 det]m9$1 & x is v r>e to be able to g  
back ?us c]ta9ly to ! s\rce ( a         
discov]y4 ,sadi ,c>not _h1 tru? to say1 
no precursor4 ,9 8 "t heat eng9es 7 n   
yet v common1 & no "o _h reflect$ mu* on
 _! !ory4 ,he 0 d\btless ! fir/ to      
prop\nd to himself c]ta9 que/ions1 &    
c]ta9ly ! fir/ to solve !m4  ,x is kn[n 
h[1 9 #ahbd1 9 8 ,rflexions sur la      
puissance motrice du feu1 he endeav\r$  
to prove t ! motive p[] ( heat is       
indep5d5t ( ! ag5ts br\ght into play =  

its realization1 & t its quantity is    
fix$ solely by ! temp]ature ( ! bodies  
betwe5 :i*1 9 ! la/ resort1 ! transport 
( caloric is effect$--at lea/ 9 all     
eng9es 9 :i* ! me?od ( develop+ ! motive
 p[] atta9s ! p]fection ( :i* x is      
capable2 & ?is is1 almo/ textually1 "o (
 ! enunciations ( ! pr9ciple at ! pres5t
 day4 ,c>not p]ceiv$ v cle>ly ! great   
fact t1 to produce "w by heat1 x is     
necess>y to h at "o's disposal a fall ( 
temp]ature4 ,on ?is po9t he expresses   
himself ) p]fect cle>ness3 ,! motive p[]
 ( a fall ( wat] dep5ds on its height & 
on ! quantity ( liquid2 ! motive p[] (  
heat dep5ds also on ! quantity ( caloric
 employ$1 & on :at might be call$--9    
fact1 :at we %all call--! height ( fall1
 t is to say1 ! diff]5ce 9 temp]ature ( 
! bodies betwe5 :i* ! ex*ange ( caloric 
takes place4  ,/>t+ ) ?is idea1 he      
endeav\rs to demon/rate1 by associat+   
two eng9es capable ( work+ 9 a rev]sible
 cycle1 t ! pr9ciple is f\nd$ on !      
impossibility ( p]petual motion4  ,8    

memoir1 n[ celebrat$1 did n produce any 
great s5sation1 & x _h almo/ fall5 into 
deep oblivion1 :i*1 9 consequ5ce ( !    
discov]y ( ! pr9ciple ( equival5ce1     
might h seem$ p]fectly ju/ifi$4 ,writt51
 9 fact1 on ! hypo!sis ( !              
inde/ructibility ( caloric1 x 0 to be   
expect$ t ?is memoir %\ld be condemn$ 9 
! "n ( ! new doctr9e1 t is1 ( ! pr9ciple
 rec5tly br\ght to light4  ,x 0 really  
mak+ a new discov]y to e/abli% t        
,c>not's fundam5tal idea surviv$ !      
de/ruction ( ! hypo!sis on ! nature (   
heat1 on :i* he seem$ to rely4 ,z he no 
d\bt himself p]ceiv$1 8 idea 0 q        
indep5d5t ( ?is hypo!sis1 s9ce1 z we h  
se51 he 0 l$ to surmise t heat c\ld     
disappe>2 b 8 demon/rations ne$$ to be  
reca/ &1 9 "s po9ts1 modifi$4  ,x is to 
,clausius t 0 res]v$ ! cr$it ( r$iscov]+
 ! pr9ciple1 & ( enunciat+ x 9 language 
con=mable to ! new doctr9es1 :ile giv+ x
 a mu* great] g5]ality4 ,! po/ulate     
arriv$ at by exp]im5tal induction1 & :i*
 mu/ be admitt$ )\t demon/ration1 is1   

accord+ to ,clausius1 t 9 a s]ies (     
trans=mations 9 :i* ! f9al is id5tical )
 ! initial /age1 x is impossible = heat 
to pass f a cold] to a w>m] body unless 
"s o!r accessory ph5om5on occurs at !   
same "t4  ,/ill m correctly1 p]haps1 an 
enunciation c be giv5 ( ! po/ulate :i*1 
9 ! ma91 is analog\s1 by say+3 ,a heat  
motor1 :i* aft] a s]ies ( trans=mations 
returns to its initial /ate1 c only     
furni% "w if !re exi/ at lea/ two s\rces
 ( heat1 & if a c]ta9 quantity ( heat is
 giv5 to "o ( ! s\rces1 :i* c nev] be ! 
hott] ( ! two4 ,by ! expression s\rce ( 
heat1 we mean a body ext]ior to ! sy/em 
& capable ( furni%+ or )draw+ heat f x4 
,/>t+ ) ?is pr9ciple1 we arrive1 z does 
,clausius1 at ! demon/ration t ! output 
( a rev]sible ma*9e work+ betwe5 two    
giv5 temp]atures is great] ?an t ( any  
non-rev]sible eng9e1 & t x is ! same =  
all rev]sible ma*9es work+ betwe5 ^! two
 temp]atures4  ,?is is ! v proposition (
 ,c>not2 b ! proposition ?us /at$1 :ile 
v useful = ! !ory ( eng9es1 does n yet  

pres5t any v g5]al int]e/4 ,clausius1   
h[ev]1 drew f x mu* m important         
consequ5ces4 ,fir/1 he %[$ t ! pr9ciple 
conduces to ! def9ition ( an absolute   
scale ( temp]ature2 & !n he 0 br\ght    
face to face ) a new notion :i* all[s a 
/rong light to be ?r[n on ! que/ions (  
physical equilibrium4 ,i ref] to        
entropy4  ,x is /ill r difficult to /rip
 entirely ?is v important notion ( all  
analytical adornm5t4 ,_m physici/s      
hesitate to utilize x1 & ev5 look ^u x )
 "s di/ru/1 because !y see 9 x a purely 
ma!matical function )\t any def9ite     
physical mean+4 ,p]haps !y are "h unduly
 sev]e1 s9ce !y (t5 admit too easily !  
objective exi/5ce ( quantities :i* !y _c
 def9e4 ,?us1 = in/ance1 x is usual     
almo/ e day to speak ( ! heat possess$  
by a body4 ,yet no body 9 reality       
possesses a def9ite quantity ( heat ev5 
relatively to any initial /ate2 s9ce    
/>t+ f ?is po9t ( dep>ture1 ! quantities
 ( heat x may h ga9$ or lo/ v>y ) ! road
 tak5 & ev5 ) ! means employ$ to foll[  

x4 ,^! expressions ( heat ga9$ or lo/   
are1 moreov]1 !mselves evid5tly         
incorrect1 = heat c no long] be consid]$
 z a sort ( fluid pass+ f "o body to    
ano!r4  ,! real reason :i* makes entropy
 some:at my/]i\s is t ?is magnitude does
 n fall directly "u ! k5 ( any ( our    
s5ses2 b x possesses ! true *>act]i/ic (
 a concrete physical magnitude1 s9ce x  
is1 9 pr9ciple at lea/1 measurable4     
,v>i\s au?ors ( !rmodynamical rese>*es1 
among/ :om ,m4 ,m\ret %\ld be p>ticul>ly
 m5tion$1 h endeav\r$ to place ?is      
*>act]i/ic 9 evid5ce4  ,consid] an      
iso!rmal trans=mation4 ,in/ead ( leav+ !
 heat ab&on$ by ! body subject$ to !    
trans=mation--wat] cond5s+ 9 a /ate (   
saturat$ vap\r1 = in/ance--to pass      
directly into an ice calorimet]1 we c   
transmit ?is heat to ! calorimet] by !  
int]m$i>y ( a rev]sible ,c>not eng9e4 ,!
 eng9e hav+ absorb$ ?is quantity ( heat1
 w only give back to ! ice a less]      
quantity ( heat2 & ! weight ( ! melt$   
ice1 inf]ior to t :i* might h be5       

directly giv5 back1 w s]ve z a measure (
 ! iso!rmal trans=mation ?us effect$4 ,x
 c be easily %[n t ?is measure is       
indep5d5t ( ! app>atus us$4 ,x          
consequ5tly becomes a num]ical elem5t   
*>act]i/ic ( ! body consid]$1 & is call$
 its entropy4 ,entropy1 ?us def9$1 is a 
v>iable :i*1 l pressure or volume1 might
 s]ve concurr5tly ) ano!r v>iable1 su* z
 pressure or volume1 to def9e ! /ate ( a
 body4  ,x mu/ be p]fectly und]/ood t   
?is v>iable c *ange 9 an indep5d5t      
mann]1 & t x is1 = in/ance1 di/9ct f !  
*ange ( temp]ature4 ,x is also di/9ct f 
! *ange :i* consi/s 9 losses or ga9s (  
heat4 ,9 *emical reactions1 = example1 !
 entropy increases )\t ! sub/ances      
borr[+ any heat4 ,:5 a p]fect gas       
dilates 9 a vacuum its entropy          
increases1 & yet ! temp]ature does n    
*ange1 & ! gas has nei!r be5 able to    
give nor receive heat4 ,we ?us come to  
conceive t a physical ph5om5on _c be    
consid]$ kn[n to u if ! v>iation (      
entropy is n giv51 z are ! v>iations (  

temp]ature & ( pressure or ! ex*anges ( 
heat4 ,! *ange ( entropy is1 prop]ly    
speak+1 ! mo/ *>act]i/ic fact ( a !rmal 
*ange4  ,x is important1 h[ev]1 to rem>k
 t if we c ?us easily def9e & measure ! 
diff]5ce ( entropy betwe5 two /ates ( ! 
same body1 ! value f\nd dep5ds on ! /ate
 arbitr>ily *os5 z ! z]o po9t ( entropy2
 b ?is is n a v s]i\s difficulty1 & is  
analog\s to t :i* occurs 9 ! evaluation 
( o!r physical magnitudes--temp]ature1  
pot5tial1 etc4  ,a grav] difficulty     
proce$s f its n be+ possible to def9e a 
diff]5ce1 or an equality1 ( entropy     
betwe5 two bodies *emically diff]5t4 ,we
 are unable1 9 fact1 to pass by any     
means1 rev]sible or n1 f "o to ! o!r1 s 
long z ! transmutation ( matt] is reg>d$
 z impossible2 b x is well und]/ood t x 
is nev]!less possible to comp>e !       
v>iations ( entropy to :i* ^! two bodies
 are bo? ( !m individually subject4     
,nei!r mu/ we conceal f ourselves t !   
def9ition supposes1 = a giv5 body1 !    
possibility ( pass+ f "o /ate to ano!r  

by a rev]sible trans=mation4            
,rev]sibility is an ideal & extreme case
 :i* _c be realiz$1 b :i* c be          
approximately atta9$ 9 _m circum/ances4 
,s ) gases & ) p]fectly ela/ic bodies1  
we effect s5sibly rev]sible             
trans=mations1 & *anges ( physical /ate 
are practically rev]sible4 ,! discov]ies
 ( ,sa9te-,claire ,deville h br\ght _m  
*emical ph5om5a into a simil> category1 
& reactions su* z solution1 :i* us$ to  
be =m]ly ! type ( an irrev]sible        
ph5om5on1 may n[ (t5 be effect$ by      
s5sibly rev]sible means4 ,be t z x may1 
:5 once ! def9ition is admitt$1 we      
arrive1 by tak+ z a basis ! pr9ciples   
set =? at ! inception1 at ! demon/ration
 ( ! celebrat$ !orem ( ,clausius3 ,!    
entropy ( a !rmally isolat$ sy/em       
cont9ues to increase incessantly4  ,x is
 v evid5t t ! !orem c only be wor?      
apply+ 9 cases :]e ! entropy c be       
exactly def9$2 b1 ev5 :5 ?us limit$1 !  
field /ill rema9s va/1 & ! h>ve/ :i* we 
c !re reap is v abundant4  ,entropy     

appe>s1 !n1 z a magnitude measur+ 9 a   
c]ta9 way ! evolution ( a sy/em1 or1 at 
lea/1 z giv+ ! direction ( ?is          
evolution4 ,?is v important consequ5ce  
c]ta9ly did n escape ,clausius1 s9ce ! v
 "n ( entropy1 :i* he *ose to designate 
?is magnitude1 itself signifies         
evolution4 ,we h succe$$ 9 def9+ ?is    
entropy by demon/rat+1 z has be5 said1 a
 c]ta9 numb] ( propositions :i* spr+ f !
 po/ulate ( ,clausius2 x is1 !re=e1     
natural to suppose t ?is po/ulate itself
 conta9s 9 pot5tia ! v idea ( a necess>y
 evolution ( physical sy/ems4 ,b z x 0  
fir/ enunciat$1 x conta9s x 9 a deeply  
hidd5 way4  ,no d\bt we %\ld make !     
pr9ciple ( ,c>not appe> 9 an int]e/+    
light by endeav\r+ to dis5gage ?is      
fundam5tal idea1 & by plac+ x1 z x 71 9 
l>ge lett]s4 ,j z1 9 elem5t>y geometry1 
we c replace ! po/ulate ( ,euclid by o!r
 equival5t propositions1 s ! po/ulate ( 
!rmodynamics is n necess>ily fix$1 & x  
is in/ructive to try to give x ! mo/    
g5]al & sugge/ive "*4  ,,mm4 ,p]r9 &    

,langev9 h made a successful attempt 9  
?is direction4 ,m4 ,p]r9 enunciates !   
foll[+ pr9ciple3 ,an isolat$ sy/em nev] 
passes twice ?r\gh ! same /ate4 ,9 ?is  
=m1 ! pr9ciple affirms t !re exi/s a    
necess>y ord] 9 ! succession ( two      
ph5om5a2 t evolution takes place 9 a    
det]m9$ direction4 ,if y pref] x1 x may 
be ?us /at$3 ,( two conv]se             
trans=mations unaccompani$ by any       
ext]nal effect1 "o only is possible4 ,= 
in/ance1 two gases may diffuse !mselves 
"o 9 ! o!r 9 con/ant volume1 b !y c\ld n
 conv]sely sep>ate !mselves             
spontane\sly4  ,/>t+ f ! pr9ciple ?us   
put =w>d1 we make ! logical d$uction t  
"o _c hope to con/ruct an eng9e :i* %\ld
 "w = an indef9ite "t by heat+ a hot    
s\rce & by cool+ a cold "o4 ,we ?us come
 aga9 into ! r\te trac$ by ,clausius1 & 
f ?is po9t we may foll[ x /rictly4      
,:atev] ! po9t ( view adopt$1 :e!r we   
reg>d ! proposition ( ,m4 ,p]r9 z !     
coroll>y ( ano!r exp]im5tal po/ulate1 or
 :e!r we consid] x z a tru? :i* we admit

 a priori & v]ify ?r\gh its consequ5ces1
 we are l$ to consid] t 9 its entirety !
 pr9ciple ( ,c>not resolves itself into 
! idea t we _c g back along ! c\rse (   
life1 & t ! evolution ( a sy/em mu/     
foll[ its necess>y progress4  ,clausius 
& ,"l ,kelv9 h drawn f ^! consid]ations 
c]ta9 well-kn[n consequ5ces on !        
evolution ( ! ,univ]se4 ,notic+ t       
entropy is a prop]ty add$ to matt]1 !y  
admit t !re is 9 ! _w a total am\nt (   
entropy2 & z all real *anges :i* are    
produc$ 9 any sy/em correspond to an    
increase ( entropy1 x may be said t !   
entropy ( ! _w is cont9ually increas+4  
,?us ! quantity ( en]gy exi/+ 9 !       
,univ]se rema9s con/ant1 b trans=ms     
itself little by little into heat       
uni=mly di/ribut$ at a temp]ature       
ev]y:]e id5tical4 ,9 ! end1 !re=e1 !re w
 be nei!r *emical ph5om5a nor           
manife/ation ( life2 ! _w w /ill exi/1 b
 )\t motion1 &1 s to speak1 dead4  ,^!  
consequ5ces mu/ be admitt$ to be v      
d\btful2 we _c 9 any c]ta9 way apply to 

! ,univ]se1 :i* is n a f9ite sy/em1 a   
proposition demon/rat$1 & t n           
unres]v$ly1 9 ! %>ply limit$ case ( a   
f9ite sy/em4 ,h]b]t ,sp5c]1 moreov]1 9 8
 book on ,fir/ ,pr9ciples1 br+s out )   
mu* =ce ! idea t1 ev5 if ! ,univ]se came
 to an end1 no?+ w\ld all[ u to conclude
 t1 once at re/1 x w\ld rema9 s         
indef9itely4 ,we may recognise t ! /ate 
9 :i* we are began at ! end ( a =m]     
evolution>y p]iod1 & t ! end ( ! exi/+  
era w m>k ! beg9n+ ( a new "o4  ,l an   
ela/ic & mobile object :i*1 ?r[n into ! 
air1 atta9s by degrees ! summit ( its   
c\rse1 !n possesses a z]o velocity & is 
= a mom5t 9 equilibrium1 & !n falls on  
t\*+ ! gr\nd to reb\nd1 s ! _w %\ld be  
subject$ to huge oscillations :i* fir/  
br+ x to a maximum ( entropy till !     
mom5t :5 !re %\ld be produc$ a sl[      
evolution 9 ! contr>y direction br++ x  
back to ! /ate f :i* x />t$4 ,?us1 9 !  
inf9ity ( "t1 ! life ( ! ,univ]se       
proce$s )\t real /op4  ,?is conception  
is1 moreov]1 9 accordance ) ! view c]ta9

 physici/s take ( ! pr9ciple ( ,c>not4  
,we %all see1 = example1 t 9 ! k9etic   
!ory we are l$ to admit t1 aft] wait+   
suffici5tly long1 we c witness ! return 
( ! v>i\s /ates ?r\gh :i* a mass ( gas1 
= example1 has pass$ 9 its s]ies (      
trans=mations4  ,if we keep to ! pres5t 
era1 evolution has a fix$ direction--t  
:i* leads to an increase ( entropy2 & x 
is possible to enquire1 9 any giv5 sy/em
 to :at physical manife/ations ?is      
increase corresponds4 ,we note t k9etic1
 pot5tial1 electrical1 & *emical =ms (  
en]gy h a great t5d5cy to trans=m       
!mselves into calorific en]gy4 ,a       
*emical reaction1 = example1 gives out  
en]gy2 b if ! reaction is n produc$ "u v
 special conditions1 ?is en]gy          
imm$iately passes into ! calorific =m4  
,?is is s true1 t *emi/s curr5tly speak 
( ! heat giv5 out by reactions in/ead ( 
reg>d+ ! en]gy dis5gag$ 9 g5]al4  ,9 all
 ^! trans=mations ! calorific en]gy     
obta9$ has n1 f a practical po9t ( view1
 ! same value at :i* x />t$4 ,"o _c1 9  

fact1 accord+ to ! pr9ciple ( ,c>not1   
trans=m x integrally into me*anical     
en]gy1 s9ce ! heat possess$ by a body c 
only yield "w on condition t a "p ( x   
falls on a body ) a l[] temp]ature4 ,?us
 appe>s ! idea t en]gies :i* ex*ange )  
ea* o!r & correspond to equal quantities
 h n ! same qualitative value4 ,=m has  
its importance1 & !re are p]sons :o     
pref] a gold5 l\is to f\r pieces ( five 
francs4 ,! pr9ciple ( ,c>not w\ld ?us   
lead u to consid] a c]ta9 classification
 ( en]gies1 & w\ld %[ u t1 9 !          
trans=mations possible1 ^! en]gies      
always t5d to a sort ( dim9ution (      
quality--t is1 to a degradation4  ,x    
w\ld ?us re9troduce an elem5t (         
diff]5tiation ( :i* x seems v difficult 
to give a me*anical explanation4 ,c]ta9 
philosoph]s & physici/s see 9 ?is fact a
 reason :i* condemns a priori all       
attempts made to give a me*anical       
explanation ( ! pr9ciple ( ,c>not4  ,x  
is "r1 h[ev]1 n to exagg]ate !          
importance t %\ld be attribut$ to !     

phrase degrad$ en]gy4 ,if ! heat is n   
equival5t to ! "w1 if heat at #ii is n  
equival5t to heat at #ajj1 t means t we 
_c 9 practice con/ruct an eng9e :i* %all
 trans=m all ?is heat into "w1 or t1 = !
 same cold s\rce1 ! output is great] :5 
! temp]ature ( ! hot s\rce is high]2 b  
if x 7 possible t ?is cold s\rce _h     
itself ! temp]ature ( absolute z]o1 !   
:ole heat w\ld reappe> 9 ! =m ( "w4 ,!  
case "h consid]$ is an ideal & extreme  
case1 & we naturally _c realize x2 b ?is
 consid]ation suffices to make x pla9 t 
! classification ( en]gies is a little  
arbitr>y & dep5ds m1 p]haps1 on !       
conditions 9 :i* mank9d lives ?an on !  
inmo/ nature ( ?+s4  ,9 fact1 ! attempts
 :i* h (t5 be5 made to ref] ! pr9ciple (
 ,c>not to me*anics h n giv5 conv9c+    
results4 ,x has ne>ly always be5        
necess>y to introduce into ! attempt "s 
new hypo!sis indep5d5t ( ! fundam5tal   
hypo!ses ( ord9>y me*anics1 & equival5t1
 9 reality1 to "o ( ! po/ulates on :i* !
 ord9>y exposition ( ! second law (     

!rmodynamics is f\nd$4 ,helmholtz1 9 a  
ju/ly celebrat$ !ory1 endeav\r$ to fit !
 pr9ciple ( ,c>not into ! pr9ciple (    
lea/ action2 b ! difficulties reg>d+ !  
me*anical int]pretation ( !             
irrev]sibility ( physical ph5om5a rema9 
entire4 ,look+ at ! "q1 h[ev]1 f ! po9t 
( view at :i* ! p>tisans ( ! k9etic     
!ories ( matt] place !mselves1 !        
pr9ciple is view$ 9 a new aspect4 ,gibbs
 & aft]w>ds ,boltzmann & ,pr(essor      
,planck h put =w>d "s v int]e/+ ideas on
 ?is subject4 ,by foll[+ ! r\te !y h    
trac$1 we come to consid] ! pr9ciple z  
po9t+ out to u t a giv5 sy/em t5ds t[>ds
 ! configuration pres5t$ by ! maximum   
probability1 &1 num]ically1 ! entropy   
w\ld ev5 be ! log>i?m ( ?is probability4
 ,?us two diff]5t gase\s masses1 enclos$
 9 two sep>ate receptacles :i* h j be5  
plac$ 9 communication1 diffuse !mselves 
"o ?r\gh ! o!r1 & x is highly improbable
 t1 9 _! mutual %ocks1 bo? k9ds (       
molecules %\ld take a di/ribution (     
velocities :i* r$uce !m by a spontane\s 

ph5om5on to ! initial /ate4  ,we %\ld h 
to wait a v long "t = s extraord9>y a   
conc\rse ( circum/ances1 b1 9 /rictness1
 x w\ld n be impossible4 ,! pr9ciple    
w\ld only be a law ( probability4 ,yet  
?is probability is all ! great] ! m     
consid]able is ! numb] ( molecules      
itself4 ,9 ! ph5om5a habitually dealt )1
 ?is numb] is su* t1 practically1 !     
v>iation ( entropy 9 a con/ant s5se     
takes1 s to speak1 ! "* ( absolute      
c]ta9ty4  ,b !re may be exceptional     
cases :]e ! complexity ( ! sy/em becomes
 insuffici5t = ! application ( !        
pr9ciple ( ,c>not2-- z 9 ! case ( !     
curi\s movem5ts ( small p>ticles susp5d$
 9 a liquid :i* are kn[n by ! "n (      
,br[nian movem5ts & c be obs]v$ "u !    
microscope4 ,! agitation "h really      
seems1 z ,m4 ,g\y has rem>k$1 to be     
produc$ & cont9u$ indef9itely1 reg>dless
 ( any diff]5ce 9 temp]ature2 & we seem 
to witness ! incessant motion1 9 an     
iso!rmal m$ium1 ( ! p>ticles :i*        
con/itute matt]4 ,p]haps1 h[ev]1 we f9d 

ourselves already 9 conditions :]e ! too
 great simplicity ( ! di/ribution ( !   
molecules deprives ! pr9ciple ( its     
value4  ,m4 ,lippmann has 9 ! same way  
%[n t1 on ! k9etic hypo!sis1 x is       
possible to con/ruct su* me*anisms t we 
c s take cognizance ( molecul> movem5ts 
t vis viva c be tak5 f !m4 ,! me*anisms 
( ,m4 ,lippmann are n1 l ! celebrat$    
app>atus at "o "t devis$ by ,maxwell1   
purely hypo!tical4 ,!y d n suppose a    
p>tition ) a hole impossible to be bor$ 
?r\gh matt] :]e ! molecul> spaces w\ld  
be l>g] ?an ! hole itself4 ,!y h f9ite  
dim5sions4 ,?us ,m4 ,lippmann consid]s a
 vase full ( oxyg5 at a con/ant         
temp]ature4 ,9 ! int]ior ( ?is vase is  
plac$ a small copp] r+1 & ! :ole is set 
9 a magnetic field4 ,! oxyg5 molecules  
are1 z we "k1 magnetic1 & :5 pass+ ?r\gh
 ! int]ior ( ! r+ !y produce 9 ?is r+ an
 induc$ curr5t4 ,dur+ ?is "t1 x is true1
 o!r molecules em]ge f ! space enclos$  
by ! circuit2 b ! two effects d n       
c\nt]balance ea* o!r1 & ! result+ curr5t

 is ma9ta9$4 ,!re is elevation (        
temp]ature 9 ! circuit 9 accordance )   
,j\le's law2 & ?is ph5om5on1 "u su*     
conditions1 is incompatible ) ! pr9ciple
 ( ,c>not4  ,x is possible--& t1 ,i ?9k1
 is ,m4 ,lippmann's idea--to draw f 8 v 
+5i\s criticism an objection to ! k9etic
 !ory1 if we admit ! absolute value ( ! 
pr9ciple2 b we may also suppose t "h    
aga9 we are 9 pres5ce ( a sy/em :]e !   
prescrib$ conditions dim9i% ! complexity
 & r5d] x1 consequ5tly1 less probable t 
! evolution is always effect$ 9 ! same  
direction4  ,9 :atev] way y look at x1 !
 pr9ciple ( ,c>not furni%es1 9 ! imm5se 
majority ( cases1 a v sure guide 9 :i*  
physici/s cont9ue to h ! mo/ entire     
confid5ce4    #d4 ,,!rmodynamics  ,to   
apply ! two fundam5tal pr9ciples (      
!rmodynamics1 v>i\s me?ods may be       
employ$1 equival5t 9 ! ma91 b pres5t+ z 
! cases v>y a great] or less conv5i5ce4 
,9 record+1 ) ! aid ( ! two quantities1 
en]gy & entropy1 ! relations :i*        
translate analytically ! two pr9ciples1 

we obta9 two relations betwe5 !         
coeffici5ts :i* occur 9 a giv5 ph5om5on2
 b x may be easi] & also m sugge/ive to 
employ v>i\s functions ( ^! quantities4 
,9 a memoir1 ( :i* "s extracts appe>$ z 
e>ly z #ahfi1 a mode/ s*ol>1 ,m4        
,massieu1 indicat$ 9 p>ticul> a         
rem>kable function :i* he t]m$ a        
*>act]i/ic function1 & by ! employm5t ( 
:i* calculations are simplifi$ 9 c]ta9  
cases4  ,9 ! same way ,j4,w4 ,gibbs1 9  
#ahge & #ahgh1 !n ,helmholtz 9 #ahhb1 &1
 9 ,france1 ,m4 ,duhem1 f ! ye> #ahhf   
onw>d1 h publi%$ works1 at fir/ ill     
und]/ood1 ( :i* ! r5[n 01 h[ev]1        
consid]able 9 ! sequel1 & 9 :i* !y made 
use ( analog\s functions "u ! names (   
available en]gy1 free en]gy1 or int]nal 
!rmodynamic pot5tial4 ,! magnitude ?us  
designat$1 atta*+1 z a consequ5ce ( !   
two pr9ciples1 to all /ates ( ! sy/em1  
is p]fectly det]m9$ :5 ! temp]ature &   
o!r normal v>iables are kn[n4 ,x all[s  
u1 by calculations (t5 v easy1 to fix ! 
conditions necess>y & suffici5t = !     

ma9t5ance ( ! sy/em 9 equilibrium by    
=eign bodies tak5 at ! same temp]ature z
 itself4  ,"o may hope to con/itute 9   
?is way1 z ,m4 ,duhem 9 a long &        
rem>kable s]ies ( op]ations has         
specially endeav\r$ to d1 a sort ( g5]al
 me*anics :i* w enable que/ions ( /atics
 to be treat$ ) accuracy1 & all !       
conditions ( equilibrium ( ! sy/em1     
includ+ ! calorific prop]ties1 to be    
det]m9$4 ,?us1 ord9>y /atics tea*es u t 
a liquid ) its vap\r on ! top =ms a     
sy/em 9 equilibrium1 if we apply to !   
two fluids a pressure dep5d+ on         
temp]ature alone4 ,!rmodynamics w furni%
 u1 9 addition1 ) ! expression ( ! heat 
( vaporization & (1 ! specific heats ( !
 two saturat$ fluids4  ,?is new /udy has
 giv5 u also mo/ valuable in=mation on  
compressible fluids & on ! !ory ( ela/ic
 equilibrium4 ,add$ to c]ta9 hypo!ses on
 electric or magnetic ph5om5a1 x gives a
 coh]5t :ole f :i* c be d$uc$ !         
conditions ( electric or magnetic       
equilibrium2 & x illum9ates ) a         

brilliant light ! calorific laws (      
electrolytic ph5om5a4  ,b ! mo/         
indisputable triumph ( ?is !rmodynamic  
/atics is ! discov]y ( ! laws :i*       
regulate ! *anges ( physical /ate or (  
*emical con/itution4 ,j4,w4 ,gibbs 0 !  
au?or ( ?is imm5se progress4 ,8 memoir1 
n[ celebrat$1 on ! equilibrium (        
het]og5e\s sub/ances1 conceal$ 9 #ahgf 9
 a review at t "t ( limit$ circulation1 
& r heavy to read1 seem$ only to conta9 
algebraic !orems applicable ) difficulty
 to reality4 ,x is kn[n t ,helmholtz    
indep5d5tly succe$$1 a few ye>s lat]1 9 
introduc+ !rmodynamics into ! doma9 (   
*emi/ry by 8 conception ( ! division (  
en]gy into free & into b\nd en]gy3 !    
fir/1 capable ( und]go+ all             
trans=mations1 & p>ticul>ly ( trans=m+  
itself into ext]nal action2 ! second1 on
 ! o!r h&1 b\nd1 & only manife/+ itself 
by giv+ out heat4 ,:5 we measure *emical
 en]gy1 we ord9>ily let x fall :olly    
into ! calorific =m2 b1 9 reality1 x    
itself includes bo? p>ts1 & x is !      

v>iation ( ! free en]gy & n t ( ! total 
en]gy measur$ by ! integral dis5gagem5t 
( heat1 ! sign ( :i* det]m9es !         
direction 9 :i* ! reactions are effect$4
  ,b if ! pr9ciple ?us enunciat$ by     
,helmholtz z a consequ5ce ( ! laws (    
!rmodynamics is at bottom id5tical ) t  
discov]$ by ,gibbs1 x is m difficult (  
application & is pres5t$ "u a m my/]i\s 
aspect4 ,x 0 n until ,m4 ,van d] ,waals 
exhum$ ! memoir ( ,gibbs1 :5 num]\s     
physici/s or *emi/s1 mo/ ( !m           
,dut*--,pr(essor ,van t',h(f1 ,bakhius  
,roozeboom1 & o!rs--utiliz$ ! rules set 
=? 9 ?is memoir = ! discussion ( ! mo/  
complicat$ *emical reactions1 t ! ext5t 
( ! new laws 0 fully und]/ood4  ,! *ief 
rule ( ,gibbs is ! "o s celebrat$ at !  
pres5t day "u ! "n ( ! ,phase ,law4 ,we 
"k t by phases are designat$ ! homog5e\s
 sub/ances into :i* a sy/em is divid$2  
?us c>bonate ( lime1 lime1 & c>bonic    
acid gas are ! ?ree phases ( a sy/em :i*
 comprises ,icel& sp> p>tially          
dissociat$ into lime & c>bonic acid gas4

 ,! numb] ( phases add$ to ! numb] (    
indep5d5t compon5ts--t is to say1 bodies
 ^: mass is left arbitr>y by ! *emical  
=mulas ( ! sub/ances ent]+ into !       
reaction--fixes ! g5]al =m ( ! law (    
equilibrium ( ! sy/em2 t is to say1 !   
numb] ( quantities :i*1 by _! v>iations 
7temp]ature & pressure71 w\ld be ( a    
nature to modify its equilibrium by     
modify+ ! con/itution ( ! phases4       
,sev]al au?ors1 ,m4 ,raveau 9 p>ticul>1 
h inde$ giv5 v simple demon/rations (   
?is law :i* are n bas$ on !rmodynamics2 
b !rmodynamics1 :i* l$ to its discov]y1 
cont9ues to give x its true scope4      
,moreov]1 x w\ld n suffice m]ely to     
det]m9e quantitatively ^? laws ( :i* x  
makes kn[n ! g5]al =m4 ,we mu/1 if we   
wi% to p5etrate deep] into details1     
p>ticul>ize ! hypo!sis1 & admit1 =      
in/ance1 ) ,gibbs t we are deal+ )      
p]fect gases2 :ile1 ?anks to            
!rmodynamics1 we c con/itute a complete 
!ory ( dissociation :i* leads to =mulas 
9 complete accord ) ! num]ical results (

 ! exp]im5t4 ,we c ?us foll[ closely all
 que/ions conc]n+ ! displacem5ts ( !    
equilibrium1 & f9d a relation ( ! fir/  
importance betwe5 ! masses ( ! bodies   
:i* react 9 ord] to con/itute a sy/em 9 
equilibrium4  ,! /atics ?us con/ruct$   
con/itutes at ! pres5t day an important 
edifice to be h5ce=? class$ among/      
hi/orical monum5ts4 ,"s !ori/s ev5 wi%  
to g a /ep beyond4 ,!y h attempt$ to    
beg9 by ! same means a m complete /udy (
 ^? sy/ems ^: /ate *anges f "o mom5t to 
ano!r4 ,?is is1 moreov]1 a /udy :i* is  
necess>y to complete satisfactorily !   
/udy ( equilibrium itself2 = )\t x grave
 d\bts w\ld exi/ z to ! conditions (    
/ability1 & x alone c give _! true mean+
 to que/ions relat+ to displacem5ts (   
equilibrium4  ,! problems ) :i* we are  
?us confront$ are s+ul>ly difficult4 ,m4
 ,duhem has giv5 u _m excell5t examples 
( ! fecundity ( ! me?od2 b if           
!rmodynamic /atics may be consid]$      
def9itely f\nd$1 x _c be said t ! g5]al 
dynamics ( sy/ems1 consid]$ z ! /udy (  

!rmal movem5ts & v>iations1 are yet z   
solidly e/abli%$4    #e4 ,,atomism  ,x  
may appe> s+ul>ly p>adoxical t1 9 a     
*apt] devot$ to g5]al views on !        
pr9ciples ( physics1 a few words %\ld be
 introduc$ on ! atomic !ories ( matt]4  
,v (t51 9 fact1 :at is call$ ! physics (
 pr9ciples is set 9 opposition to !     
hypo!ses on ! con/itution ( matt]1      
p>ticul>ly to atomic !ories4 ,i h       
already said t1 ab&on+ ! inve/igation ( 
! unfa?omable my/]y ( ! con/itution ( ! 
,univ]se1 "s physici/s ?9k !y may f9d1 9
 c]ta9 g5]al pr9ciples1 suffici5t guides
 to conduct !m across ! physical _w4 ,b 
,i h also said1 9 exam9+ ! hi/ory ( ^?  
pr9ciples1 t if !y are to-day consid]$  
exp]im5tal tru?s1 indep5d5t ( all !ories
 relat+ to matt]1 !y h1 9 fact1 ne>ly   
all be5 discov]$ by s*ol>s :o reli$ on  
molecul> hypo!ses3 & ! "q sugge/s itself
 :e!r ?is is m]e *ance1 or :e!r ?is     
*ance may n be orda9$ by high] reasons4 
,9 a v pr(\nd "w :i* appe>$ a few ye>s  
ago1 entitl$ ,essai critique sur        

l'hypo!se des atomes1 ,m4 ,hannequ91 a  
philosoph] :o is also an erudite s*ol>1 
exam9$ ! "p tak5 by atomism 9 ! hi/ory (
 sci5ce4 ,he notes t atomism & sci5ce 7 
born1 9 ,greece1 ( ! same problem1 & t 9
 mod]n times ! revival ( ! "o 0 closely 
connect$ ) t ( ! o!r4 ,he %[s1 too1 by v
 close analysis1 t ! atomic hypo!sis is 
ess5tial to ! optics ( ,fresnel & (     
,cau*y2 t x p5etrates into ! /udy (     
heat2 & t1 9 its g5]al features1 x      
presid$ at ! bir? ( mod]n *emi/ry & is  
l9k$ ) all its progress4 ,he concludes t
 x is1 9 a mann]1 ! s\l ( our k (       
,nature1 & t contempor>y !ories are on  
?is po9t 9 accord ) hi/ory3 = ^! !ories 
consecrate ! prepond]ance ( ?is hypo!sis
 9 ! doma9 ( sci5ce4  ,if ,m4 ,hannequ9 
_h n be5 prematurely cut (f 9 ! full    
expansion ( 8 vigor\s tal5t1 he might h 
add$ ano!r *apt] to 8 excell5t book4 ,he
 w\ld h witness$ a prodigi\s budd+ (    
atomi/ic ideas1 accompani$1 x is true1  
by wide modifications 9 ! mann] 9 :i* ! 
atom is to be reg>d$1 s9ce ! mo/ rec5t  

!ories make mat]ial atoms into c5tres   
con/itut$ ( atoms ( electricity4 ,on !  
o!r h&1 he w\ld h f\nd 9 ! bur/+ =? ( ^!
 new doctr9es "o m pro( 9 support ( 8   
idea t sci5ce is indissolubly b\nd to   
atomism4  ,f ! philosophical po9t (     
view1 ,m4 ,hannequ91 exam9+ ! reasons   
:i* may h call$ ^! l9ks into be+1       
arrives at ! idea t !y necess>ily proce$
 f ! con/itution ( our k1 or1 p]haps1 f 
t ( ,nature itself4 ,moreov]1 ?is orig91
 d\ble 9 appe>ance1 is s+le at bottom4  
,our m9ds c\ld n1 9 fact1 deta* & come  
out ( !mselves to grasp reality & !     
absolute 9 ,nature4 ,accord+ to ! idea (
 ,desc>tes1 x is ! de/9y ( our m9ds only
 to take hold ( & to und]/& t :i*       
proce$s f !m4  ,?us atomism1 :i* is1    
p]haps1 only an appe>ance conta9+ ev5 "s
 contradictions1 is yet a well-f\nd$    
appe>ance1 s9ce x con=ms to ! laws ( our
 m9ds2 & ?is hypo!sis is1 9 a way1      
necess>y4  ,we may dispute ! conclusions
 ( ,m4 ,hannequ91 b no "o w refuse to   
recognise1 z he does1 t atomic !ories   

occupy a prepond]at+ "p 9 ! doctr9es (  
physics2 & ! position :i* !y h ?us      
conqu]$ gives !m1 9 a way1 ! "r ( say+ t
 !y re/ on a real pr9ciple4 ,x is 9 ord]
 to recognise ?is "r t sev]al           
physici/s--,m4 ,langev91 = example--ask 
t atoms be promot$ f ! rank ( hypo!ses  
to t ( pr9ciples4 ,by ?is !y mean t !   
atomi/ic ideas =c$ ^u u by an almo/     
obligatory induction bas$ on v exact    
exp]im5ts1 enable u to co-ord9ate a     
consid]able am\nt ( facts1 to con/ruct a
 v g5]al syn!sis1 & to =esee a great    
numb] ( ph5om5a4  ,x is ( mom5t1        
moreov]1 to ?or\ghly und]/& t atomism   
does n necess>ily set up ! hypo!sis (   
c5tres ( attraction act+ at a di/ance1 &
 x mu/ n be confus$ ) molecul> physics1 
:i* has1 on ! o!r h&1 und]gone v s]i\s  
*ecks4 ,! molecul> physics greatly 9    
fav\r "s fifty ye>s ago leads to su*    
complex repres5tations & to solutions   
(t5 s undet]m9$1 t ! mo/ c\rage\s are   
we>i$ ) uphold+ x & x has fall5 into "s 
discr$it4 ,x re/$ on ! fundam5tal       

pr9ciples ( me*anics appli$ to molecul> 
actions2 & t 01 no d\bt1 an ext5sion    
legitimate en\gh1 s9ce me*anics is      
itself only an exp]im5tal sci5ce1 & its 
pr9ciples1 e/abli%$ = ! movem5ts ( matt]
 tak5 z a :ole1 %\ld n be appli$ outside
 ! doma9 :i* belongs to !m4 ,atomism1 9 
fact1 t5ds m & m1 9 mod]n !ories1 to    
imitate ! pr9ciple ( ! cons]vation (    
en]gy or t ( entropy1 to dis5gage itself
 f ! artificial bonds :i* atta*$ x to   
me*anics1 & to put itself =w>d z an     
indep5d5t pr9ciple4  ,atomi/ic ideas    
also h und]gone evolution1 & ?is sl[    
evolution has be5 consid]ably quick5$ "u
 ! influ5ce ( mod]n discov]ies4 ,^! rea*
 back to ! mo/ remote antiquity1 & to   
foll[ _! developm5t we %\ld h to write !
 hi/ory ( human ?\ght :i* !y h always   
accompani$ s9ce ! "t ( ,leucippus1      
,democritus1 ,epicurus1 & ,lucretius4 ,!
 fir/ obs]v]s :o notic$ t ! volume ( a  
body c\ld be dim9i%$ by compression or  
cold1 or augm5t$ by heat1 & :o saw a    
soluble solid body mix completely ) !   

wat] :i* dissolv$ x1 mu/ h be5 compell$ 
to suppose t matt] 0 n disp]s$          
cont9u\sly ?r\gh\t ! space x seem$ to   
occupy4 ,!y 7 ?us br\ght to consid] x   
discont9u\s1 & to admit t a sub/ance    
hav+ ! same composition & ! same        
prop]ties 9 all its p>ts--9 a ^w1       
p]fectly homog5e\s--ceases to pres5t ?is
 homog5eity :5 consid]$ )9 a suffici5tly
 small volume4  ,mod]n exp]im5t]s h     
succe$$ by direct exp]im5ts 9 plac+ 9   
evid5ce ?is het]og5e\s "* ( matt] :5    
tak5 9 small mass4 ,?us1 = example1 !   
sup]ficial t5sion1 :i* is con/ant = !   
same liquid at a giv5 temp]ature1 no    
long] has ! same value :5 ! ?ickness ( !
 lay] ( liquid becomes extremely small4 
,newton notic$ ev5 9 8 "t t a d>k zone  
is se5 to =m on a soap bubble at ! mom5t
 :5 x becomes s ?9 t x mu/ bur/4        
,pr(essor ,re9old & ,sir ,ar?ur ,rck] h 
%[n t ?is zone is no long] exactly      
sph]ical2 & f ?is we mu/ conclude t !   
sup]ficial t5sion1 con/ant = all        
?icknesses above a c]ta9 limit1 comm5ces

 to v>y :5 ! ?ickness falls bel[ a      
critical value1 :i* ^! au?ors e/imate1  
on optical gr\nds1 at ab\t fifty        
million?s ( a millimetre4  ,f exp]im5ts 
on capill>ity1 ,pr(4 ,qu9cke has obta9$ 
simil> results ) reg>d to lay]s (       
solids4 ,b x is n only capill>y         
prop]ties :i* all[ ?is *>act]i/ic to be 
reveal$4 ,all ! prop]ties ( a body are  
modifi$ :5 tak5 9 small mass2 ,m4 ,mesl9
 proves ?is 9 a v +5i\s way z reg>ds    
optical prop]ties1 & ,mr ,v9c5t 9       
respect ( electric conductivity4 ,m4    
,h\llevigue1 :o1 9 a *apt] ( 8 excell5t 
"w1 ,du ,laboratoire  l',us9e1 has v    
cle>ly set =? ! mo/ int]e/+             
consid]ations on atomic hypo!ses1 has   
rec5tly demon/rat$ t copp] & silv] cease
 to comb9e ) iod9e z soon z !y are      
pres5t 9 a ?ickness ( less ?an ?irty    
million?s ( a millimetre4 ,x is ?is same
 dim5sion likewise t is possess$1       
accord+ to ,m4 ,wi5]1 by ! smalle/      
?icknesses x is possible to deposit on  
glass4 ,^! lay]s are s ?9 t !y _c be    

p]ceiv$1 b _! pres5ce is reveal$ by a   
*ange 9 ! prop]ties ( ! light reflect$  
by !m4  ,?us1 bel[ fifty to ?irty       
million?s ( a millimetre ! prop]ties (  
matt] dep5d on its ?ickness4 ,!re are   
!n1 no d\bt1 only a few molecules to be 
met )1 & x may be conclud$1 9           
consequ5ce1 t ! discont9u\s elem5ts (   
bodies--t is1 ! molecules-- h l9e>      
dim5sions ( ! ord] ( magnitude ( !      
million? ( a millimetre4 ,consid]ations 
reg>d+ m complex ph5om5a1 = in/ance !   
ph5om5a ( electricity by contact1 & also
 ! k9etic !ory ( gases1 br+ u to ! same 
conclusion4  ,! idea ( ! discont9uity ( 
matt] =ces itself ^u u = _m o!r reasons4
 ,all mod]n *emi/ry is f\nd$ on ?is     
pr9ciple2 & laws l ! law ( multiple     
proportions1 introduce an evid5t        
discont9uity to :i* we f9d analogies 9 !
 law ( electrolysis4 ,! elem5ts ( bodies
 we are ?us br\ght to reg>d might1 z    
reg>ds solids at all ev5ts1 be consid]$ 
z immobile2 b ?is immobility c\ld n     
expla9 ! ph5om5a ( heat1 &1 z x is      

entirely inadmissible = gases1 x seems v
 improbable x c absolutely occur 9 any  
/ate4 ,we are ?us l$ to suppose t ^!    
elem5ts are animat$ by v complicat$     
movem5ts1 ea* "o proce$+ 9 clos$        
trajectories 9 :i* ! lea/ v>iations (   
temp]ature or pressure cause            
modifications4  ,! atomi/ic hypo!sis %[s
 itself rem>kably fecund 9 ! /udy (     
ph5om5a produc$ 9 gases1 & "h ! mutual  
indep5d5ce ( ! p>ticles r5d]s ! "q      
relatively m simple &1 p]haps1 all[s !  
pr9ciples ( me*anics to be m c]ta9ly    
ext5d$ to ! movem5ts ( molecules4  ,!   
k9etic !ory ( gases c po9t to unque/ion$
 successes2 & ! idea ( ,daniel          
,b]n\illi1 :o1 z e>ly z #agch1 consid]$ 
a gase\s mass to be =m$ ( a consid]able 
numb] ( molecules animat$ by rapid      
movem5ts ( translation1 has be5 put into
 a =m precise en\gh = ma!matical        
analysis1 & we h ?us f\nd ourselves 9 a 
position to con/ruct a really solid     
f\ndation4 ,x w be at once conceiv$1 on 
?is hypo!sis1 t pressure is ! resultant 

( ! %ocks ( ! molecules aga9/ ! walls ( 
! conta9+ vessel1 & we at once come to !
 demon/ration t ! law ( ,m>iotte is a   
natural consequ5ce ( ?is orig9 (        
pressure2 s9ce1 if ! volume occupi$ by a
 c]ta9 numb] ( molecules is d\bl$1 !    
numb] ( %ocks p] second on ea* squ>e    
c5timetre ( ! walls becomes half z mu*4 
,b if we attempt to c>ry ?is fur!r1 we  
f9d ourselves 9 pres5ce ( a s]i\s       
difficulty4 ,x is impossible to m5tally 
foll[ e "o ( ! _m individual molecules  
:i* compose ev5 a v limit$ mass ( gas4  
,! pa? foll[$ by ?is molecule may be e  
in/ant modifi$ by ! *ance ( runn+ aga9/ 
ano!r1 or by a %ock :i* may make x      
reb\nd 9 ano!r direction4  ,! difficulty
 w\ld be insoluble if *ance _h n laws ( 
its own4 ,x 0 ,maxwell :o fir/ ?\ght (  
introduc+ into ! k9etic !ory !          
calculation ( probabilities4 ,will>d    
,gibbs & ,boltzmann lat] on develop$ ?is
 idea1 & h f\nd$ a /ati/ical me?od :i*  
does n1 p]haps1 give absolute c]ta9ty1 b
 :i* is c]ta9ly mo/ int]e/+ & curi\s4   

,molecules are gr\p$ 9 su* a way t ^?   
belong+ to ! same gr\p may be consid]$ z
 hav+ ! same /ate ( movem5t2 !n an      
exam9ation is made ( ! numb] ( molecules
 9 ea* gr\p1 & :at are ! *anges 9 ?is   
numb] f "o mom5t to ano!r4 ,x is ?us (t5
 possible to det]m9e ! "p :i* ! diff]5t 
gr\ps h 9 ! total prop]ties ( ! sy/em & 
9 ! ph5om5a :i* may occur4  ,su* a      
me?od1 analog\s to ! "o employ$ by      
/ati/icians = foll[+ ! social ph5om5a 9 
a population1 is all ! m legitimate !   
great] ! numb] ( individuals c\nt$ 9 !  
av]ages2 n[1 ! numb] ( molecules conta9$
 9 a limit$ space-- = example1 9 a      
c5timetre cube tak5 9 normal            
conditions--is su* t no population c\ld 
ev] atta9 s high a figure4 ,all         
consid]ations1 ^? we h indicat$ z well z
 o!rs :i* might be invok$ 7= example1 ! 
rec5t rese>*es ( ,m4 ,spr+ on ! limit ( 
visibility ( fluoresc5ce71 give ?is     
result3--t !re are1 9 ?is space1 "s     
tw5ty ?\s& millions ( molecules4 ,ea* ( 
^! mu/ receive 9 ! space ( a millimetre 

ab\t t5 ?\s& %ocks1 & be t5 ?\s& times  
?ru/ out ( its c\rse4 ,! free pa? ( a   
molecule is !n v small1 b x c be s+ul>ly
 augm5t$ by dim9i%+ ! numb] ( !m4 ,tait 
& ,dew> h calculat$ t1 9 a good mod]n   
vacuum1 ! l5g? ( ! free pa? ( ! rema9+  
molecules n tak5 away by ! air-pump     
easily rea*es a few c5timetres4  ,by    
develop+ ?is !ory1 we come to consid] t1
 = a giv5 temp]ature1 e molecule 7& ev5 
e individual p>ticle1 atom1 or ion7 :i* 
takes "p 9 ! movem5t has1 on ! av]age1 !
 same k9etic en]gy 9 e body1 & t ?is    
en]gy is proportional to ! absolute     
temp]ature2 s t x is repres5t$ by ?is   
temp]ature multipli$ by a con/ant       
quantity :i* is a univ]sal con/ant4     
,?is result is n an hypo!sis b a v great
 probability4 ,?is probability increases
 :5 x is not$ t ! same value = ! con/ant
 is met ) 9 ! /udy ( v v>i$ ph5om5a2 =  
example1 9 c]ta9 !ories on radiation4   
,kn[+ ! mass & en]gy ( a molecule1 x is 
easy to calculate its spe$2 & we f9d t !
 av]age spe$ is ab\t #djj metres p]     

second = c>bonic anhydride1 #ejj =      
nitrog51 & #ahej = hydrog5 at #j ,c4 &  
at ord9>y pressure4 ,i %all h occasion1 
lat] on1 to speak ( mu* m consid]able   
spe$s ?an ^! z animat+ o!r p>ticles4  ,!
 k9etic !ory has p]mitt$ ! diffusion (  
gases to be expla9$1 & ! div]s          
circum/ances ( ! ph5om5on to be         
calculat$4 ,x has all[$ u to %[1 z ,m4  
,brill\9 has done1 t ! coeffici5t (     
diffusion ( two gases does n dep5d on ! 
proportion ( ! gases 9 ! mixture2 x     
gives a v /rik+ image ( ! ph5om5a (     
viscosity & conductivity2 & x leads u to
 ?9k t ! coeffici5ts ( friction & (     
conductivity are indep5d5t ( ! d5sity2  
:ile all ^! previsions h be5 v]ifi$ by  
exp]im5t4 ,x has also invad$ optics2 &  
by rely+ on ! pr9ciple ( ,doppl]1       
,pr(essor ,mi*elson has succe$$ 9 obta9+
 f x an explanation ( ! l5g? pres5t$ by 
! spectral rays ( ev5 ! mo/ r>efi$      
gases4  ,b h[ev] int]e/+ are ^! results1
 !y w\ld n h suffic$ to ov]come !       
repugnance ( c]ta9 physici/s =          

speculations :i*1 an impos+ ma!matical  
baggage not)/&+1 seem$ to !m too        
hypo!tical4 ,! !ory1 moreov]1 /opp$ at !
 molecule1 & appe>$ to sugge/ no idea   
:i* c\ld lead to ! discov]y ( ! key to !
 ph5om5a :]e molecules ex]cise a mutual 
influ5ce on ea* o!r4 ,! k9etic hypo!sis1
 !re=e1 rema9$ 9 "s disfav\r ) a great  
numb] ( p]sons1 p>ticul>ly 9 ,france1   
until ! la/ few ye>s1 :5 all ! rec5t    
discov]ies ( ! conductivity ( gases & ( 
! new radiations came to procure = x a  
new & luxuriant effloresc5ce4 ,x may be 
said t ! atomi/ic syn!sis1 b ye/]day s  
decri$1 is to-day triumphant4  ,!       
elem5ts :i* ent] into ! e>li] k9etic    
!ory1 & :i*1 to avoid confusion1 %\ld be
 always designat$ by ! "n ( molecules1 7
 n1 tru? to say1 9 ! eyes ( ! *emi/s1 ! 
f9al t]m ( ! divisibility ( matt]4 ,x is
 well kn[n t1 to !m1 except 9 c]ta9     
p>ticul> bodies l ! vap\r ( m]cury &    
argon1 ! molecule comprises sev]al      
atoms1 & t1 9 comp\nd bodies1 ! numb] ( 
^! atoms may ev5 be fairly consid]able4 

,b physici/s r>ely ne$$ to h rec\rse to 
! consid]ation ( ^! atoms4 ,!y spoke (  
!m to expla9 c]ta9 p>ticul>ities ( !    
propagation ( s\nd1 & to enunciate laws 
relat+ to specific heats2 b1 9 g5]al1 !y
 /opp$ at ! consid]ation ( ! molecule4  
,! pres5t !ories c>ry ! division mu*    
fur!r4 ,i %all n dwell n[ on ^! !ories1 
s9ce1 9 ord] to ?or\ghly und]/& !m1 _m  
o!r facts mu/ be exam9$4 ,b to avoid all
 confusion1 x rema9s und]/ood t1        
contr>y1 no d\bt1 to etymology1 b 9     
con=mity ) pres5t cu/om1 ,i %all cont9ue
 9 :at foll[s to call atoms ^? p>ticles 
( matt] :i* h till n[ be5 spok5 (2 ^!   
atoms be+ !mselves1 accord+ to mod]n    
views1 s+ul>ly complex edifices =m$ (   
elem5ts1 ( :i* we %all h occasion to    
indicate ! nature lat]4     ,,*apt] ,,iv
  ,,! ,,v>i\s ,,/ates ,,( ,,matt]    #a4
 ,,! ,,/atics ,,( ,,fluids  ,! division 
( bodies into gase\s1 liquid1 & solid1 &
 ! di/9ction e/abli%$ = ! same sub/ance 
betwe5 ! ?ree /ates1 reta9 a great      
importance = ! applications & usages (  

daily life1 b h long s9ce lo/ _!        
absolute value f ! sci5tific po9t (     
view4  ,s f> z conc]ns ! liquid & gase\s
 /ates p>ticul>ly1 ! already antiquat$  
rese>*es ( ,&rews confirm$ ! ideas (    
,cagni>d de la ,t\r & e/abli%$ !        
cont9uity ( ! two /ates4 ,a gr\p (      
physical /udies has ?us be5 con/itut$ on
 :at may be call$ ! /atics ( fluids1 9  
:i* we exam9e ! relations exi/+ betwe5 !
 pressure1 ! volume1 & ! temp]ature (   
bodies1 & 9 :i* are compris$1 "u ! t]m  
fluid1 gases z well z liquids4  ,^!     
rese>*es des]ve att5tion by _! int]e/ & 
! g5]ality ( ! results to :i* !y h l$4  
,!y also give a rem>kable example ( !   
happy effects :i* may be obta9$ by !    
comb9$ employm5t ( ! v>i\s me?ods (     
inve/igation us$ 9 explor+ ! doma9 (    
nature4 ,!rmodynamics has1 9 fact1 all[$
 u to obta9 num]ical relations betwe5 ! 
v>i\s coeffici5ts1 & atomic hypo!ses h  
l$ to ! e/abli%m5t ( "o capital         
relation1 ! *>act]i/ic equation (       
fluids2 :ile1 on ! o!r h&1 exp]im5t 9   

:i* ! progress made 9 ! art ( measurem5t
 has be5 utiliz$1 has furni%$ ! mo/     
valuable in=mation on all ! laws (      
compressibility & dilatation4  ,!       
classical "w ( ,&rews 0 n v wide4 ,&rews
 did n g mu* beyond pressures close to !
 normal & ord9>y temp]atures4 ,( late   
ye>s sev]al v int]e/+ & peculi> cases h 
be5 exam9$ by ,,mm4 ,cailletet1 ,ma?ias1
 ,batelli1 ,l$uc1 ,p4 ,*appuis1 & o!r   
physici/s4 ,sir ,w4 ,ramsay & ,mr ,s4   
,"y h made kn[n ! iso!rmal diagrams#f ( 
a c]ta9 numb] ( liquid bodies at !      
ord9>y temp]ature4 ,!y h ?us be5 able1  
:ile keep+ to some:at re/rict$ limits ( 
temp]ature & pressure1 to t\* ^u ! mo/  
important que/ions1 s9ce !y f\nd        
!mselves 9 ! region ( ! saturation curve
 & ( ! critical po9t4  ,footnote #f3 ,by
 iso!rmal diagram is meant ! patt]n or  
complex =m$ :5 ! iso!rmal l9es are      
arrang$ 9 curves ( :i* ! pressure is !  
ord9ate & ! volume ! abscissa4--,,ed4   
,b ! mo/ complete & sy/ematic body (    
rese>*es is due to ,m4 ,amagat1 :o      

und]took ! /udy ( a c]ta9 numb] (       
bodies1 "s liquid & "s gase\s1 ext5d+ ! 
scope ( 8 exp]im5ts s z to embrace !    
diff]5t phases ( ! ph5om5a & to comp>e  
toge!r1 n only ! results relat+ to !    
same bodies1 b also ^? conc]n+ diff]5t  
bodies :i* happ5 to be 9 ! same         
conditions ( temp]ature & pressure1 b 9 
v diff]5t conditions z reg>ds _!        
critical po9ts4  ,f ! exp]im5tal po9t ( 
view1 ,m4 ,amagat has be5 able1 )       
extreme skill1 to conqu] ! mo/ s]i\s    
difficulties4 ,he has manag$ to measure 
) precision pressures am\nt+ to #cjjj   
atmosph]es1 & also ! v small volumes !n 
occupi$ by ! fluid mass "u consid]ation4
 ,?is la/ measurem5t1 :i* necessitates  
num]\s corrections1 is ! mo/ delicate "p
 ( ! op]ation4 ,^! rese>*es h dealt ) a 
c]ta9 numb] ( diff]5t bodies4 ,^? relat+
 to c>bonic acid & e?yl5e take 9 !      
critical po9t4 ,o!rs1 on hydrog5 &      
nitrog51 = in/ance1 are v ext5d$4 ,o!rs1
 aga91 su* z ! /udy ( ! compressibility 
( wat]1 h a special int]e/1 on acc\nt ( 

! peculi> prop]ties ( ?is sub/ance4 ,m4 
,amagat1 by a v concise discussion ( !  
exp]im5ts1 has also be5 able to         
def9itely e/abli% ! laws (              
compressibility & dilatation ( fluids "u
 con/ant pressure1 & to det]m9e ! value 
( ! v>i\s coeffici5ts z well z _!       
v>iations4 ,x ought to be possible to   
cond5se all ^! results into a s+le =mula
 repres5t+ ! volume1 ! temp]ature1 & !  
pressure4 ,rank9 &1 subsequ5tly1        
,recknagel1 & !n ,hirn1 =m]ly propos$   
=mulas ( t k9d2 b ! mo/ fam\s1 ! "o :i* 
fir/ appe>$ to conta9 9 a satisfactory  
mann] all ! facts :i* exp]im5ts br\ght  
to light & l$ to ! production ( _m o!rs1
 0 ! celebrat$ equation ( ,van d]       
,waals4  ,pr(essor ,van d] ,waals arriv$
 at ?is relation by rely+ ^u            
consid]ations d]iv$ f ! k9etic !ory (   
gases4 ,if we keep to ! simple idea at !
 bottom ( ?is !ory1 we at once          
demon/rate t ! gas ought to obey ! laws 
( ,m>iotte & ( ,gay-,lussac1 s t !      
*>act]i/ic equation w\ld be obta9$ by ! 

/atem5t t ! product ( ! numb] :i* is !  
measure ( ! volume by t :i* is ! measure
 ( ! pressure is equal to a con/ant     
coeffici5t multipli$ by ! degree ( !    
absolute temp]ature4 ,b to get at ?is   
result we neglect two important factors4
  ,we d n take into acc\nt1 9 fact1 !   
attraction :i* ! molecules mu/ ex]cise  
on ea* o!r4 ,n[1 ?is attraction1 :i* is 
nev] absolutely non-exi/5t1 may become  
consid]able :5 ! molecules are drawn    
clos] toge!r2 t is to say1 :5 !         
compress$ gase\s mass occupies a m & m  
re/rict$ volume4 ,on ! o!r h&1 we       
assimilate ! molecules1 z a fir/        
approximation1 to mat]ial po9ts )\t     
dim5sions2 9 ! evaluation ( ! pa?       
trav]s$ by ea* molecule no notice is    
tak5 ( ! fact t1 at ! mom5t ( ! %ock1 _!
 c5tres ( gravity are /ill sep>at$ by a 
di/ance equal to twice ! radius ( !     
molecule4  ,m4 ,van d] ,waals has s\ght 
out ! modifications :i* mu/ be introduc$
 into ! simple *>act]i/ic equation to   
br+ x ne>] to reality4 ,he ext5ds to !  

case ( gases ! consid]ations by :i*     
,laplace1 9 8 fam\s !ory ( capill>ity1  
r$uc$ ! effect ( ! molecul> attraction  
to a p]p5dicul> pressure ex]cis$ on !   
surface ( a liquid4 ,?is leads him to   
add to ! ext]nal pressure1 t due to !   
reciprocal attractions ( ! gase\s       
p>ticles4 ,on ! o!r h&1 :5 we attribute 
f9ite dim5sions to ^! p>ticles1 we mu/  
give a high] value to ! numb] ( %ocks   
produc$ 9 a giv5 "t1 s9ce ! effect ( ^! 
dim5sions is to dim9i% ! mean pa? !y    
trav]se 9 ! "t :i* elapses betwe5 two   
consecutive %ocks4  ,! calculation ?us  
pursu$ leads to our add+ to ! pressure 9
 ! simple equation a t]m :i* is         
designat$ ! int]nal pressure1 & :i* is !
 quoti5t ( a con/ant by ! squ>e ( !     
volume2 also to our d$uct+ f ! volume a 
con/ant :i* is ! quadruple ( ! total &  
inv>iable volume :i* ! gase\s molecules 
w\ld occupy did !y t\* "o ano!r4  ,!    
exp]im5ts fit 9 fairly well ) ! =mula ( 
,van d] ,waals1 b consid]able           
discrepancies occur :5 we ext5d its     

limits1 p>ticul>ly :5 ! pressures       
?r\gh\t a r wid] int]val are consid]$2 s
 t o!r & r m complex =mulas1 on :i* !re 
is no advantage 9 dwell+1 h be5 propos$1
 &1 9 c]ta9 cases1 bett] repres5t !     
facts4  ,b ! mo/ rem>kable result ( ,m4 
,van d] ,waals' calculations is !       
discov]y ( correspond+ /ates4 ,= a long 
"t physici/s spoke ( bodies tak5 9 a    
comp>able /ate4 ,dalton1 = example1     
po9t$ out t liquids h vap\r-pressures   
equal to ! temp]atures equally di/ant f 
_! boil+-po9t2 b t if1 9 ?is p>ticul>   
prop]ty1 liquids 7 comp>able "u ^!      
conditions ( temp]ature1 z reg>ds o!r   
prop]ties ! p>allelism 0 no long] to be 
v]ifi$4 ,no g5]al rule 0 f\nd until ,m4 
,van d] ,waals fir/ enunciat$ a prim>y  
law1 viz41 t if ! pressure1 ! volume1 & 
! temp]ature are e/imat$ by tak+ z units
 ! critical quantities1 ! con/ants      
special to ea* body disappe> 9 !        
*>act]i/ic equation1 :i* ?us becomes !  
same = all fluids4  ,! words correspond+
 /ates ?us take a p]fectly precise      

signification4 ,correspond+ /ates are ^?
 = :i* ! num]ical values ( ! pressure1  
volume1 & temp]ature1 express$ by tak+ z
 units ! values correspond+ to !        
critical po9t1 are equal2 &1 9          
correspond+ /ates any two fluids h      
exactly ! same prop]ties4  ,m4          
,natanson1 & subsequ5tly ,p4 ,curie &   
,m4 ,mesl91 h %[n by v>i\s consid]ations
 t ! same result may be arriv$ at by    
*oos+ units :i* correspond to any       
correspond+ /ates2 x has also be5 %[n t 
! !orem ( correspond+ /ates 9 no way    
implies ! exactitude ( ,van d] ,waals'  
=mula4 ,9 reality1 ?is is simply due to 
! fact t ! *>act]i/ic equation only     
conta9s ?ree con/ants4  ,! philosophical
 importance & ! practical int]e/ ( !    
discov]y nev]!less rema9 consid]able4 ,z
 0 to be expect$1 numb]s ( exp]im5t]s h 
s\ght :e!r ^! consequ5ces are duly      
v]ifi$ 9 reality4 ,m4 ,amagat1          
p>ticul>ly1 has made use = ?is purpose (
 a mo/ orig9al & simple me?od4 ,he      
rem>ks t1 9 all its g5]ality1 ! law may 

be translat$ ?us3 ,if ! iso!rmal        
diagrams ( two sub/ances be drawn to !  
same scale1 tak+ z unit ( volume & (    
pressure ! values ( ! critical con/ants1
 ! two diagrams %\ld co9cide2 t is to   
say1 _! sup]position %\ld pres5t !      
aspect ( "o diagram app]ta9+ to a s+le  
sub/ance4 ,fur!r1 if we possess !       
diagrams ( two bodies drawn to any      
scales & ref]able to any units :atev]1 z
 ! *anges ( units mean *anges 9 ! scale 
( ! axes1 we ought to make "o ( !       
diagrams simil> to ! o!r by l5g!n+ or   
%ort5+ x 9 ! direction ( "o ( ! axes4   
,m4 ,amagat !n photographs two iso!rmal 
diagrams1 leav+ "o fix$1 b arrang+ ! o!r
 s t x may be free to turn r\nd ea* axis
 ( ! co-ord9ates2 & by project+1 by     
means ( a magic lant]n1 ! second on !   
fir/1 he arrives 9 c]ta9 cases at an    
almo/ complete co9cid5ce4  ,?is         
me*anical means ( pro( ?us disp5ses )   
labori\s calculations1 b its s5sibility 
is unequally di/ribut$ ov] ! diff]5t    
regions ( ! diagram4 ,m4 ,raveau has    

po9t$ out an equally simple way ( v]ify+
 ! law1 by rem>k+ t if ! log>i?ms ( !   
pressure & volume are tak5 z            
co-ord9ates1 ! co-ord9ates ( two        
correspond+ po9ts diff] by two con/ant  
quantities1 & ! correspond+ curves are  
id5tical4  ,f ^! comp>isons1 & f o!r    
important rese>*es1 among :i* %\ld be   
p>ticul>ly m5tion$ ^? ( ,mr ,s4 ,"y &   
,m4 ,ma?ias1 x results t ! laws (       
correspond+ /ates h n1 un=tunately1 !   
degree ( g5]ality :i* we at fir/        
attribut$ to !m1 b t !y are satisfactory
 :5 appli$ to c]ta9 gr\ps ( bodies4#g   
,footnote #g3 ,mr ,pre/on ?us puts x3 ,!
 law ( correspond+ /ates seems to be n  
q1 b v ne>ly true = ^! sub/ances i4e4 ! 
halog5 d]ivatives ( b5z5e2 b 9 ! case ( 
! o!r sub/ances exam9$1 ! majority ( ^! 
g5]alizations 7 ei!r only r\ghly true or
 altoge!r dep>t$ f 7,!ory ( ,heat1      
,london1 #aijd1 p4 #ead47--;,,ed4  ,if 9
 ! /udy ( ! /atics ( a simple fluid !   
exp]im5tal results are already complex1 
we ought to expect mu* great]           

difficulties :5 we come to deal )       
mixtures2 /ill ! problem has be5        
approa*$1 & _m po9ts are already cle>$  
up4  ,mix$ fluids may fir/ ( all be     
reg>d$ z compos$ ( a l>ge numb] (       
inv>iable p>ticles4 ,9 ?is p>ticul>ly   
simple case ,m4 ,van d] ,waals has      
e/abli%$ a *>act]i/ic equation ( !      
mixtures :i* is f\nd$ on me*anical      
consid]ations4 ,v>i\s v]ifications ( ?is
 =mula h be5 effect$1 & x has1 9        
p>ticul>1 be5 ! object ( v important    
rem>ks by ,m4 ,daniel ,b]!lot4  ,x is   
int]e/+ to note t !rmodynamics seems    
p[]less to det]m9e ?is equation1 = x    
does n tr\ble itself ab\t ! nature ( !  
bodies ob$i5t to its laws2 b1 on ! o!r  
h&1 x int]v5es to det]m9e ! prop]ties ( 
coexi/+ phases4 ,if we exam9e !         
conditions ( equilibrium ( a mixture :i*
 is n subject$ to ext]nal =ces1 x w be  
demon/rat$ t ! di/ribution mu/ come back
 to a juxtaposition ( homog5e\s phases2 
9 a giv5 volume1 matt] ought s to       
arrange itself t ! total sum ( free     

en]gy has a m9imum value4 ,?us1 9 ord]  
to elucidate all que/ions relat+ to !   
numb] & qualities ( ! phases into :i* ! 
sub/ance divides itself1 we are l$ to   
reg>d ! geometrical surface :i* = a giv5
 temp]ature repres5ts ! free en]gy4  ,i 
am unable to ent] "h into ! detail ( !  
que/ions connect$ ) ! !ories ( ,gibbs1  
:i* h be5 ! object ( num]\s !oretical   
/udies1 & also ( a s]ies1 ev] m & m     
abundant1 ( exp]im5tal rese>*es4 ,m4    
,duhem1 9 p>ticul>1 has publi%$1 on !   
subject1 memoirs ( ! highe/ importance1 
& a great numb] ( exp]im5t]s1 mo/ly     
s*ol>s work+ 9 ! physical laboratory (  
,leyd5 "u ! guidance ( ! ,director1 ,mr 
,kam]l+h ,onnes1 h endeav\r$ to v]ify ! 
anticipations ( ! !ory4  ,we are a      
little less advanc$ z reg>ds abnormal   
sub/ances2 t is to say1 ^? compos$ (    
molecules1 p>tly simple & p>tly complex1
 & ei!r dissociat$ or associat$4 ,^!    
cases mu/ naturally be gov]n$ by v      
complex laws4 ,rec5t rese>*es by ,,mm4  
,van d] ,waals1 ,alexeif1 ,ro?mund1     

,kn51 ,lehfeld1 etc41 ?r[1 h[ev]1 "s    
light on ! "q4  ,! daily m num]\s       
applications ( ! laws ( correspond+     
/ates h r5d]$ highly important !        
det]m9ation ( ! critical con/ants :i*   
p]mit ^! /ates to be def9$4 ,9 ! case ( 
homog5e\s bodies ! critical elem5ts h a 
simple1 cle>1 & precise s5se2 ! critical
 temp]ature is t ( ! s+le iso!rmal l9e  
:i* pres5ts a po9t ( inflexion at a     
horizontal tang5t2 ! critical pressure &
 ! critical volume are ! two co-ord9ates
 ( ?is po9t ( inflexion4  ,! ?ree       
critical con/ants may be det]m9$1 z ,mr 
,s4 ,"y & ,m4 ,amagat h %[n1 by a direct
 me?od bas$ on ! consid]ation ( !       
saturat$ /ates4 ,results1 p]haps m      
precise1 may also be obta9$ if "o keeps 
to two con/ants or ev5 to a s+le "o--   
temp]ature1 = example--by employ+ v>i\s 
special me?ods4 ,_m o!rs1 ,,mm4         
,cailletet & ,col>deau1 ,m4 ,"y1 ,m4,j4 
,*appuis1 etc41 h proce$$ ?us4  ,! case 
( mixtures is mu* m complicat$4 ,a b9>y 
mixture has a critical space in/ead ( a 

critical po9t4 ,?is space is compris$   
betwe5 two extreme temp]atures1 ! l[]   
correspond+ to :at is call$ ! fold+     
po9t1 ! high] to t :i* we call ! po9t ( 
contact ( ! mixture4 ,betwe5 ^! two     
temp]atures an iso!rmal compression     
yields a quantity ( liquid :i*          
increases1 !n rea*es a maximum1         
dim9i%es1 & disappe>s4 ,?is is !        
ph5om5on ( retrograde cond5sation4 ,we  
may say t ! prop]ties ( ! critical po9t 
( a homog5e\s sub/ance are1 9 a way1    
divid$1 :5 x is a "q ( a b9>y mixture1  
betwe5 ! two po9ts m5tion$4             
,calculation has enabl$ ,m4 ,van d]     
,waals1 by ! application ( 8 k9etic     
!ories1 & ,m4 ,duhem1 by means (        
!rmodynamics1 to =esee mo/ ( ! results  
:i* h s9ce be5 v]ifi$ by exp]im5t4 ,all 
^! facts h be5 admirably set =? &       
sy/ematically co-ord9at$ by ,m4 ,ma?ias1
 :o1 by 8 own rese>*es1 moreov]1 has    
made contributions ( ! highe/ value to !
 /udy ( que/ions reg>d+ ! cont9uity ( ! 
liquid & gase\s /ates4  ,! fur!r k (    

critical elem5ts has all[$ ! laws (     
correspond+ /ates to be m closely exam9$
 9 ! case ( homog5e\s sub/ances4 ,x has 
%[n t1 z ,i h already said1 bodies mu/  
be arrang$ 9 gr\ps1 & ?is fact cle>ly   
proves t ! prop]ties ( a giv5 fluid are 
n det]m9$ by its critical con/ants      
alone1 & t x is necess>y to add to !m "s
 o!r specific p>amet]s2 ,m4 ,ma?ias &   
,m4 ,d4 ,b]!lot h indicat$ "s :i* seem  
to play a consid]able "p4  ,x results   
also f ?is t ! *>act]i/ic equation ( a  
fluid _c yet be consid]$ p]fectly kn[n4 
,nei!r ! equation ( ,van d] ,waals nor !
 m complicat$ =mulas :i* h be5 propos$  
by v>i\s au?ors are 9 p]fect con=mity ) 
reality4 ,we may ?9k t rese>*es ( ?is   
k9d w only be successful if att5tion is 
conc5trat$1 n only on ! ph5om5a (       
compressibility & dilatation1 b also on 
! calorimetric prop]ties ( bodies4      
,!rmodynamics inde$ e/abli%es relations 
betwe5 ^? prop]ties & o!r con/ants1 b   
does n all[ ev]y?+ to be =ese54  ,sev]al
 physici/s h effect$ v int]e/+          

calorimetric measurem5ts1 ei!r1 l ,m4   
,p]ot1 9 ord] to v]ify ,clapeyron's     
=mula reg>d+ ! heat ( vaporization1 or  
to asc]ta9 ! values ( specific heats &  
_! v>iations :5 ! temp]ature or !       
pressure happ5s to *ange4 ,m4 ,ma?ias   
has ev5 succe$$ 9 completely det]m9+ !  
specific heats ( liquefi$ gases & ( _!  
saturat$ vap\rs1 z well z ! heat (      
int]nal & ext]nal vaporization4    #b4  
,,! ,,liquefaction ,,( ,,gases1 ,,& ,,! 
,,prop]ties ,,( ,,bodies ,,at ,a        
,,l[ ,,temp]ature  ,! sci5tific         
advantages ( all ^! rese>*es h be5      
great1 &1 z ne>ly always happ5s1 !      
practical consequ5ces d]iv$ f !m h also 
be5 mo/ important4 ,x is ow+ to ! m     
complete k ( ! g5]al prop]ties ( fluids 
t imm5se progress has be5 made ^! la/   
few ye>s 9 ! me?ods ( liquefy+ gases4   
,f a !oretical po9t ( view ! new        
processes ( liquefaction c be class$ 9  
two categories4 ,l9de's ma*9e & ^?      
resembl+ x utilize1 z is kn[n1 expansion
 )\t any notable production ( ext]nal   

"w4 ,?is expansion1 nev]!less1 causes a 
fall 9 ! temp]ature1 because ! gas 9 !  
exp]im5t is n a p]fect gas1 &1 by an    
+5i\s process1 ! refrig]ations produc$  
are made cumulative4  ,sev]al physici/s 
h propos$ to employ a me?od :]eby       
liquefaction %\ld be obta9$ by expansion
 ) recup]able ext]nal "w4 ,?is me?od1   
propos$ z long ago z #ahfj by ,siem5s1  
w\ld (f] consid]able advantages4        
,!oretically1 ! liquefaction w\ld be m  
rapid1 & obta9$ mu* m economically2 b   
un=tunately 9 ! exp]im5t s]i\s ob/acles 
are met )1 especially f ! difficulty (  
obta9+ a suitable lubricant "u int5se   
cold = ^? p>ts ( ! ma*9e :i* h to be 9  
movem5t if ! app>atus is to "w4  ,m4    
,claude has rec5tly made great progress 
on ?is po9t by ! use1 dur+ ! runn+ ( !  
ma*9e1 ( ! e!r ( petrol1 :i* is         
uncongealable1 & a good lubricant = !   
mov+ p>ts4 ,:5 once ! desir$ region (   
cold is rea*$1 air itself is us$1 :i*   
moi/5s ! metals b does n completely     
avoid friction2 s t ! results w\ld h    

rema9$ only middl+1 _h n ?is +5i\s      
physici/ devis$ a new improvem5t :i* has
 "s analogy ) sup]heat+ ( /eam 9 /eam   
eng9es4 ,he slightly v>ies ! initial    
temp]ature ( ! compress$ air on ! v]ge (
 liquefaction s z to avoid a zone ( deep
 p]turbations 9 ! prop]ties ( fluids1   
:i* w\ld make ! "w ( expansion v feeble 
& ! cold produc$ consequ5tly slight4    
,?is improvem5t1 simple z x is 9        
appe>ance1 pres5ts sev]al o!r advantages
 :i* imm$iately treble ! output4  ,!    
special object ( ,m4 ,claude 0 to obta9 
oxyg5 9 a practical mann] by ! actual   
di/illation ( liquid air4 ,s9ce nitrog5 
boils at -#aid & oxyg5 at -#ahj4e ,c41  
if liquid air be evaporat$1 ! nitrog5   
escapes1 especially at ! comm5cem5t ( ! 
evaporation1 :ile ! oxyg5 conc5trates 9 
! residual liquid1 :i* f9ally consi/s ( 
pure oxyg51 :ile at ! same "t !         
temp]ature rises to ! boil+-po9t        
7-#ahj4e ,c47 ( oxyg54 ,b liquid air is 
co/ly1 & if "o 7 cont5t to evaporate x =
 ! purpose ( collect+ a "p ( ! oxyg5 9 !

 residuum1 ! process w\ld h a v poor    
result f ! comm]cial po9t ( view4 ,z    
e>ly z #ahib1 ,mr ,p>k9son ?\ght (      
improv+ ! output by recov]+ ! cold      
produc$ by liquid air dur+ its          
evaporation2 b an incorrect idea1 :i*   
seems to h result$ f c]ta9 exp]im5ts (  
,dew>--! idea t ! ph5om5on ( !          
liquefaction ( air w\ld n be1 ow+ to    
c]ta9 peculi>ities1 ! exact conv]se ( t 
( vaporization--l$ to ! employm5t ( v   
imp]fect app>atus4 ,m4 ,claude1 h[ev]1  
by mak+ use ( a me?od :i* he calls !    
rev]sal#h me?od1 obta9s a complete      
rectification 9 a rem>kably simple mann]
 & "u extremely advantage\s economic    
conditions4 ,app>atus1 ( surpris+ly     
r$uc$ dim5sions b ( great effici5cy1 is 
n[ 9 daily "w1 :i* easily enables m ?an 
a ?\s& cubic metres ( oxyg5 to be obta9$
 at ! rate1 p] horse-p[]1 ( m ?an a     
cubic metre p] h\r4  ,footnote #h3      
,me?ode avec ret\r en arri]e4--,,ed  ,x 
is 9 ,engl&1 ?anks to ! skill ( ,sir    
,james ,dew> & 8 pupils--?anks also1 x  

mu/ be said1 to ! g5]osity ( ! ,royal   
,in/itution1 :i* has devot$ consid]able 
sums to ^! co/ly exp]im5ts--t ! mo/     
num]\s & sy/ematic rese>*es h be5       
effect$ on ! production ( int5se cold4  
,i %all "h note only ! m important      
results1 especially ^? relat+ to !      
prop]ties ( bodies at l[ temp]atures4   
,_! electrical prop]ties1 9 p>ticul>1   
und]go "s int]e/+ modifications4 ,! ord]
 :i* metals assume 9 po9t ( conductivity
 is no long] ! same z at ord9>y         
temp]atures4 ,?us at -#bjj ,c4 copp] is 
a bett] conductor ?an silv]4 ,!         
resi/ance dim9i%es ) ! temp]ature1 &1   
d[n to ab\t -#bjj1 ?is dim9ution is     
almo/ l9e>1 & x w\ld seem t ! resi/ance 
t5ds t[>ds z]o :5 ! temp]ature approa*es
 ! absolute z]o4 ,b1 aft] -#bjj1 !      
patt]n ( ! curves *anges1 & x is easy to
 =esee t at absolute z]o ! resi/ivities 
( all metals w\ld /ill h1 contr>y to :at
 0 =m]ly suppos$1 a notable value4      
,solidifi$ electrolytes :i*1 at         
temp]atures f> bel[ _! fusion po9t1 /ill

 reta9 a v appreciable conductivity1    
become1 on ! contr>y1 p]fect insulators 
at l[ temp]atures4 ,_! dielectric       
con/ants assume relatively high values4 
,,mm4 ,curie & ,compan1 :o h /udi$ ?is  
"q f _! own po9t ( view1 h not$1        
moreov]1 t ! specific inductive capacity
 *anges consid]ably ) ! temp]ature4  ,9 
! same way1 magnetic prop]ties h be5    
/udi$4 ,a v int]e/+ result is t f\nd 9  
oxyg53 ! magnetic susceptibility ( ?is  
body increases at ! mom5t (             
liquefaction4 ,nev]!less1 ?is increase1 
:i* is enorm\s 7s9ce ! susceptibility   
becomes sixte5 hundr$ times great] ?an x
 0 at fir/71 if we take x 9 connection )
 equal volumes1 is mu* less consid]able 
if tak5 9 equal masses4 ,x mu/ be       
conclud$ f ?is fact t ! magnetic        
prop]ties app>5tly d n belong to !      
molecules !mselves1 b dep5d on _! /ate (
 aggregation4  ,! me*anical prop]ties ( 
bodies also und]go important            
modifications4 ,9 g5]al1 _! cohesion is 
greatly increas$1 & ! dilatation produc$

 by slight *anges ( temp]ature is       
consid]able4 ,sir ,james ,dew> has      
effect$ c>eful measurem5ts ( !          
dilatation ( c]ta9 bodies at l[         
temp]atures3 = example1 ( ice4 ,*anges 9
 col\r occur1 & v]milion & iodide (     
m]cury pass into pale orange4           
,phosphoresc5ce becomes m int5se1 & mo/ 
bodies ( complex /ructure--milk1 eggs1  
fea!rs1 cotton1 & fl[]s--become         
phosphoresc5t4 ,! same is ! case ) c]ta9
 simple bodies1 su* z oxyg51 :i* is     
trans=m$ into ozone & emits a :ite light
 9 ! process4  ,*emical aff9ity is almo/
 put an end to2 phosphorus & potassium  
rema9 in]t 9 liquid oxyg54 ,x %\ld1     
h[ev]1 be not$1 & ?is rem>k has d\btless
 "s int]e/ = ! !ories ( photographic    
action1 t photographic sub/ances reta91 
ev5 at ! temp]ature ( liquid hydrog51 a 
v consid]able "p ( _! s5sitiv5ess to    
light4  ,sir ,james ,dew> has made "s   
important applications ( l[ temp]atures 
9 *emical analysis2 he also utilizes !m 
to create a vacuum4 ,8 rese>*es h1 9    

fact1 prov$ t ! pressure ( air congeal$ 
by liquid hydrog5 _c exce$ ! million? ( 
an atmosph]e4 ,we h1 !n1 9 ?is process1 
an orig9al & rapid means ( creat+ an    
excell5t vacuum 9 app>atus ( v diff]5t  
k9ds--a means :i*1 9 c]ta9 cases1 may be
 p>ticul>ly conv5i5t4#i  ,footnote #i3  
,pr(essor ,soddy1 9 a pap] read be=e !  
,royal ,society on ! #ae? ,novemb]      
#aijf1 w>ns exp]im5t]s aga9/ vacua      
creat$ by *>coal cool$ 9 liquid air 7!  
me?od ref]r$-to 9 ! text71 unless z mu* 
( ! air z possible is fir/ remov$ ) a   
pump & replac$ by "s argon-free gas4    
,accord+ to him1 nei!r helium nor argon 
is absorb$ by *>coal4 ,by ! use (       
electrically-heat$ calcium1 he claims to
 h produc$ an almo/ p]fect              
vacuum4--,,ed4  ,?anks to ^! /udies1 a  
consid]able field has be5 op5$ up =     
biological rese>*1 b 9 ?is1 :i* is n our
 subject1 ,i %all notice "o po9t only4  
,x has be5 prov$ t vital g]ms--bact]ia1 
= example--may be kept = sev5 days at   
-#aij;,c4 )\t _! vitality be+ modifi$4  

,phosphoresc5t organisms cease1 x is    
true1 to %9e at ! temp]ature ( liquid   
air1 b ?is fact is simply due to !      
oxidations & o!r *emical reactions :i*  
keep up ! phosphoresc5ce be+ !n susp5d$1
 = phosphoresc5t activity reappe>s s    
soon z ! temp]ature is aga9 suffici5tly 
rais$4 ,an important conclusion has be5 
drawn f ^! exp]im5ts :i* affects        
cosmogonical !ories3 s9ce ! cold ( space
 c\ld n kill ! g]ms ( life1 x is 9 no   
way absurd to suppose t1 "u prop]       
conditions1 a g]m may be transmitt$ f "o
 planet to ano!r4  ,among ! discov]ies  
made ) ! new processes1 ! "o :i* mo/    
/rik+ly int]e/$ public att5tion is t (  
new gases 9 ! atmosph]e4 ,we "k h[ ,sir 
,william ,ramsay & ,dr4 ,trav]s fir/    
obs]v$ by means ( ! spectroscope !      
*>act]i/ics ( ! companions ( argon 9 !  
lea/ volatile "p ( ! atmosph]e4 ,sir    
,james ,dew> on ! "o h&1 & ,sir ,william
 ,ramsay on ! o!r1 subsequ5tly sep>at$ 9
 addition to argon & helium1 crypton1   
x5on1 & neon4 ,! process employ$ consi/s

 ess5tially 9 fir/ solidify+ ! lea/     
volatile "p ( ! air & !n caus+ x to     
evaporate ) extreme sl[ness4 ,a tube )  
electrodes enables ! spectrum ( ! gas 9 
process ( di/illation to be obs]v$4 ,9  
?is mann]1 ! spectra ( ! v>i\s gases may
 be se5 foll[+ "o ano!r 9 ! inv]se ord] 
( _! volatility4 ,all ^! gases are      
monoatomic1 l m]cury2 t is to say1 !y   
are 9 ! mo/ simple /ate1 !y possess no  
int]nal molecul> en]gy 7unless x is t   
:i* heat is capable ( supply+71 & !y ev5
 seem to h no *emical en]gy4 ,ev]y?+    
leads to ! belief t !y %[ ! exi/5ce on !
 e>? ( an e>li] /ate ( ?+s n[ vani%$4 ,x
 may be suppos$1 = in/ance1 t helium &  
neon1 ( :i* ! molecul> mass is v slight1
 7 =m]ly m abundant on our planet2 b at 
an epo* :5 ! temp]ature ( ! globe 0     
high]1 ! v spe$ ( _! molecules may h    
rea*$ a consid]able value1 exce$+1 =    
in/ance1 elev5 kilometres p] second1 :i*
 suffices to expla9 :y !y %\ld h left   
our atmosph]e4 ,crypton & neon1 :i* h a 
d5sity f\r times great] ?an oxyg51 may1 

on ! contr>y1 h p>tly disappe>$ by      
solution at ! bottom ( ! sea1 :]e x is n
 absurd to suppose t consid]able        
quantities w\ld be f\nd liquefi$ at     
great dep?s4#aj  ,footnote #aj3 ,ano!r  
view1 viz4 t ^! in]t gases are a k9d (  
wa/e product ( radioactive *anges1 is   
also ga9+ gr\nd4 ,! discov]y ( !        
radioactive m9]al malacone1 :i* gives (f
 bo? helium & argon1 goes to support    
?is4 ,see ,messrs ,ket*9 & ,w9t]son's   
pap] on ! subject at ! ,*emical         
,society1 #ah? ,octob] #aijf4--;,,ed4   
,x is probable1 moreov]1 t ! high]      
regions ( ! atmosph]e are n compos$ ( ! 
same air z t ar\nd u4 ,sir ,james ,dew> 
po9ts out t ,dalton's law dem&s t e gas 
compos+ ! atmosph]e %\ld h1 at all      
heights & temp]atures1 ! same pressure z
 if x 7 alone1 ! pressure decreas+ !    
less quickly1 all ?+s be+ equal1 z its  
d5sity becomes less4 ,x results f ?is t 
! temp]ature becom+ gradually l[] z we  
rise 9 ! atmosph]e1 at a c]ta9 altitude 
!re c no long] rema9 any traces ( oxyg5 

or nitrog51 :i* no d\bt liquefy1 & !    
atmosph]e mu/ be almo/ exclusively      
compos$ ( ! mo/ volatile gases1 includ+ 
hydrog51 :i* ,m4,a4 ,gauti] has1 l ,"l  
,rayleigh & ,sir ,william ,ramsay1 prov$
 to exi/ 9 ! air4 ,! spectrum ( !       
,aurora borealis1 9 :i* are f\nd ! l9es 
( ^? p>ts ( ! atmosph]e :i* _c be       
liquefi$ 9 liquid hydrog51 toge!r ) !   
l9es ( argon1 crypton1 & x5on1 is q 9   
con=mity ) ?is po9t ( view4 ,x is1      
h[ev]1 s+ul> t x %\ld be ! spectrum (   
crypton1 t is to say1 ( ! heavie/ gas ( 
! gr\p1 :i* appe>s mo/ cle>ly 9 ! upp]  
regions ( ! atmosph]e4  ,among ! gases  
mo/ difficult to liquefy1 hydrog5 has   
be5 ! object ( p>ticul> rese>* & (      
really quantitative exp]im5ts4 ,its     
prop]ties 9 a liquid /ate are n[ v      
cle>ly kn[n4 ,its boil+-po9t1 measur$ ) 
a helium !rmomet] :i* has be5 comp>$ )  
!rmomet]s ( oxyg5 & hydrog51 is -#beb2  
its critical temp]ature is -#bda ,c42   
its critical pressure1 #ae atmosph]es4  
,x is f\r times light] ?an wat]1 x does 

n pres5t any absorption spectrum1 & its 
specific heat is ! greate/ kn[n4 ,x is n
 a conductor ( electricity4 ,solidifi$  
at #ae absolute1 x is f> f rem9d+ "o by 
its aspect ( a metal2 x r resembles a   
piece ( p]fectly pure ice1 & ,dr ,trav]s
 attributes to x a cry/all9e /ructure4  
,! la/ gas :i* has resi/$ liquefaction1 
helium1 has rec5tly be5 obta9$ 9 a      
liquid /ate2 x appe>s to h its          
boil+-po9t 9 ! neighb\rhood ( #f        
absolute4#aa  ,footnote #aa3 ,m4 ,po9c> 
is "h 9 error4 ,helium has nev] be5     
liquefi$4--,,ed4    #c4 ,,solids ,,&    
,,liquids  ,! int]e/ ( ! results to :i* 
! rese>*es on ! cont9uity betwe5 !      
liquid & ! gase\s /ates h l$ is s great1
 t numb]s ( s*ol>s h naturally be5      
induc$ to inquire :e!r some?+ analog\s  
might n be f\nd 9 ! case ( liquids &    
solids4 ,we might ?9k t a simil>        
cont9uity ought to be !re met )1 t !    
univ]sal "* ( ! prop]ties ( matt] =bade 
all real discont9uity betwe5 two diff]5t
 /ates1 & t1 9 tru?1 ! solid 0 a        

prolongation ( ! liquid /ate4  ,to      
discov] :e!r ?is supposition is correct1
 x conc]ns u to comp>e ! prop]ties (    
liquids & solids4 ,if we f9d t all      
prop]ties are common to ! two /ates we h
 ! "r to believe1 ev5 if !y pres5t$     
!mselves 9 diff]5t degrees1 t1 by a     
cont9u\s s]ies ( int]m$i>y bodies1 ! two
 classes might yet be connect$4 ,if1 on 
! o!r h&1 we discov] t !re exi/s 9 ^!   
two classes "s quality ( a diff]5t      
nature1 we mu/ necess>ily conclude t !re
 is a discont9uity :i* no?+ c remove4   
,! di/9ction e/abli%$1 f ! po9t ( view (
 daily cu/om1 betwe5 solids & liquids1  
proce$s especially f ! difficulty t we  
meet ) 9 ! "o case1 & ! facility 9 !    
o!r1 :5 we wi% to *ange _! =m tempor>ily
 or p]man5tly by ! action ( me*anical   
=ce4 ,?is di/9ction only corresponds1   
h[ev]1 9 reality1 to a diff]5ce 9 !     
value ( c]ta9 coeffici5ts4 ,x is        
impossible to discov] by ?is means any  
absolute *>act]i/ic :i* e/abli%es a     
sep>ation betwe5 ! two classes4 ,mod]n  

rese>*es prove ?is cle>ly4 ,x is n )\t  
use1 9 ord] to well und]/& !m1 to /ate  
precisely ! mean+ ( a few t]ms g5]ally r
 loosely employ$4  ,if a conjunction (  
=ces act+ on a homog5e\s mat]ial mass   
happ5s to de=m x )\t compress+ or dilat+
 x1 two v di/9ct k9ds ( reactions may   
appe> :i* oppose !mselves to ! ef=t     
ex]cis$4 ,dur+ ! "t ( de=mation1 & dur+ 
t "t only1 ! fir/ make _! influ5ce felt4
 ,!y dep5d ess5tially on ! great] or    
less rapidity ( ! de=mation1 !y cease ) 
! movem5t1 & c\ld n1 9 any case1 br+ !  
body back to its pri/9e /ate (          
equilibrium4 ,! exi/5ce ( ^! reactions  
leads u to ! idea ( viscosity or int]nal
 friction4  ,! second k9d ( reactions   
are ( a diff]5t nature4 ,!y cont9ue to  
act :5 ! de=mation rema9s /ation>y1 &1  
if ! ext]nal =ces happ5 to disappe>1 !y 
are capable ( caus+ ! body to return to 
its initial =m1 provid$ a c]ta9 limit   
has n be5 exce$$4 ,^! la/ con/itute     
rigidity4  ,at fir/ sight a solid body  
appe>s to h a f9ite rigidity & an       

inf9ite viscosity2 a liquid1 on !       
contr>y1 pres5ts a c]ta9 viscosity1 b no
 rigidity4 ,b if we exam9e ! matt] m    
closely1 beg9n+ ei!r ) ! solids or ) !  
liquids1 we see ?is di/9ction vani%4    
,tresca %[$ long ago t int]nal friction 
is n inf9ite 9 a solid2 c]ta9 bodies c1 
s to speak1 at once fl[ & be m\ld$4     
,m4,w4 ,spr+ has giv5 _m examples ( su* 
ph5om5a4 ,on ! o!r h&1 viscosity 9      
liquids is nev] non-exi/5t2 = 7 x s =   
wat]1 = example1 9 ! celebrat$ exp]im5t 
effect$ by ,j\le = ! det]m9ation ( !    
me*anical equival5t ( ! caloric1 !      
liquid borne along by ! floats w\ld     
slide )\t friction on ! surr\nd+ liquid1
 & ! "w done by movem5t w\ld be ! same  
:e!r ! floats did or did n plunge into !
 liquid mass4  ,9 c]ta9 cases obs]v$    
long ago ) :at are call$ pa/y bodies1   
?is viscosity atta9s a value almo/      
comp>able to t obs]v$ by ,m4 ,spr+ 9 "s 
solids4 ,nor does rigidity all[ u to    
e/abli% a b>ri] betwe5 ! two /ates4     
,not)/&+ ! extreme mobility ( _!        

p>ticles1 liquids conta91 9 fact1       
ve/iges ( ! prop]ty :i* we =m]ly wi%$ to
 consid] ! special *>act]i/ic ( solids4 
,maxwell be=e succe$$ 9 r5d]+ ! exi/5ce 
( ?is rigidity v probable by exam9+ !   
optical prop]ties ( a de=m$ lay] (      
liquid4 ,b a ,russian physici/1 ,m4     
,s*w$(f1 has gone fur!r1 & has be5 able 
by direct exp]im5ts to %[ t a %ea? (    
liquid set betwe5 two solid cyl9d]s     
t5ds1 :5 "o ( ! cyl9d]s is subject$ to a
 slight rotation1 to return to its      
orig9al position1 & gives a measurable  
torsion to a ?read uphold+ ! cyl9d]4 ,f 
! k ( ?is torsion ! rigidity c be d$uc$4
 ,9 ! case ( a solution conta9+ #a_/b p]
 c5t4 ( gelat9e1 x is f\nd t ?is        
rigidity1 enorm\s comp>$ ) t ( wat]1 is 
/ill1 h[ev]1 "o trillion eight hundr$ & 
=ty billion times less ?an t ( /eel4    
,?is figure1 exact )9 a few billions1   
proves t ! rigidity is v slight1 b      
exi/s2 & t suffices = a *>act]i/ic      
di/9ction to be f\nd$ on ?is prop]ty4 ,9
 a g5]al way1 ,m4 ,spr+ has also        

e/abli%$ t we meet 9 solids1 9 a degree 
m or less m>k$1 ) ! prop]ties ( liquids4
 ,:5 !y are plac$ 9 suitable conditions 
( pressure & "t1 !y fl[ ?r\gh orifices1 
transmit pressure 9 all directions1     
diffuse & dissolve "o into ! o!r1 &     
react *emically on ea* o!r4 ,!y may be  
sold]$ toge!r by compression2 by ! same 
means alloys may be produc$2 & fur!r1   
:i* seems to cle>ly prove t matt] 9 a   
solid /ate is n depriv$ ( all molecul>  
mobility1 x is possible to realise      
suitable limit$ reactions & equilibria  
betwe5 solid salts1 & ^! equilibria obey
 ! fundam5tal laws ( !rmodynamics4  ,?us
 ! def9ition ( a solid _c be drawn f its
 me*anical prop]ties4 ,x _c be said1    
aft] :at we h j se51 t solid bodies     
reta9 _! =m1 nor t !y h a limit$        
ela/icity1 = ,m4 ,spr+ has made kn[n a  
case :]e ! ela/icity ( solids is )\t any
 limit4  ,x 0 ?\ght t 9 ! case ( a      
diff]5t ph5om5on--t ( cry/allization--we
 might arrive at a cle> di/9ction1      
because "h we %\ld he deal+ ) a specific

 quality2 & t cry/alliz$ bodies w\ld be 
! true solids1 amorph\s bodies be+ at t 
"t reg>d$ z liquids visc\s 9 ! extreme4 
,b ! /udies ( a ,g]man physici/1        
,pr(essor ,o4 ,lehmann1 seem to prove t 
ev5 ?is means is n infallible4 ,pr(essor
 ,lehmann has succe$$1 9 fact1 9 obta9+ 
) c]ta9 organic comp\nds-- oleate (     
potassium1 = in/ance--"u c]ta9          
conditions "s peculi> /ates to :i* he   
has giv5 ! "n ( semi-fluid & liquid     
cry/als4 ,^! s+ul> ph5om5a c only be    
obs]v$ & /udi$ by means ( a microscope1 
& ! ,c>lsruhe ,pr(essor _h to devise an 
+5i\s app>atus :i* enabl$ him to br+ !  
prep>ation at ! requir$ temp]ature on to
 ! v plate ( ! microscope4  ,x is ?us   
made evid5t t ^! bodies act on pol>iz$  
light 9 ! mann] ( a cry/al4 ,^? t ,m4   
,lehmann t]ms semi-liquid /ill pres5t   
traces ( polyh$ric delimitation1 b ) !  
peaks & angles r\nd$ by surface-t5sion1 
:ile ! o!rs t5d to a /rictly sph]ical   
=m4 ,! optical exam9ation ( ! fir/-nam$ 
bodies is v difficult1 because          

appe>ances may be produc$ :i* are due to
 ! ph5om5a ( refraction & imitate ^? (  
pol>ization4 ,= ! o!r k9d1 :i* are (t5 z
 mobile z wat]1 ! fact t !y pol>ize     
light is absolutely unque/ionable4      
,un=tunately1 all ^! liquids are turbid1
 & x may be object$ t !y are n          
homog5e\s4 ,?is want ( homog5eity may1  
accord+ to ,m4 ,qu9cke1 be due to !     
exi/5ce ( p>ticles susp5d$ 9 a liquid 9 
contact ) ano!r liquid miscible ) x &   
envelop+ x z might a membrane1 & !      
ph5om5a ( pol>ization w\ld ?us be q     
naturally expla9$4#ab  ,footnote #ab3   
,pr(essor ,qu9cke's la/ hypo!sis is t   
all liquids on solidify+ pass ?r\gh a   
/age int]m$iate betwe5 solid & liquid1 9
 :i* !y =m :at he calls foam-cells1 &   
assume a visc\s /ructure resembl+ t (   
jelly4 ,see ,proc4 ,roy4 ,soc4 ,a41     
#bcrd ,july #aijf4--;,,ed4  ,m4 ,tamman 
is ( op9ion t x is m a "q ( an emulsion1
 &1 on ?is hypo!sis1 ! action on light  
w\ld actually be t :i* has be5 obs]v$4  
,v>i\s exp]im5t]s h endeav\r$ ( rec5t   

ye>s to elucidate ?is "q4 ,x _c be      
consid]$ absolutely settl$1 b ^! v      
curi\s exp]im5ts1 pursu$ ) great pati5ce
 & rem>kable +5uity1 all[ u to ?9k t !re
 really exi/ c]ta9 int]m$i>y =ms betwe5 
cry/als & liquids 9 :i* bodies /ill     
reta9 a peculi> /ructure1 & consequ5tly 
act on light1 b nev]!less possess       
consid]able pla/icity4  ,let u note t ! 
"q ( ! cont9uity ( ! liquid & solid     
/ates is n q ! same z ! "q ( kn[+ :e!r  
!re exi/ bodies int]m$iate 9 all        
respects betwe5 ! solids & liquids4 ,^! 
two problems are (t5 wrongly confus$4 ,!
 gap betwe5 ! two classes ( bodies may  
be fill$ by c]ta9 sub/ances ) int]m$iate
 prop]ties1 su* z pa/y bodies & bodies  
liquid b /ill cry/alliz$1 because !y h n
 yet completely lo/ _! peculi> /ructure4
 ,yet ! transition is n necess>ily      
e/abli%$ 9 a cont9u\s fa%ion :5 we are  
deal+ ) ! passage ( "o & ! same         
det]m9ate sub/ance f ! liquid to ! solid
 =m4 ,we conceive t ?is *ange may take  
place by ins5sible degrees 9 ! case ( an

 amorph\s body4 ,b x seems h>dly        
possible to consid] ! case ( a cry/al1 9
 :i* molecul> movem5ts mu/ be ess5tially
 regul>1 z a natural sequ5ce to ! case (
 ! liquid :]e we are1 on ! contr>y1 9   
pres5ce ( an extremely disord]$ /ate (  
movem5t4  ,m4 ,tamman has demon/rat$ t  
amorph\s solids may v well1 9 fact1 be  
reg>d$ z sup]pos$ liquids end[$ ) v     
great viscosity4 ,b x is no long] ! same
 ?+ :5 ! solid is once 9 ! cry/alliz$   
/ate4 ,!re is !n a solution ( cont9uity 
( ! v>i\s prop]ties ( ! sub/ance1 & !   
two phases may co-exi/4  ,we might      
presume also1 by analogy ) :at happ5s ) 
liquids & gases1 t if we foll[$ ! curve 
( trans=mation ( ! cry/all9e into !     
liquid phase1 we might arrive at a k9d (
 critical po9t at :i* ! discont9uity (  
_! prop]ties w\ld vani%4  ,pr(essor     
,poynt+1 & aft] him ,pr(essor ,planck & 
,pr(essor ,o/wald1 suppos$ ?is to be !  
case1 b m rec5tly ,m4 ,tamman has %[n t 
su* a po9t does n exi/1 & t ! region (  
/ability ( ! cry/alliz$ /ate is limit$  

on all sides4 ,all along ! curve (      
trans=mation ! two /ates may exi/ 9     
equilibrium1 b we may ass]t t x is      
impossible to realize a cont9u\s s]ies (
 int]m$i>ies betwe5 ^! two /ates4 ,!re w
 always be a m or less m>k$ discont9uity
 9 "s ( ! prop]ties4  ,9 ! c\rse ( 8    
rese>*es ,m4 ,tamman has be5 l$ to c]ta9
 v important obs]vations1 & has met )   
fre% allotropic modifications 9 ne>ly   
all sub/ances1 :i* s+ul>ly complicate ! 
"q4 ,9 ! case ( wat]1 = in/ance1 he f9ds
 t ord9>y ice trans=ms itself1 "u a giv5
 pressure1 at ! temp]ature ( -#hj ,c4   
into ano!r cry/all9e v>iety :i* is d5s] 
?an wat]4  ,! /atics ( solids "u high   
pressure is z yet1 !re=e1 h>dly draft$1 
b x seems to promise results :i* w n be 
id5tical ) ^? obta9$ = ! /atics (       
fluids1 ?\gh x w pres5t at lea/ an equal
 int]e/4    #d4 ,,! ,,de=mations ,,(    
,,solids  ,if ! me*anical prop]ties ( ! 
bodies int]m$iate betwe5 solids &       
liquids h only lately be5 ! object (    
sy/ematic /udies1 admitt$ly solid       

sub/ances h be5 /udi$ = a long "t4 ,yet1
 not)/&+ ! abundance ( rese>*es publi%$ 
on ela/icity by !ori/s & exp]im5t]s1    
num]\s que/ions ) reg>d to !m /ill rema9
 9 susp5se4  ,we only propose to briefly
 indicate "h a few problems rec5tly     
exam9$1 )\t go+ into ! details (        
que/ions :i* belong m to ! doma9 (      
me*anics ?an to t ( pure physics4  ,!   
de=mations produc$ 9 solid bodies by    
increas+ ef=ts arrange !mselves 9 two   
di/9ct p]iods4 ,if ! ef=ts are weak1 !  
de=mations produc$ are also v weak &    
disappe> :5 ! ef=t ceases4 ,!y are !n   
t]m$ ela/ic4 ,if ! ef=ts exce$ a c]ta9  
value1 a "p only ( ^! de=mations        
disappe>1 & a "p are p]man5t4  ,! purity
 ( ! note emitt$ by a s\nd has be5 (t5  
invok$ z a pro( ( ! p]fect iso*ronism ( 
! oscillation1 &1 consequ5tly1 z a      
demon/ration a po/]iori ( ! correctness 
( ! e>ly law ( ,hoocke gov]n+ ela/ic    
de=mations4 ,?is law has1 h[ev]1 dur+ "s
 ye>s be5 frequ5tly disput$4 ,c]ta9     
me*anicians or physici/s freely admit x 

to be incorrect1 especially z reg>ds    
extremely weak de=mations4 ,accord+ to a
 !ory 9 "s fav\r1 especially 9 ,g]many1 
i4e4 ! !ory ( ,ba*1 ! law :i* connects !
 ela/ic de=mations ) ! ef=ts w\ld be an 
expon5tial "o4 ,rec5t exp]im5ts by      
,pr(essors ,kohlraus* & ,gruncis51      
execut$ "u v>i$ & precise conditions on 
brass1 ca/ iron1 slate1 & wr\ght iron1 d
 n appe> to confirm ,ba*'s law4 ,no?+1 9
 po9t ( fact1 au?orises ! rejection ( ! 
law ( ,hoocke1 :i* pres5ts itself z !   
mo/ natural & mo/ simple approximation  
to reality4  ,! ph5om5a ( p]man5t       
de=mation are v complex1 & x c]ta9ly    
seems t !y _c be expla9$ by ! old]      
!ories :i* insi/$ t ! molecules only    
act$ along ! /raight l9e :i* jo9$ _!    
c5tres4 ,x becomes necess>y1 !n1 to     
con/ruct m complete hypo!ses1 z ! ,,mm4 
,coss]at h done 9 "s excell5t memoirs1 &
 we may !n succe$ 9 gr\p+ toge!r ! facts
 result+ f new exp]im5ts4 ,among !      
exp]im5ts ( :i* e !ory mu/ take acc\nt  
may be m5tion$ ^? by :i* ,colonel       

,h>tmann has plac$ 9 evid5ce !          
importance ( ! l9es :i* are produc$ on !
 surface ( metals :5 ! limit ( ela/icity
 is exce$$4  ,x is to que/ions ( ! same 
ord] t ! m9ute & pati5t rese>*es ( ,m4  
,b\asse h be5 direct$4 ,?is physici/1 z 
+5i\s z he is pr(\nd1 has pursu$ =      
sev]al ye>s exp]im5ts on ! mo/ delicate 
po9ts relat+ to ! !ory ( ela/icity1 & he
 has succe$$ 9 def9+ ) a precision n    
always atta9$ ev5 9 ! be/ e/eem$ works1 
! de=mations to :i* a body mu/ be       
subject$ 9 ord] to obta9 comp>able      
exp]im5ts4 ,) reg>d to ! slight         
oscillations ( torsion :i* he has       
specially /udi$1 ,m4 ,b\asse arrives at 
! conclusion1 9 an acute discussion1 t  
we h>dly "k any?+ m ?an 0 proclaim$ a   
hundr$ ye>s ago by ,c\lomb4 ,we see1 by 
?is example1 t admirable z is ! progress
 accompli%$ 9 c]ta9 regions ( physics1  
!re /ill exi/ _m ov]-neglect$ regions   
:i* rema9 9 pa9ful d>kness4 ,! skill %[n
 by ,m4 ,b\asse au?orises u to hope t1  
?anks to 8 rese>*es1 a /rong light w "s 

day illum9e ^! unkn[n corn]s4  ,a       
p>ticul>ly int]e/+ *apt] on ela/icity is
 t relat+ to ! /udy ( cry/als2 & 9 ! la/
 few ye>s x has be5 ! object ( rem>kable
 rese>*es on ! "p ( ,m4 ,voigt4 ,^!     
rese>*es h p]mitt$ a few controv]sial   
que/ions betwe5 !ori/s & exp]im5t]s to  
be solv$3 9 p>ticul>1 ,m4 ,voigt has    
v]ifi$ ! consequ5ces ( ! calculations1  
tak+ c>e n to make1 l ,cau*y & ,poisson1
 ! hypo!sis ( c5tral =ces a m]e function
 ( di/ance1 & has recogniz$ a pot5tial  
:i* dep5ds on ! relative ori5tation ( ! 
molecules4 ,^! consid]ations also apply 
to quasi-isotropic bodies :i* are1 9    
fact1 networks ( cry/als4  ,c]ta9       
occasional de=mations :i* are produc$ & 
disappe> sl[ly may be consid]$ z        
int]m$iate betwe5 ela/ic & p]man5t      
de=mations4 ,( ^!1 ! !rmal de=mation (  
glass :i* manife/s itself by !          
displacem5t ( ! z]o ( a !rmomet] is an  
example4 ,s also ! modifications :i* !  
ph5om5a ( magnetic hy/]esis or !        
v>iations ( resi/ivity h j demon/rat$4  

,_m !ori/s h tak5 9 h& ^! difficult     
que/ions4 ,m4 ,brill\9 endeav\rs to     
int]pret ^! v>i\s ph5om5a by ! molecul> 
hypo!sis4 ,! attempt may seem bold1 s9ce
 ^! ph5om5a are1 = ! mo/ "p1 ess5tially 
irrev]sible1 & seem1 consequ5tly1 n     
adaptable to me*anics4 ,b ,m4 ,brill\9  
makes a po9t ( %[+ t1 "u c]ta9          
conditions1 irrev]sible ph5om5a may be  
creat$ betwe5 two mat]ial po9ts1 !      
actions ( :i* dep5d solely on _!        
di/ance2 & he furni%es /rik+ in/ances   
:i* appe> to prove t a great numb] (    
irrev]sible physical & *emical ph5om5a  
may be ascrib$ to ! exi/5ce ( /ates (   
un/able equilibria4  ,m4 ,duhem has     
approa*$ ! problem f ano!r side1 &      
endeav\rs to br+ x )9 ! range (         
!rmodynamics4 ,yet ord9>y !rmodynamics  
c\ld n acc\nt = exp]im5tally realizable 
/ates ( equilibrium 9 ! ph5om5a (       
viscosity & friction1 s9ce ?is sci5ce   
decl>es !m to be impossible4 ,m4 ,duhem1
 h[ev]1 arrives at ! idea t ! e/abli%m5t
 ( ! equations ( !rmodynamics           

presupposes1 among o!r hypo!ses1 "o :i* 
is entirely arbitr>y1 namely3 t :5 !    
/ate ( ! sy/em is giv51 ext]nal actions 
capable ( ma9ta9+ x 9 t /ate are det]m9$
 )\t ambiguity1 by equations t]m$       
conditions ( equilibrium ( ! sy/em4 ,if 
we reject ?is hypo!sis1 x w !n be       
all[able to introduce into !rmodynamics 
laws previ\sly exclud$1 & x w be        
possible to con/ruct1 z ,m4 ,duhem has  
done1 a mu* m compreh5sive !ory4  ,!    
ideas ( ,m4 ,duhem h be5 illu/rat$ by   
rem>kable exp]im5tal "w4 ,m4 ,m>*is1 =  
example1 guid$ by ^! ideas1 has /udi$ ! 
p]man5t modifications produc$ 9 glass by
 an oscillation ( temp]ature4 ,^!       
modifications1 :i* may be call$ ph5om5a 
( ! hy/]esis ( dilatation1 may be foll[$
 9 v appreciable fa%ion by means ( a    
glass !rmomet]4 ,! g5]al results are q 9
 accord ) ! previsions ( ,m4 ,duhem4 ,m4
 ,l5oble 9 rese>*es on ! traction (     
metallic wires1 & ,m4 ,*evali] 9        
exp]im5ts on ! p]man5t v>iations ( !    
electrical resi/ance ( wires ( an alloy 

( plat9um & silv] :5 submitt$ to        
p]iodical v>iations ( temp]ature1 h     
likewise af=d$ v]ifications ( ! !ory    
prop\nd$ by ,m4 ,duhem4  ,9 ?is !ory1 ! 
repres5tative sy/em is consid]$ dep5d5t 
on ! temp]ature ( "o or sev]al o!r      
v>iables1 su* z1 = example1 a *emical   
v>iable4 ,a simil> idea has be5 develop$
 9 a v f9e set ( memoirs on nickel /eel1
 by ,m4 ,*4 ,ed4 ,guillaume4 ,! em95t   
physici/1 :o1 by 8 e>li] rese>*es1 has  
greatly contribut$ to ! light ?r[n on ! 
analog\s "q ( ! displacem5t ( ! z]o 9   
!rmomet]s1 concludes1 f fre% rese>*es1 t
 ! residual ph5om5a are due to *emical  
v>iations1 & t ! return to ! prim>y     
*emical /ate causes ! v>iation to       
disappe>4 ,he applies 8 ideas n only to 
! ph5om5a pres5t$ by irrev]sible /eels1 
b also to v diff]5t facts2 = example1 to
 phosphoresc5ce1 c]ta9 p>ticul>ities (  
:i* may be int]pret$ 9 an analog\s      
mann]4  ,nickel /eels pres5t ! mo/      
curi\s prop]ties1 & ,i h already po9t$  
out ! p>am\nt importance ( "o ( !m1     

h>dly capable ( p]ceptible dilatation1 =
 its application to metrology &         
*ronometry4#ac ,o!rs1 also discov]$ by  
,m4 ,guillaume 9 ! c\rse ( /udies       
conduct$ ) r>e success & rem>kable      
+5uity1 may r5d] great s]vices1 because 
x is possible to regulate1 s to speak1  
at w _! me*anical or magnetic prop]ties4
  ,footnote #ac3 ,! metal kn[n z        
inv>4--,,ed4  ,! /udy ( alloys 9 g5]al  
is1 moreov]1 "o ( ^? 9 :i* !            
introduction ( ! me?ods ( physics has   
produc$ ! greate/ effects4 ,by !        
microscopic exam9ation ( a poli%$       
surface or ( "o ind5t$ by a reag5t1 by !
 det]m9ation ( ! electromotive =ce (    
elem5ts ( :i* an alloy =ms "o ( ! poles1
 & by ! measurem5t ( ! resi/ivities1 !  
d5sities1 & ! diff]5ces ( pot5tial or   
contact1 ! mo/ valuable indications z to
 _! con/itution are obta9$4 ,m4 ,le     
,*ateli]1 ,m4 ,*>py1 ,m4 ,dumas1 ,m4    
,osmond1 9 ,france2 ,sir ,w4 ,rob]ts    
,au/5 & ,mr4 ,/ansfield1 9 ,engl&1 h    
giv5 manifold examples ( ! f]tility ( ^!

 me?ods4 ,! "q1 moreov]1 has _h a new   
light ?r[n ^u x by ! application ( !    
pr9ciples ( !rmodynamics & ( ! phase    
rule4  ,alloys are g5]ally kn[n 9 ! two 
/ates ( solid & liquid4 ,fus$ alloys    
consi/ ( "o or sev]al solutions ( !     
compon5t metals & ( a c]ta9 numb] (     
def9ite comb9ations4 ,_! composition may
 ?us be v complex3 b ,gibbs' rule gives 
u at once important in=mation on ! po9t1
 s9ce x indicates t !re _c exi/1 9      
g5]al1 m ?an two di/9ct solutions 9 an  
alloy ( two metals4  ,solid alloys may  
be class$ l liquid ones4 ,two metals or 
m dissolve "o into ! o!r1 & =m a solid  
solution q analog\s to ! liquid         
solution4 ,b ! /udy ( ^! solid solutions
 is r5d]$ s+ul>ly difficult by ! fact t 
! equilibrium s rapidly rea*$ 9 ! case (
 liquids 9 ?is case takes days &1 9     
c]ta9 cases1 p]haps ev5 c5turies to     
become e/abli%$4     ,,*apt] ,v         
,,solutions ,,& ,,electrolytic          
,,dissociation    #a4 ,,solution        
,vaporization & fusion are n ! only     

means by :i* ! physical /ate ( a body   
may be *ang$ )\t modify+ its *emical    
con/itution4 ,f ! mo/ remote p]iods     
solution has also be5 kn[n & /udi$1 b   
only 9 ! la/ tw5ty ye>s h we obta9$ o!r 
?an empirical in=mation reg>d+ ?is      
ph5om5on4  ,x is natural to employ "h   
also ! me?ods :i* h all[$ u to p5etrate 
into ! k ( o!r trans=mations4 ,! problem
 ( solution may be approa*$ by way (    
!rmodynamics & ( ! hypo!ses ( k9etics4  
,z long ago z #aheh1 ,kir*h(f1 by       
attribut+ to sal9e solutions-- t is to  
say1 to mixtures ( wat] & a non-volatile
 liquid l sulphuric acid--! prop]ties ( 
int]nal en]gy1 discov]$ a relation      
betwe5 ! quantity ( heat giv5 out on !  
addition ( a c]ta9 quantity ( wat] to a 
solution & ! v>iations to :i*           
cond5sation & temp]ature subject !      
vap\r-t5sion ( ! solution4 ,he calculat$
 = ?is purpose ! v>iations ( en]gy :i*  
are produc$ :5 pass+ f "o /ate to ano!r 
by two diff]5t s]ies ( trans=mations2 &1
 by comp>+ ! two expressions ?us obta9$1

 he e/abli%$ a relation betwe5 ! v>i\s  
elem5ts ( ! ph5om5on4 ,b1 = a long "t   
aft]w>ds1 ! "q made little progress1    
because !re seem$ to be h>dly any means 
( introduc+ into ?is /udy ! second      
pr9ciple ( !rmodynamics4#ad ,x 0 !      
memoir ( ,gibbs :i* at la/ op5$ out ?is 
ri* doma9 & enabl$ x to be rationally   
exploit$4 ,z e>ly z #ahhf1 ,m4 ,duhem   
%[$ t ! !ory ( ! !rmodynamic pot5tial   
furni%$ precise in=mation on solutions  
or liquid mixtures4 ,he ?us discov]$ ov]
 aga9 ! fam\s law on ! l[]+ ( !         
congelation temp]ature ( solv5ts :i* _h 
j be5 e/abli%$ by ,m4 ,ra\lt aft] a long
 s]ies ( n[ classic rese>*es4  ,footnote
 #ad3 ,! second pr9ciple ref]r$ to has  
be5 ?us enunciat$3 ,9 e eng9e t produces
 "w !re is a fall ( temp]ature1 & !     
maximum output ( a p]fect eng9e--i4e4 ! 
ratio betwe5 ! heat consum$ 9 "w & !    
heat suppli$--dep5ds only on ! extreme  
temp]atures betwe5 :i* ! fluid is       
evolv$4--,demanet1 ,notes de ,physique  
,exprim5tale1 ,l\va91 #aije1 fasc4 #b1  

p4 #adg4 ,clausius put x 9 a negative   
=m1 z ?us3 ,no eng9e c ( itself1 )\t !  
aid ( ext]nal ag5cy1 transf] heat f a   
body at l[ temp]ature to a body at a    
high temp]ature4 ,cf4 ,ganot's ,physics1
 #ag? ,engli% edition1  #ejh4--;,,ed4   
,9 ! m9ds ( _m p]sons1 h[ev]1 grave     
d\bts p]si/$4 ,solution appe>$ to be an 
ess5tially irrev]sible ph5om5on4 ,x 0   
!re=e1 9 all /rictness1 impossible to   
calculate ! entropy ( a solution1 &     
consequ5tly to be c]ta9 ( ! value ( !   
!rmodynamic pot5tial4 ,! objection w\ld 
be s]i\s ev5 to-day1 &1 9 calculations1 
:at is call$ ! p>adox ( ,gibbs w\ld be  
an ob/acle4  ,we %\ld n hesitate1 h[ev]1
 to apply ! ,phase ,law to solutions1 & 
?is law already gives u ! key to a c]ta9
 numb] ( facts4 ,x puts 9 evid5ce1 =    
example1 ! "p play$ by ! eutectic po9t--
 t is to say1 ! po9t at :i* 7to keep to 
! simple case 9 :i* we h to d ) two     
bodies only1 ! solv5t & ! solute7 !     
solution is 9 equilibrium at once ) !   
two possible solids1 ! dissolv$ body & !

 solv5t solidifi$4 ,! k ( ?is po9t      
expla9s ! prop]ties ( refrig]at+        
mixtures1 & x is also "o ( ! mo/ useful 
= ! !ory ( alloys4 ,! scruples (        
physici/s ought to h be5 remov$ on !    
memorable occasion :5 ,pr(essor ,van    
t',h(f demon/rat$ t solution c op]ate   
rev]sibly by reason ( ! ph5om5a (       
osmosis4 ,b ! exp]im5t c only succe$ 9 v
 r>e cases2 &1 on ! o!r h&1 ,pr(essor   
,van t',h(f 0 naturally l$ to ano!r v   
bold conception4 ,he reg>d$ ! molecule (
 ! dissolv$ body z a gase\s "o1 &       
assimilat$ solution1 n z _h hi!rto be5 !
 rule1 to fusion1 b to a k9d (          
vaporization4 ,naturally 8 ideas 7 n    
imm$iately accept$ by ! s*ol>s mo/      
closely id5tifi$ ) ! classic tradition4 
,x may p]haps n be )\t use to exam9e "h 
! pr9ciples ( ,pr(essor ,van t',h(f's   
!ory4    #b4 ,,osmosis  ,osmosis1 or    
diffusion ?r\gh a septum1 is a ph5om5on 
:i* has be5 kn[n = "s "t4 ,! discov]y ( 
x is attribut$ to ! ,abb ,nollet1 :o is 
suppos$ to h obs]v$ x 9 #agdh1 dur+ "s  

rese>*es on liquids 9 ebullition4 ,a    
classic exp]im5t by ,dutro*et1 effect$  
ab\t #ahcj1 makes ?is ph5om5on cle>4    
,into pure wat] is plung$ ! l[] "p ( a  
v]tical tube conta9+ pure alcohol1 op5  
at ! top & clos$ at ! bottom by a       
membrane1 su* z a pig's bladd]1 )\t any 
visible p]=ation4 ,9 a v %ort "t x w be 
f\nd1 by means ( an areomet] = in/ance1 
t ! wat] outside conta9s alcohol1 :ile !
 alcohol ( ! tube1 pure at fir/1 is n[  
dilut$4 ,two curr5ts h !re=e pass$ ?r\gh
 ! membrane1 "o ( wat] f ! outside to ! 
inside1 & "o ( alcohol 9 ! conv]se      
direction4 ,x is also not$ t a diff]5ce 
9 ! levels has occurr$1 & t ! liquid 9 !
 tube n[ rises to a consid]able height4 
,x mu/ !re=e be admitt$ t ! fl[ ( ! wat]
 has be5 m rapid ?an t ( ! alcohol4 ,at 
! comm5cem5t1 ! wat] mu/ h p5etrat$ into
 ! tube mu* m rapidly ?an ! alcohol left
 x4 ,h5ce ! diff]5ce 9 ! levels1 &1     
consequ5tly1 a diff]5ce ( pressure on ! 
two faces ( ! membrane4 ,?is diff]5ce   
goes on increas+1 rea*es a maximum1 !n  

dim9i%es1 & vani%es :5 ! diffusion is   
complete1 f9al equilibrium be+ !n       
atta9$4  ,! ph5om5on is evid5tly        
connect$ ) diffusion4 ,if wat] is v     
c>efully p\r$ on to alcohol1 ! two      
lay]s1 sep>ate at fir/1 m+le by degrees 
till a homog5e\s sub/ance is obta9$4 ,! 
bladd] seems n to h prev5t$ ?is         
diffusion f tak+ place1 b x seems to h  
%[n itself m p]meable to wat] ?an to    
alcohol4 ,may x n !re=e be suppos$ t !re
 mu/ exi/ divid+ walls 9 :i* ?is        
diff]5ce ( p]meability becomes great] & 
great]1 :i* w\ld be p]meable to ! solv5t
 & absolutely imp]meable to ! solute8   
,if ?is be s1 ! ph5om5a ( ^!            
semi-p]meable walls1 z !y are t]m$1 c be
 obs]v$ 9 p>ticul>ly simple conditions4 
,! answ] to ?is "q has be5 furni%$ by   
biologi/s1 at :i* we _c be surpris$4 ,! 
ph5om5a ( osmosis are naturally ( ! fir/
 importance 9 ! action ( organisms1 & = 
a long "t h attract$ ! att5tion (       
naturali/s4 ,de ,vries imag9$ t !       
contractions notic$ 9 ! protoplasm (    

cells plac$ 9 sal9e solutions 7 due to a
 ph5om5on ( osmosis1 &1 ^u exam9+ m     
closely c]ta9 peculi>ities ( cell life1 
v>i\s s*ol>s h demon/rat$ t liv+ cells  
are enclos$ 9 membranes p]meable to     
c]ta9 sub/ances & entirely imp]meable to
 o!rs4 ,x 0 int]e/+ to try to reproduce 
artificially semi-p]meable walls        
analog\s to ^? ?us met ) 9 nature2#ae & 
,traube & ,pfeff] seem to h succe$$ 9 "o
 p>ticul> case4 ,traube has po9t$ out t 
! v delicate membrane ( f]rocyanide (   
potassium :i* is obta9$ ) "s difficulty 
by expos+ x to ! reaction ( sulphate (  
copp]1 is p]meable to wat]1 b w n p]mit 
! passage ( ! majority ( salts4 ,pfeff]1
 by produc+ ^! walls 9 ! int]/ices ( a  
por\s porcela91 has succe$$ 9 giv+ !m   
suffici5t rigidity to all[ measurem5ts  
to be made4 ,x mu/ be all[$ t1          
un=tunately1 no physici/ or *emi/ has   
be5 z lucky z ^! two botani/s2 & !      
attempts to reproduce semi-p]meable     
walls completely answ]+ to ! def9ition1 
h nev] giv5 b m$iocre results4 ,if1     

h[ev]1 ! exp]im5tal difficulty has n be5
 ov]come 9 an entirely satisfactory     
mann]1 x at lea/ appe>s v probable t su*
 walls may nev]!less exi/4#af  ,footnote
 #ae3 ,see next note4--,,ed4  ,footnote 
#af3 ,m4 ,/ephane ,l$uc1 ,pr(essor (    
,biology ( ,nantes1 has made _m         
exp]im5ts 9 ?is connection1 & !         
artificial cells exhibit$ by him to !   
,association franaise p\r l'avancem5t   
des ,sci5ces1 at _! meet+ at ,gr5oble 9 
#aijd & reproduc$ 9 _! ,actes1 are      
p>ticul>ly notewor?y4--,,ed4            
,nev]!less1 9 ! case ( gases1 !re exi/s 
an excell5t example ( a semi-p]meable   
wall1 & a p>tition ( plat9um br\ght to a
 high] ?an r$ heat is1 z %[n by ,m4     
,vill>d 9 "s +5i\s exp]im5ts1 completely
 imp]meable to air1 & v p]meable1 on !  
contr>y1 to hydrog54 ,x c also be       
exp]im5tally demon/rat$ t on tak+ two   
recipi5ts sep>at$ by su* a p>tition1 &  
bo? conta9+ nitrog5 mix$ ) v>y+         
proportions ( hydrog51 ! la/-nam$ gas w 
pass ?r\gh ! p>tition 9 su* a way t !   

conc5tration--t is to say1 ! mass ( gas 
p] unit ( volume-- w become ! same on   
bo? sides4 ,only !n w equilibrium be    
e/abli%$2 &1 at t mom5t1 an excess (    
pressure w naturally be produc$ 9 t     
recipi5t :i*1 at ! comm5cem5t1 conta9$ !
 gas ) ! smalle/ quantity ( hydrog54    
,?is exp]im5t enables u to anticipate   
:at w happ5 9 a liquid m$ium )          
semi-p]meable p>titions4 ,betwe5 two    
recipi5ts1 "o conta9+ pure wat]1 ! o!r1 
say1 wat] ) sug> 9 solution1 sep>at$ by 
"o ( ^! p>titions1 !re w be produc$     
m]ely a movem5t ( ! pure t[>ds ! sug>$  
wat]1 & foll[+ ?is1 an increase (       
pressure on ! side ( ! la/4 ,b ?is      
increase w n be )\t limits4 ,at a c]ta9 
mom5t ! pressure w cease to increase & w
 rema9 at a fix$ value :i* n[ has a giv5
 direction4 ,?is is ! osmotic pressure4 
,pfeff] demon/rat$ t1 = ! same sub/ance1
 ! osmotic pressure is proportional to !
 conc5tration1 & consequ5tly 9 inv]se   
ratio to ! volume occupi$ by a simil>   
mass ( ! solute4 ,he gave figures f :i* 

x 0 easy1 z ,pr(essor ,van t',h(f f\nd1 
to draw ! conclusion t1 9 a con/ant     
volume1 ! osmotic pressure is           
proportional to ! absolute temp]ature4  
,de ,vries1 moreov]1 by 8 rem>ks on liv+
 cells1 ext5d$ ! results :i* ,pfeff] _h 
appli$ to "o case only--t is1 to ! "o t 
he _h be5 able to exam9e exp]im5tally4  
,su* are ! ess5tial facts ( osmosis4 ,we
 may seek to int]pret !m & to ?or\ghly  
exam9e ! me*anism ( ! ph5om5on2 b x mu/ 
be ackn[l$g$ t z reg>ds ?is po9t1       
physici/s are n entirely 9 accord4 ,9 ! 
op9ion ( ,pr(essor ,n]n/1 ! p]meability 
( semi-p]meable membranes is simply due 
to diff]5ces ( solubility 9 "o ( !      
sub/ances ( ! membrane itself4 ,o!r     
physici/s ?9k x attributable1 ei!r to ! 
diff]5ce 9 ! dim5sions ( ! molecules1 ( 
:i* "s might pass ?r\gh ! pores ( !     
membrane & o!rs be /opp$ by _! relative 
size1 or to ^! molecules' great] or less
 mobility4 ,= o!rs1 aga91 x is !        
capill>y ph5om5a :i* "h act a           
prepond]at+ "p4  ,?is la/ idea is       

already an old "o3 ,jag]1 ,m1 &         
,pr(essor ,traube h all endeav\r$ to %[ 
t ! direction & spe$ ( osmosis are      
det]m9$ by diff]5ces 9 !                
surface-t5sions2 & rec5t exp]im5ts1     
especially ^? ( ,batelli1 seem to prove 
t osmosis e/abli%es itself 9 ! way :i*  
be/ equalizes ! surface-t5sions ( !     
liquids on bo? sides ( ! p>tition4      
,solutions possess+ ! same              
surface-t5sion1 ?\gh n 9 molecul>       
equilibrium1 w\ld ?us be always 9       
osmotic equilibrium4 ,we mu/ n conceal f
 ourselves t ?is result w\ld be 9       
contradiction ) ! k9etic !ory4    #c4   
,,application ,,to ,,! ,,!ory ,,(       
,,solution  ,if !re really exi/         
p>titions p]meable to "o body &         
imp]meable to ano!r1 x may be imag9$ t !
 homog5e\s mixture ( ^! two bodies might
 be effect$ 9 ! conv]se way4 ,x c be    
easily conceiv$1 9 fact1 t by ! aid (   
osmotic pressure x w\ld be possible1 =  
example1 to dilute or conc5trate a      
solution by driv+ ?r\gh ! p>tition 9 "o 

direction or ano!r a c]ta9 quantity ( ! 
solv5t by means ( a pressure kept equal 
to ! osmotic pressure4 ,?is is !        
important fact :i* ,pr(essor ,van t'    
,h(f p]ceiv$4 ,! exi/5ce ( su* a wall 9 
all possible cases evid5tly rema9s only 
a v legitimate hypo!sis1--a fact :i*    
ought n to be conceal$4  ,rely+ solely  
on ?is po/ulate1 ,pr(essor ,van t' ,h(f 
easily e/abli%$1 by ! mo/ correct me?od1
 c]ta9 prop]ties ( ! solutions ( gases 9
 a volatile liquid1 or ( non-volatile   
bodies 9 a volatile liquid4 ,to /ate    
precisely ! o!r relations1 we mu/ admit1
 9 addition1 ! exp]im5tal laws discov]$ 
by ,pfeff]4 ,b )\t any hypo!sis x       
becomes possible to demon/rate ! laws ( 
,ra\lt on ! l[]+ ( ! vap\r-t5sion & ( ! 
freez+ po9t ( solutions1 & also ! ratio 
:i* connects ! heat ( fusion ) ?is      
decrease4  ,^! consid]able results c    
evid5tly be invok$ z a po/]iori pro(s ( 
! exactitude ( ! exp]im5tal laws (      
osmosis4 ,!y are n1 h[ev]1 ! only ones t
 ,pr(essor ,van t' ,h(f has obta9$ by ! 

same me?od4 ,?is illu/ri\s s*ol> 0 ?us  
able to f9d anew ,guldb]g & ,waage's law
 on *emical equilibrium at a con/ant    
temp]ature1 & to %[ h[ ! position ( !   
equilibrium *anges :5 ! temp]ature      
happ5s to *ange4  ,if n[ we /ate1 9     
con=mity ) ! laws ( ,pfeff]1 t ! product
 ( ! osmotic pressure by ! volume ( !   
solution is equal to ! absolute         
temp]ature multipli$ by a coeffici5t1 & 
!n look = ! num]ical figure ( ?is latt] 
9 a solution ( sug>1 = in/ance1 we f9d t
 ?is value is ! same z t ( ! analog\s   
coeffici5t ( ! *>act]i/ic equation ( a  
p]fect gas4 ,!re is 9 ?is a co9cid5ce   
:i* has also be5 utiliz$ 9 ! prec$+     
!rmodynamic calculations4 ,x may be     
purely =tuit\s1 b we c h>dly refra9 f   
f9d+ 9 x a physical mean+4  ,pr(essor   
,van t',h(f has consid]$ ?is co9cid5ce a
 demon/ration t !re exi/s a /rong       
analogy betwe5 a body 9 solution & a    
gas2 z a matt] ( fact1 x may seem t1 9 a
 solution1 ! di/ance betwe5 ! molecules 
becomes comp>able to ! molecul> di/ances

 met ) 9 gases1 & t ! molecule acquires 
! same degree ( lib]ty & ! same         
simplicity 9 bo? ph5om5a4 ,9 t case x   
seems probable t solutions w be subject 
to laws indep5d5t ( ! *emical nature ( !
 dissolv$ molecule & comp>able to ! laws
 gov]n+ gases1 :ile if we adopt ! k9etic
 image = ! gas1 we %all be l$ to        
repres5t to ourselves 9 a simil> way !  
ph5om5a :i* manife/ !mselves 9 a        
solution4 ,osmotic pressure w !n appe>  
to be due to ! %ock ( ! dissolv$        
molecules aga9/ ! membrane4 ,x w come f 
"o side ( ?is p>tition to sup]pose      
itself on ! hydro/atic pressure1 :i*    
latt] mu/ h ! same value on bo? sides4  
,! analogy ) a p]fect gas naturally     
becomes mu* great] z ! solution becomes 
m dilut$4 ,x !n imitates gas 9 "s o!r   
prop]ties2 ! int]nal "w ( ! v>iation (  
volume is nil1 & ! specific heat is only
 a function ( ! temp]ature4 ,a solution 
:i* is dilut$ by a rev]sible me?od is   
cool$ l a gas :i* exp&s                 
adiabatically4#ag  ,footnote #ag3 ,t is1

 )\t receiv+ or emitt+ any heat4--,,ed4 
,x mu/1 h[ev]1 be ackn[l$g$ t1 9 o!r    
po9ts1 ! analogy is mu* less p]fect4 ,! 
op9ion :i* sees 9 solution a ph5om5on   
resembl+ fusion1 & :i* has left an      
indelible trace 9 ev]yday language 7we  
%all always say3 to melt sug> 9 wat]7 is
 c]ta9ly n )\t f\ndation4 ,c]ta9 ( !    
reasons :i* might be invok$ to uphold   
?is op9ion are too evid5t to be repeat$ 
"h1 ?\gh o!rs m recondite might be      
quot$4 ,! fact t ! int]nal en]gy g5]ally
 becomes indep5d5t ( ! conc5tration :5 !
 dilution rea*es ev5 a mod]ately high   
value is r 9 fav\r ( ! hypo!sis (       
fusion4  ,we mu/ n =get1 h[ev]1 !       
cont9uity ( ! liquid & gase\s /ates2 &  
we may consid] x 9 an absolute way a "q 
devoid ( s5se to ask :e!r 9 a solution !
 solute is 9 ! liquid or ! gase\s /ate4 
,x is 9 ! fluid /ate1 & p]haps 9        
conditions oppos$ to ^? ( a body 9 !    
/ate ( a p]fect gas4 ,x is kn[n1 (      
c\rse1 t 9 ?is case ! manometrical      
pressure mu/ be reg>d$ z v great 9      

relation to ! int]nal pressure :i*1 9 ! 
*>act]i/ic equation1 is add$ to ! o!r4  
,may x n seem possible t 9 ! solution x 
is1 on ! contr>y1 ! int]nal pressure :i*
 is dom9ant1 ! manometric pressure      
becom+ ( no acc\nt8 ,! co9cid5ce ( !    
=mulas w\ld ?us be v]ifi$1 = all !      
*>act]i/ic equations are symmetrical )  
reg>d to ^! two pressures4 ,f ?is po9t (
 view ! osmotic pressure w\ld be        
consid]$ z ! result ( an attraction     
betwe5 ! solv5t & ! solute2 & x w\ld    
repres5t ! diff]5ce betwe5 ! int]nal    
pressures ( ! solution & ( ! pure       
solv5t4 ,^! hypo!ses are highly int]e/+1
 & v sugge/ive2 b f ! way 9 :i* ! facts 
h be5 set =?1 x w appe>1 no d\bt1 t !re 
is no obligation to admit !m 9 ord] to  
believe 9 ! legitimacy ( ! application (
 !rmodynamics to ! ph5om5a ( solution4  
#d4 ,,electrolytic ,,dissociation  ,f ! 
outset ,pr(essor ,van t' ,h(f 0 br\ght  
to ackn[l$ge t a great numb] ( solutions
 =m$ v notable exceptions :i* 7 v       
irregul> 9 appe>ance4 ,! analogy ) gases

 did n seem to be ma9ta9$1 = ! osmotic  
pressure _h a v diff]5t value f t       
indicat$ by ! !ory4 ,ev]y?+1 h[ev]1 came
 "r if "o multipli$ by a factor1 det]m9$
 accord+ to ea* case1 b great] ?an      
unity1 ! con/ant ( ! *>act]i/ic =mula4  
,simil> div]g5ces 7 manife/$ 9 ! delays 
obs]v$ 9 congelation1 & disappe>$ :5    
subject$ to an analog\s correction4     
,?us ! freez+-po9t ( a normal solution1 
conta9+ a molecule gramme 7t is1 ! numb]
 ( grammes equal to ! figure repres5t+ !
 molecul> mass7 ( alcohol or sug> 9     
wat]1 falls #a4he ,c4 ,if ! laws (      
solution 7 id5tically ! same = a        
solution ( sea-salt1 ! same depression  
%\ld be notic$ 9 a sal9e solution also  
conta9+ #a molecule p] litre4 ,9 fact1 !
 fall rea*es #c4bf1 & ! solution behaves
 z if x conta9$1 n #a1 b #a4ge normal   
molecules p] litre4 ,! consid]ation ( ! 
osmotic pressures w\ld lead to simil>   
obs]vations1 b we "k t ! exp]im5t w\ld  
be m difficult & less precise4  ,we may 
wond] :e!r any?+ really analog\s to ?is 

c be met ) 9 ! case ( a gas1 & we are   
?us l$ to consid] ! ph5om5a (           
dissociation4#ah ,if we heat a body :i*1
 9 a gase\s /ate1 is capable (          
dissociation--hydriodic acid1 =         
example--at a giv5 temp]ature1 an       
equilibrium is e/abli%$ betwe5 ?ree     
gase\s bodies1 ! acid1 ! iod9e1 & !     
hydrog54 ,! total mass w foll[ ) fair   
clos5ess ,m>iotte's law1 b ! *>act]i/ic 
con/ant w no long] be ! same z 9 ! case 
( a non-dissociat$ gas4 ,we "h no long] 
h to d ) a s+le molecule1 s9ce ea*      
molecule is 9 "p dissociat$4  ,footnote 
#ah3 ,dissociation mu/ be di/+ui%$ f    
decomposition1 :i* is :at occurs :5 !   
:ole ( a p>ticle 7comp\nd1 molecule1    
atom1 etc47 breaks up into its compon5t 
p>ts4 ,9 dissociation ! break+ up is    
only p>tial1 & ! resultant consi/s ( a  
mixture ( decompos$ & undecompos$ p>ts4 
,see ,ganot's ,physics1 #ag? ,engli%    
edition1  #cie1 = examples4--,,ed4  ,!  
comp>ison ( ! two cases leads to !      
employm5t ( a new image = repres5t+ !   

ph5om5on :i* has be5 produc$ ?r\gh\t !  
sal9e solution4 ,we h introduc$ a s+le  
molecule ( salt1 & ev]y?+ occurs z if   
!re 7 #a4ge molecules4 ,may x n really  
be said t ! numb] is #a4ge1 because !   
sea-salt is p>tly dissociat$1 & a       
molecule has become trans=m$ into #j4ge 
molecule ( sodium1 #j4ge ( *lorium1 &   
#j4be ( salt8  ,?is is a way ( speak+   
:i* seems1 at fir/ sight1 /rangely      
contradict$ by exp]im5t4 ,pr(essor ,van 
t' ,h(f1 l o!r *emi/s1 w\ld c]ta9ly h   
reject$--9 fact1 he did s at fir/-- su* 
a conception1 if1 ab\t ! same "t1 an    
illu/ri\s ,sw$i% s*ol>1 ,m4 ,arrh5ius1  
_h n be5 br\ght to ! same idea by ano!r 
road1 &1 _h n by /at+ x precisely &     
modify+ x1 pres5t$ x 9 an acceptable =m4
  ,a brief exam9ation w easily %[ t all 
! sub/ances :i* are exceptions to ! laws
 ( ,van t',h(f are precisely ^? :i* are 
capable ( conduct+ electricity :5       
und]go+ decomposition--t is to say1 are 
electrolytes4 ,! co9cid5ce is absolute1 
& _c be simply due to *ance4  ,n[1 !    

ph5om5a ( electrolysis h1 = a long "t1  
=c$ ^u u an almo/ necess>y image4 ,!    
sal9e molecule is always decompos$1 z we
 "k1 9 ! prim>y ph5om5on ( electrolysis 
into two elem5ts :i* ,f>aday t]m$ ions4 
,second>y reactions1 no d\bt1 (t5 come  
to complicate ! "q1 b ^! are *emical    
reactions belong+ to ! g5]al ord] ( ?+s1
 & h no?+ to d ) ! electric action work+
 on ! solution4 ,! simple ph5om5on is   
always ! same--decomposition into two   
ions1 foll[$ by ! appe>ance ( "o ( ^!   
ions at ! positive & ( ! o!r at !       
negative electrode4 ,b z ! v slighte/   
exp5diture ( en]gy is suffici5t to      
produce ! comm5cem5t ( electrolysis1 x  
is necess>y to suppose t ^! two ions are
 n unit$ by any =ce4 ,?us ! two ions    
are1 9 a way1 dissociat$4 ,clausius1 :o 
0 ! fir/ to repres5t ! ph5om5a by ?is   
symbol1 suppos$1 9 ord] n to %ock !     
feel+s ( *emi/s too mu*1 t ?is          
dissociation only affect$ an            
inf9itesimal fraction ( ! total numb] ( 
! molecules ( ! salt1 & !reby escap$ all

 *eck4  ,?is concession 0 un=tunate1 & !
 hypo!sis ?us lo/ ! great] "p ( its     
usefulness4 ,m4 ,arrh5ius 0 bold]1 &    
frankly recogniz$ t dissociation occurs 
at once 9 ! case ( a great numb] (      
molecules1 & t5ds to increase m & m z ! 
solution becomes m dilute4 ,x foll[s !  
comp>ison ) a gas :i*1 :ile p>tially    
dissociat$ 9 an enclos$ space1 becomes  
:olly s 9 an inf9ite "o4  ,m4 ,arrh5ius 
0 l$ to adopt ?is hypo!sis by !         
exam9ation ( exp]im5tal results relat+  
to ! conductivity ( electrolytes4 ,9    
ord] to int]pret c]ta9 facts1 x has to  
be recogniz$ t a "p only ( ! molecules 9
 a sal9e solution c be consid]$ z       
conductors ( electricity1 & t by add+   
wat] ! numb] ( molecul> conductors is   
increas$4 ,?is increase1 too1 ?\gh rapid
 at fir/1 soon becomes sl[]1 & approa*es
 a c]ta9 limit :i* an inf9ite dilution  
w\ld enable x to atta94 ,if ! conduct+  
molecules are ! dissociat$ molecules1 !n
 ! dissociation 7s long z x is a "q (   
/rong acids & salts7 t5ds to become     

complete 9 ! case ( an unlimit$         
dilution4  ,! opposition ( a l>ge numb] 
( *emi/s & physici/s to ! ideas ( ,m4   
,arrh5ius 0 at fir/ v fi]ce4 ,x mu/ be  
not$ ) regret t1 9 ,france p>ticul>ly1  
rec\rse 0 _h to an arm :i* s*ol>s (t5   
wield r clumsily4 ,!y jok$ ab\t ^! free 
ions 9 solution1 & !y ask$ to see ?is   
*lor9e & ?is sodium :i* swam ab\t ! wat]
 9 a /ate ( lib]ty4 ,b 9 sci5ce1 z      
else:]e1 irony is n argum5t1 & x soon _h
 to be ackn[l$g$ t ! hypo!sis ( ,m4     
,arrh5ius %[$ itself s+ul>ly f]tile & _h
 to be reg>d$1 at all ev5ts1 z a v      
expressive image1 if n1 inde$1 entirely 
9 con=mity ) reality4  ,x w\ld c]ta9ly  
be contr>y to all exp]i5ce1 & ev5 to    
common s5se itself1 to suppose t 9      
dissolv$ *loride ( sodium !re is really 
free sodium1 if we suppose ^! atoms (   
sodium to be absolutely id5tical )      
ord9>y atoms4 ,b !re is a great         
diff]5ce4 ,9 ! "o case ! atoms are      
electrifi$1 & c>ry a relatively         
consid]able positive *>ge1 insep>able f 

_! /ate z ions1 :ile 9 ! o!r !y are 9 ! 
neutral /ate4 ,we may suppose t !       
pres5ce ( ?is *>ge br+s ab\t            
modifications z ext5sive z "o pleases 9 
! *emical prop]ties ( ! atom4 ,?us !    
hypo!sis w be remov$ f all discussion ( 
a *emical ord]1 s9ce x w h be5 made     
pla/ic en\gh be=eh& to adapt itself to  
all ! kn[n facts2 & if we object t      
sodium _c subsi/ 9 wat] because x       
in/antane\sly decomposes ! latt]1 !     
answ] is simply t ! sodium ion does n   
decompose wat] z does ord9>y sodium4    
,/ill1 o!r objections might be rais$ :i*
 c\ld n be s easily refut$4 ,"o1 to :i* 
*emi/s n unreasonably atta*$ great      
importance1 0 ?is3--,if a c]ta9 quantity
 ( *loride ( sodium is dissociat$ into  
*lor9e & sodium1 x %\ld be possible1 by 
diffusion1 = example1 :i* br+s out      
pla9ly ! ph5om5a ( dissociation 9 gases1
 to extract f ! solution a "p ei!r ( !  
*lor9e or ( ! sodium1 :ile ! correspond+
 "p ( ! o!r comp\nd w\ld rema94 ,?is    
result w\ld be 9 flagrant contradiction 

) ! fact t1 ev]y:]e & always1 a solution
 ( salt conta9s /rictly ! same          
proportions ( its compon5t elem5ts4  ,m4
 ,arrh5ius answ]s to ?is t ! electrical 
=ces 9 ord9>y conditions prev5t         
sep>ation by diffusion or by any o!r    
process4 ,pr(essor ,n]n/ goes fur!r1 &  
has %[n t ! conc5tration curr5ts :i* are
 produc$ :5 two electrodes ( ! same     
sub/ance are plung$ into two unequally  
conc5trat$ solutions may be int]pret$ by
 ! hypo!sis t1 9 ^! p>ticul> conditions1
 ! diffusion does br+ ab\t a sep>ation (
 ! ions4 ,?us ! argum5t is turn$ r\nd1 &
 ! pro( suppos$ to be giv5 ( !          
incorrectness ( ! !ory becomes a fur!r  
reason 9 its fav\r4  ,x is possible1 no 
d\bt1 to adduce a few o!r exp]im5ts :i* 
are n v fav\rable to ,m4 ,arrh5ius's    
po9t ( view1 b !y are isolat$ cases2 &1 
on ! :ole1 8 !ory has enabl$ _m isolat$ 
facts1 till !n scatt]$1 to be           
co-ord9at$1 & has all[$ v v>i$ ph5om5a  
to be l9k$ toge!r4 ,x has also          
sugge/$--&1 moreov]1 /ill daily         

sugge/s--rese>*es ( ! highe/ ord]4  ,9 !
 fir/ place1 ! !ory ( ,arrh5ius expla9s 
electrolysis v simply4 ,! ions :i*1 s to
 speak1 w&] ab\t haphaz>d1 & are uni=mly
 di/ribut$ ?r\gh\t ! liquid1 /e] a      
regul> c\rse z soon z we dip 9 ! tr\gh  
conta9+ ! electrolyte ! two electrodes  
connect$ ) ! poles ( ! dynamo or g5]ator
 ( electricity4 ,!n ! *>g$ positive ions
 travel 9 ! direction ( ! electromotive 
=ce & ! negative ions 9 ! opposite      
direction4 ,on rea*+ ! electrodes !y    
yield up to !m ! *>ges !y c>ry1 & ?us   
pass f ! /ate ( ion into t ( ord9>y     
atom4 ,moreov]1 = ! solution to rema9 9 
equilibrium1 ! vani%$ ions mu/ be       
imm$iately replac$ by o!rs1 & ?us ! /ate
 ( ionisation ( ! electrolyte rema9s    
con/ant & its conductivity p]si/s4  ,all
 ! peculi>ities ( electrolysis are      
capable ( int]pretation3 ! ph5om5a ( !  
transport ( ions1 ! f9e exp]im5ts ( ,m4 
,b\ty1 ^? ( ,pr(essor ,kohlraus* & (    
,pr(essor ,o/wald on v>i\s po9ts 9      
electrolytic conduction1 all support !  

!ory4 ,! v]ifications ( x c ev5 be      
quantitative1 & we c =esee num]ical     
relations betwe5 conductivity & o!r     
ph5om5a4 ,! measurem5t ( ! conductivity 
p]mits ! numb] ( molecules dissociat$ 9 
a giv5 solution to be calculat$1 & !    
numb] is ?us f\nd to be precisely ! same
 z t arriv$ at if x is wi%$ to remove ! 
disagreem5t betwe5 reality & !          
anticipations :i* result f ! !ory (     
,pr(essor ,van t' ,h(f4 ,! laws (       
cryoscopy1 ( tonometry1 & ( osmosis ?us 
aga9 become /rict1 & no exception to !m 
rema9s4  ,if ! dissociation ( salts is a
 reality & is complete 9 a dilute       
solution1 any ( ! prop]ties ( a sal9e   
solution :atev] %\ld be repres5t$       
num]ically z ! sum ( ?ree values1 ( :i* 
"o conc]ns ! positive ion1 a second !   
negative ion1 & ! ?ird ! solv5t4 ,!     
prop]ties ( ! solutions w\ld !n be :at  
are call$ additive prop]ties4 ,num]\s   
v]ifications may be attempt$ by v       
diff]5t roads4 ,!y g5]ally succe$ v     
well2 & :e!r we measure ! electric      

conductivity1 ! d5sity1 ! specific      
heats1 ! index ( refraction1 ! p[] (    
rotatory pol>ization1 ! col\r1 or !     
absorption spectrum1 ! additive prop]ty 
w ev]y:]e be f\nd 9 ! solution4  ,!     
hypo!sis1 s conte/$ at ! outset by !    
*emi/s1 is1 moreov]1 assur+ its triumph 
by important conque/s 9 ! doma9 (       
*emi/ry itself4 ,x p]mits u to give a   
vivid explanation ( *emical reaction1 & 
= ! old motto ( ! *emi/s1 ,corpora non  
agunt1 nisi soluta1 x sub/itutes a mod]n
 "o1 ,x is especially ! ions :i* react4 
,?us1 = example1 all salts ( iron1 :i*  
conta9 iron 9 ! /ate ( ions1 give simil>
 reactions2 b salts su* z f]rocyanide ( 
potassium1 9 :i* iron does n play ! "p (
 an ion1 nev] give ! *>act]i/ic         
reactions ( iron4  ,pr(essor ,o/wald & 8
 pupils h drawn f ! hypo!sis ( ,arrh5ius
 manifold consequ5ces :i* h be5 ! cause 
( consid]able progress 9 physical       
*emi/ry4 ,pr(essor ,o/wald has %[n1 9   
p>ticul>1 h[ ?is hypo!sis p]mits !      
quantitative calculation ( ! conditions 

( equilibrium ( electrolytes &          
solutions1 & especially ( ! ph5om5a (   
neutralization4 ,if a dissolv$ salt is  
p>tly dissociat$ into ions1 ?is solution
 mu/ be limit$ by an equilibrium betwe5 
! non-dissociat$ molecule & ! two ions  
result+ f ! dissociation2 &1 assimilat+ 
! ph5om5on to ! case ( gases1 we may    
take = its /udy ! laws ( ,gibbs & (     
,guldb]g & ,waage4 ,! results are       
g5]ally v satisfactory1 & new rese>*es  
daily furni% new *ecks4  ,pr(essor      
,n]n/1 :o be=e gave1 z has be5 said1 a  
rem>kable int]pretation ( ! diffusion ( 
electrolytes1 has1 9 ! direction po9t$  
out by ,m4 ,arrh5ius1 develop$ a !ory ( 
! entire ph5om5a ( electrolysis1 :i*1 9 
p>ticul>1 furni%es a /rik+ explanation (
 ! me*anism ( ! production (            
electromotive =ce 9 galvanic batt]ies4  
,ext5d+ ! analogy1 already s happily    
invok$1 betwe5 ! ph5om5a met ) 9        
solutions & ^? produc$ 9 gases1         
,pr(essor ,n]n/ supposes t metals t5d1 z
 x 71 to vaporize :5 9 pres5ce ( a      

liquid4 ,a piece ( z9c introduc$1 =     
example1 into pure wat] gives bir? to a 
few metallic ions4 ,^! ions become      
positively *>g$1 :ile ! metal naturally 
takes an equal *>ge1 b ( contr>y sign4  
,?us ! solution & ! metal are bo?       
electrifi$2 b ?is sort ( vaporization is
 h9d]$ by electro/atic attraction1 & z !
 *>ges borne by ! ions are consid]able1 
an equilibrium w be e/abli%$1 al?\gh !  
numb] ( ions :i* ent] ! solution w be v 
small4  ,if ! liquid1 in/ead ( be+ a    
solv5t l pure wat]1 conta9s an          
electrolyte1 x already conta9s metallic 
ions1 ! osmotic pressure ( :i* w be     
opposite to t ( ! solution4 ,?ree cases 
may !n pres5t !mselves--ei!r !re w be   
equilibrium1 or ! electro/atic          
attraction w oppose itself to ! pressure
 ( solution & ! metal w be negatively   
*>g$1 or1 f9ally1 ! attraction w act 9 !
 same direction z ! pressure1 & ! metal 
w become positively & ! solution        
negatively *>g$4 ,develop+ ?is idea1    
,pr(essor ,n]n/ calculates1 by means ( !

 action ( ! osmotic pressures1 !        
v>iations ( en]gy br\ght into play & !  
value ( ! diff]5ces ( pot5tial by !     
contact ( ! electrodes & electrolytes4  
,he d$uces ?is f ! electromotive =ce ( a
 s+le batt]y cell :i* becomes ?us       
connect$ ) ! values ( ! osmotic         
pressures1 or1 if y w1 ?anks to !       
relation discov]$ by ,van t' ,h(f1 ) !  
conc5trations4 ,"s p>ticul>ly int]e/+   
electrical ph5om5a ?us become connect$ )
 an already v important gr\p1 & a new   
bridge is built :i* unites two regions  
long consid]$ =eign to ea* o!r4  ,!     
rec5t discov]ies on ! ph5om5a produc$ 9 
gases :5 r5d]$ conductors ( electricity 
almo/ =ce ^u u1 z we %all see1 ! idea t 
!re exi/ 9 ^! gases electrifi$ c5tres   
mov+ ?r\gh ! field1 & ?is idea gives    
/ill great] probability to ! analog\s   
!ory expla9+ ! me*anism ( ! conductivity
 ( liquids4 ,x w also be useful1 9 ord] 
to avoid confusion1 to re/ate )         
precision ?is notion ( electrolytic     
ions1 & to asc]ta9 _! magnitude1 *>ge1 &

 velocity4  ,! two classic laws (       
,f>aday w supply u ) important          
in=mation4 ,! fir/ indicates t !        
quantity ( electricity pass+ ?r\gh !    
liquid is proportional to ! quantity (  
matt] deposit$ on ! electrodes4 ,?is    
leads u at once to ! consid]ation t1 9  
any giv5 solution1 all ! ions possess   
individual *>ges equal 9 absolute value4
  ,! second law may be /at$ 9 ^! t]ms3  
an atom-gramme ( metal c>ries ) x into  
electrolysis a quantity ( electricity   
proportionate to its val5cy4#ai         
,footnote #ai3 ,! val5cy or atomicity ( 
an elem5t may be def9$ z ! p[] x        
possesses ( ent]+ into comp\nds 9 a     
c]ta9 fix$ proportion4 ,z hydrog5 is    
g5]ally tak5 z ! /&>d1 9 practice !     
val5cy ( an atom is ! numb] ( hydrog5   
atoms x w comb9e ) or replace4 ,?us     
*lor9e & ! re/ ( ! halog5s1 ! atoms (   
:i* comb9e ) "o atom ( hydrog51 are     
call$ unival5t1 oxyg5 a bival5t elem5t1 
& s on4--,,ed4  ,num]\s exp]im5ts h made
 kn[n ! total mass ( hydrog5 capable (  

c>ry+ "o c\lomb1 & x w !re=e be possible
 to e/imate ! *>ge ( an ion ( hydrog5 if
 ! numb] ( atoms ( hydrog5 9 a giv5 mass
 be kn[n4 ,?is la/ figure is already    
furni%$ by consid]ations d]iv$ f !      
k9etic !ory1 & agrees ) ! "o :i* c be   
d$uc$ f ! /udy ( v>i\s ph5om5a4 ,!      
result is t an ion ( hydrog5 hav+ a mass
 ( #a4c x #aj-bj grammes be>s a *>ge (  
#a4c ,x #aj-bj electromagnetic units2 & 
! second law w imm$iately enable ! *>ge 
( any o!r ion to be simil>ly e/imat$4   
,! measurem5ts ( conductivity1 jo9$ to  
c]ta9 consid]ations relat+ to !         
diff]5ces ( conc5tration :i* appe> r\nd 
! electrode 9 electrolysis1 all[ ! spe$ 
( ! ions to be calculat$4 ,?us1 9 a     
liquid conta9+ #a_/aj? ( a hydrog5-ion  
p] litre1 ! absolute spe$ ( an ion w\ld 
be #c_/aj?s ( a millimetre p] second 9 a
 field :]e ! fall ( pot5tial w\ld be #a 
volt p] c5timetre4 ,sir ,oliv] ,lodge1  
:o has made direct exp]im5ts to measure 
?is spe$1 has obta9$ a figure v         
approximate to ?is4 ,?is value is v     

small comp>$ to t :i* we %all meet ) 9  
gases4  ,ano!r consequ5ce ( ! laws (    
,f>aday1 to :i*1 z e>ly z #ahha1        
,helmholtz drew att5tion1 may be        
consid]$ z ! />t+-po9t ( c]ta9 new      
doctr9es we %all come across lat]4      
,helmholtz says3 ,if we accept !        
hypo!sis t simple bodies are compos$ (  
atoms1 we are oblig$ to admit t1 9 !    
same way1 electricity1 :e!r positive or 
negative1 is compos$ ( elem5t>y p>ts :i*
 behave l atoms ( electricity4  ,!      
second law seems1 9 fact1 analog\s to ! 
law ( multiple proportions 9 *emi/ry1 & 
x %[s u t ! quantities ( electricity    
c>ri$ v>y f ! simple to ! d\ble or      
treble1 accord+ z x is a "q ( a uni-1   
bi-1 or trival5t metal2 & z ! *emical   
law leads up to ! conception ( ! mat]ial
 atom1 s does ! electrolytic law sugge/ 
! idea ( an electric atom4     ,,*apt]  
,,vi  ,,! ,,e!r    #a4 ,,! ,,lum9if]\s  
,,e!r  ,x is 9 ! works ( ,desc>tes t we 
f9d ! fir/ idea ( attribut+ ^? physical 
ph5om5a :i* ! prop]ties ( matt] fail to 

expla9 to "s subtle matt] :i* is !      
receptacle ( ! en]gy ( ! univ]se4  ,9   
our times ?is idea has _h extraord9>y   
luck4 ,aft] hav+ be5 eclips$ = two      
hundr$ ye>s by ! success ( ! immortal   
syn!sis ( ,newton1 x ga9$ an entirely   
new spl5d\r ) ,fresnel & 8 foll[]s4     
,?anks to _! admirable discov]ies1 !    
fir/ /age seem$ accompli%$1 ! laws (    
optics 7 repres5t$ by a s+le hypo!sis1  
m>vell\sly fitt$ to all[ u to anticipate
 unkn[n ph5om5a1 & all ^! anticipations 
7 subsequ5tly fully v]ifi$ by exp]im5t4 
,b ! rese>*es ( ,f>aday1 ,maxwell1 &    
,h]tz au?oriz$ /ill great] ambitions2 & 
x really seem$ t ?is m$ium1 to :i* x 0  
agre$ to give ! anci5t "n ( e!r1 & :i*  
_h already expla9$ light & radiant heat1
 w\ld also be suffici5t to expla9       
electricity4 ,?us ! hope began to take  
=m t we might succe$ 9 demon/rat+ !     
unity ( all physical =ces4 ,x 0 ?\ght t 
! k ( ! laws relat+ to ! inmo/ movem5ts 
( ?is e!r might give u ! key to all     
ph5om5a1 & might make u acqua9t$ ) !    

me?od 9 :i* en]gy is /or$ up1           
transmitt$1 & p>cell$ out 9 its ext]nal 
manife/ations4  ,we _c /udy "h all !    
problems :i* are connect$ ) ! physics ( 
! e!r4 ,to d ?is a complete treatise on 
optics w\ld h to be writt5 & a v l5g?y  
"o on electricity4 ,i %all simply       
endeav\r to %[ rapidly h[ 9 ! la/ few   
ye>s ! ideas relative to ! con/itution (
 ?is e!r h evolv$1 & we %all see if x be
 possible )\t self-delusion to imag9e t 
a s+le m$ium c really all[ u to gr\p all
 ! kn[n facts 9 "o compreh5sive         
arrangem5t4  ,z con/ruct$ by ,fresnel1 !
 hypo!sis ( ! lum9\s e!r1 :i* _h s great
 a /ruggle at ! outset to ov]come !     
/ubborn resi/ance ( ! p>tisans ( ! !n   
classic !ory ( emission1 seem$1 on !    
contr>y1 to possess 9 ! sequel an       
un%akable /r5g?4 ,lam1 ?\gh a prud5t    
ma!matician1 wrote3 ,! exi/5ce ( !      
e!real fluid is inconte/ably demon/rat$ 
by ! propagation ( light ?r\gh !        
planet>y spaces1 & by ! explanation1 s  
simple & s complete1 ( ! ph5om5a (      

diffraction 9 ! wave !ory ( light2 & he 
adds3 ,! laws ( d\ble refraction prove )
 no less c]ta9ty t ! e!r exi/s 9 all    
diaphan\s m$ia4 ,?us ! e!r 0 no long] an
 hypo!sis1 b 9 "s sort a tangible       
reality4 ,b ! e!real fluid ( :i* !      
exi/5ce 0 ?us proclaim$ has "s s+ul>    
prop]ties4  ,7 x only a "q ( expla9+    
rectil9e> propagation1 reflexion1       
refraction1 diffraction1 & int]f]5ces   
not)/&+ grave difficulties at ! outset &
 ! objections =mulat$ by ,laplace &     
,poisson 7"s ( :i*1 ?\gh treat$ some:at 
lightly at ! pres5t day1 h n lo/ all    
value71 we %\ld be "u no obligation to  
make any hypo!sis o!r ?an t ( !         
undulations ( an ela/ic m$ium1 )\t      
decid+ 9 advance any?+ z to ! nature &  
direction ( ! vibrations4  ,?is m$ium   
w\ld1 naturally--s9ce x exi/s 9 :at we  
call ! void--be consid]$ z impond]able4 
,x may be comp>$ to a fluid ( negligible
 mass--s9ce x (f]s no appreciable       
resi/ance to ! motion ( ! planets--b is 
end[$ ) an enorm\s ela/icity1 because ! 

velocity ( ! propagation ( light is     
consid]able4 ,x mu/ be capable (        
p5etrat+ into all transp>5t bodies1 & ( 
reta9+ !re1 s to speak1 a con/ant       
ela/icity1 b mu/ !re become cond5s$1    
s9ce ! spe$ ( propagation 9 ^! bodies is
 less ?an 9 a vacuum4 ,su* prop]ties    
belong to no mat]ial gas1 ev5 ! mo/     
r>efi$1 b !y admit ( no ess5tial        
contradiction1 & t is ! important       
po9t4#bj  ,footnote #bj3 ,s9ce ?is 0    
writt51 h[ev]1 m5 ( sci5ce h become less
 unanim\s ?an !y =m]ly 7 on ?is po9t4 ,!
 vet]an *emi/ ,pr(essor ,m5deleff has   
giv5 reasons = ?9k+ t ! e!r is an in]t  
gas ) an atomic weight a million times  
less ?an t ( hydrog51 & a velocity (    
#bbej kilometres p] second 7,pr9ciples (
 ,*emi/ry1 ,eng4 ed41 #aije1 vol4 ii4 p4
 #ebf74 ,on ! o!r h&1 ! well-kn[n       
physici/ ,dr ,a4,h4 ,bu*]]1 speak+ at ! 
,natur=s*]v]sammlung1 held at ,/uttg>t 9
 #aijf1 decl>$ 8 disbelief 9 ! exi/5ce (
 ! e!r1 :i* he ?\ght c\ld n be reconcil$
 at once ) ! ,maxwellian !ory & ! kn[n  

facts4--,,ed4  ,x 0 ! /udy ( ! ph5om5a (
 pol>ization :i* l$ ,fresnel to 8 bold  
conception ( transv]se vibrations1 &    
subsequ5tly induc$ him to p5etrate fur!r
 into ! con/itution ( ! e!r4 ,we "k !   
exp]im5t ( ,arago on ! non9t]f]5ce (    
pol>iz$ rays 9 rectangul> planes4 ,:ile 
two sy/ems ( waves1 proce$+ f ! same    
s\rce ( natural light & propagat+       
!mselves 9 ne>ly p>allel directions1    
increase or become de/roy$ accord+ to   
:e!r ! nature ( ! sup]pos$ waves are ( !
 same or ( contr>y signs1 ! waves ( !   
rays pol>iz$ 9 p]p5dicul> planes1 on !  
o!r h&1 c nev] int]f]e ) ea* o!r4       
,:atev] ! diff]5ce ( _! c\rse1 !        
int5sity ( ! light is always ! sum ( !  
int5sity ( ! two rays4  ,fresnel p]ceiv$
 t ?is exp]im5t absolutely compels u to 
reject ! hypo!sis ( longitud9al         
vibrations act+ along ! l9e (           
propagation 9 ! direction ( ! rays4 ,to 
expla9 x1 x mu/ ( necessity be admitt$1 
on ! contr>y1 t ! vibrations are        
transv]se & p]p5dicul> to ! ray4 ,v]det 

c\ld say1 9 all tru?1 ,x is n possible  
to d5y ! transv]se direction ( lum9\s   
vibrations1 )\t at ! same "t d5y+ t     
light consi/s ( an undulatory movem5t4  
,su* vibrations d n & _c exi/ 9 any     
m$ium resembl+ a fluid4 ,! *>act]i/ic ( 
a fluid is t its diff]5t p>ts c displace
 !mselves ) reg>d to "o ano!r )\t any   
reaction appe>+ s long z a v>iation (   
volume is n produc$4 ,!re c]ta9ly may   
exi/1 z we h se51 c]ta9 traces (        
rigidity 9 a liquid1 b we _c conceive   
su* a ?+ 9 a body inf9itely m subtle ?an
 r>efi$ gas4 ,among mat]ial bodies1 a   
solid alone really possesses ! rigidity 
suffici5t = ! production )9 x (         
transv]se vibrations & = _! ma9t5ance   
dur+ _! propagation4  ,s9ce we h to     
attribute su* a prop]ty to ! e!r1 we may
 add t on ?is po9t x resembles a solid1 
& ,"l ,kelv9 has %[n t ?is solid1 w\ld  
be mu* m rigid ?an /eel4 ,?is conclusion
 produces great surprise 9 all :o he> x 
= ! fir/ "t1 & x is n r>e to he> x      
appeal$ to z an argum5t aga9/ ! actual  

exi/5ce ( ! e!r4 ,x does n seem1 h[ev]1 
t su* an argum5t c be decisive4 ,!re is 
no reason = suppos+ t ! e!r ought to be 
a sort ( ext5sion ( ! bodies we are     
accu/om$ to h&le4 ,its prop]ties may    
a/oni% our ord9>y way ( ?9k+1 b ?is r   
unsci5tific a/oni%m5t is n a reason =   
d\bt+ its exi/5ce4 ,real difficulties   
w\ld appe> only if we 7 l$ to attribute 
to ! e!r1 n s+ul> prop]ties :i* are     
seldom f\nd unit$ 9 ! same sub/ance1 b  
prop]ties logically contradictory4 ,9   
%ort1 h[ev] odd su* a m$ium may appe> to
 u1 x _c be said t !re is any absolute  
incompatibility betwe5 its attributes4  
,x w\ld ev5 be possible1 if we wi%$1 to 
sugge/ images capable ( repres5t+ ^!    
contr>y appe>ances4 ,v>i\s au?ors h done
 s4 ,?us1 ,m4 ,b\ss9esq assumes t ! e!r 
behaves l a v r>efi$ gas 9 respect ( !  
cele/ial bodies1 because ^! la/ move1   
:ile ba!d 9 x1 9 all directions &       
relatively sl[ly1 :ile !y p]mit x to    
reta91 s to speak1 its p]fect           
homog5eity4 ,on ! o!r h&1 its own       

undulations are s rapid t s f> z !y are 
conc]n$ ! conditions become v diff]5t1 &
 its fluidity has1 "o might say1 no     
long] ! "t to come 94 ,h5ce its rigidity
 alone appe>s4  ,ano!r consequ5ce1 v    
important 9 pr9ciple1 ( ! fact t        
vibrations ( light are transv]se1 has   
be5 well put 9 evid5ce by ,fresnel4 ,he 
%[$ h[ we h1 9 ord] to und]/& ! action  
:i* excites )\t cond5sation ! slid+ (   
successive lay]s ( ! e!r dur+ !         
propagation ( a vibration1 to consid] ! 
vibrat+ m$ium z be+ compos$ ( molecules 
sep>at$ by f9ite di/ances4 ,c]ta9       
au?ors1 x is true1 h propos$ !ories 9   
:i* ! action at a di/ance ( ^! molecules
 are replac$ by actions ( contact betwe5
 p>allelepip$s slid+ ov] "o ano!r2 b1 at
 bottom1 ^! two po9ts ( view bo? lead u 
to conceive ! e!r z a discont9u\s m$ium1
 l matt] itself4 ,! ideas ga!r$ f ! mo/ 
rec5t exp]im5ts also br+ u to ! same    
conclusion4    #b4 ,,radiations  ,9 !   
e!r ?us con/itut$ !re are !re=e         
propagat$ transv]se vibrations1 reg>d+  

:i* all exp]im5ts 9 optics furni% v     
precise in=mation4 ,! amplitude ( ^!    
vibrations is exce$+ly small1 ev5 9     
relation to ! wave-l5g?1 small z ^! la/ 
are4 ,if1 9 fact1 ! amplitude ( !       
vibrations acquir$ a noticeable value 9 
comp>ison ) ! wave-l5g?1 ! spe$ (       
propagation %\ld increase ) ! amplitude4
 ,yet1 9 spite ( "s curi\s exp]im5ts :i*
 seem to e/abli% t ! spe$ ( light does  
alt] a little ) its int5sity1 we h      
reason to believe t1 z reg>ds light1 !  
amplitude ( ! oscillations 9 relation to
 ! wave-l5g? is incomp>ably less ?an 9 !
 case ( s\nd4  ,x has become ! cu/om to 
*>act]ise ea* vibration by ! pa? :i* !  
vibratory movem5t trav]ses dur+ ! space 
( a vibration--by ! l5g? ( wave1 9 a    
^w--r ?an by ! duration ( ! vibration   
itself4 ,to measure wave-l5g?s1 ! me?ods
 mu/ be employ$ to :i* ,i h already     
allud$ on ! subject ( measurem5ts (     
l5g?4 ,pr(essor ,mi*elson1 on ! "o h&1 &
 ,,mm4 ,p]ot & ,fabry1 on ! o!r1 h      
devis$ exce$+ly +5i\s processes1 :i* h  

l$ to results ( really unhop$-=         
precision4 ,! v exact k also ( ! spe$ ( 
! propagation ( light all[s ! duration (
 a vibration to be calculat$ :5 once !  
wave-l5g? is kn[n4 ,x is ?us f\nd t1 9 !
 case ( visible light1 ! numb] ( !      
vibrations f ! end ( ! violet to !      
infra-r$ v>ies f f\r hundr$ to two      
hundr$ billions p] second4 ,?is gamut is
 n1 h[ev]1 ! only "o ! e!r c give4 ,= a 
long "t we h kn[n ultra-violet          
radiations /ill m rapid1 &1 on ! o!r h&1
 infra-r$ ones m sl[1 :ile 9 ! la/ few  
ye>s ! field ( kn[n radiations has be5  
s+ul>ly ext5d$ 9 bo? directions4  ,x is 
to ,m4 ,rub5s & 8 fell[-work]s t are due
 ! mo/ brilliant conque/s 9 ! matt] (   
great wave-l5g?s4 ,he _h rem>k$ t1 9 _! 
/udy1 ! difficulty ( rese>* proce$s f ! 
fact t ! extreme waves ( ! infra-r$     
spectrum only conta9 a small "p ( !     
total en]gy emitt$ by an inc&esc5t body2
 s t if1 = ! purpose ( /udy1 !y are     
fur!r disp]s$ by a prism or a grat+1 !  
int5sity at any "o po9t becomes s slight

 z to be no long] obs]vable4 ,8 orig9al 
idea 0 to obta91 )\t prism or grat+1 a  
homog5e\s p5cil ( great wave-l5g?       
suffici5tly int5se to be exam9$4 ,= ?is 
purpose ! radiant s\rce us$ 0 a /rip (  
plat9um cov]$ ) fluor9e or p[d]$ qu>tz1 
:i* emits num]\s radiations close to two
 b&s ( l9e> absorption 9 ! absorption   
spectra ( fluor9e & qu>tz1 "o ( :i* is  
situat$ 9 ! infra-r$4 ,! radiations ?us 
emitt$ are sev]al times reflect$ on     
fluor9e or on qu>tz1 z ! case may be2 & 
z1 9 proximity to ! b&s1 ! absorption is
 ( ! ord] ( t ( metallic bodies = lum9\s
 rays1 we no long] meet 9 ! p5cil sev]al
 times reflect$ or 9 ! rays rema9+ aft] 
?is k9d ( filtration1 ) any b radiations
 ( great wave-l5g?4 ,?us1 = in/ance1 9 !
 case ( ! qu>tz1 9 ! neighb\rhood ( a   
radiation correspond+ to a wave-l5g? (  
#h4e microns1 ! absorption is ?irty     
times great] 9 ! region ( ! b& ?an 9 !  
neighb\r+ region1 & consequ5tly1 aft]   
?ree reflexions1 :ile ! correspond+     
radiations w n h be5 weak5$1 ! neighb\r+

 waves w be s1 on ! contr>y1 9 !        
proportion ( #a to #bg1jjj4  ,) mirrors 
( rock salt & ( sylv9e#ba !re h be5     
obta9$1 by tak+ an inc&esc5t gas light  
7,au]7 z s\rce1 radiations ext5d+ z f> z
 #gj microns2 & ^! la/ are ! greate/    
wave-l5g?s obs]v$ 9 optical ph5om5a4 ,^!
 radiations are l>gely absorb$ by !     
vap\r ( wat]1 & x is no d\bt ow+ to ?is 
absorption t !y are n f\nd 9 ! sol>     
spectrum4 ,on ! o!r h&1 !y easily pass  
?r\gh gutta-p]*a1 india-rubb]1 &        
insulat+ sub/ances 9 g5]al4  ,footnote  
#ba3 ,a natural *lorate ( potassium1    
g5]ally ( volcanic orig94--,,ed4  ,at ! 
opposite end ( ! spectrum ! k ( !       
ultra-violet regions has be5 greatly    
ext5d$ by ! rese>*es ( ,l5>d4 ,^!       
extremely rapid radiations h be5 %[n by 
t em95t physici/ to occur 9 ! light ( ! 
electric sp>ks :i* fla% betwe5 two metal
 po9ts1 & :i* are produc$ by a l>ge     
induction coil ) cond5s] & a ,wehnelt   
break4 ,pr(essor ,s*umann has succe$$ 9 
photograph+ !m by deposit+ bromide (    

silv] directly on glass plates )\t fix+ 
x ) gelat9e2 & he has1 by ! same        
process1 photograph$ 9 ! spectrum (     
hydrog5 a ray ) a wave-l5g? ( only #j4a 
micron4  ,! spectroscope 0 =m$ entirely 
( fluor-sp>1 & a vacuum _h be5 creat$ 9 
x1 = ^! radiations are extremely        
absorbable by ! air4  ,not)/&+ ! extreme
 smallness ( ! lum9\s wave-l5g?s1 x has 
be5 possible1 aft] num]\s fruitless     
trials1 to obta9 /ation>y waves analog\s
 to ^? :i*1 9 ! case ( s\nd1 are produc$
 9 organ pipes4 ,! m>vell\s application 
,m4 ,lippmann has made ( ^! waves to    
completely solve ! problem ( photography
 9 col\rs is well kn[n4 ,?is discov]y1 s
 important 9 itself & s in/ructive1 s9ce
 x %[s u h[ ! mo/ delicate anticipations
 ( !ory may be v]ifi$ 9 all _!          
consequ5ces1 & lead ! physici/ to !     
solution ( ! problems occurr+ 9         
practice1 has ju/ly become popul>1 & !re
 is1 !re=e1 no ne$ to describe x "h 9   
detail4  ,pr(essor ,wi5] obta9$ /ation>y
 waves "s little :ile be=e ,m4          

,lippmann's discov]y1 9 a lay] ( a      
s5sitive sub/ance hav+ a gra9           
suffici5tly small 9 relation to ! l5g? (
 wave4 ,8 aim 0 to solve a "q ( great   
importance to a complete k ( ! e!r4     
,fresnel f\nd$ 8 !ory ( d\ble refraction
 & reflexion by transp>5t surfaces1 on !
 hypo!sis t ! vibration ( a ray (       
pol>iz$ light is p]p5dicul> to ! plane (
 pol>ization4 ,b ,neumann has propos$1  
on ! contr>y1 a !ory 9 :i* he recognizes
 t ! lum9\s vibration is 9 ?is v plane4 
,he r supposes1 9 opposition to         
,fresnel's idea1 t ! d5sity ( ! e!r     
rema9s ! same 9 all m$ia1 :ile its      
coeffici5t ( ela/icity is v>iable4  ,v  
rem>kable exp]im5ts on disp]sion by ,m4 
,c>vallo prove inde$ t ! idea ( ,fresnel
 01 if n necess>y = u to adopt1 at lea/ 
! m probable ( ! two2 b ap>t f ?is      
indication1 & contr>y to ! hypo!sis (   
,neumann1 ! two !ories1 f ! po9t ( view 
( ! explanation ( all kn[n facts1 really
 appe> to be equival5t4 ,are we !n 9    
pres5ce ( two me*anical explanations1   

diff]5t inde$1 b nev]!less bo? adaptable
 to all ! facts1 & betwe5 :i* x w always
 be impossible to make a *oice8 ,or1 on 
! contr>y1 %all we succe$ 9 realis+ an  
exp]im5tum crucis1 an exp]im5t at ! po9t
 :]e ! two !ories cross1 :i* w def9itely
 settle ! "q8  ,pr(essor ,wi5] ?\ght he 
c\ld draw f 8 exp]im5t a firm conclusion
 on ! po9t 9 dispute4 ,he produc$       
/ation>y waves ) light pol>iz$ at an    
angle ( #de1bb & e/abli%$ t1 :5 light is
 pol>iz$ 9 ! plane ( incid5ce1 ! fr+es  
p]si/2 b t1 on ! o!r h&1 !y disappe> :5 
! light is pol>iz$ p]p5dicul>ly to ?is  
plane4 ,if x be admitt$ t a photographic
 impression results f ! active =ce ( !  
vibratory movem5t ( ! e!r1 ! "q is1 9   
fact1 completely elucidat$1 & !         
discrepancy is aboli%$ 9 ,fresnel's     
fav\r4  ,footnote #bb3 ,t is to say1 he 
reflect$ ! beam ( pol>iz$ light by a    
mirror plac$ at t angle4 ,see ,turpa91  
,leons lem5taires de ,physique1 t4 ii4  
p4 #caa1 = details ( ! exp]im5t4--,,ed4 
,m4,h4 ,po9c> has po9t$ out1 h[ev]1 t we

 "k no?+ z to ! me*anism ( !            
photographic impression4 ,we _c consid] 
x evid5t t x is ! k9etic en]gy ( ! e!r  
:i* produces ! decomposition ( !        
s5sitive salt2 & if1 on ! contr>y1 we   
suppose x to be due to ! pot5tial en]gy1
 all ! conclusions are rev]s$1 &        
,neumann's idea triumphs4  ,rec5tly a v 
clev] physici/1 ,m4 ,cotton1 especially 
kn[n = 8 skilful rese>*es 9 ! doma9 (   
optics1 has tak5 up anew ! /udy (       
/ation>y waves4 ,he has made v precise  
quantitative exp]im5ts1 & has           
demon/rat$1 9 8 turn1 t x is impossible1
 ev5 ) sph]ical waves1 to succe$ 9      
det]m9+ on :i* ( ! two vectors :i* h to 
be reg>d$ 9 all !ories ( light on !     
subject ( pol>ization ph5om5a ! lum9\s  
int5sity & ! *emical action really      
dep5d4 ,?is "q1 !re=e1 no long] exi/s = 
^? physici/s :o admit t lum9\s          
vibrations are electrical oscillations4 
,:atev]1 !n1 ! hypo!sis =m$1 :e!r x be  
electric =ce or1 on ! contr>y1 magnetic 
=ce :i* we place 9 ! plane (            

pol>ization1 ! mode ( propagation =ese5 
w always be 9 accord ) ! facts obs]v$4  
#c4 ,,! ,,electromagnetic ,,e!r  ,! idea
 ( attribut+ ! ph5om5a ( electricity to 
p]turbations produc$ 9 ! m$ium :i*      
transmits ! light is already ( old /&+2 
& ! physici/s :o witness$ ! triumph (   
,fresnel's !ories c\ld n fail to        
conceive t ?is fluid1 :i* fills ! :ole (
 space & p5etrates into all bodies1     
might also play a prepond]ant "p 9      
electrical actions4 ,"s ev5 =m$ too ha/y
 hypo!ses on ?is po9t2 = ! h\r _h n     
arriv$ :5 x 0 possible to place !m on a 
suffici5tly s\nd basis1 & ! kn[n facts 7
 n num]\s en\gh to give ! necess>y      
precision4  ,! f\nd]s ( mod]n           
electricity also ?\ght x wis] to adopt1 
) reg>d to ?is sci5ce1 ! attitude tak5  
by ,newton 9 connection ) gravitation3  
,9 ! fir/ place to obs]ve facts1 to v>y 
! circum/ances ( ^! z mu* z possible1 to
 accompany ?is fir/ "w by precise       
measurem5ts 9 ord] to d$uce f !m g5]al  
laws f\nd$ solely on exp]im5t1 & to     

d$uce f ^! laws1 indep5d5tly ( all      
hypo!ses on ! nature ( ! =ces produc+ ! 
ph5om5a1 ! ma!matical value ( ^! =ces--t
 is to say1 ! =mula repres5t+ !m4 ,su* 0
 ! sy/em pursu$ by ,newton4 ,x has1 9   
g5]al1 be5 adopt$ 9 ,france by ! s*ol>s 
to :om physics owe ! great progress made
 ( late ye>s1 & x has s]v$ z my guide 9 
all my rese>*es on electrodynamic       
ph5om5a4444 ,x is = ?is reason t ,i h   
avoid$ speak+ ( ! ideas ,i may h on !   
nature ( ! cause ( ! =ce emanat+ f      
voltaic conductors4  ,?us did ,ampre    
express himself4 ,! illu/ri\s physici/  
rightly consid]$ ! results obta9$ by him
 ?r\gh foll[+ ?is wise me?od z wor?y (  
comp>ison ) ! laws ( attraction2 b he   
knew t :5 ?is fir/ halt+-place 0 rea*$  
!re 0 /ill fur!r to g1 & t ! evolution (
 ideas mu/ necess>ily cont9ue4  ,)      
:atev] physical cause1 he adds1 we may  
wi% to connect ! ph5om5a produc$ by     
electro-dynamic action1 ! =mula ,i h    
obta9$ w always rema9 ! expression ( !  
facts1 & he explicitly indicat$ t if "o 

c\ld succe$ 9 d$uc+ 8 =mula f !         
consid]ation ( ! vibrations ( a fluid   
di/ribut$ ?r\gh space1 an enorm\s /ep   
w\ld h be5 tak5 9 ?is dep>tm5t (        
physics4 ,he add$1 h[ev]1 t ?is rese>*  
appe>$ to him premature1 & w\ld *ange   
no?+ 9 ! results ( 8 "w1 s9ce1 to accord
 ) facts1 ! hypo!sis adopt$ w\ld always 
h to agree ) ! =mula :i* exactly        
repres5ts !m4  ,x is n devoid ( int]e/  
to obs]ve t ,ampre himself1 not)/&+ 8   
caution1 really =m$ "s hypo!ses1 &      
recogniz$ t electrical ph5om5a 7 gov]n$ 
by ! laws ( me*anics4 ,yet ! pr9ciples (
 ,newton !n appe>$ to be un%akable4     
,f>aday 0 ! fir/ to demon/rate1 by cle> 
exp]im5t1 ! influ5ce ( ! m$ia 9         
electricity & magnetic ph5om5a1 & he    
attribut$ ?is influ5ce to c]ta9         
modifications 9 ! e!r :i* ^! m$ia       
enclose4 ,8 fundam5tal conception 0 to  
reject action at a di/ance1 & to        
localize 9 ! e!r ! en]gy ^: evolution is
 ! cause ( ! actions manife/$1 z1 =     
example1 9 ! dis*>ge ( a cond5s]4       

,consid] ! b>rel ( a pump plac$ 9 a     
vacuum & clos$ by a pi/on at ea* end1 & 
let u introduce betwe5 ^! a c]ta9 mass (
 air4 ,! two pi/ons1 ?r\gh ! ela/ic =ce 
( ! gas1 repel ea* o!r ) a =ce :i*1     
accord+ to ! law ( ,m>iotte1 v>ies 9    
inv]se ratio to ! di/ance4 ,! me?od     
fav\r$ by ,ampre w\ld fir/ ( all all[   
?is law ( repulsion betwe5 ! two pi/ons 
to be discov]$1 ev5 if ! exi/5ce ( a gas
 enclos$ 9 ! b>rel ( ! pump 7           
unsuspect$2 & x w\ld !n be natural to   
localize ! pot5tial en]gy ( ! sy/em on !
 surface ( ! two pi/ons4 ,b if !        
ph5om5on is m c>efully exam9$1 we %all  
discov] ! pres5ce ( ! air1 & we %all    
und]/& t e "p ( ! volume ( ?is air c\ld1
 if x 7 drawn (f into a recipi5t ( equal
 volume1 c>ry away ) x a fraction ( !   
en]gy ( ! sy/em1 & t consequ5tly ?is    
en]gy belongs really to ! air & n to !  
pi/ons1 :i* are !re solely = ! purpose (
 enabl+ ?is en]gy to manife/ its        
exi/5ce4  ,f>aday made1 9 "s sort1 an   
equival5t discov]y :5 he p]ceiv$ t !    

electrical en]gy belongs1 n to ! coat+s 
( ! cond5s]1 b to ! dielectric :i*      
sep>ates !m4 ,8 audaci\s views reveal$  
to him a new _w1 b to explore ?is _w a  
sur] & m pati5t me?od 0 ne$$4  ,maxwell 
succe$$ 9 /at+ ) precision c]ta9 po9ts (
 ,f>aday's ideas1 & he gave !m !        
ma!matical =m :i*1 (t5 wrongly1         
impresses physici/s1 b :i* :5 x exactly 
encloses a !ory1 is a c]ta9 pro( t ?is  
!ory is at lea/ coh]5t & logical4#bc    
,footnote #bc3 ,x w no d\bt be a %ock to
 ^? :om ,pr(essor ,h5ry ,arm/rong has   
lately call$ ! ma!matically-m9d$ to f9d 
a memb] ( ! ,po9c> family speak+        
disrespectfully ( ! sci5ce !y h done s  
mu* to illu/rate4 ,"o may p]haps comp>e 
! expression 9 ! text ) ,m4 ,h5ri       
,po9c>'s rem>k 9 8 la/ allocution to !  
,acadmie des ,sci5ces1 t ,ma!matics are 
sometimes a nuisance1 & ev5 a dang]1 :5 
!y induce u to affirm m ?an we "k       
7,comptes-r5dus1 #ag? ,decemb] #aijf74  
,! "w ( ,maxwell is ov]-elaborat$1      
complex1 difficult to read1 & (t5       

ill-und]/ood1 ev5 at ! pres5t day4      
,maxwell is m conc]n$ 9 discov]+ :e!r x 
is possible to give an explanation (    
electrical & magnetic ph5om5a :i* %all  
be f\nd$ on ! me*anical prop]ties ( a   
s+le m$ium1 ?an 9 /at+ ?is explanation 9
 precise t]ms4 ,he is aw>e t if we c\ld 
succe$ 9 con/ruct+ su* an int]pretation1
 x w\ld be easy to propose an inf9ity ( 
o!rs1 entirely equival5t f ! po9t ( view
 ( ! exp]im5tally v]ifiable consequ5ces2
 & 8 especial ambition is !re=e to      
extract f ! premises a g5]al view1 & to 
place 9 evid5ce some?+ :i* w\ld rema9 ! 
common prop]ty ( all ! !ories4  ,he     
succe$$ 9 %[+ t if ! electro/atic en]gy 
( an electromagnetic field be consid]$  
to repres5t pot5tial en]gy1 & its       
electrodynamic ! k9etic en]gy1 x becomes
 possible to satisfy bo? ! pr9ciple (   
lea/ action & t ( ! cons]vation ( en]gy2
 f t mom5t--if we elim9ate a few        
difficulties :i* exi/ reg>d+ ! /ability 
( ! solutions--! possibility ( f9d+     
me*anical explanations ( electromagnetic

 ph5om5a mu/ be consid]$ z demon/rat$4  
,he ?us succe$$1 moreov]1 9 /at+        
precisely ! notion ( two electric &     
magnetic fields :i* are produc$ 9 all   
po9ts ( space1 & :i* are /rictly        
int]-connect$1 s9ce ! v>iation ( ! "o   
imm$iately & compulsorily gives bir? to 
! o!r4  ,f ?is hypo!sis he d$uc$ t1 9 ! 
m$ium :]e ?is en]gy is localiz$1 an     
electromagnetic wave is propagat$ ) a   
velocity equal to ! relation ( ! units (
 electric mass 9 ! electromagnetic &    
electro/atic sy/ems4 ,n[1 exp]im5ts made
 kn[n s9ce 8 "t h prov$ t ?is relation  
is num]ically equal to ! spe$ ( light1 &
 ! m precise exp]im5ts made 9           
consequ5ce--among :i* %\ld be cit$ !    
p>ticul>ly c>eful ones ( ,m4 ,max       
,abraham--h only r5d]$ ! co9cid5ce /ill 
m complete4  ,x is natural h5ce=? to    
suppose t ?is m$ium is id5tical ) !     
lum9\s e!r1 & t a lum9\s wave is an     
electromagnetic wave--t is to say1 a    
succession ( alt]nat+ curr5ts1 :i* exi/ 
9 ! dielectric & ev5 9 ! void1 & possess

 an enorm\s frequ5cy1 inasmu* z !y *ange
 _! direction ?\s&s ( billions ( times  
p] second1 & by reason ( ?is frequ5cy   
produce consid]able induction effects4  
,maxwell did n admit ! exi/5ce ( op5    
curr5ts4 ,to 8 m9d1 !re=e1 an electrical
 vibration c\ld n produce cond5sations (
 electricity4 ,x 01 9 consequ5ce1       
necess>ily transv]se1 & ?us co9cid$ ) ! 
vibration ( ,fresnel2 :ile ! correspond+
 magnetic vibration 0 p]p5dicul> to x1 &
 w\ld co9cide ) ! lum9\s vibration (    
,neumann4  ,maxwell's !ory ?us e/abli%es
 a close correlation betwe5 ! ph5om5a ( 
! lum9\s & ^? ( ! electromagnetic waves1
 or1 we might ev5 say1 ! complete       
id5tity ( ! two4 ,b x does n foll[ f ?is
 t we ought to reg>d ! v>iation ( an    
electric field produc$ at "s "o po9t z  
necess>ily consi/+ ( a real displacem5t 
( ! e!r r\nd t po9t4 ,! idea ( ?us br++ 
electrical ph5om5a back to ! me*anics ( 
! e!r is n1 !n1 =c$ ^u u1 & ! contr>y   
idea ev5 seems m probable4 ,x is n !    
optics ( ,fresnel :i* absorbs ! sci5ce (

 electricity1 x is r ! optics :i* is    
swall[$ up by a m g5]al !ory4 ,!        
attempts ( popul>iz]s :o endeav\r to    
repres5t1 9 all _! details1 ! me*anism (
 ! electric ph5om5a1 ?us appe> va9      
en\gh1 & ev5 pu]ile4 ,x is useless to   
f9d out to :at mat]ial body ! e!r may be
 comp>$1 if we cont5t ourselves ) see+ 9
 x a m$ium ( :i*1 at e po9t1 two vectors
 def9e ! prop]ties4  ,= a long "t1      
!re=e1 we c\ld rem>k t ! !ory ( ,fresnel
 simply suppos$ a m$ium 9 :i* some?+    
p]iodical 0 propagat$1 )\t its be+      
necess>y to admit ?is some?+ to be a    
movem5t2 b we _h to wait n only =       
,maxwell1 b also = ,h]tz1 be=e ?is idea 
assum$ a really sci5tific %ape4 ,h]tz   
insi/$ on ! fact t ! six equations ( !  
electric field p]mit all ! ph5om5a to be
 anticipat$ )\t its be+ necess>y to     
con/ruct "o hypo!sis or ano!r1 & he put 
^! equations into a v symmetrical =m1   
:i* br+s completely 9 evid5ce ! p]fect  
reciprocity betwe5 electrical & magnetic
 actions4 ,he did yet m1 = he br\ght to 

! ideas ( ,maxwell ! mo/ /rik+          
confirmation by 8 memorable rese>*es on 
electric oscillations4    #d4           
,,electrical ,,oscillations  ,!         
exp]im5ts ( ,h]tz are well kn[n4 ,we "k 
h[ ! ,bonn physici/ develop$1 by means (
 oscillat+ electric dis*>ges1           
displacem5t curr5ts & induction effects 
9 ! :ole ( ! space r\nd ! sp>k-gap2 & h[
 he excit$ by induction at "s po9t 9 a  
wire a p]turbation :i* aft]w>ds is      
propagat$ along ! wire1 & h[ a resonator
 enabl$ him to detect ! effect produc$4 
,! mo/ important po9t made evid5t by !  
obs]vation ( int]f]5ce ph5om5a &        
subsequ5tly v]ifi$ directly by ,m4      
,blondlot1 is t ! electromagnetic       
p]turbation is propagat$ ) ! spe$ (     
light1 & ?is result condemns = ev] all !
 hypo!ses :i* fail to attribute any "p  
to ! int]v5+ m$ia 9 ! propagation ( an  
induction ph5om5on4  ,if ! induc+ action
 71 9 fact1 to op]ate directly betwe5 ! 
induc+ & ! induc$ circuits1 !           
propagation %\ld be in/antane\s2 = if an

 int]val 7 to occur betwe5 ! mom5t :5 ! 
cause act$ & ! "o :5 ! effect 0 produc$1
 dur+ ?is int]val !re w\ld no long] be  
any?+ any:]e1 s9ce ! int]v5+ m$ium does 
n come into play1 & ! ph5om5on w\ld !n  
disappe>4  ,leav+ on "o side ! manifold 
b purely electrical consequ5ces ( ?is & 
! num]\s rese>*es relat+ to ! production
 or to ! prop]ties ( ! waves--"s ( :i*1 
^? ( ,,mm4 ,s>raz9 & de la ,rive1       
,righi1 ,turpa91 ,leb$eff1 ,decombe1    
,b>billon1 ,drude1 ,gutton1 ,lamotte1   
,le*]1 etc41 are1 h[ev]1 ( ! highe/     
ord]--,i %all only m5tion "h ! /udies m 
p>ticul>ly direct$ to ! e/abli%m5t ( !  
id5tity ( ! electromagnetic & ! lum9\s  
waves4  ,! only diff]5ces :i* subsi/ are
 necess>ily ^? due to ! consid]able     
discrepancy :i* exi/s betwe5 ! durations
 ( ! p]iods ( ^! two categories ( waves4
 ,! l5g? ( wave correspond+ to ! fir/   
sp>k-gap ( ,h]tz 0 ab\t #f metres1 & !  
longe/ waves p]ceptible by ! ret9a are  
#g_/aj ( a micron4#bd  ,footnote #bd3   
,see footnote #c4  ,^! radiations are s 

f> ap>t t x is n a/oni%+ t _! prop]ties 
h n a p]fect similitude4 ,?us ph5om5a l 
^? ( diffraction1 :i* are negligible 9 !
 ord9>y conditions "u :i* light is      
obs]v$1 may "h assume a prepond]at+     
importance4 ,to play ! "p1 = example1 ) 
! ,h]tzian waves1 :i* a mirror #a       
millimetre squ>e plays ) reg>d to light1
 w\ld require a colossal mirror :i* w\ld
 atta9 ! size ( a myriametre#be squ>e4  
,footnote #be3 ,i4e41 #aj1jjj           
metres4--,,ed4  ,! ef=ts ( physici/s h  
to-day1 h[ev]1 fill$ up1 9 great "p1 ?is
 int]val1 & f bo? banks at once !y h    
lab\r$ to build a bridge betwe5 ! two   
doma9s4 ,we h se5 h[ ,rub5s %[$ u       
calorific rays #fj metres long2 on ! o!r
 h&1 ,,mm4 ,le*]1 ,bose1 & ,lampa h     
succe$$1 "o aft] ! o!r1 9 gradually     
obta9+ oscillations ) %ort] & %ort]     
p]iods4 ,!re h be5 produc$1 & are n[ be+
 /udi$1 electromagnetic waves ( f\r     
millimetres2 & ! gap subsi/+ 9 !        
spectrum betwe5 ! rays left undetect$ by
 sylv9e & ! radiations ( ,m4 ,lampa n[  

h>dly comprise m ?an five octaves--t is 
to say1 an int]val p]ceptibly equal to t
 :i* sep>ates ! rays obs]v$ by ,m4      
,rub5s f ! la/ :i* are evid5t to ! eye4 
,! analogy !n becomes q close1 & 9 !    
rema9+ rays ! prop]ties1 s to speak1    
*>act]i/ic ( ! ,h]tzian waves1 beg9 to  
appe>4 ,= ^! waves1 z we h se51 ! mo/   
transp>5t bodies are ! mo/ p]fect       
electrical insulators2 :ile bodies /ill 
slightly conduct+ are entirely opaque4  
,! index ( refraction ( ^! sub/ances    
t5ds 9 ! case ( great wave-l5g?s to     
become1 z ! !ory anticipates1 ne>ly !   
squ>e root ( ! dielectric con/ant4      
,,mm4 ,rub5s & ,ni*ols h ev5 produc$ ) !
 waves :i* rema9 ph5om5a ( electric     
resonance q simil> to ^? :i* an ,italian
 s*ol>1 ,m4 ,g>basso1 obta9$ ) electric 
waves4 ,?is physici/ %[$ t1 if !        
electric waves are made to imp+e on a   
flat wood5 /&1 on :i* are a s]ies (     
resonators p>allel to ea* o!r & uni=mly 
arrang$1 ^! waves are h>dly reflect$    
save 9 ! case :]e ! resonators h ! same 

p]iod z ! sp>k-gap4 ,if ! rema9+ rays   
are all[$ to fall on a glass plate      
silv]$ & divid$ by a diamond fix$ on a  
divid+ ma*9e into small rectangles (    
equal dim5sions1 !re w be obs]v$        
v>iations 9 ! reflect+ p[] accord+ to ! 
ori5tation ( ! rectangles1 "u conditions
 entirely comp>able ) ! exp]im5t (      
,g>basso4  ,9 ord] t ! ph5om5on be      
produc$ x is necess>y t ! rema9+ waves  
%\ld be previ\sly pol>iz$4 ,?is is      
because1 9 fact1 ! me*anism employ$ to  
produce ! electric oscillations evid5tly
 gives out vibrations :i* occur on a    
s+le plane & are subsequ5tly pol>iz$4   
,we _c !re=e entirely assimilate a      
radiation proce$+ f a sp>k-gap to a ray 
( natural light4 ,= ! syn!sis ( light to
 be realiz$1 /ill o!r conditions mu/ be 
compli$ )4 ,dur+ a lum9\s impression1 ! 
direction & ! phase *ange millions (    
times 9 ! vibration s5sible to ! ret9a1 
yet ! damp+ ( ?is vibration is v sl[4 ,)
 ! ,h]tzian oscillations all ^!         
conditions are *ang$--! damp+ is v rapid

 b ! direction rema9s inv>iable4  ,e "t1
 h[ev]1 t we deal ) g5]al ph5om5a :i*   
are indep5d5t ( ^! special conditions1 !
 p>allelism is p]fect2 & ) ! waves1 we h
 put 9 evid5ce ! reflexion1 refraction1 
total reflexion1 d\ble reflexion1       
rotatory pol>ization1 disp]sion1 & !    
ord9>y int]f]5ces produc$ by rays       
travell+ 9 ! same direction & cross+ ea*
 o!r at a v acute angle1 or ! int]f]5ces
 analog\s to ^? :i* ,wi5] obs]v$ ) rays 
( ! contr>y direction4  ,a v important  
consequ5ce ( ! electromagnetic !ory     
=ese5 by ,maxwell is t ! lum9\s waves   
:i* fall on a surface mu/ ex]cise on ?is
 surface a pressure equal to ! radiant  
en]gy :i* exi/s 9 ! unit ( volume ( !   
surr\nd+ space4 ,m4 ,leb$eff a few ye>s 
ago all[$ a %eaf ( rays f an arc lamp to
 fall on a deflection radiomet]1#bf &   
?us succe$$ 9 reveal+ ! exi/5ce ( ?is   
pressure4 ,its value is suffici5t1 9 !  
case ( matt] ( little d5sity & f9ely    
divid$1 to r$uce & ev5 *ange into       
repulsion ! attractive action ex]cis$ on

 bodies by ! sun4 ,?is is a fact =m]ly  
conjectur$ by ,faye1 & mu/ c]ta9ly play 
a great "p 9 ! de=mation ( ! heads (    
comets4  ,footnote #bf3 ,by ?is ,m4     
,po9c> appe>s to mean a radiomet] 9 :i* 
! vanes are n entirely free to move z 9 
! radiomet] ( ,crookes b are susp5d$ by 
"o or two ?reads z 9 ! in/rum5t devis$  
by ,pr(essor ,poynt+4--,,ed4  ,m        
rec5tly1 ,,mm4 ,ni*ols & ,hull h        
und]tak5 exp]im5ts on ?is po9t4 ,!y h   
measur$ n only ! pressure1 b also !     
en]gy ( ! radiation by means ( a special
 bolomet]4 ,!y h ?us arriv$ at num]ical 
v]ifications :i* are entirely 9 con=mity
 ) ! calculations ( ,maxwell4  ,!       
exi/5ce ( ^! pressures may be o!rwise   
=ese5 ev5 ap>t f ! electromagnetic !ory1
 by add+ to ! !ory ( undulations !      
pr9ciples ( !rmodynamics4 ,b>toli1 & m  
rec5tly ,dr ,l>mor1 h %[n1 9 fact1 t if 
^! pressures did n exi/1 x w\ld be      
possible1 )\t any o!r ph5om5on1 to pass 
heat f a cold into a w>m body1 & ?us    
transgress ! pr9ciple ( ,c>not4    #e4  

,,! ,x ,,rays  ,x appe>s to-day q       
probable t ! ,x rays %\ld be class$     
among ! ph5om5a :i* h _! seat 9 ! lum9\s
 e!r4 ,d\btless x is n necess>y to      
recall "h h[1 9 ,decemb] #ahie1 ,rntg51 
hav+ wrapp$ 9 black pap] a ,crookes tube
 9 action1 obs]v$ t a fluoresc5t        
plat9ocyanide ( b>ium scre5 plac$ 9 !   
neighb\rhood1 _h become visible 9 ! d>k1
 & t a photographic plate _h receiv$ an 
impress4 ,! rays :i* come f ! tube1 9   
conditions n[ well kn[n1 are n deviat$  
by a magnet1 &1 z ,m4 ,curie & ,m4      
,sagnac h conclusively %[n1 !y c>ry no  
electric *>ge4 ,!y are subject to nei!r 
reflection nor refraction1 & v precise &
 v +5i\s measurem5ts by ,m4 ,g\y h %[n  
t1 9 _! case1 ! refraction index ( !    
v>i\s bodies _c be m ?an a million?     
remov$ f unity4  ,we knew f ! outset t  
!re exi/$ v>i\s ,x rays diff]+ f ea* o!r
 z1 = in/ance1 ! col\rs ( ! spectrum1 & 
^! are di/+ui%$ f ea* o!r by _! unequal 
p[] ( pass+ ?r\gh sub/ances4 ,m4        
,sagnac1 p>ticul>ly1 has %[n t !re c be 

obta9$ a gradually decreas+ scale ( m or
 less absorbable rays1 s t ! great] "p (
 _! photographic action is /opp$ by a   
simple %eet ( black pap]4 ,^! rays      
figure among ! second>y rays discov]$1 z
 is kn[n1 by ?is +5i\s physici/4 ,! ,x  
rays fall+ on matt] are ?us subject$ to 
trans=mations :i* may be comp>$ to ^?   
:i* ! ph5om5a ( lum9esc5ce produce on ! 
ultra-violet rays4  ,m4 ,b5oi/ has f\nd$
 on ! transp>5cy ( matt] to ! rays a    
sure & practical me?od ( all[+ !m to be 
di/+ui%$1 & has ?us be5 enabl$ to def9e 
a specific "* analog\s to ! col\r ( !   
rays ( light4 ,x is probable also t !   
diff]5t rays d n transport individually 
! same quantity ( en]gy4 ,we h n yet    
obta9$ on ?is po9t precise results1 b x 
is r\ghly kn[n1 s9ce ! exp]im5ts ( ,,mm4
 ,ru!r=d & ,m',clung1 :at quantity (    
en]gy corresponds to a p5cil ( ,x rays4 
,^! physici/s h f\nd t ?is quantity w\ld
 be1 on an av]age1 five hundr$ times    
l>g] ?an t br\ght by an analog\s p5cil (
 sol> light to ! surface ( ! e>?4 ,:at  

is ! nature ( ?is en]gy8 ,! "q does n   
appe> to h be5 yet solv$4  ,x c]ta9ly   
appe>s1 accord+ to ,pr(essors ,haga &   
,w9d & to ,pr(essor ,somm]feld1 t ) ! ,x
 rays curi\s exp]im5ts ( diffraction may
 be produc$4 ,dr ,b>kla has %[n also t  
!y c manife/ true pol>ization4 ,!       
second>y rays emitt$ by a metallic      
surface :5 /ruck by ,x rays v>y1 9 fact1
 9 int5sity :5 ! position ( ! plane (   
incid5ce r\nd ! prim>y p5cil is *ang$4  
,v>i\s physici/s h endeav\r$ to measure 
! spe$ ( propagation1 b x seems m & m   
probable t x is v ne>ly t ( light4#bg   
,footnote #bg3 ,see especially !        
exp]im5ts ( ,pr(essor ,e4 ,m>x 7,vi5na71
 ,annal5 d] ,physik1 vol4 xx4 7,no4 #i (
 #aijf71 pp4 #fgg et seq41 :i* seem     
conclusive on ?is po9t4--,,ed4  ,i mu/  
"h leave out ! description ( a cr[d (   
o!r exp]im5ts4 ,"s v int]e/+ rese>*es by
 ,m4 ,brunhes1 ,m4 ,broca1 ,m4          
,col>deau1 ,m4 ,vill>d1 9 ,france1 & by 
_m o!rs abroad1 h p]mitt$ ! elucidation 
( sev]al int]e/+ problems relative to ! 

duration ( ! emission or to ! be/       
disposition to be adopt$ = ! production 
( ! rays4 ,! only po9t :i* w deta9 u is 
! important "q z to ! nature ( ! ,x rays
 !mselves2 ! prop]ties :i* h j be5      
br\ght to m9d are ^? :i* appe> ess5tial 
& :i* e !ory mu/ reckon )4  ,! mo/      
natural hypo!sis w\ld be to consid] !   
rays z ultra-violet radiations ( v %ort 
wave-l5g?1 or radiations :i* are 9 a    
mann] ultra-ultra-violet4 ,?is          
int]pretation c /ill1 at ?is pres5t     
mom5t1 be ma9ta9$1 & ! rese>*es ( ,,mm4 
,buisson1 ,righi1 ,l5>d1 & ,m]rit ,/ew>t
 h ev5 e/abli%$ t rays ( v %ort         
wave-l5g?s produce on metallic          
conductors1 f ! po9t ( view ( electrical
 ph5om5a1 effects q analog\s to ^? ( !  
,x rays4 ,ano!r resemblance results also
 f ! exp]im5ts by :i* ,m4 ,p]reau       
e/abli%$ t ^! rays act on ! electric    
resi/ance ( sel5ium4 ,new & valuable    
argum5ts h ?us add$ =ce to ^? :o incl9e 
t[>ds a !ory :i* has ! m]it ( br++ a new
 ph5om5on )9 ! pale ( ph5om5a previ\sly 

kn[n4  ,nev]!less ! %orte/ ultra-violet 
radiations1 su* z ^? ( ,m4 ,s*umann1 are
 /ill capable ( refraction by qu>tz1 &  
?is diff]5ce con/itutes1 9 ! m9ds ( _m  
physici/s1 a s]i\s en\gh reason to      
decide !m to reject ! m simple hypo!sis4
 ,moreov]1 ! rays ( ,s*umann are1 z we h
 se51 extraord9>ily absorbable1--s mu* s
 t !y h to be obs]v$ 9 a vacuum4 ,! mo/ 
/rik+ prop]ty ( ! ,x rays is1 on !      
contr>y1 ! facility ) :i* !y pass ?r\gh 
ob/acles1 & x is impossible n to atta*  
consid]able importance to su* a         
diff]5ce4  ,"s attribute ?is m>vell\s   
radiation to longitud9al vibrations1    
:i*1 z ,m4 ,duhem has %[n1 w\ld be      
propagat$ 9 dielectric m$ia ) a spe$    
equal to t ( light4 ,b ! mo/ g5]ally    
accept$ idea is ! "o =mulat$ f ! fir/ by
 ,sir ,george ,/okes & foll[$ up by     
,pr(essor ,wie*]t4 ,accord+ to ?is !ory 
! ,x rays %\ld be due to a succession ( 
indep5d5t pulsations ( ! e!r1 />t+ f !  
po9ts :]e ! molecules project$ by !     
ca?ode ( ! ,crookes tube meet !         

antica?ode4 ,^! pulsations are n        
cont9u\s vibrations l ! radiations ( !  
spectrum2 !y are isolat$ & extremely    
%ort2 !y are1 besides1 transv]se1 l !   
undulations ( light1 & ! !ory %[s t !y  
mu/ be propagat$ ) ! spe$ ( light4 ,!y  
%\ld pres5t nei!r refraction nor        
reflection1 b1 "u c]ta9 conditions1 !y  
may be subject to ! ph5om5a (           
diffraction4 ,all ^! *>act]i/ics are    
f\nd 9 ! ,rntg5 rays4  ,pr(essor ,j4,j4 
,?omson adopts an analog\s idea1 & /ates
 ! precise way 9 :i* ! pulsations may be
 produc$ at ! mom5t :5 ! electrifi$     
p>ticles =m+ ! ca?ode rays sudd5ly /rike
 ! antica?ode wall4 ,! electromagnetic  
induction behaves 9 su* a way t !       
magnetic field is n annihilat$ :5 !     
p>ticle /ops1 & ! new field produc$1 :i*
 is no long] 9 equilibrium1 is propagat$
 9 ! dielectric l an electric pulsation4
 ,! electric & magnetic pulsations      
excit$ by ?is me*anism may give bir? to 
effects simil> to ^? ( light4 ,_! slight
 amplitude1 h[ev]1 is ! cause ( !re "h  

be+ nei!r refraction nor diffraction    
ph5om5a1 save 9 v special conditions4   
,if ! ca?ode p>ticle is n /opp$ 9 z]o   
"t1 ! pulsation w take a great]         
amplitude1 & be1 9 consequ5ce1 m easily 
absorbable2 to ?is is probably to be    
attribut$ ! diff]5ces :i* may exi/      
betwe5 diff]5t tubes & diff]5t rays4  ,x
 is "r to add t "s au?ors1 not)/&+ !    
prov$ impossibility ( deviat+ !m 9 a    
magnetic field1 h n r5\nc$ ! idea (     
comp>+ !m ) ! ca?ode rays4 ,!y suppose1 
= in/ance1 t ! rays are =m$ by electrons
 animat$ ) s great a velocity t _!      
in]tia1 con=mably ) !ories :i* ,i %all  
exam9e lat]1 no long] p]mit !m to be    
/opp$ 9 _! c\rse2 ?is is1 = in/ance1 !  
!ory upheld by ,mr ,su!rl&4 ,we "k1 too1
 t to ,m4 ,gu/ave ,le ,bon !y repres5t !
 extreme limit ( mat]ial ?+s1 "o ( ! la/
 /ages be=e ! vani%+ ( matt] on its     
return to ! e!r4  ,ev]yone has he>d ( ! 
,n rays1 ^: "n recalls ! t[n ( ,nancy1  
:]e !y 7 discov]$4 ,9 "s ( _! s+ul>     
prop]ties !y are ak9 to ! ,x rays1 :ile 

9 o!rs !y are widely div]g5t f !m4  ,m4 
,blondlot1 "o ( ! ma/]s ( contempor>y   
physics1 deeply respect$ by all :o "k   
him1 admir$ by ev]yone = ! p5etration ( 
8 m9d1 & ! au?or ( works rem>kable = !  
orig9ality & sur5ess ( 8 me?od1 discov]$
 !m 9 radiations emitt$ f v>i\s s\rces1 
su* z ! sun1 an inc&esc5t light1 a ,n]n/
 lamp1 & ev5 bodies previ\sly expos$ to 
! sun's rays4 ,! ess5tial prop]ty :i*   
all[s !m to be reveal$ is _! action on a
 small induction sp>k1 ( :i* !y increase
 ! brilliancy2 ?is ph5om5on is visible  
to ! eye & is r5d]$ objective by        
photography4  ,v>i\s o!r physici/s &    
numb]s ( physiologi/s1 foll[+ ! pa? op5$
 by ,m4 ,blondlot1 publi%$ dur+ #aijc & 
#aijd manifold b (t5 r ha/y memoirs1 9  
:i* !y relat$ ! results ( _! rese>*es1  
:i* d n appe> to h be5 always conduct$ )
 ! accuracy desirable4 ,^! results 7 mo/
 /range2 !y seem$ de/9$ to revolutionise
 :ole regions n only ( ! doma9 (        
physics1 b likewise ( ! biological      
sci5ces4 ,un=tunately ! me?od (         

obs]vation 0 always f\nd$ on ! v>iations
 9 visibility ( ! sp>k or ( a           
phosphoresc5t sub/ance1 & x soon became 
manife/ t ^! v>iations 7 n p]ceptible to
 all eyes4  ,no =eign exp]im5t] has     
succe$$ 9 repeat+ ! exp]im5ts1 :ile 9   
,france _m physici/s h fail$2 & h5ce !  
"q has mu* agitat$ public op9ion4 ,are  
we face to face ) a v s+ul> case (      
sugge/ion1 or is special tra9+ &        
p>ticul> dispositions requir$ to make ! 
ph5om5on app>5t8 ,x is n possible1 at ! 
pres5t mom5t1 to decl>e ! problem solv$2
 b v rec5t exp]im5ts by ,m4 ,gutton & a 
note by ,m4 ,masc>t h reanimat$ !       
confid5ce ( ^? :o hop$ t su* a s*ol> z  
,m4 ,blondlot c\ld n h be5 delud$ by    
appe>ances4 ,h[ev]1 ^! la/ pro(s 9 fav\r
 ( ! exi/5ce ( ! rays h !mselves be5    
conte/$1 & h n succe$$ 9 br++ conviction
 to ev]yone4  ,x seems v probable inde$ 
t c]ta9 ( ! mo/ s+ul> conclusions arriv$
 at by c]ta9 au?ors on ! subject w lapse
 into des]v$ oblivion4 ,b negative      
exp]im5ts prove no?+ 9 a case l ?is1 & !

 fact t mo/ exp]im5t]s h fail$ :]e ,m4  
,blondlot & 8 pupils h succe$$ may      
con/itute a presumption1 b _c be reg>d$ 
z a demon/rative argum5t4 ,h5ce we mu/  
/ill wait2 x is exce$+ly possible t !   
illu/ri\s physici/ ( ,nancy may succe$ 9
 discov]+ objective actions ( ! ,n rays 
:i* %all be indisputable1 & may ?us     
e/abli% on a firm basis a discov]y wor?y
 ( ^? o!rs :i* h made 8 "n s ju/ly      
celebrat$4  ,accord+ to ,m4 ,blondlot ! 
,n rays c be pol>is$1 refract$1 &       
disp]s$1 :ile !y h wavel5g?s compris$ )9
 4#jjcj micron1 & 4#jgfj micron--t is to
 say1 betwe5 an eigh? & a fif? ( t f\nd 
= ! extreme ultra-violet rays4 ,!y might
 be1 p]haps1 simply rays ( a v %ort     
p]iod4 ,_! exi/5ce1 /ripp$ ( !          
p>asitical & some:at s+ul> prop]ties    
s\ght to be attribut$ to !m1 w\ld ?us   
appe> natural en\gh4 ,x w\ld1 moreov]1  
be extremely important1 & lead1 no d\bt1
 to mo/ curi\s applications2 x c be     
conceiv$1 9 fact1 t su* rays might s]ve 
to reveal :at occurs 9 ^? portions (    

matt] ^: too m9ute dim5sions escape     
microscopic exam9ation on acc\nt ( !    
ph5om5a ( diffraction4  ,f :atev] po9t (
 view we look at x1 & :atev] may be !   
fate ( ! discov]y1 ! hi/ory ( ! ,n rays 
is p>ticul>ly in/ructive1 & mu/ give    
food = reflection to ^? int]e/$ 9       
que/ions ( sci5tific me?ods4    #f4 ,,! 
,,e!r ,,& ,,gravitation  ,! /rik+       
success ( ! hypo!sis ( ! e!r 9 optics   
has1 9 our own days1 /r5g!n$ ! hope (   
be+ able to expla91 by an analog\s      
repres5tation1 ! action ( gravitation4  
,= a long "t1 philosoph]s :o reject$ !  
idea t pond]ability is a prim>y &       
ess5tial quality ( all bodies h s\ght to
 r$uce _! weight to pressures ex]cis$ 9 
a v subtle fluid4 ,?is 0 ! conception ( 
,desc>tes1 & 0 p]haps ! true idea (     
,newton himself4 ,newton po9ts out1 9 _m
 passages1 t ! laws he _h discov]$ 7    
indep5d5t ( ! hypo!ses t c\ld be =m$ on 
! way 9 :i* univ]sal attraction 0       
produc$1 b t ) suffici5t exp]im5ts !    
true cause ( ?is attraction might "o day

 be rea*$4 ,9 ! preface to ! second     
edition ( ! ,optics he writes3 ,to prove
 t ,i h n consid]$ weight z a univ]sal  
prop]ty ( bodies1 ,i h add$ a "q z to   
its cause1 pref]r+ ?is =m ( "q because  
my int]pretation does n entirely satisfy
 me 9 ! abs5ce ( exp]im5t2 & he puts !  
"q 9 ?is %ape3 ,is n ?is m$ium 7! e!r7 m
 r>efi$ 9 ! int]ior ( d5se bodies l !   
sun1 ! planets1 ! comets1 ?an 9 ! empty 
spaces :i* sep>ate !m8 ,pass+ f ^!      
bodies to great di/ances1 does x n      
become cont9ually d5s]1 & 9 t way does x
 n produce ! weight ( ^! great bodies ) 
reg>d to ea* o!r & ( _! p>ts ) reg>d to 
^! bodies1 ea* body t5d+ to leave ! mo/ 
d5se = ! mo/ r>efi$ p>ts8  ,evid5tly ?is
 view is incomplete1 b we may endeav\r  
to /ate x precisely4 ,if we admit t ?is 
m$ium1 ! prop]ties ( :i* w\ld expla9 !  
attraction1 is ! same z ! lum9\s e!r1 we
 may fir/ ask ourselves :e!r ! action ( 
gravitation is itself also due to       
oscillations4 ,"s au?ors h endeav\r$ to 
f\nd a !ory on ?is hypo!sis1 b we are   

imm$iately br\ght face to face ) v s]i\s
 difficulties4 ,gravity appe>s1 9 fact1 
to pres5t q exceptional *>act]i/ics4 ,no
 ag5t1 n ev5 ^? :i* dep5d ^u ! e!r1 su* 
z light & electricity1 has any influ5ce 
on its action or its direction4 ,all    
bodies are1 s to speak1 absolutely      
transp>5t to univ]sal attraction1 & no  
exp]im5t has succe$$ 9 demon/rat+ t its 
propagation is n in/antane\s4 ,f v>i\s  
a/ronomical obs]vations1 ,laplace       
conclud$ t its velocity1 9 any case1 mu/
 exce$ fifty million times t ( light4 ,x
 is subject nei!r to reflection nor to  
refraction2 x is indep5d5t ( ! /ructure 
( bodies2 & n only is x inexhau/ible1 b 
also 7z is po9t$ out1 accord+ to ,m4    
,hannequ91 by an ,engli% s*ol>1 ,james  
,croll7 ! di/ribution ( ! effects ( !   
attract+ =ce ( a mass ov] ! manifold    
p>ticles :i* may successively ent] !    
field ( its action 9 no way dim9i%es !  
attraction x ex]cises on ea* ( !m       
respectively1 a ?+ :i* is se5 n[h]e else
 9 nature4  ,nev]!less x is possible1 by

 means ( c]ta9 hypo!ses1 to con/ruct    
int]pretations :]eby ! appropriate      
movem5ts ( an ela/ic m$ium %\ld expla9 !
 facts cle>ly en\gh4 ,b ^! movem5ts are 
v complex1 & x seems almo/ inconceivable
 t ! same m$ium c\ld possess            
simultane\sly ! /ate ( movem5t          
correspond+ to ! transmission ( a lum9\s
 ph5om5on & t con/antly impos$ on x by !
 transmission ( gravitation4  ,ano!r    
celebrat$ hypo!sis 0 devis$ by ,lesage1 
( ,g5eva4 ,lesage suppos$ space to be   
ov]run 9 all directions by curr5ts (    
ultramundane corpuscles4 ,?is hypo!sis1 
conte/$ by ,maxwell1 is int]e/+4 ,x     
might p]haps be tak5 up aga9 9 our days1
 & x is n impossible t ! assimilation ( 
^! corpuscles to electrons might give a 
satisfactory image4#bh  ,footnote #bh3  
,m4 ,sagnac 7,le ,radium1 ,jan4 #aijf1  
p4 #ad71 foll[+ p]haps ,pr(essors ,el/] 
& ,geitel1 has lately tak5 up ?is idea  
anew4--,,ed4  ,m4 ,crmieux has rec5tly  
und]tak5 exp]im5ts direct$1 z he ?9ks1  
to %[+ t ! div]g5ces betwe5 ! ph5om5a ( 

gravitation & all ! o!r ph5om5a 9 nature
 are m app>5t ?an real4 ,?us ! evolution
 9 ! he>t ( ! e!r ( a quantity (        
gravific en]gy w\ld n be entirely       
isolat$1 & z 9 ! case ( all evolutions (
 all en]gy ( :atev] k9d1 x %\ld provoke 
a p>tial trans=mation into en]gy ( a    
diff]5t =m4 ,?us aga9 ! lib]at$ en]gy ( 
gravitation w\ld v>y :5 pass+ f "o      
mat]ial to ano!r1 z f gases into        
liquids1 or f "o liquid to a diff]5t "o4
  ,on ?is la/ po9t ! rese>*es ( ,m4     
,crmieux h giv5 affirmative results3 if 
we imm]se 9 a l>ge mass ( "s liquid     
sev]al drops ( ano!r n miscible ) !     
fir/1 b ( id5tical d5sity1 we =m a mass 
repres5t+ no d\bt a discont9uity 9 !    
e!r1 & we may ask ourselves :e!r1 9     
con=mity ) :at happ5s 9 all o!r ph5om5a 
( nature1 ?is discont9uity has n a      
t5d5cy to disappe>4  ,if we abide by !  
ord9>y consequ5ces ( ! ,newtonian !ory (
 pot5tial1 ! drops %\ld rema9           
motionless1 ! hydro/atic impulsion =m+  
an exact equilibrium to _! mutual       

attraction4 ,n[ ,m4 ,crmieux rem>ks t1 z
 a matt] ( fact1 !y sl[ly approa* ea*   
o!r4  ,su* exp]im5ts are v delicate2 & )
 all ! precautions tak5 by ! au?or1 x _c
 yet be ass]t$ t he has remov$ all      
possibility ( ! action ( ! ph5om5a (    
capill>ity nor all possible errors      
proce$+ f extremely slight diff]5ces (  
temp]ature4 ,b ! attempt is int]e/+ &   
des]ves to be foll[$ up4  ,?us1 !       
hypo!sis ( ! e!r does n yet expla9 all !
 ph5om5a :i* ! consid]ations relat+ to  
matt] are ( !mselves p[]less to         
int]pret4 ,if we wi%$ to repres5t to    
ourselves1 by ! me*anical prop]ties ( a 
m$ium fill+ ! :ole ( ! univ]se1 all     
lum9\s1 electric1 & gravitation ph5om5a1
 we %\ld be l$ to attribute to ?is m$ium
 v /range & almo/ contradictory         
*>act]i/ics2 & yet x w\ld be /ill m     
inconceivable t ?is m$ium %\ld be d\ble 
or treble1 t !re %\ld be two or ?ree    
e!rs ea* occupy+ space z if x 7 alone1 &
 int]p5etrat+ x )\t ex]cis+ any action  
on "o ano!r4 ,we are ?us br\ght1 by a   

close exam9ation ( facts1 r to ! idea t 
! prop]ties ( ! e!r are n :olly r$ucible
 to ! rules ( ord9>y me*anics4  ,!      
physici/ has !re=e n yet succe$$ 9      
answ]+ ! "q (t5 put to him by !         
philosoph]3 ,has ! e!r really an        
objective exi/5ce8 ,h[ev]1 x is n       
necess>y to "k ! answ] 9 ord] to utilize
 ! e!r4 ,9 its ideal prop]ties we f9d ! 
means ( det]m9+ ! =m ( equations :i* are
 valid1 & to ! le>n$ deta*$ f all       
metaphysical prepossession ?is is !     
ess5tial po9t4     ,,*apt] ,,vii  ,a    
,,*apt] ,,9 ,,! ,,hi/ory ,,( ,,sci5ce3  
,,wireless ,,telegraphy    #a  ,i h     
endeav\r$ 9 ?is book to set =?          
imp>tially ! ideas dom9ant at ?is mom5t 
9 ! doma9 ( physics1 & to make kn[n !   
facts ess5tial to !m4 ,i h _h to quote !
 au?ors ( ! pr9cipal discov]ies 9 ord]  
to be able to class &1 9 "s sort1 to "n 
^! discov]ies2 b ,i 9 no way claim to   
write ev5 a summ>y hi/ory ( ! physics ( 
! day4  ,i am n unaw>e t1 z has (t5 be5 
said1 contempor>y hi/ory is ! mo/       

difficult ( all hi/ories to write4 ,a   
c]ta9 /ep backw>ds seems necess>y 9 ord]
 to enable u to appreciate correctly !  
relative importance ( ev5ts1 & details  
conceal ! full view f eyes :i* are too  
close to !m1 z ! trees prev5t u f see+ !
 =e/4 ,! ev5t :i* produces a great      
s5sation has (t5 only insignificant     
consequ5ces2 :ile ano!r1 :i* seem$ at ! 
outset ( ! lea/ importance & little     
wor?y ( note1 has 9 ! long run a        
widespread & deep influ5ce4  ,if1 h[ev]1
 we deal ) ! hi/ory ( a positive        
discov]y1 contempor>ies :o possess      
imm$iate in=mation1 & are 9 a position  
to collect au!ntic evid5ce at fir/ h&1 w
 make1 by br++ to x _! s9c]e te/imony1 a
 "w ( erudition :i* may be v useful1 b  
:i* we may be tempt$ to look ^u z v easy
 ( execution4 ,yet su* a lab\r1 ev5 :5  
limit$ to ! /udy ( a v m9ute "q or ( a  
rec5t inv5tion1 is f> f be+ accompli%$  
)\t ! hi/orian /umbl+ ov] s]i\s         
ob/acles4  ,an inv5tion is nev]1 9      
reality1 to be attribut$ to a s+le      

au?or4 ,x is ! result ( ! "w ( _m       
collaborators :o sometimes h no         
acqua9tance ) "o ano!r1 & is (t5 ! fruit
 ( obscure lab\rs4 ,public op9ion1      
h[ev]1 wilfully simple 9 face ( a       
s5sational discov]y1 insi/s t ! hi/orian
 %\ld also act z judge2 & x is !        
hi/orian's task to dis5tangle ! tru? 9 !
 mid/ ( ! conte/1 & to decl>e infallibly
 to :om ! ackn[l$gm5ts ( mank9d %\ld be 
paid4 ,he mu/1 9 8 capacity z skill$    
exp]t1 expose piracies1 detect ! mo/    
c>efully hidd5 plagi>isms1 & discuss !  
delicate "q ( priority2 :ile he mu/ n be
 delud$ by ^? :o d n fe> to ann\nce1 9  
bold acc5ts1 t !y h solv$ problems ( :i*
 !y f9d ! solution imm95t1 & :o1 ! day  
aft] its f9al elucidation by ?ird       
p>ties1 proclaim !mselves its true      
discov]]s4 ,he mu/ rise above a         
p>tiality :i* deems itself excusable    
because x proce$s f national pride2 &1  
f9ally1 he mu/ seek ) pati5ce = :at has 
gone be=e4 ,:ile ?us retreat+ /ep by /ep
 he runs ! risk ( los+ himself 9 ! night

 ( "t4  ,an example ( ye/]day seems to  
%[ ! difficulties ( su* a task4 ,among  
rec5t discov]ies ! inv5tion ( wireless  
telegraphy is "o ( ^? :i* h rapidly     
become popul>1 & looks1 z x 71 an exact 
subject cle>ly m>k$ out4 ,_m attempts h 
already be5 made to write its hi/ory4   
,mr ,j4,j4 ,fahie publi%$ 9 ,engl& z    
e>ly z #ahii an int]e/+ "w entitl$ !    
,hi/ory ( ,wireless ,telegraphy2 & ab\t 
! same "t ,m4 ,broca publi%$ 9 ,france a
 v exhau/ive "w nam$ ,la ,telegraphie   
sans fil4 ,among ! reports pres5t$ to ! 
,congrs int]national de physique 7,p>is1
 #aijj71 ,signor ,righi1 an illu/ri\s   
,italian s*ol>1 ^: p]sonal ef=ts h      
l>gely contribut$ to ! inv5tion ( !     
pres5t sy/em ( telegraphy1 devot$ a     
*apt]1 %ort1 b suffici5tly complete1 ( 8
 ma/]ly report on ,h]tzian waves1 to !  
hi/ory ( wireless telegraphy4 ,! same   
au?or1 9 association ) ,h]r ,b]nh>d     
,dessau1 has likewise writt5 a m        
important "w1 ,die ,telegraphie ohne    
,draht2 & ,la ,telegraphie sans fil et  

les ondes lectriques ( ,,mm4 ,j4        
,b\lang] & ,g4 ,f]ri may also be        
consult$ ) advantage1 z may ,la         
,telegraphie sans fil ( ,signor ,dom9ico
 ,mazotto4 ,q rec5tly ,mr ,a4 ,/ory has 
giv5 u 9 a little volume call$ ,! ,/ory 
( ,wireless ,telegraphy1 a cond5s$ b v  
precise recapitulation ( all ! attempts 
:i* h be5 made to e/abli% telegraphic   
communication )\t ! int]m$i>y ( a       
conduct+ wire4 ,mr ,/ory has exam9$ _m  
docum5ts1 has sometimes br\ght curi\s   
facts to light1 & has /udi$ ev5 ! mo/   
rec5tly adopt$ app>atus4  ,x may be     
int]e/+1 by utilis+ ! in=mation suppli$ 
by ^! au?ors & supplem5t+ !m :5 necess>y
 by o!rs1 to trace ! s\rces ( ?is mod]n 
discov]y1 to foll[ its developm5ts1 &   
?us to prove once m h[ mu* a matt]1 mo/ 
simple 9 appe>ance1 dem&s ext5sive &    
complex rese>*es on ! "p ( an au?or     
desir\s ( writ+ a def9itive "w4    #b   
,! fir/1 & n ! lea/ difficulty1 is to   
cle>ly def9e ! subject4 ,! words        
wireless telegraphy1 :i* at fir/ seem to

 correspond to a simple & p]fectly cle> 
idea1 may 9 reality apply to two s]ies (
 que/ions1 v diff]5t 9 ! m9d ( a        
physici/1 betwe5 :i* x is important to  
di/+ui%4 ,! transmission ( signals dem&s
 ?ree organs :i* all appe> indisp5sable3
 ! transmitt]1 ! receiv]1 &1 betwe5 !   
two1 an int]m$i>y e/abli%+ !            
communication4 ,?is int]m$i>y is g5]ally
 ! mo/ co/ly "p ( ! in/allation & ! mo/ 
difficult to set up1 :ile x is "h t !   
s5sible losses ( en]gy at ! exp5se (    
good output occur4 ,& yet our pres5t    
ideas cause u to consid] ?is int]m$i>y z
 m ?an ev] impossible to suppress2 s9ce1
 if we are def9itely quit ( ! conception
 ( action at a di/ance1 x becomes       
inconceivable to u t en]gy c be         
communicat$ f "o po9t to ano!r )\t be+  
c>ri$ by "s int]v5+ m$ium4 ,b1          
practically1 ! l9e w be suppress$ if1   
in/ead ( con/ruct+ x artificially1 we   
use to replace x "o ( ! natural m$ia :i*
 sep>ate two po9ts on ! e>?4 ,^! natural
 m$ia are divid$ into two v di/9ct      

categories1 & f ?is classification arise
 two s]ies ( que/ions to be exam9$4     
,betwe5 ! two po9ts 9 "q !re are1 fir/1 
! mat]ial m$ia su* z ! air1 ! e>?1 & !  
wat]4 ,= a long "t we h us$ =           
transmissions to a di/ance ! ela/ic     
prop]ties ( ! air1 & m rec5tly !        
electric conductivity ( ! soil & ( wat]1
 p>ticul>ly t ( ! sea4  ,mod]n physics  
leads u on ! o!r h&1 z we h se51 to     
consid] t !re exi/s ?r\gh\t ! :ole ( !  
univ]se ano!r & m subtle m$ium :i*      
p5etrates ev]y:]e1 is end[$ ) ela/icity 
9 vacuo1 & reta9s its ela/icity :5 x    
p5etrates into a great numb] ( bodies1  
su* z ! air4 ,?is m$ium is ! lum9\s e!r 
:i* possesses1 z we _c d\bt1 ! prop]ty (
 be+ able to transmit en]gy1 s9ce x     
itself br+s to u by f> ! l>g] "p ( !    
en]gy :i* we possess on e>? & :i* we f9d
 9 ! movem5ts ( ! atmosph]e1 or (       
wat]falls1 & 9 ! coal m9es proce$+ f !  
decomposition ( c>bon comp\nds "u !     
influ5ce ( ! sol> en]gy4 ,= a long "t   
also be=e ! exi/5ce ( ! e!r 0 kn[n1 !   

duty ( transmitt+ signals 0 entru/$ to  
x4 ,?us ?r\gh ! ages a d\ble evolution  
is unfold$ :i* has to be foll[$ by !    
hi/orian :o is ambiti\s ( complet5ess4  
#c  ,if su* an hi/orian 7 to exam9e f ! 
beg9n+ ! fir/ ord] ( que/ions1 he might1
 no d\bt1 speak only briefly ( !        
attempts e>li] ?an electric telegraphy4 
,)\t seek+ to be p>adoxical1 he c]ta9ly 
ought to m5tion ! inv5tion ( !          
speak+-trumpet & o!r simil> inv5tions   
:i* = a long "t h enabl$ mank9d1 by !   
+5i\s use ( ! ela/ic prop]ties ( !      
natural m$ia1 to communicate at great]  
di/ances ?an !y c\ld h atta9$ )\t ! aid 
( art4 ,aft] ?is 9 "s sort prehi/oric   
p]iod _h be5 rapidly run ?r\gh1 he w\ld 
h to foll[ v closely ! developm5t (     
electric telegraphy4 ,almo/ f ! outset1 
& %ortly aft] ,ampre _h made public !   
idea ( con/ruct+ a telegraph1 & ! day   
aft] ,gauss & ,web] set up betwe5 _!    
h\ses 9 ,gtt+5 ! fir/ l9e really us$1 x 
0 ?\ght t ! conduct+ prop]ties ( ! e>? &
 wat] might be made ( s]vice4  ,! hi/ory

 ( ^! trials is v long1 & is closely    
mix$ up ) ! hi/ory ( ord9>y telegraphy2 
long *apt]s = "s "t pa/ h be5 devot$ to 
x 9 telegraphic treatises4 ,x 0 9 #ahch1
 h[ev]1 t ,pr(essor ,c4,a4 ,/e9heil (   
,muni* express$1 = ! fir/ "t1 ! cle>    
idea ( suppress+ ! return wire & replac+
 x by a connection ( ! l9e wire to !    
e>?4 ,he ?us at "o /ep cov]$ half ! way1
 ! easie/1 x is true1 :i* 0 to lead to !
 f9al goal1 s9ce he sav$ ! use ( "o-half
 ( ! l9e ( wire4 ,/e9heil1 advis$1      
p]haps1 by ,gauss1 _h1 moreov]1 a v     
exact conception ( ! "p tak5 by ! e>?   
consid]$ z a conduct+ body4 ,he seems to
 h well und]/ood t1 9 c]ta9 conditions1 
! resi/ance ( su* a conductor1 ?\gh     
suppos$ to be unlimit$1 might be        
indep5d5t ( ! di/ance ap>t ( !          
electrodes :i* c>ry ! curr5t & all[ x to
 g =?4 ,he likewise ?\ght ( us+ !       
railway l9es to transmit telegraphic    
signals4  ,sev]al s*ol>s :o f ! fir/ _h 
turn$ _! m9ds to telegraphy1 _h analog\s
 ideas4 ,x 0 ?us t ,s4,f4,b4 ,morse1    

sup]9t5d5t ( ! ,gov]nm5t telegraphs 9 ! 
,unit$ ,/ates1 ^: "n is univ]sally kn[n 
9 connection ) ! v simple app>atus      
inv5t$ by him1 made exp]im5ts 9 ! autumn
 ( #ahdb be=e a special commission 9    
,new ,york & a num]\s public audi5ce1 to
 %[ h[ surely & h[ easily 8 app>atus    
work$4 ,9 ! v mid/ ( 8 exp]im5ts a v    
happy idea occurr$ to him ( replac+ by !
 wat] ( a canal1 ! l5g? ( ab\t a mile ( 
wire :i* _h be5 sudd5ly & accid5tally   
de/roy$4 ,?is accid5t1 :i* = a mom5t    
compromis$ ! legitimate success !       
celebrat$ eng9e] expect$1 ?us sugge/$ to
 him a fruitful idea :i* he did n =get4 
,he subsequ5tly repeat$ attempts to ?us 
utilise ! e>? & wat]1 & obta9$ "s v     
rem>kable results4  ,x is n possible to 
quote "h all ! rese>*es und]tak5 ) !    
same purpose1 to :i* are m p>ticul>ly   
atta*$ ! names ( ,s4,w4 ,wilk9s1        
,:eat/one1 & ,h4 ,highton1 9 ,engl&2 (  
,bonetti 9 ,italy1 ,g9tl 9 ,au/ria1     
,b\*ot & ,donat 9 ,france2 b !re are "s 
:i* _c be recall$ )\t emotion4  ,on !   

#ag? ,decemb] #ahgj1 a physici/ :o has  
left 9 ! ,univ]sity ( ,p>is a la/+ "n1  
,m4 d',almeida1 at t "t ,pr(essor at !  
,lyce ,h5ri ,,iv4 & lat]                
,inspector-,g5]al ( ,public ,in/ruction1
 quitt$ ,p>is1 !n besieg$1 9 a balloon1 
& desc5d$ 9 ! mid/ ( ! ,g]man l9es4 ,he 
succe$$1 aft] a p]il\s j\rney1 9 ga9+   
,havre by way ( ,bordeaux & ,lyons2 &   
aft] procur+ ! necess>y app>atus 9      
,engl&1 he desc5d$ ! ,se9e z f> z       
,poissy1 :i* he rea*$ on ! #ad? ,janu>y 
#ahga4 ,aft] 8 dep>ture1 two o!r s*ol>s1
 ,,mm4 ,desa9s & ,b\rb\ze1 reliev+ ea*  
o!r day & night1 wait$ at ,p>is1 9 a    
:]ry on ! ,se9e1 ready to receive !     
signal :i* !y await$ ) patriotic        
anxiety4 ,x 0 a "q ( work+ a process    
devis$ by ! la/-nam$ pair1 9 :i* ! wat] 
( ! riv] act$ ! "p ( ! l9e wire4 ,on !  
#bcrd ,janu>y ! communication at la/    
seem$ to be e/abli%$1 b un=tunately1    
fir/ ! armi/ice & !n ! surr5d] ( ,p>is  
r5d]$ useless ! valuable result ( ?is   
noble ef=t4  ,special m5tion is also due

 to ! exp]im5ts made by ! ,indian       
,telegraph ,(fice1 "u ! direction ( ,mr 
,johnson & aft]w>ds ( ,mr ,w4,f4        
,melhui%4 ,!y l$1 inde$1 9 #ahhi to su* 
satisfactory results t a telegraph      
s]vice1 9 :i* ! l9e wire 0 replac$ by ! 
e>?1 work$ practically & regul>ly4 ,o!r 
attempts 7 also made dur+ ! latt] half (
 ! n9ete5? c5tury to transmit signals   
?r\gh ! sea4 ,!y prec$$ ! epo* :51 ?anks
 to num]\s physici/s1 among :om ,"l     
,kelv9 und\bt$ly occupies a prepond]at+ 
position1 we succe$$ 9 s9k+ ! fir/      
cable2 b !y 7 n ab&on$1 ev5 aft] t date1
 = !y gave hopes ( a mu* m economical   
solution ( ! problem4 ,among ! mo/      
int]e/+ are rememb]$ ^? t ,s4,w4 ,wilk9s
 c>ri$ on = a long "t betwe5 ,france &  
,engl&4 ,l ,cooke & ,:eat/one1 he ?\ght 
( us+ z a receiv] an app>atus :i* 9 "s  
features resembles ! pres5t receiv] ( ! 
subm>9e telegraph4 ,lat]1 ,george ,e4   
,d]+1 !n ,james ,b[man & ,l9dsay1 made  
on ! same l9es trials :i* are wor?y (   
be+ rememb]$4  ,b x is only 9 our own   

days t ,sir ,william ,h4 ,preece at la/ 
obta9$ = ! fir/ "t really practical     
results4 ,sir ,william himself effect$ &
 caus$ to be execut$ by 8 associates--he
 is *ief consult+ eng9e] to ! ,g5]al    
,po/ ,(fice 9 ,engl&-- rese>*es conduct$
 ) mu* me?od & bas$ on precise !oretical
 consid]ations4 ,he ?us succe$$ 9       
e/abli%+ v easy1 cle>1 & regul>         
communications betwe5 v>i\s places2 =   
example1 across ! ,bri/ol ,*annel4 ,!   
long s]ies ( op]ations accompli%$ by s  
_m seek]s1 ) ! object ( sub/itut+ a     
mat]ial & natural m$ium = ! artificial  
l9es ( metal1 ?us met ) an und\bt$      
success :i* 0 soon to be eclips$ by !   
widely-kn[n exp]im5ts direct$ into a    
diff]5t l9e by ,m>coni4  ,x is "r to add
 t ,sir ,william ,preece _h himself     
utilis$ induction ph5om5a 9 8 exp]im5ts1
 & _h begun rese>*es ) ! aid ( electric 
waves4 ,mu* is due to him = ! welcome he
 gave to ,m>coni2 x is c]ta9ly ?anks to 
! advice & ! mat]ial support he f\nd 9  
,sir ,william t ! "y s*ol> succe$$ 9    

effect+ 8 s5sational exp]im5ts4    #d   
,! />t+-po9t ( ! exp]im5ts bas$ on !    
prop]ties ( ! lum9\s e!r1 & hav+ = _!   
object ! transmission ( signals1 is v   
remote2 & x w\ld be a v labori\s task to
 hunt up all ! "w accompli%$ 9 t        
direction1 ev5 if we 7 to conf9e        
ourselves to ^? 9 :i* electrical        
reactions play a "p4 ,an electric       
reaction1 an electro/atic influ5ce1 or  
an electromagnetic ph5om5on1 is         
transmitt$ at a di/ance ?r\gh ! air by !
 int]m$i>y ( ! lum9\s e!r4 ,b electric  
influ5ce c h>dly be us$1 z ! di/ances x 
w\ld all[ u to trav]se w\ld be mu* too  
re/rict$1 & electro/atic actions are (t5
 v erratic4 ,! ph5om5a ( induction1 :i* 
are v regul> & ins5sible to ! v>iations 
( ! atmosph]e1 h1 on ! o!r h&1 = a long 
"t appe>$ s]viceable = telegraphic      
purposes4  ,we might f9d1 9 a c]ta9     
numb] ( ! attempts j m5tion$1 a p>tial  
employm5t ( ^! ph5om5a4 ,l9dsay1 =      
in/ance1 9 8 project ( communication    
across ! sea1 attribut$ to !m a         

consid]able rle4 ,^! ph5om5a ev5 p]mitt$
 a true telegraphy )\t int]m$i>y wire   
betwe5 ! transmitt] & ! receiv]1 at v   
re/rict$ di/ances1 x is true1 b 9       
peculi>ly int]e/+ conditions4 ,x is1 9  
fact1 ow+ to !m t ,c4 ,br[n1 & lat]     
,edison & ,gillil&1 succe$$ 9 e/abli%+  
communications ) tra9s 9 motion4  ,mr   
,will\ghby ,s4 ,smi? & ,mr ,*>les ,a4   
,/ev5son also und]took exp]im5ts dur+ ! 
la/ tw5ty ye>s1 9 :i* !y us$ induction1 
b ! mo/ rem>kable attempts are p]haps ^?
 ( ,pr(essor ,emile ,ra!nau4 ,) !       
assi/ance ( ,pr(essor ,rub5s & ( ,h]r   
,w4 ,ra!nau1 ?is physici/ effect$1 at ! 
reque/ ( ! ,g]man ,m9i/ry ( ,m>9e1 a    
s]ies ( rese>*es :i* enabl$ him1 by     
means ( a comp\nd sy/em ( conduction &  
induction by alt]nat+ curr5ts1 to obta9 
cle> & regul> communications at a       
di/ance ( f\r kilometres4 ,among !      
precursors also %\ld be m5tion$ ,graham 
,bell2 ! inv5tor ( ! telephone ?\ght (  
employ+ 8 admirable app>atus z a receiv]
 ( induction ph5om5a transmitt$ f a     

di/ance2 ,edison1 ,h]r ,sa*] ( ,vi5na1  
,m4 ,h5ry ,duf\r ( ,lausanne1 &         
,pr(essor ,tr[bridge ( ,bo/on1 also made
 int]e/+ attempts 9 ! same direction4   
,9 all ^! exp]im5ts occurs ! idea (     
employ+ an oscillat+ curr5t4 ,moreov]1 x
 0 kn[n = a long "t--s9ce1 9 #ahdb1 !   
great ,am]ican physici/ ,h5ry prov$ t ! 
dis*>ges f a ,leyd5 j> 9 ! attic ( 8    
h\se caus$ sp>ks 9 a metallic circuit on
 ! gr\nd floor--t a flux :i* v>ies      
rapidly & p]iodically is mu* m          
efficaci\s ?an a simple flux1 :i* latt] 
c only produce at a di/ance a ph5om5on (
 slight int5sity4 ,?is idea ( !         
oscillat+ curr5t 0 closely ak9 to t :i* 
0 at la/ to lead to an entirely         
satisfactory solution3 t is1 to a       
solution :i* is f\nd$ on ! prop]ties (  
electric waves4    #e  ,hav+ ?us got to 
! ?re%old ( ! def9itive edifice1 !      
hi/orian1 :o has conduct$ 8 read]s ov] !
 two p>allel r\tes :i* h j be5 m>k$ out1
 w be br\ght to ask himself :e!r he has 
be5 a suffici5tly fai?ful guide & has n 

omitt$ to draw att5tion to all ess5tial 
po9ts 9 ! regions pass$ ?r\gh4  ,ought  
we n to place by ! side1 or p]haps 9    
front1 ( ! au?ors :o h devis$ !         
practical appliances1 ^? s*ol>s :o h    
con/ruct$ ! !ories & realis$ !          
laboratory exp]im5ts ( :i*1 aft] all1 ! 
app>atus are only ! imm$iate            
applications8 ,if we speak ( !          
propagation ( a curr5t 9 a mat]ial      
m$ium1 c "o =get ! names ( ,f\ri] & (   
,ohm1 :o e/abli%$ by !oretical          
consid]ations ! laws :i* preside ov] ?is
 propagation8 ,:5 "o looks at ! ph5om5a 
( induction1 w\ld x n be j to rememb] t 
,arago =esaw !m1 & t ,mi*ael ,f>aday    
discov]$ !m8 ,x w\ld be a delicate1 &   
also a r pu]ile task1 to class m5 (     
g5ius 9 ord] ( m]it4 ,! m]it ( an       
inv5tor l ,edison & t ( a !ori/ l ,cl]k 
,maxwell h no common measure1 & mank9d  
is indebt$ = its great progress to ! "o 
z mu* z to ! o!r4  ,be=e relat+ h[      
success att5d$ ! ef=ts to utilise       
electric waves = ! transmission (       

signals1 we _c )\t +ratitude pass ov] 9 
sil5ce ! !oretical speculations & ! "w (
 pure sci5ce :i* l$ to ! k ( ^! waves4  
,x w\ld !re=e be j1 )\t go+ fur!r back  
?an ,f>aday1 to say h[ t illu/ri\s      
physici/ drew att5tion to ! "p tak5 by  
insulat+ m$ia 9 electrical ph5om5a1 & to
 insi/ also on ! admirable memoirs 9 :i*
 = ! fir/ "t ,cl]k ,maxwell made a solid
 bridge betwe5 ^? two great *apt]s (    
,physics1 optics & electricity1 :i* till
 !n _h be5 indep5d5t ( ea* o!r4 ,& no   
d\bt x w\ld be impossible n to evoke !  
memory ( ^? :o1 by e/abli%+1 on ! o!r   
h&1 ! solid & magnific5t /ructure (     
physical optics1 & prov+ by _! immortal 
works ! undulatory nature ( light1      
prep>$ f ! opposite direction ! future  
unity4 ,9 ! hi/ory ( ! applications (   
electrical undulations1 ! names ( ,"y1  
,fresnel1 ,fizeau1 & ,f\cault mu/ be    
inscrib$2 )\t ^! s*ol>s1 ! assimilation 
betwe5 electrical & lum9\s ph5om5a :i*  
!y discov]$ & /udi$ w\ld evid5tly h be5 
impossible4  ,s9ce !re is an absolute   

id5tity ( nature betwe5 ! electric & !  
lum9\s waves1 we %\ld1 9 all ju/ice1    
also consid] z precursors ^? :o devis$ !
 fir/ lum9\s telegraphs4 ,claude ,*appe 
inconte/ably effect$ wireless           
telegraphy1 ?anks to ! lum9\s e!r1 & !  
le>n$ m51 su* z ,colonel ,mang91 :o     
p]fect$ optical telegraphy1 indirectly  
sugge/$ c]ta9 improvem5ts lately        
introduc$ into ! pres5t me?od4  ,b !    
physici/ ^: "w %\ld mo/ ( all be put 9  
evid5ce is1 )\t fe> ( contradiction1    
,he9ri* ,h]tz4 ,x 0 he :o demon/rat$    
irrefutably1 by exp]im5ts n[ classic1 t 
an electric dis*>ge produces an         
undulatory di/urbance 9 ! e!r conta9$ 9 
! insulat+ m$ia 9 its neighb\rhood2 x 0 
he :o1 z a pr(\nd !ori/1 a clev]        
ma!matician1 & an exp]im5t] ( prodigi\s 
dext]ity1 made kn[n ! me*anism ( !      
production1 & fully elucidat$ t ( !     
propagation ( ^! electromagnetic waves4 
,he mu/ naturally himself h ?\ght t 8   
discov]ies might be appli$ to !         
transmission ( signals4 ,x w\ld appe>1  

h[ev]1 t :5 int]rogat$ by a ,muni*      
eng9e] nam$ ,hub] z to ! possibility (  
utilis+ ! waves = transmissions by      
telephone1 he answ]$ 9 ! negative1 &    
dwelt on c]ta9 consid]ations relative to
 ! diff]5ce betwe5 ! p]iods ( s\nds & ^?
 ( electrical vibrations4 ,?is answ]    
does n all[ u to judge :at might h      
happ5$1 _h n a cruel dea? c>ri$ (f 9    
#ahid1 at ! age ( ?irty-five1 ! great & 
un=tunate physici/4  ,we might also f9d 
9 c]ta9 works e>li] ?an ! exp]im5ts (   
,h]tz attempts at transmission 9 :i*1   
unconsci\sly no d\bt1 ph5om5a 7 already 
set 9 op]ation :i* w\ld1 at ?is day1 be 
class$ z electric oscillations4 ,x is   
all[able no d\bt1 n to speak ( an       
,am]ican quack1 ,mahlon ,loomis1 :o1    
accord+ to ,mr ,/ory1 pat5t$ 9 #ahgj a  
project ( communication 9 :i* he utilis$
 ! ,rocky ,m\nta9s on "o side & ,mont   
,blanc on ! o!r1 z gigantic ant5nae to  
e/abli% communication across !          
,atlantic2 b we _c pass ov] 9 sil5ce ! v
 rem>kable rese>*es ( ! ,am]ican        

,pr(essor ,dolbe>1 :o %[$1 at !         
electrical exhibition ( ,philadelphia 9 
#ahhd1 a set ( app>atus enabl+ signals  
to be transmitt$ at a di/ance1 :i* he   
describ$ z an exceptional application ( 
! pr9ciples ( electro/atic induction4   
,?is app>atus compris$ gr\ps ( coils &  
cond5s]s by means ( :i* he obta9$1 z we 
_c n[ d\bt1 effects due to true electric
 waves4  ,place %\ld also be made = a   
well-kn[n inv5tor1 ,d4,e4 ,hughes1 :o f 
#ahgi to #ahhf foll[$ up "s v curi\s    
exp]im5ts 9 :i* also ^! oscillations    
c]ta9ly play$ a consid]able "p4 ,x 0 ?is
 physici/ :o inv5t$ ! microphone1 & ?us1
 9 ano!r way1 drew att5tion to !        
v>iations ( contact resi/ance1 a        
ph5om5on n f> f t produc$ 9 !           
radio-conductors ( ,branly1 :i* are     
important organs 9 ! ,m>coni sy/em4     
,un=tunately1 fatigu$ & 9 ill-heal?1    
,hughes ceas$ 8 rese>*es at ! mom5t     
p]haps :5 !y w\ld h giv5 him f9al       
results4  ,9 an ord] ( ideas diff]5t 9  
appe>ance1 b closely l9k$ at bottom ) ! 

"o j m5tion$1 mu/ be recall$ ! discov]y 
( radiophony 9 #ahhj by ,graham ,bell1  
:i* 0 =e%ad[$ 9 #ahge by ,c4,a4 ,br[n4  
,a lum9\s ray fall+ on a sel5ium cell   
produces a v>iation ( electric          
resi/ance1 ?anks to :i* a s\nd signal c 
be transmitt$ by light4 ,t delicate     
in/rum5t ! radiophone1 con/ruct$ on ?is 
pr9ciple1 has wide analogies ) !        
app>atus ( to-day4    #f  ,/>t+ f !     
exp]im5ts ( ,h]tz1 ! hi/ory ( wireless  
telegraphy almo/ m]ges into t ( !       
rese>*es on electrical waves4 ,all !    
progress realis$ 9 ! mann] ( produc+ &  
receiv+ ^! waves necess>ily help$ to    
give rise to ! application already      
indicat$4 ,! exp]im5ts ( ,h]tz1 aft] be+
 *eck$ 9 e laboratory1 & hav+ ent]$ into
 ! /rong doma9 ( our mo/ c]ta9 k1 7 ab\t
 to yield ! expect$ fruit4  ,exp]im5t]s 
l ,sir ,oliv] ,lodge 9 ,engl&1 ,righi 9 
,italy1 ,s>raz9 & de la ,rive 9         
,switz]l&1 ,blondlot 9 ,france1 ,le*] 9 
,g]many1 ,bose 9 ,india1 ,leb$eff 9     
,russia1 & !ori/s l ,m4,h4 ,po9c> &     

,pr(essor ,bj]knes1 :o devis$ +5i\s     
arrangem5ts or elucidat$ c]ta9 po9ts    
left d>k1 are among ! artisans ( ! "w   
:i* foll[$ its natural evolution4  ,x 0 
,pr(essor ,r4 ,?relfall :o seems to h   
be5 ! fir/ to cle>ly propose1 9 #ahij1 !
 application ( ! ,h]tzian waves to      
telegraphy1 b x 0 c]ta9ly ,sir ,w4      
,crookes :o1 9 a v rem>kable article 9 !
 ,=tnightly ,review ( ,febru>y #ahib1   
po9t$ out v cle>ly ! road to be foll[$4 
,he ev5 %[$ 9 :at conditions ! ,morse   
receiv] might be appli$ to ! new sy/em (
 telegraphy4  ,ab\t ! same p]iod an     
,am]ican physici/1 well kn[n by 8       
celebrat$ exp]im5ts on high frequ5cy    
curr5ts--exp]im5ts1 too1 :i* are n      
unconnect$ ) ^? on electric             
oscillations1--,m4 ,tesla1 demon/rat$ t 
^! oscillations c\ld be transmitt$ to m 
consid]able di/ances by mak+ use ( two  
v]tical ant5nae1 t]m9at$ by l>ge        
conductors4  ,a little lat]1 ,sir ,oliv]
 ,lodge succe$$1 by ! aid ( ! coh]]1 9  
detect+ waves at relatively long        

di/ances1 & ,mr ,ru!r=d obta9$ simil>   
results ) a magnetic indicator ( 8 own  
inv5tion4  ,an important "q (           
meteorology1 ! /udy ( atmosph]ic        
dis*>ges1 at ?is date l$ a few s*ol>s1 &
 m p>ticul>ly ! ,russian1 ,m4 ,pop(f1 to
 set up app>atus v analog\s to ! receiv+
 app>atus ( ! pres5t wireless           
telegraphy4 ,?is compris$ a long ant5na 
& fil+s-tube1 & ,m4 ,pop(f ev5 po9t$ out
 t 8 app>atus might well s]ve = !       
transmission ( signals z soon z a       
g5]ator ( waves p[]ful en\gh _h be5     
discov]$4  ,f9ally1 on ! #bnd ,june     
#ahif1 a "y ,italian1 born 9 ,bologna on
 ! #be? ,april #ahgd1 ,guglielmo        
,m>coni1 pat5t$ a sy/em ( wireless      
telegraphy de/9$ to become rapidly      
popul>4 ,br\ght up 9 ! laboratory (     
,pr(essor ,righi1 "o ( ! physici/s :o _h
 done mo/ to confirm & ext5d ! exp]im5ts
 ( ,h]tz1 ,m>coni _h long be5 famili> ) 
! prop]ties ( electric waves1 & 0 well  
us$ to _! manipulation4 ,he aft]w>ds _h 
! good =tune to meet ,sir ,william 7!n  

,mr7 ,preece1 :o 0 to him an advis] ( ! 
highe/ au?ority4  ,x has sometimes be5  
said t ! ,m>coni sy/em conta9s no?+     
orig9al2 t ! app>atus = produc+ ! waves 
0 ! oscillator ( ,righi1 t ! receiv] 0 t
 employ$ = "s two or ?ree ye>s by       
,pr(essor ,lodge & ,mr ,bose1 & 0 f\nd$ 
on an e>li] discov]y by a ,fr5* s*ol>1  
,m4 ,branly2 &1 f9ally1 t ! g5]al       
arrangem5t 0 t e/abli%$ by ,m4 ,pop(f4  
,! p]sons :o ?us r summ>ily judge ! "w (
 ,m4 ,m>coni %[ a sev]ity approa*+      
inju/ice4 ,x _c1 9 tru?1 be d5i$ t ! "y 
s*ol> has br\ght a /rictly p]sonal      
contribution to ! solution ( ! problem  
he propos$ to himself4 ,ap>t f 8        
=]unn]s1 & :5 _! attempts 7 almo/       
unkn[n1 he _h ! v great m]it ( adroitly 
arrang+ ! mo/ fav\rable comb9ation1 & he
 0 ! fir/ to succe$ 9 obta9+ practical  
results1 :ile he %[$ t ! electric waves 
c\ld be transmitt$ & receiv$ at di/ances
 enorm\s comp>$ to ^? atta9$ be=e 8 day4
 ,allud+ to a well-kn[n anecdote relat+ 
to ,*ri/oph] ,columbus1 ,sir ,w4 ,preece

 v ju/ly said3 ,! =]unn]s & rivals (    
,m>coni no d\bt knew ( ! eggs1 b he x 0 
:o taught !m to make !m /& on end4 ,?is 
judgm5t w1 )\t any d\bt1 be ! "o t      
hi/ory w def9itely pron\nce on !        
,italian s*ol>4    #g  ,! app>atus :i*  
enables ! electric waves to be reveal$1 
! detector or indicator1 is ! mo/       
delicate organ 9 wireless telegraphy4 ,x
 is n necess>y to employ z an indicator 
a fil+s-tube or radio-conductor4 ,"o c1 
9 pr9ciple1 = ! purpose ( con/ruct+ a   
receiv]1 ?9k ( any "o ( ! multiple      
effects produc$ by ! ,h]tzian waves4 ,9 
_m sy/ems 9 use1 & 9 ! new "o ( ,m>coni 
himself1 ! use ( ^! tubes has be5 ab&on$
 & replac$ by magnetic detectors4       
,nev]!less1 ! fir/ & ! /ill mo/ frequ5t 
successes are due to radio-conductors1 &
 public op9ion has n err$ 9 attribut+ to
 ! inv5tor ( ?is +5i\s app>atus a       
consid]able & almo/ prepond]ant "p 9 !  
inv5tion ( wave telegraphy4  ,! hi/ory (
 ! discov]y ( radio-conductors is %ort1 
b x des]ves1 f its importance1 a *apt]  

to itself 9 ! hi/ory ( wireless         
telegraphy4 ,f a !oretical po9t ( view1 
! ph5om5a produc$ 9 ^? tubes %\ld be set
 by ! side ( ^? /udi$ by ,graham ,bell1 
,c4,a4 ,br[n1 & ,summ] ,ta9t]1 f ! ye>  
#ahgh onw>d4 ,! v>iations to :i* lum9\s 
waves give rise 9 ! resi/ance ( sel5ium 
& o!r sub/ances are1 d\btless1 n        
unconnect$ ) ^? :i* ! electric waves    
produce 9 fil+s4 ,a connection c also be
 e/abli%$ betwe5 ?is effect ( ! waves & 
! v>iations ( contact resi/ance :i*     
enabl$ ,hughes to con/ruct ! microphone1
 t admirable in/rum5t :i* is "o ( !     
ess5tial organs ( telephony4  ,m        
directly1 z an antec$5t to ! discov]y1  
%\ld be quot$ ! rem>k made by ,v>ley 9  
#ahgj1 t coal-du/ *anges 9 conductivity 
:5 ! electromotive =ce ( ! curr5t :i*   
passes ?r\gh x is made to v>y4 ,b x 0 9 
#ahhd t an ,italian pr(essor1 ,signor   
,calzec*i-,one/i1 demon/rat$ 9 a s]ies (
 rem>kable exp]im5ts t ! metallic fil+s 
conta9$ 9 a tube ( insulat+ mat]ial1    
into :i* two metallic electrodes are    

ins]t$1 acquire a notable conductivity  
"u diff]5t influ5ces su* z extra        
curr5ts1 induc$ curr5ts1 sonor\s        
vibrations1 etc41 & t ?is conductivity  
is easily de/roy$2 z1 = in/ance1 by     
turn+ ! tube ov] & ov]4  ,9 sev]al      
memoirs publi%$ 9 #ahij & #ahia1 ,m4    
,ed4 ,branly indep5d5tly po9t$ out      
simil> ph5om5a1 & made a mu* m complete 
& sy/ematic /udy ( ! "q4 ,he 0 ! fir/ to
 note v cle>ly t ! action describ$ c\ld 
be obta9$ by simply mak+ sp>ks pass 9 ! 
neighb\rhood ( ! radio-conductor1 & t _!
 great resi/ance c\ld be re/or$ to !    
fil+s by giv+ a slight %ake to ! tube or
 to its supports4  ,! idea ( utilis+ su*
 a v int]e/+ ph5om5on z an indicator 9 !
 /udy ( ! ,h]tzian waves seems to h     
occurr$ simultane\sly to sev]al         
physici/s1 among :om %\ld be especially 
m5tion$ ,m4 ,ed4 ,branly himself1 ,sir  
,oliv] ,lodge1 & ,,mm4 ,le ,roy] & ,van 
,bes*em1 & its use 9 laboratories       
rapidly became q common4  ,! action ( ! 
waves on metallic p[d]s has1 h[ev]1     

rema9$ "s :at my/]i\s2 = t5 ye>s x has  
be5 ! subject ( important rese>*es by   
,pr(essor ,lodge1 ,m4 ,branly1 & a v    
great numb] ( ! mo/ di/+ui%$ physici/s4 
,x is impossible to notice "h all ^!    
rese>*es1 b f a rec5t & v int]e/+ "w (  
,m4 ,blanc1 x w\ld seem t ! ph5om5on is 
alli$ to t ( ionisation4    #h  ,!      
hi/ory ( wireless telegraphy does n end 
) ! fir/ exp]im5ts ( ,m>coni2 b f !     
mom5t _! success 0 ann\nc$ 9 ! public   
press1 ! "q left ! doma9 ( pure sci5ce  
to ent] into t ( comm]ce4 ,! hi/orian's 
task "h becomes diff]5t1 b ev5 m        
delicate2 & he w enc\nt] difficulties   
:i* c be only kn[n to "o ab\t to write !
 hi/ory ( a comm]cial inv5tion4  ,!     
actual improvem5ts effect$ 9 ! sy/em are
 kept secret by ! rival companies1 & !  
mo/ important results are patriotically 
left 9 d>kness by ! le>n$ (fic]s :o     
op]ate discreetly 9 view ( ! national   
def5ce4 ,mean:ile1 m5 ( bus9ess desir\s 
( br++ out a company proclaim1 ) great  
n\ri% ( adv]tisem5ts1 t !y are ab\t to  

exploit a process sup]ior to all o!rs4  
,on ?is slipp]y gr\nd ! imp>tial        
hi/orian mu/ nev]!less v5ture2 & he may 
n refuse to relate ! progress           
accompli%$1 :i* is consid]able4 ,!re=e1 
aft] hav+ describ$ ! exp]im5ts c>ri$ out
 = ne>ly t5 ye>s by ,m>coni himself1    
fir/ across ! ,bri/ol ,*annel1 !n at    
,spezzia1 betwe5 ! coa/ & ! ironclad    
,san ,b>tolommeo1 & f9ally by means (   
gigantic app>atus betwe5 ,am]ica &      
,engl&1 he mu/ give ! names ( ^? :o1 9 !
 diff]5t civilis$ c\ntries1 h contribut$
 to ! improvem5t ( ! sy/em (            
communication by waves2 :ile he mu/     
describe :at preci\s s]vices ?is sy/em  
has already r5d]$ to ! art ( w>1 &      
happily also to peaceful navigation4  ,f
 ! po9t ( view ( ! !ory ( ! ph5om5a1 v  
rem>kable results h be5 obta9$ by v>i\s 
physici/s1 among :om %\ld be p>ticul>ly 
m5tion$ ,m4 ,tissot1 ^: brilliant /udies
 h ?r[n a bright light on diff]5t       
int]e/+ po9ts1 su* z ! rle ( ! ant5nae4 
,x w\ld be equally impossible to pass   

ov] 9 sil5ce o!r rec5t attempts 9 a     
slightly diff]5t groove4 ,m>coni's      
sy/em1 h[ev] improv$ x may be to-day1   
has "o grave defect4 ,! syn*ronism ( !  
two pieces ( app>atus1 ! transmitt] & ! 
receiv]1 is n p]fect1 s t a message s5t 
(f by "o /ation may be captur$ by "s o!r
 /ation4 ,! fact t ! ph5om5a ( resonance
 are n utilis$1 fur!r prev5ts ! quantity
 ( en]gy receiv$ by ! receiv] f be+     
consid]able1 & h5ce ! effects reap$ are 
v weak1 s t ! sy/em rema9s some:at      
fitful & ! communications are (t5       
di/urb$ by atmosph]ic ph5om5a4 ,causes  
:i* r5d] ! air a mom5t>y conductor1 su* 
z electrical dis*>ges1 ionisation1 etc41
 moreov] naturally prev5t ! waves f     
pass+1 ! e!r ?us los+ its ela/icity4    
,pr(essor ,f]d9& ,braun ( ,/rasburg has 
conceiv$ ! idea ( employ+ a mix$ sy/em1 
9 :i* ! e>? & ! wat]1 :i*1 z we h se51 h
 (t5 be5 utilis$ to conduct a curr5t =  
transmitt+ a signal1 w s]ve z a sort (  
guide to ! waves !mselves4 ,! n[        
well-kn[n !ory ( ! propagation ( waves  

guid$ by a conductor enables x to be    
=ese5 t1 accord+ to _! p]iods1 ^! waves 
w p5etrate m or less deeply into !      
natural m$ium1 f :i* fact has be5 devis$
 a me?od ( sep>at+ !m accord+ to _!     
frequ5cy4 ,by apply+ ?is !ory1 ,m4      
,braun has c>ri$ out1 fir/ 9 !          
=tifications ( ,/rasburg1 & !n betwe5 ! 
isl& ( ,heligol& & ! ma9l&1 exp]im5ts   
:i* h giv5 rem>kable results4 ,we might 
m5tion also ! rese>*es1 9 a some:at     
analog\s ord] ( ideas1 by an ,engli%    
eng9e]1 ,mr ,arm/rong1 by ,dr ,lee de   
,=e/1 & also by ,pr(essor ,fess5d54     
,hav+ ?us arriv$ at ! end ( ?is long    
j\rney1 :i* has tak5 him f ! fir/       
attempts d[n to ! mo/ rec5t exp]im5ts1 !
 hi/orian c yet set up no o!r claim b t 
( hav+ writt5 ! comm5cem5t ( a hi/ory   
:i* o!rs mu/ cont9ue 9 ! future4        
,progress does n /op1 & x is nev]       
p]missible to say t an inv5tion has     
rea*$ its f9al =m4  ,%\ld ! hi/orian    
desire to give a conclusion to 8 lab\r &
 answ] ! "q ! read] w\ld d\btless n fail

 to put to him1 ,to :om1 9 %ort1 %\ld ! 
inv5tion ( wireless telegraphy m        
p>ticul>ly be attribut$8 he %\ld c]ta9ly
 fir/ give ! "n ( ,h]tz1 ! g5ius :o     
discov]$ ! waves1 !n t ( ,m>coni1 :o 0 !
 fir/ to transmit signals by ! use (    
,h]tzian undulations1 & %\ld add ^? ( ! 
s*ol>s :o1 l ,morse1 ,pop(f1 ,sir ,w4   
,preece1 ,lodge1 &1 above all1 ,branly1 
h devis$ ! arrangem5ts necess>y = _!    
transmission4 ,b he might !n recall :at 
,voltaire wrote 9 ! ,philosophical      
,diction>y3  ,:at6 ,we wi% to "k :at 0 !
 exact !ology ( ,?ot1 ( ,z]du/1 (       
,san*unia?on1 ( ! fir/ ,brahm9s1 & we   
are ignorant ( ! inv5tor ( ! %uttle6 ,! 
fir/ weav]1 ! fir/ mason1 ! fir/ smi?1 7
 no d\bt great g5iuses1 b !y 7          
disreg>d$4 ,:y8 ,because none ( !m      
inv5t$ a p]fect$ art4 ,! "o :o holl[$   
out an oak to cross a riv] nev] made a  
galley2 ^? :o pil$ up r\gh /ones )      
gird]s ( wood did n plan ! ,pyramids4   
,ev]y?+ is made by degrees & ! glory    
belongs to no "o4  ,to-day1 m ?an ev]1 !

 words ( ,voltaire are true3 sci5ce     
becomes m & m imp]sonal1 & %e tea*es u t
 progress is ne>ly always due to ! unit$
 ef=ts ( a cr[d ( work]s1 & is ?us ! be/
 s*ool ( social solid>ity4     ,,*apt]  
,,viii  ,,! ,,conductivity ,,( ,,gases  
,,& ,,! ,,ions    #a4 ,,! ,,conductivity
 ,,( ,,gases  ,if we 7 conf9$ to ! facts
 ,i h set =? above1 we might conclude t 
two classes ( ph5om5a are to-day be+    
int]pret$ ) increas+ correctness 9 spite
 ( ! few difficulties :i* h be5 po9t$   
out4 ,! hypo!sis ( ! molecul>           
con/itution ( matt] enables u to gr\p   
toge!r "o ( ^! classes1 & ! hypo!sis ( !
 e!r leads u to co-ord9ate ! o!r4  ,b ^!
 two classes ( ph5om5a _c be consid]$   
indep5d5t ( ea* o!r4 ,relations evid5tly
 exi/ betwe5 matt] & ! e!r1 :i* manife/ 
!mselves 9 _m cases accessible to       
exp]im5t1 & ! se>* = ^! relations appe>s
 to be ! p>am\nt problem ! physici/ %\ld
 set himself4 ,! "q has1 = a long "t1   
be5 attack$ on v>i\s sides1 b ! rec5t   
discov]ies 9 ! conductivity ( gases1 ( !

 radioactive sub/ances1 & ( ! ca?ode &  
simil> rays1 h all[$ u ( late ye>s to   
reg>d x 9 a new light4 ,)\t wi%+ to set 
out "h 9 detail facts :i* = ! mo/ "p are
 well kn[n1 we w endeav\r to gr\p ! *ief
 ( !m r\nd a few ess5tial ideas1 & w    
seek to /ate precisely ! data !y af=d u 
= ! solution ( ?is grave problem4  ,x 0 
! /udy ( ! conductivity ( gases :i* at !
 v fir/ furni%$ ! mo/ important         
in=mation1 & all[$ u to p5etrate m      
deeply ?an _h till !n be5 possible into 
! inmo/ con/itution ( matt]1 & ?us to1 z
 x 71 cat* 9 ! act ! actions t matt] c  
ex]cise on ! e!r1 or1 reciprocally1 ^? x
 may receive f x4  ,x might1 p]haps1 h  
be5 =ese5 t su* a /udy w\ld prove       
rem>kably fruitful4 ,! exam9ation ( !   
ph5om5a ( electrolysis _h1 9 fact1 l$ to
 results ( ! highe/ importance on !     
con/itution ( liquids1 & ! gase\s m$ia  
:i* pres5t$ !mselves z p>ticul>ly simple
 9 all _! prop]ties ought1 x w\ld seem1 
to h suppli$ f ! v fir/ a field (       
inve/igation easy to "w & highly        

productive4  ,?is1 h[ev]1 0 n at all !  
case4 ,exp]im5tal complications spr++ up
 at e /ep obscur$ ! problem4 ,"o g5]ally
 f\nd "o's self 9 ! pres5ce ( viol5t    
disruptive dis*>ges ) a tra9 ( accessory
 ph5om5a1 due1 = in/ance1 to ! use (    
metallic electrodes1 & made evid5t by ! 
complex appe>ance ( aigrettes &         
effluves2 or else "o _h to deal ) heat$ 
gases difficult to h&le1 :i* 7 conf9$ 9 
receptacles ^: walls play$ a tr\blesome 
"p & succe$$ 9 veil+ ! simplicity ( !   
fundam5tal facts4 ,not)/&+1 !re=e1 !    
ef=ts ( a great numb] ( seek]s1 no g5]al
 idea dis5gag$ itself out ( a mass ( (t5
 contradictory in=mation4  ,_m          
physici/s1 9 ,france p>ticul>ly1 disc>d$
 ! /udy ( que/ions :i* seem$ s confus$1 
& x mu/ ev5 be frankly ackn[l$g$ t "s   
among !m _h a really unf\nd$ di/ru/ (   
c]ta9 results :i* %\ld h be5 consid]$   
prov$1 b :i* _h ! mis=tune to be 9      
contradiction ) ! !ories 9 curr5t use4  
,all ! classic ideas relat+ to          
electrical ph5om5a l$ to ! consid]ation 

t !re exi/$ a p]fect symmetry betwe5 !  
two electricities1 positive & negative4 
,9 ! pass+ ( electricity ?r\gh gases !re
 is manife/$1 on ! contr>y1 an evid5t   
dissymmetry4 ,! anode & ! ca?ode are    
imm$iately di/+ui%$ 9 a tube ( r>efi$   
gas by _! peculi> appe>ance2 & !        
conductivity does n appe>1 "u c]ta9     
conditions1 to be ! same = ! two modes (
 electrification4  ,x is n devoid (     
int]e/ to note t ,erman1 a ,g]man s*ol>1
 once v celebrat$ & n[ g5]ally =gott51  
drew att5tion z e>ly z #ahae to !       
unipol> conductivity ( a flame4 ,8      
contempor>ies1 z may be ga!r$ f ! p]usal
 ( ! treatises on physics ( t p]iod1    
atta*$ great importance to ?is discov]y2
 b1 z x 0 some:at inconv5i5t & did n    
readily fit 9 ) ord9>y /udies1 x 0 9 due
 c\rse neglect$1 !n consid]$ z          
insuffici5tly e/abli%$1 & f9ally :olly  
=gott54  ,all ^! some:at obscure facts1 
& "s o!rs--su* z ! diff]5t action (     
ultra-violet radiations on positively & 
negatively *>g$ bodies--are n[1 on !    

contr>y1 ab\t to be co-ord9at$1 ?anks to
 ! mod]n ideas on ! me*anism (          
conduction2 :ile ^! ideas w also all[ u 
to int]pret ! mo/ /rik+ dissymmetry (   
all1 i4e4 t reveal$ by electrolysis     
itself1 a dissymmetry :i* c]ta9ly c n be
 d5i$1 b to :i* suffici5t att5tion has n
 be5 giv54  ,x is to a ,g]man physici/1 
,giese1 t we owe ! fir/ notions on !    
me*anism ( ! conductivity ( gases1 z we 
n[ conceive x4 ,9 two memoirs publi%$ 9 
#ahhb & #ahhi1 he pla9ly arrives at !   
conception t conduction 9 gases is n due
 to _! molecules1 b to c]ta9 fragm5ts ( 
!m or to ions4 ,giese 0 a =]unn]1 b 8   
ideas c\ld n triumph s long z !re 7 no  
means ( obs]v+ conduction 9 simple      
circum/ances4 ,b ?is means has n[ be5   
suppli$ 9 ! discov]y ( ! ,x rays4       
,suppose we pass ?r\gh "s gas at ord9>y 
pressure1 su* z hydrog51 a p5cil ( ,x   
rays4 ,! gas1 :i* till !n has behav$ z a
 p]fect insulator1#bi sudd5ly acquires a
 rem>kable conductivity4 ,if into ?is   
hydrog5 two metallic electrodes 9       

communication ) ! two poles ( a batt]y  
are introduc$1 a curr5t is set up 9 v   
special conditions :i* rem9d u1 :5 !y   
are *eck$ by exp]im5ts1 ( ! me*anism :i*
 all[s ! passage ( electricity 9        
electrolysis1 & :i* is s well repres5t$ 
to u :5 we picture to ourselves ?is     
passage z due to ! migration t[>ds !    
electrodes1 "u ! action ( ! field1 ( !  
two sets ( ions produc$ by ! spontane\s 
division ( ! molecule )9 ! solution4    
,footnote #bi3 ,at lea/1 s long z x is n
 introduc$ betwe5 ! two coat+s ( a      
cond5s] hav+ a diff]5ce ( pot5tial      
suffici5t to ov]come :at ,m4 ,b\ty calls
 its dielectric cohesion4 ,we leave on  
"o side ?is ph5om5on1 reg>d+ :i* ,m4    
,b\ty has arriv$ at extremely important 
results by a v rem>kable s]ies (        
exp]im5ts2 b ?is "q rightly belongs to a
 special /udy ( electrical ph5om5a :i*  
is n yet writt54  ,let u !re=e recognise
 ) ,j4,j4 ,?omson & ! _m physici/s :o1 9
 8 wake1 h tak5 up & develop$ ! idea (  
,giese1 t1 "u ! influ5ce ( ! ,x rays1 = 

reasons :i* w h to be det]m9$ lat]1     
c]ta9 gase\s molecules h become divid$  
into two portions1 ! "o positively & !  
o!r negatively electrifi$1 :i* we w     
call1 by analogy ) ! k9dr$ ph5om5on 9   
electrolysis1 by ! "n ( ions4 ,if ! gas 
be !n plac$ 9 an electric field1        
produc$1 = in/ance1 by two metallic     
plates connect$ ) ! two poles ( a batt]y
 respectively1 ! positive ions w travel 
t[>ds ! plate connect$ ) ! negative     
pole1 & ! negative ions 9 ! contr>y     
direction4 ,!re is ?us produc$ a curr5t 
due to ! transport to ! electrodes ( !  
*>ges :i* exi/$ on ! ions4  ,if ! gas   
?us ionis$ be left to itself1 9 ! abs5ce
 ( any electric field1 ! ions1 yield+ to
 _! mutual attraction1 mu/ f9ally meet1 
comb9e1 & recon/itute a neutral         
molecule1 ?us return+ to _! initial     
condition4 ,! gas 9 a %ort :ile loses ! 
conductivity :i* x _h acquir$2 or ?is   
is1 at lea/1 ! ph5om5on at ord9>y       
temp]atures4 ,b if ! temp]ature is      
rais$1 ! relative spe$s ( ! ions at !   

mom5t ( impact may be great en\gh to    
r5d] x impossible = ! recomb9ation to be
 produc$ 9 its entirety1 & "p ( !       
conductivity w rema94  ,e elem5t (      
volume r5d]$ a conductor !re=e furni%es1
 9 an electric field1 equal quantities (
 positive & negative electricity4 ,if we
 admit1 z m5tion$ above1 t ^! lib]at$   
quantities are borne by ions ea* be>+ an
 equal *>ge1 ! numb] ( ^! ions w be     
proportional to ! quantity (            
electricity1 & in/ead ( speak+ ( a      
quantity ( electricity1 we c\ld use !   
equival5t t]m ( numb] ( ions4 ,= !      
excitem5t produc$ by a giv5 p5cil ( ,x  
rays1 ! numb] ( ions lib]at$ w be fix$4 
,?us1 f a giv5 volume ( gas !re c only  
be extract$ an equally det]m9ate        
quantity ( electricity4  ,! conductivity
 produc$ is n gov]n$ by ,ohm's law4 ,!  
int5sity is n proportional to !         
electromotive =ce1 & x increases at fir/
 z ! electromotive =ce augm5ts2 b x     
approa*es asymptotically to a maximum   
value :i* corresponds to ! numb] ( ions 

lib]at$1 & c !re=e s]ve z a measure ( ! 
p[] ( ! excitem5t4 ,x is ?is curr5t :i* 
is t]m$ ! curr5t ( saturation4  ,m4     
,righi has ably demon/rat$ t ionis$ gas 
does n obey ! law ( ,ohm by an exp]im5t 
v p>adoxical 9 appe>ance4 ,he f\nd t1 ! 
great] ! di/ance ( ! two electrode      
plates f ea*1 ! great] may be1 )9 c]ta9 
limits1 ! int5sity ( ! curr5t4 ,! fact  
is v cle>ly int]pret$ by ! !ory (       
ionisation1 s9ce ! great] ! l5g? ( !    
gase\s column ! great] mu/ be ! numb] ( 
ions lib]at$4  ,"o ( ! mo/ /rik+        
*>act]i/ics ( ionis$ gases is t (       
dis*>g+ electrifi$ conductors4 ,?is     
ph5om5on is n produc$ by ! dep>ture ( ! 
*>ge t ^! conductors may possess1 b by !
 adv5t ( opposite *>ges br\ght to !m by 
ions :i* obey ! electro/atic attraction 
& ab&on _! own electrification :5 !y    
come 9 contact ) ^! conductors4  ,?is   
mode ( reg>d+ ! ph5om5a is extremely    
conv5i5t & em95tly sugge/ive4 ,x may1 no
 d\bt1 be ?\ght t ! image ( ! ions is n 
id5tical ) objective reality1 b we are  

compell$ to ackn[l$ge t x repres5ts )   
absolute fai?fulness all ! details ( !  
ph5om5a4  ,o!r facts1 moreov]1 w give to
 ?is hypo!sis a /ill great] value2 we   
%all ev5 be able1 s to speak1 to grasp  
^! ions individually1 to c\nt !m1 & to  
measure _! *>ge4    #b4 ,,!             
,,cond5sation ,,( ,,wat]-,,vap\r ,,by   
,,ions  ,if ! pressure ( a vap\r--t (   
wat]1 = in/ance--9 ! atmosph]e rea*es ! 
value ( ! maximum pressure correspond+  
to ! temp]ature ( ! exp]im5t1 ! elem5t>y
 !ory tea*es u t ! slighte/ decrease 9  
temp]ature w induce a cond5sation2 t    
small drops w =m1 & ! mi/ w turn into   
ra94  ,9 reality1 matt]s d n occur 9 s  
simple a mann]4 ,a m or less consid]able
 delay may take place1 & ! vap\r w rema9
 sup]saturat$4 ,we easily discov] t ?is 
ph5om5on is due to ! int]v5tion (       
capill>y action4 ,on a drop ( liquid a  
surface-t5sion takes effect :i* gives   
rise to a pressure :i* becomes great] ! 
small] ! diamet] ( ! drop4  ,pressure   
facilitates evaporation1 & on m closely 

exam9+ ?is reaction we arrive at !      
conclusion t vap\r c nev] spontane\sly  
cond5se itself :5 liquid drops already  
=m$ are n pres5t1 unless =ces ( ano!r   
nature int]v5e to dim9i% ! effect ( !   
capill>y =ces4 ,9 ! mo/ frequ5t cases1  
^! =ces come f ! du/ :i* is always 9    
susp5sion 9 ! air1 or :i* exi/s 9 any   
recipi5t4 ,gra9s ( du/ act by reason (  
_! hygrometrical p[]1 & =m g]ms r\nd :i*
 drops pres5tly =m4 ,x is possible to   
make use1 z did ,m4 ,c\li] z e>ly z     
#ahge1 ( ?is ph5om5on to c>ry (f ! g]ms 
( cond5sation1 by produc+ by expansion 9
 a bottle conta9+ a little wat] a       
prelim9>y mi/ :i* purifies ! air4 ,9    
subsequ5t exp]im5ts x w be f\nd almo/   
impossible to produce fur!r cond5sation 
( vap\r4  ,b ^! =ces may also be (      
electrical orig94 ,von ,helmholtz long  
s9ce %[$ t electricity ex]cises an      
influ5ce on ! cond5sation ( ! vap\r (   
wat]1 & ,mr ,c4,t4,r4 ,wilson1 ) ?is    
view1 has made truly quantitative       
exp]im5ts4 ,x 0 rapidly discov]$ aft] ! 

app>ition ( ! ,x rays t gases t h become
 conductors1 t is1 ionis$ gases1 also   
facilitate ! cond5sation ( sup]saturat$ 
wat] vap\r4  ,we are ?us l$ by a new    
road to ! belief t electrifi$ c5tres    
exi/ 9 gases1 & t ea* c5tre draws to    
itself ! neighb\r+ molecules ( wat]1 z  
an electrifi$ rod ( res9 does ! light   
bodies ar\nd x4 ,!re is produc$ 9 ?is   
mann] r\nd ea* ion an assemblage (      
molecules ( wat] :i* con/itute a g]m    
capable ( caus+ ! =mation ( a drop (    
wat] out ( ! cond5sation ( excess vap\r 
9 ! ambi5t air4 ,z might be expect$1 !  
drops are electrifi$1 & take to !mselves
 ! *>ge ( ! c5tres r\nd :i* !y are =m$2 
moreov]1 z _m drops are creat$ z !re are
 ions4 ,!reaft] we h only to c\nt ^!    
drops to asc]ta9 ! numb] ( ions :i*     
exi/$ 9 ! gase\s mass4  ,to effect ?is  
c\nt+1 sev]al me?ods h be5 us$1 diff]+ 9
 pr9ciple b lead+ to simil> results4 ,x 
is possible1 z ,mr ,c4,t4,r4 ,wilson &  
,pr(essor ,j4,j4 ,?omson h done1 to     
e/imate1 on ! "o h&1 ! weight ( ! mi/   

:i* is produc$ 9 det]m9$ conditions1 &  
on ! o!r1 ! av]age weight ( ! drops1    
accord+ to ! =mula =m]ly giv5 by ,sir   
,g4 ,/okes1 by d$uct+ _! diamet] f !    
spe$ ) :i* ?is mi/ falls2 or we c1 )    
,pr(essor ,lemme1 det]m9e ! av]age      
radius ( ! drops by an optical process1 
viz4 by measur+ ! diamet] ( ! fir/      
diffraction r+ produc$ :5 look+ ?r\gh ! 
mi/ at a po9t ( light4  ,we ?us get to a
 v high numb]4 ,!re are1 = in/ance1 "s  
tw5ty million ions p] c5timetre cube :5 
! rays h produc$ _! maximum effect1 b   
high z ?is figure is1 x is /ill v small 
comp>$ ) ! total numb] ( molecules4 ,all
 conclusions drawn f k9etic !ory lead u 
to ?9k t 9 ! same space !re mu/ exi/1 by
 ! side ( a molecule divid$ into two    
ions1 a ?\s& millions rema9+ 9 a neutral
 /ate & intact4  ,mr ,c4,t4,r4 ,wilson  
has rem>k$ t ! positive & negative ions 
d n produce cond5sation ) ! same        
facility4 ,! ions ( a contr>y sign may  
be almo/ completely sep>at$ by plac+ !  
ionis$ gas 9 a suitably dispos$ field4  

,9 ! neighb\rhood ( a negative disk !re 
rema9 h>dly any b positive ions1 & aga9/
 a positive disk none b negative2 & 9   
effect+ a sep>ation ( ?is k9d1 x w be   
notic$ t cond5sation by negative ions is
 easi] ?an by ! positive4  ,x is1       
consequ5tly1 possible to cause          
cond5sation on negative c5tres only1 &  
to /udy sep>ately ! ph5om5a produc$ by !
 two k9ds ( ions4 ,x c ?us be v]ifi$ t  
!y really be> *>ges equal 9 absolute    
value1 & ^! *>ges c ev5 be e/imat$1 s9ce
 we already "k ! numb] ( drops4 ,?is    
e/imate c be made1 = example1 by comp>+ 
! spe$ ( ! fall ( a mi/ 9 fields (      
diff]5t values1 or1 z did ,j4,j4        
,?omson1 by measur+ ! total quantity (  
electricity lib]at$ ?r\gh\t ! gas4  ,at 
! degree ( approximation :i* su*        
exp]im5ts imply1 we f9d t ! *>ge ( a    
drop1 & consequ5tly ! *>ge borne by an  
ion1 is s5sibly #c4d x #aj-aj           
electro/atic or #a4a x #aj-bj           
electromagnetic units4 ,?is *>ge is v   
ne> t :i* ! /udy ( ! ph5om5a ( ord9>y   

electrolysis leads u to attribute to a  
unival5t atom produc$ by electrolytic   
dissociation4  ,su* a co9cid5ce is      
evid5tly v /rik+2 b x w n be ! only "o1 
= :atev] ph5om5on be /udi$ x w always   
appe> t ! smalle/ *>ge we c conceive z  
isolat$ is t m5tion$4 ,we are1 9 fact1 9
 pres5ce ( a natural unit1 or1 if y w1 (
 an atom ( electricity4  ,we mu/1 h[ev]1
 gu>d aga9/ ! belief t ! gase\s ion is  
id5tical ) ! electrolytic ion4 ,s5sible 
diff]5ces betwe5 ^? are imm$iately      
app>5t1 & /ill great] ones w be discov]$
 on clos] exam9ation4  ,z ,m4 ,p]r9 has 
%[n1 ! ionisation produc$ by ! ,x-rays 9
 no way dep5ds on ! *emical composition 
( ! gas2 & :e!r we take a volume (      
gase\s hydro*loric acid or a mixture (  
hydrog5 & *lor9e 9 ! same condition1 all
 ! results w be id5tical3 & *emical     
aff9ities play no "p "h4  ,we c also    
obta9 o!r in=mation reg>d+ ions3 we c   
asc]ta91 = in/ance1 _! velocities1 &    
also get an idea ( _! ord] ( magnitude4 
,by treat+ ! spe$s possess$ by ! lib]at$

 *>ges z compon5ts ( ! kn[n spe$ ( a    
gase\s curr5t1 ,mr ,zel5y measures !    
mobilities1 t is to say1 ! spe$s acquir$
 by ! positive & negative *>ges 9 a     
field equal to ! electro/atic unit4 ,he 
has ?us f\nd t ^! mobilities are        
diff]5t1 & t !y v>y1 = example1 betwe5  
#djj & #bjj c5timetres p] second = ! two
 *>ges 9 dry gases1 ! positive be+ less 
mobile ?an ! negative ions1 :i* sugge/s 
! idea t !y are ( great] mass4#cj       
,footnote #cj3 ,a full acc\nt ( ^!      
exp]im5ts1 :i* 7 execut$ at ! ,cav5di%  
,laboratory1 is to be f\nd 9            
,philosophical ,transactions1 ,a41 vol4 
cxcv4 7#aija71 pp4 #aic et seq4--,,ed4  
,m4 ,langev91 :o has made himself !     
eloqu5t apo/le ( ! new doctr9es 9       
,france1 & has done mu* to make !m      
und]/ood & admitt$1 has p]sonally       
und]tak5 exp]im5ts analog\s to ^? ( ,m4 
,zel5y1 b mu* m complete4 ,he has /udi$ 
9 a v +5i\s mann]1 n only ! mobilities1 
b also ! law ( recomb9ation :i*         
regulates ! spontane\s return ( ! gas to

 its normal /ate4 ,he has det]m9$       
exp]im5tally ! relation ( ! numb] (     
recomb9ations to ! numb] ( collisions   
betwe5 two ions ( contr>y sign1 by /udy+
 ! v>iation produc$ by a *ange 9 ! value
 ( ! field1 9 ! quantity ( electricity  
:i* c be collect$ 9 ! gas sep>at+ two   
p>allel metallic plates1 aft] ! passage 
?r\gh x = a v %ort "t ( ! ,rntg5 rays   
emitt$ dur+ "o dis*>ge ( a ,crookes     
tube4 ,if ! image ( ! ions is inde$     
con=mable to reality1 ?is relation mu/  
evid5tly always be small] ?an unity1 &  
mu/ t5d t[>ds ?is value :5 ! mobility ( 
! ions dim9i%es1 t is to say1 :5 !      
pressure ( ! gas increases4 ,! results  
obta9$ are 9 p]fect accord ) ?is        
anticipation4  ,on ! o!r h&1 ,m4        
,langev9 has succe$$1 by foll[+ !       
displacem5t ( ! ions betwe5 ! p>allel   
plates aft] ! ionisation produc$ by !   
radiation1 9 det]m9+ ! absolute values (
 ! mobilities ) great precision1 & has  
?us cle>ly plac$ 9 evid5ce ! irregul>ity
 ( ! mobilities ( ! positive & negative 

ions respectively4 ,_! mass c be        
calculat$ :5 we "k1 ?r\gh exp]im5ts (   
?is k9d1 ! spe$ ( ! ions 9 a giv5 field1
 & on ! o!r h&--z we c n[ e/imate _!    
electric *>ge--! =ce :i* moves !m4 ,!y  
evid5tly progress m sl[ly ! l>g] !y are2
 & 9 ! visc\s m$ium con/itut$ by ! gas1 
! displacem5t is effect$ at a spe$      
s5sibly proportional to ! motive p[]4   
,at ! ord9>y temp]ature ^! masses are   
relatively consid]able1 & are great] = !
 positive ?an = ! negative ions1 t is to
 say1 !y are ab\t ! ord] ( "s t5        
molecules4 ,! ions1 !re=e1 seem to be   
=m$ by an agglom]ation ( neutral        
molecules ma9ta9$ r\nd an electrifi$    
c5tre by electro/atic attraction4 ,if ! 
temp]ature rises1 ! !rmal agitation w   
become great en\gh to prev5t ! molecules
 f rema9+ l9k$ to ! c5tre4 ,by          
measurem5ts effect$ on ! gases ( flames1
 we arrive at v diff]5t values ( !      
masses f ^? f\nd = ord9>y ions1 & above 
all1 v diff]5t ones = ions ( contr>y    
sign4 ,! negative ions h mu* m          

consid]able velocities ?an ! positive   
ones4 ,! latt] also seem to be ( ! same 
size z atoms2 & ! fir/-nam$ mu/1        
consequ5tly1 be consid]$ z v mu* small]1
 & probably ab\t a ?\s& times less4     
,?us1 = ! fir/ "t 9 sci5ce1 ! idea      
appe>s t ! atom is n ! smalle/ fraction 
( matt] to be consid]$4 ,fragm5ts a ?\s&
 times small] may exi/ :i* possess1     
h[ev]1 a negative *>ge4 ,^! are !       
electrons1 :i* o!r consid]ations w aga9 
br+ to our notice4    #c4 ,,h[ ,,ions   
,,are ,,produc$  ,x is v seldom t a     
gase\s mass does n conta9 a few ions4   
,!y may h be5 =m$ f _m causes1 = al?\gh 
to give precision to our /udies1 & to   
deal ) a well asc]ta9$ case1 ,i m5tion$ 
only ionisation by ! ,x rays 9 ! fir/   
in/ance1 ,i ought n to give ! impression
 t ! ph5om5on is conf9$ to ^! rays4 ,x  
is1 on ! contr>y1 v g5]al1 & ionisation 
is j z well produc$ by ! ca?ode rays1 by
 ! radiations emitt$ by radio-active    
bodies1 by ! ultra-violet rays1 by heat+
 to a high temp]ature1 by c]ta9 *emical 

actions1 & f9ally by ! impact ( ! ions  
already exi/+ 9 neutral molecules4  ,(  
late ye>s ^! new que/ions h be5 ! object
 ( a multitude ( rese>*es1 & if x has n 
always be5 possible to avoid "s         
confusion1 yet c]ta9 g5]al conclusions  
may be drawn4 ,! ionisation by flames1 9
 p>ticul>1 is fairly well kn[n4 ,= x to 
be produc$ spontane\sly1 x w\ld appe> t 
!re mu/ exi/ simultane\sly a r high     
temp]ature & a *emical action 9 ! gas4  
,accord+ to ,m4 ,moreau1 ! ionisation is
 v m>k$ :5 ! flame conta9s ! vap\r ( !  
salt ( an alkali or ( an alkal9e e>?1 b 
mu* less s :5 x conta9s t ( o!r salts4  
,arrh5ius1 ,mr ,c4,t4,r4 ,wilson1 & ,m4 
,moreau1 h /udi$ all ! circum/ances ( ! 
ph5om5on2 & x seems inde$ t !re is a    
some:at close analogy betwe5 :at fir/   
occurs 9 ! sal9e vap\rs & t :i* is not$ 
9 liquid electrolytes4 ,!re %\ld be     
produc$1 z soon z a c]ta9 temp]ature is 
rea*$1 a dissociation ( ! sal9e         
molecule2 &1 z ,m4 ,moreau has %[n 9 a  
s]ies ( v well conduct$ rese>*es1 ! ions

 =m$ at ab\t #ajj;,c4 seem con/itut$ by 
an electrifi$ c5tre ( ! size ( a gas    
molecule1 surr\nd$ by "s t5 lay]s ( o!r 
molecules4 ,we are ?us deal+ ) r l>ge   
ions1 b accord+ to ,mr ,wilson1 ?is     
cond5sation ph5om5on does n affect !    
numb] ( ions produc$ by dissociation4 ,9
 proportion z ! temp]ature rises1 !     
molecules cond5s$ r\nd ! nucleus        
disappe>1 &1 z 9 all o!r circum/ances1 !
 negative ion t5ds to become an         
electron1 :ile ! positive ion cont9ues !
 size ( an atom4  ,9 o!r cases1 ions are
 f\nd /ill l>g] ?an ^? ( sal9e vap\rs1  
z1 = example1 ^? produc$ by phosphorus4 
,x has long be5 kn[n t air 9 !          
neighb\rhood ( phosphorus becomes a     
conductor1 & ! fact1 po9t$ out z f> back
 z #ahhe by ,matteucci1 has be5 well    
/udi$ by v>i\s exp]im5t]s1 by ,,mm4     
,el/] & ,geitel 9 #ahij1 = in/ance4 ,on 
! o!r h&1 9 #ahic ,mr ,b>us e/abli%$ t !
 approa* ( a /ick ( phosphorus br+s ab\t
 ! cond5sation ( wat] vap\r1 & we really
 h be=e u1 !re=e1 9 ?is in/ance1 an     

ionisation4 ,m4 ,blo* has succe$$ 9     
dis5tangl+ ! ph5om5a1 :i* are "h v      
complex1 & 9 %[+ t ! ions produc$ are ( 
consid]able dim5sions2 = _! spe$ 9 !    
same conditions is on ! av]age a ?\s&   
times less ?an t ( ions due to ! ,x     
rays4 ,m4 ,blo* has e/abli%$ also t !   
conductivity ( rec5tly-prep>$ gases1    
already /udi$ by sev]al au?ors1 0       
analog\s to t :i* is produc$ by         
phosphorus1 & t x is intimately connect$
 ) ! pres5ce ( ! v t5u\s solid or liquid
 du/ :i* ^! gases c>ry ) !m1 :ile ! ions
 are ( ! same ord] ( magnitude4 ,^! l>ge
 ions exi/1 moreov]1 9 small quantities 
9 ! atmosph]e2 & ,m4 ,langev9 lately    
succe$$ 9 reveal+ _! pres5ce4  ,x may   
happ51 & ?is n )\t s+ul>ly complicat+   
matt]s1 t ! ions :i* 7 9 ! mid/ (       
mat]ial molecules produce1 z ! result ( 
collisions1 new divisions 9 ^! la/4 ,o!r
 ions are ?us born1 & ?is production is 
9 "p comp5sat$ = by recomb9ations betwe5
 ions ( opposite signs4 ,! impacts w be 
m active 9 ! ev5t ( ! gas be+ plac$ 9 a 

field ( =ce & ( ! pressure be+ slight1 !
 spe$ atta9$ be+ !n great] & all[+ !    
active =ce to rea* a high value4 ,!     
en]gy necess>y = ! production ( an ion  
is1 9 fact1 accord+ to ,pr(essor ,ru!r=d
 & ,pr(essor ,/>k1 some?+ consid]able1 &
 x mu* exce$s ! analog\s =ce 9          
electrolytic decomposition4  ,x is !re=e
 9 tubes ( r>efi$ gas t ?is ionisation  
by impact w be p>ticul>ly felt4 ,?is    
gives u ! reason = ! aspect pres5t$ by  
,geissl] tubes4 ,g5]ally1 9 ! case (    
dis*>ges1 new ions produc$ by !         
molecules /ruck come to add !mselves to 
! electrons produc$1 z w be se51 by !   
ca?ode4 ,a full discussion has l$ to !  
int]pretation ( all ! kn[n facts1 & to  
our und]/&+1 = in/ance1 :y !re exi/     
bright or d>k spaces 9 c]ta9 regions ( !
 tube4 ,m4 ,pellat1 9 p>ticul>1 has giv5
 "s v f9e examples ( ?is concordance    
betwe5 ! !ory & ! facts he has skilfully
 obs]v$4  ,9 all ! circum/ances1 !n1 9  
:i* ions appe>1 _! =mation has d\btless 
be5 provok$ by a me*anism analog\s to t 

( ! %ock4 ,! ,x rays1 if !y are         
attributable to sudd5 v>iations 9 !     
e!r--t is to say1 a v>iation ( ! two    
vectors ( ,h]tz-- !mselves produce )9 ! 
atom a k9d ( electric impulse :i* breaks
 x into two electrifi$ fragm5ts2 i4e4 ! 
positive c5tre1 ! size ( ! molecule     
itself1 & ! negative c5tre1 con/itut$ by
 an electron a ?\s& times small]4 ,r\nd 
^! two c5tres1 at ! ord9>y temp]ature1  
are agglom]at$ by attraction o!r        
molecules1 & 9 ?is mann] ! ions ^:      
prop]ties h j be5 /udi$ are =m$4    #d4 
,,electrons ,,9 ,,metals  ,! success ( !
 ionic hypo!sis z an int]pretation ( !  
conductivity ( electrolytes & gases has 
sugge/$ ! desire to try if a simil>     
hypo!sis c repres5t ! ord9>y            
conductivity ( metals4 ,we are ?us l$ to
 conceptions :i* at fir/ sight seem     
audaci\s because !y are contr>y to our  
habits ( m9d4 ,!y mu/ n1 h[ev]1 be      
reject$ on t acc\nt4 ,electrolytic      
dissociation at fir/ c]ta9ly appe>$ at  
lea/ z /range2 yet x has end$ by =c+    

itself ^u u1 & we c\ld1 at ! pres5t day1
 h>dly disp5se ) ! image x pres5ts to u4
  ,! idea t ! conductivity ( metals is n
 ess5tially diff]5t f t ( electrolytic  
liquids or gases1 9 ! s5se t ! passage (
 ! curr5t is connect$ ) ! transport (   
small electrifi$ p>ticles1 is already ( 
old date4 ,x 0 enunciat$ by ,w4 ,web]1 &
 aft]w>ds develop$ by ,giese1 b has only
 obta9$ its true scope ?r\gh ! effect ( 
rec5t discov]ies4 ,x 0 ! rese>*es (     
,riecke1 lat]1 ( ,drude1 &1 above all1  
^? ( ,j4,j4 ,?omson1 :i* h all[$ x to   
assume an acceptable =m4 ,all ^!        
attempts are connect$ h[ev] ) ! g5]al   
!ory ( ,lor5tz1 :i* we w exam9e lat]4   
,x w be admitt$ t metallic atoms c1 l ! 
sal9e molecule 9 a solution1 p>tially   
dissociate !mselves4 ,electrons1 v mu*  
small] ?an atoms1 c move ?r\gh !        
/ructure1 consid]able to !m1 :i* is     
con/itut$ by ! atom f :i* !y h j be5    
deta*$4 ,!y may be comp>$ to ! molecules
 ( a gas :i* is enclos$ 9 a por\s body4 
,9 ord9>y conditions1 not)/&+ ! great   

spe$ ) :i* !y are animat$1 !y are unable
 to travel long di/ances1 because !y    
quickly f9d _! road b>r$ by a mat]ial   
atom4 ,!y h to und]go innum]able        
impacts1 :i* ?r[ !m fir/ 9 "o direction 
& !n 9 ano!r4 ,! passage ( a curr5t is a
 sort ( fl[ ( ^! electrons 9 a det]m9$  
direction4 ,?is electric fl[ br+s1      
h[ev]1 no modification to ! mat]ial     
m$ium trav]s$1 s9ce e electron :i*      
disappe>s at any po9t is replac$ by     
ano!r :i* appe>s at once1 & 9 all metals
 ! electrons are id5tical4  ,?is        
hypo!sis leads u to anticipate c]ta9    
facts :i* exp]i5ce confirms4 ,?us ,j4,j4
 ,?omson %[s t if1 9 c]ta9 conditions1 a
 conductor is plac$ 9 a magnetic field1 
! ions h to describe an epicycloid1 & _!
 j\rney is ?us l5g!n$1 :ile ! electric  
resi/ance mu/ increase4 ,if ! field is 9
 ! direction ( ! displacem5t1 !y        
describe helices r\nd ! l9es ( =ce & !  
resi/ance is aga9 augm5t$1 b 9 diff]5t  
proportions4 ,v>i\s exp]im5t]s h not$   
ph5om5a ( ?is k9d 9 diff]5t sub/ances4  

,= a long "t x has be5 notic$ t a       
relation exi/s betwe5 ! calorific & !   
electric conductivity2 ! relation ( ^!  
two conductivities is s5sibly ! same =  
all metals4 ,! mod]n !ory t5ds to %[    
simply t x mu/ inde$ be s4 ,calorific   
conductivity is due1 9 fact1 to an      
ex*ange ( electrons betwe5 ! hot & !    
cold regions1 ! heat$ electrons hav+ !  
great] velocity1 & consequ5tly ! m      
consid]able en]gy4 ,! calorific ex*anges
 !n obey laws simil> to ^? :i* gov]n    
electric ex*anges2 & calculation ev5    
leads to ! exact values :i* !           
measurem5ts h giv54#ca  ,footnote #ca3  
,! :ole ( ?is argum5t is brilliantly set
 =? by ,pr(essor ,lor5tz 9 a lecture    
deliv]$ to ! ,electrote*nik]v]e9 at     
,b]l9 9 ,decemb] #aijd1 & repr9t$1 )    
additions1 9 ! ,ar*ives ,nerl&aises (   
#aijf4--;,,ed4  ,9 ! same way ,pr(essor 
,hesehus has expla9$ h[ contact         
electrification is produc$1 by ! t5d5cy 
( bodies to equalise _! sup]ficial      
prop]ties by means ( a transport (      

electrons1 & ,mr ,jeans has %[n t we    
%\ld discov] ! exi/5ce ( ! well-kn[n    
laws ( di/ribution ov] conduct+ bodies 9
 electro/atic equilibrium4 ,a metal c1 9
 fact1 be electrifi$1 t is to say1 may  
possess an excess ( positive or negative
 electrons :i* _c easily leave x 9      
ord9>y conditions4 ,to cause !m to d s  
w\ld ne$ an appreciable am\nt ( "w1 on  
acc\nt ( ! enorm\s diff]5ce ( ! specific
 inductive capacities ( ! metal & ( !   
insulat+ m$ium 9 :i* x is plung$4       
,electrons1 h[ev]1 :i*1 on arriv+ at !  
surface ( ! metal1 possess$ a k9etic    
en]gy sup]ior to ?is "w1 might be %ot =?
 & w\ld be dis5gag$ z a vap\r escapes f 
a liquid4 ,n[1 ! numb] ( ^! rapid       
electrons1 at fir/ v slight1 increases1 
accord+ to ! k9etic !ory1 :5 !          
temp]ature rises1 & !re=e we mu/ reckon 
t a wire1 on be+ heat$1 gives out       
electrons1 t is to say1 loses negative  
electricity & s5ds into ! surr\nd+ m$ia 
electrifi$ c5tres capable ( produc+ !   
ph5om5a ( ionisation4 ,edison1 9 #ahhd1 

%[$ t f ! filam5t ( an inc&esc5t lamp   
!re escap$ negative electric *>ges4     
,s9ce !n1 ,ri*>dson & ,j4,j4 ,?omson h  
exam9$ analog\s ph5om5a4 ,?is emission  
is a v g5]al ph5om5on :i*1 no d\bt1     
plays a consid]able "p 9 cosmic physics4
 ,pr(essor ,arrh5ius expla9s1 = in/ance1
 ! pol> auroras by ! action ( simil>    
corpuscules emitt$ by ! sun4  ,9 o!r    
ph5om5a we seem inde$ to be confront$ by
 an emission1 n ( negative electrons1 b 
( positive ions4 ,?us1 :5 a wire is     
heat$1 n 9 vacuo1 b 9 a gas1 ?is wire   
beg9s to electrify neighb\r+ bodies     
positively4 ,j4,j4 ,?omson has measur$ !
 mass ( ^! positive ions & f9ds x       
consid]able1 i4e4 ab\t #aej times t ( an
 atom ( hydrog54 ,"s are ev5 l>g]1 &    
con/itute almo/ a real gra9 ( du/4 ,we  
"h d\btless meet ) ! ph5om5a (          
disaggregation und]gone by metals at a  
r$ heat4     ,,*apt] ,,ix  ,,ca?ode     
,,rays ,,& ,,radioactive ,,bodies    #a4
 ,,! ,,ca?ode ,,rays  ,a wire trav]s$ by
 an electric curr5t is1 z has j be5     

expla9$1 ! seat ( a movem5t ( electrons4
 ,if we cut ?is wire1 a flood (         
electrons1 l a curr5t ( wat] :i*1 at !  
po9t :]e a pipe bur/s1 fl[s out 9       
abundance1 w appe> to spr+ out betwe5 ! 
two ends ( ! break4  ,if ! en]gy ( !    
electrons is suffici5t1 ^! electrons w 9
 fact ru% =? & be propagat$ 9 ! air or 9
 ! insulat+ m$ium int]pos$2 b ! ph5om5a 
( ! dis*>ge w 9 g5]al be v complex4 ,we 
%all "h only exam9e a p>ticul>ly simple 
case1 viz41 t ( ! ca?ode rays2 & )\t    
ent]+ into details1 we %all only note ! 
results relat+ to ^! rays :i* furni%    
valuable argum5ts 9 fav\r ( ! electronic
 hypo!sis & supply solid mat]ials = !   
con/ruction ( new !ories ( electricity &
 matt]4  ,= a long "t x 0 notic$ t !    
ph5om5a 9 a ,geissl] tube *ang$ _!      
aspect consid]ably1 :5 ! gas pressure   
became v weak1 )\t1 h[ev]1 a complete   
vacuum be+ =m$4 ,f ! ca?ode !re is %ot  
=? normally & 9 a /raight l9e a flood )9
 ! tube1 d>k b capable ( impress+ a     
photographic plate1 ( develop+ !        

fluoresc5ce ( v>i\s sub/ances           
7p>ticul>ly ! glass walls ( ! tube71 & (
 produc+ calorific & me*anical effects4 
,^! are ! ca?ode rays1 s nam$ 9 #ahhc by
 ,e4 ,wi$emann1 & _! "n1 :i* 0 unkn[n to
 a great numb] ( physici/s till b>ely   
twelve ye>s ago1 has become popul> at ! 
pres5t day4  ,ab\t #ahfi1 ,hittorf made 
an already v complete /udy ( !m & put 9 
evid5ce _! pr9cipal prop]ties2 b x 0 !  
rese>*es ( ,sir ,w4 ,crookes 9 especial 
:i* drew att5tion to !m4 ,! celebrat$   
physici/ =esaw t ! ph5om5a :i* 7 ?us    
produc$ 9 r>efi$ gases 71 9 spite ( _! v
 great complication1 m simple ?an ^?    
pres5t$ by matt] "u ! conditions 9 :i* x
 is g5]ally met )4  ,he devis$ a        
celebrat$ !ory no long] admissible 9 its
 entirety1 because x is n 9 complete    
accord ) ! facts1 :i* 01 h[ev]1 v       
int]e/+1 & conta9$1 9 g]m1 c]ta9 ( our  
pres5t ideas4 ,9 ! op9ion ( ,crookes1 9 
a tube 9 :i* ! gas has be5 r>efi$ we are
 9 pres5ce ( a special /ate ( matt]4 ,! 
numb] ( ! gas molecules has become small

 en\gh = _! indep5d5ce to be almo/      
absolute1 & !y are able 9 ?is s-call$   
radiant /ate to trav]se long spaces )\t 
dep>t+ f a /raight l9e4 ,! ca?ode rays  
are due to a k9d ( molecul> bomb>dm5t ( 
! walls ( ! tubes1 & ( ! scre5s :i* c be
 introduc$ into !m2 & x is ! molecules1 
electrifi$ by _! contact ) ! ca?ode & !n
 =cibly repell$ by electro/atic action1 
:i* produce1 by _! movem5t & _! vis     
viva1 all ! ph5om5a obs]v$4 ,moreov]1 ^!
 electrifi$ molecules animat$ )         
extremely rapid velocities correspond1  
accord+ to ! !ory v]ifi$ 9 ! celebrat$  
exp]im5t ( ,r[l& on convection curr5ts1 
to a true electric curr5t1 & c be       
deviat$ by a magnet4  ,not)/&+ ! success
 ( ,crookes' exp]im5ts1 _m physici/s-- !
 ,g]mans especially--did n ab&on an     
hypo!sis entirely diff]5t f t ( radiant 
matt]4 ,!y cont9u$ to reg>d ! ca?ode    
radiation z due to p>ticul> radiations (
 a nature /ill little kn[n b produc$ 9 !
 lum9\s e!r4 ,?is int]pretation seem$1  
inde$1 9 #ahid1 de/9$ to triumph        

def9itely ?r\gh ! rem>kable discov]y (  
,l5>d1 a discov]y :i*1 9 its turn1 0 to 
provoke s _m o!rs & to br+ ab\t         
consequ5ces ( :i* ! importance seems e  
day m consid]able4  ,pr(essor ,l5>d's   
fundam5tal idea 0 to /udy ! ca?ode rays 
"u conditions diff]5t f ^? 9 :i* !y are 
produc$4 ,^! rays are born 9 a v r>efi$ 
space1 "u conditions p]fectly det]m9$ by
 ,sir ,w4 ,crookes2 b x 0 a "q :e!r1 :5 
once produc$1 !y w\ld be capable (      
propagat+ !mselves 9 o!r m$ia1 su* z a  
gas at ord9>y pressure1 or ev5 9 an     
absolute vacuum4 ,exp]im5t alone c\ld   
answ] ?is "q1 b !re 7 difficulties 9 !  
way ( ?is :i* seem$ almo/ insurm\ntable4
 ,! rays are /opp$ by glass ev5 ( slight
 ?ickness1 & h[ !n c\ld ! almo/ vacu\s  
space 9 :i* !y h to come into exi/5ce be
 sep>at$ f ! space1 absolutely vacu\s or
 fill$ ) gas1 into :i* x 0 desir$ to br+
 !m8  ,! artifice us$ 0 sugge/$ to      
,pr(essor ,l5>d by an exp]im5t ( ,h]tz4 
,! great physici/ _h1 9 fact1 %ortly    
be=e 8 premature dea?1 tak5 up ?is      

important "q ( ! ca?ode rays1 & 8 g5ius 
left !re1 z else:]e1 its p[]ful impress4
 ,he _h %[n t metallic plates ( v slight
 ?ickness 7 transp>5t to ! ca?ode rays2 
& ,pr(essor ,l5>d succe$$ 9 obta9+      
plates imp]meable to air1 b :i* yet     
all[$ ! p5cil ( ca?ode rays to pass     
?r\gh !m4  ,n[ if we take a ,crookes    
tube ) ! extremity h]metically clos$ by 
a metallic plate ) a slit across !      
diamet] ( #a mm4 9 wid?1 & /op ?is slit 
) a %eet ( v ?9 alum9ium1 x w be        
imm$iately notic$ t ! rays pass ?r\gh ! 
alum9ium & pass outside ! tube4 ,!y are 
propagat$ 9 air at atmosph]ic pressure1 
& !y c also p5etrate into an absolute   
vacuum4 ,!y !re=e c no long] be         
attribut$ to radiant matt]1 & we are l$ 
to ?9k t ! en]gy br\ght into play 9 ?is 
ph5om5on mu/ h its seat 9 ! light-be>+  
e!r itself4  ,b x is a v /range light   
:i* is ?us subject to magnetic action1  
:i* does n obey ! pr9ciple ( equal      
angles1 & = :i* ! mo/ v>i\s gases are   
already di/urb$ m$ia4 ,accord+ to       

,crookes x possesses also ! s+ul>       
prop]ty ( c>ry+ ) x electric *>ges4     
,?is convection ( negative electricity  
by ! ca?ode rays seems q inexplicable on
 ! hypo!sis t ! rays are e!real         
radiations4 ,no?+ !n rema9$ 9 ord] to   
ma9ta9 ?is hypo!sis1 except to d5y !    
convection1 :i*1 besides1 0 only        
e/abli%$ by indirect exp]im5ts4 ,t !    
reality ( ?is transport has be5 plac$   
beyond dispute by means ( an extremely  
elegant exp]im5t :i* is all ! m conv9c+ 
t x is s v simple1 is due to ,m4 ,p]r94 
,9 ! int]ior ( a ,crookes tube he       
collect$ a p5cil ( ca?ode rays 9 a metal
 cyl9d]4 ,accord+ to ! elem5t>y         
pr9ciples ( electricity ! cyl9d] mu/    
become *>g$ ) ! :ole *>ge1 if !re be "o1
 br\ght to x by ! rays1 & naturally     
v>i\s precautions _h to be tak54 ,b !   
result 0 v precise1 & d\bt c\ld no long]
 exi/--! rays 7 electrifi$4  ,x might h 
be51 & inde$ 01 ma9ta9$1 "s "t aft] ?is 
exp]im5t 0 publi%$1 t :ile ! ph5om5a 7  
complex inside ! tube1 outside1 ?+s     

might p]haps occur diff]5tly4 ,l5>d     
himself1 h[ev]1 ) t abs5ce ( ev5        
involunt>y prejudice common to all great
 m9ds1 und]took to demon/rate t ! op9ion
 he at fir/ held c\ld no long] be       
accept$1 & succe$$ 9 repeat+ ! exp]im5t 
( ,m4 ,p]r9 on ca?ode rays 9 ! air & ev5
 9 vacuo4  ,on ! wrecks ( ! two         
contradictory hypo!ses ?us de/roy$1 &   
out ( ! mat]ials f :i* !y _h be5 built1 
a !ory has be5 con/ruct$ :i* co-ord9ates
 all ! kn[n facts4 ,?is !ory is         
fur!rmore closely alli$ to ! !ory (     
ionisation1 &1 l ?is latt]1 is bas$ on !
 concept ( ! electron4 ,ca?ode rays are 
electrons 9 rapid motion4  ,! ph5om5a   
produc$ bo? inside & outside a ,crookes 
tube are1 h[ev]1 g5]ally complex4 ,9    
,l5>d's fir/ exp]im5ts1 & 9 _m o!rs     
effect$ lat] :5 ?is region ( physics 0  
/ill v little kn[n1 a few confusions may
 be notic$ ev5 at ! pres5t day4  ,at !  
spot :]e ! ca?ode rays /rike ! walls ( !
 tube ! ess5tially diff]5t ,x rays      
appe>4 ,^! diff] f ! ca?ode radiations  

by be+ nei!r electrifi$ nor deviat$ by a
 magnet4 ,9 _! turn ^! ,x rays may give 
bir? to ! second>y rays ( ,m4 ,sagnac2 &
 (t5 we f9d ourselves 9 pres5ce (       
effects f ^! la/-nam$ radiations & n f !
 true ca?ode rays4  ,! electrons1 :5 !y 
are propagat$ 9 a gas1 c ionise !       
molecules ( ?is gas & unite ) ! neutral 
atoms to =m negative ions1 :ile positive
 ions also appe>4 ,!re are likewise     
produc$1 at ! exp5se ( ! gas /ill       
subsi/+ aft] r>efication )9 ! tube1     
positive ions :i*1 attract$ by ! ca?ode 
& rea*+ x1 are n all neutralis$ by !    
negative electrons1 & c1 if ! ca?ode be 
p]=at$1 pass ?r\gh x1 & if n1 pass r\nd 
x4 ,we h !n :at are call$ ! canal rays (
 ,gold/e91 :i* are deviat$ by an        
electric or magnetic field 9 a contr>y  
direction to ! ca?ode rays2 b1 be+ l>g]1
 give weak deviations or may ev5 rema9  
undeviat$ ?r\gh los+ _! *>ge :5 pass+   
?r\gh ! ca?ode4  ,x may also be ! p>ts (
 ! walls at a di/ance f ! ca?ode :i* s5d
 a positive ru% to ! latt]1 by a simil> 

me*anism4 ,x may be1 aga91 t 9 c]ta9    
regions ( ! tube ca?ode rays are met )  
diffus$ by "s solid object1 )\t hav+    
!reby *ang$ _! nature4 ,all ^!          
complexities h be5 cle>$ up by ,m4      
,vill>d1 :o has publi%$1 on ^! que/ions1
 "s rem>kably +5i\s & p>ticul>ly c>eful 
exp]im5ts4  ,m4 ,vill>d has also /udi$ !
 ph5om5a ( ! coil+ ( ! rays 9 a field1 z
 already po9t$ out by ,hittorf & ,plck]4
 ,:5 a magnetic field acts on ! ca?ode  
p>ticle1 ! latt] foll[s a trajectory1   
g5]ally helicoidal1 :i* is anticipat$ by
 ! !ory4 ,we "h h to d ) a "q (         
balli/ics1 & exp]im5ts duly confirm !   
anticipations ( ! calculation4          
,nev]!less1 r s+ul> ph5om5a appe> 9 !   
case ( c]ta9 values ( ! field1 & ^!     
ph5om5a1 dimly se5 by ,plck] & ,birkel&1
 h be5 ! object ( exp]im5ts by ,m4      
,vill>d4 ,! two faces ( ! ca?ode seem to
 emit rays :i* are deviat$ 9 a direction
 p]p5dicul> to ! l9es ( =ce by an       
electric field1 & d n seem to be        
electrifi$4 ,m4 ,vill>d calls !m        

magneto-ca?ode rays1 & accord+ to ,m4   
,=t9 ^! rays may be ord9>y ca?ode rays1 
b ( v slight velocity4  ,9 c]ta9 cases !
 ca?ode itself may be sup]ficially      
disaggregat$1 & extremely t5u\s p>ticles
 deta* !mselves1 :i*1 be+ c>ri$ (f at "r
 angles to its surface1 may deposit     
!mselves l a v ?9 film on objects plac$ 
9 _! pa?4 ,v>i\s physici/s1 among !m ,m4
 ,h\llevigue1 h /udi$ ?is ph5om5on1 & 9 
! case ( pressures betwe5 #a_/bj &      
#a_/ajj ( a millimetre1 ! la/-nam$ s*ol>
 has obta9$ mirrors ( mo/ metals1 a     
ph5om5on he designates by ! "n (        
ionopla/y4  ,b 9 spite ( all ^!         
accessory ph5om5a1 :i* ev5 sometimes    
conceal ^? fir/ obs]v$1 ! exi/5ce ( !   
electron 9 ! ca?odic flux rema9s !      
ess5tial *>act]i/ic4  ,! electron c be  
appreh5d$ 9 ! ca?odic ray by ! /udy (   
its ess5tial prop]ties2 & ,j4,j4 ,?omson
 gave great value to ! hypo!sis by 8    
measurem5ts4 ,at fir/ he meant to       
det]m9e ! spe$ ( ! ca?ode rays by direct
 exp]im5t1 & by obs]v+1 9 a revolv+     

mirror1 ! relative displacem5t ( two b&s
 due to ! excitem5t ( two fluoresc5t    
scre5s plac$ at diff]5t di/ances f !    
ca?ode4 ,b he soon p]ceiv$ t ! effect ( 
! fluoresc5ce 0 n in/antane\s1 & t !    
lapse ( "t might =m a great s\rce (     
error1 & he !n _h rec\rse to indirect   
me?ods4 ,x is possible1 by a simple     
calculation1 to e/imate ! deviations    
produc$ on ! rays by a magnetic & an    
electric field respectively z a function
 ( ! spe$ ( propagation & ( ! relation (
 ! *>ge to ! mat]ial mass ( ! electron4 
,! measurem5t ( ^! deviations w !n p]mit
 ?is spe$ & ?is relation to be asc]ta9$4
  ,o!r processes may be us$ :i* all give
 ! same two quantities by two suitably  
*os5 measurem5ts4 ,su* are ! radius ( ! 
curve tak5 by ! trajectory ( ! p5cil 9 a
 p]p5dicul> magnetic field & ! measure (
 ! fall ( pot5tial "u :i* ! dis*>ge     
takes place1 or ! measure ( ! total     
quantity ( electricity c>ri$ 9 "o second
 & ! measure ( ! calorific en]gy :i* may
 be giv51 dur+ ! same p]iod1 to a       

!rmo-electric junction4 ,! results agree
 z well z c be expect$1 hav+ reg>d to ! 
difficulty ( ! exp]im5ts2 ! values ( !  
spe$ agree also ) ^? :i* ,pr(essor      
,wie*]t has obta9$ by direct measurem5t4
  ,! spe$ nev] dep5ds on ! nature ( !   
gas conta9$ 9 ! ,crookes tube1 b v>ies )
 ! value ( ! fall ( pot5tial at !       
ca?ode4 ,x is ( ! ord] ( "o t5? ( ! spe$
 ( light1 & x may rise z high z "o ?ird4
 ,! ca?ode p>ticle !re=e goes ab\t ?ree 
?\s& times fa/] ?an ! e>? 9 its orbit4  
,! relation is also inv>iable1 ev5 :5 ! 
sub/ance ( :i* ! ca?ode is =m$ is *ang$ 
or "o gas is sub/itut$ = ano!r4 ,x is1  
on ! av]age1 a ?\s& times great] ?an !  
correspond+ relation 9 electrolysis4 ,z 
exp]im5t has %[n1 9 all ! circum/ances  
:]e x has be5 possible to effect        
measurem5ts1 ! equality ( ! *>ges c>ri$ 
by all corpuscules1 ions1 atoms1 etc41  
we ought to consid] t ! *>ge ( !        
electron is "h1 aga91 t ( a unival5t ion
 9 electrolysis1 & !re=e t its mass is  
only a small fraction ( t ( ! atom (    

hydrog51 viz41 ( ! ord] ( ab\t a ?\s&?  
"p4 ,?is is ! same result z t to :i* we 
7 l$ by ! /udy ( flames4  ,! ?or\gh     
exam9ation ( ! ca?ode radiation1 !n1    
confirms u 9 ! idea t e mat]ial atom c  
be dissociat$ & w yield an electron mu* 
small] ?an itself--& always id5tical    
:atev] ! matt] :5ce x comes1--! re/ ( ! 
atom rema9+ *>g$ ) a positive quantity  
equal & contr>y to t borne by !         
electron4 ,9 ! pres5t case ^! positive  
ions are no d\bt ^? t we aga9 meet ) 9 !
 canal rays4 ,pr(essor ,wi5 has %[n t _!
 mass is really1 9 fact1 ( ! ord] ( !   
mass ( atoms4 ,al?\gh !y are all =m$ (  
id5tical electrons1 !re may be v>i\s    
ca?ode rays1 because ! velocity is n    
exactly ! same = all electrons4 ,?us is 
expla9$ ! fact t we c sep>ate !m & t we 
c produce a sort ( spectrum by ! action 
( ! magnet1 or1 aga91 z ,m4 ,desl&res   
has %[n 9 a v int]e/+ exp]im5t1 by t (  
an electro/atic field4 ,?is also        
probably expla9s ! ph5om5a /udi$ by ,m4 
,vill>d1 & previ\sly po9t$ out4    #b4  

,,radioactive ,,sub/ances  ,ev5 9 ord9>y
 conditions1 c]ta9 sub/ances call$      
radioactive emit1 q outside any p>ticul>
 reaction1 radiations complex inde$1 b  
:i* pass ?r\gh fairly ?9 lay]s ( m9]als1
 impress photographic plates1 excite    
fluoresc5ce1 & ionize gases4 ,9 ^!      
radiations we aga9 f9d electrons :i* ?us
 escape spontane\sly f radioactive      
bodies4  ,x is n necess>y to give "h a  
hi/ory ( ! discov]y ( radium1 = e "o    
kn[s ! admirable rese>*es ( ,m4 &       
,madame ,curie4 ,b subsequ5t to ^! fir/ 
/udies1 a great numb] ( facts h         
accumulat$ = ! la/ six ye>s1 among :i*  
"s p f9d !mselves a little lo/4 ,x may1 
p]haps1 n be useless to indicate !      
ess5tial results actually obta9$4  ,!   
rese>*es on radioactive sub/ances h _!  
/>t+-po9t 9 ! discov]y ( ! rays (       
uranium made by ,m4 ,becqu]el 9 #ahif4  
,z e>ly z #ahfg ,niepce de ,/ ,victor   
prov$ t salts ( uranium impress$        
photographic plates 9 ! d>k2 b at t "t !
 ph5om5on c\ld only pass = a s+ul>ity   

attributable to phosphoresc5ce1 & !     
valuable rem>ks ( ,niepce fell into     
oblivion4 ,m4 ,becqu]el e/abli%$1 aft]  
"s hesitations natural 9 ! face (       
ph5om5a :i* seem$ s contr>y to accept$  
ideas1 t ! radiat+ prop]ty 0 absolutely 
indep5d5t ( phosphoresc5ce1 t all !     
salts ( uranium1 ev5 ! uran\s salts :i* 
are n phosphoresc5t1 give simil> radiant
 effects1 & t ^! ph5om5a correspond to a
 cont9u\s emission ( en]gy1 b d n seem  
to be ! result ( a /orage ( en]gy "u !  
influ5ce ( "s ext]nal radiation4        
,spontane\s & con/ant1 ! radiation is   
ins5sible to v>iations ( temp]ature &   
light4  ,! nature ( ^! radiations 0 n   
imm$iately und]/ood1#cb & _! prop]ties  
seem$ contradictory4 ,?is 0 because we 7
 n deal+ ) a s+le category ( rays4 ,b   
among/ all ! effects !re is "o :i*      
con/itutes = ! radiations tak5 z a :ole1
 a v]itable process = ! measurem5t (    
radioactivity4 ,?is is _! ioniz+ action 
on gases4 ,a v complete /udy ( !        
conductivity ( air "u ! influ5ce ( rays 

( uranium has be5 made by v>i\s         
physici/s1 p>ticul>ly by ,pr(essor      
,ru!r=d1 & has %[n t ! laws ( ! ph5om5on
 are ! same z ^? ( ! ionization due to !
 action ( ! ,rntg5 rays4  ,footnote #cb3
 ,9 8 "w on ,l'volution de la ,matire1  
,m4 ,gu/ave ,le ,bon recalls t 9 #ahig  
he publi%$ sev]al notes 9 ! ,acadmie des
 ,sci5ces1 9 :i* he ass]t$ t ! prop]ties
 ( uranium 7 only a p>ticul> case ( a v 
g5]al law1 & t ! radiations emitt$ did n
 pol>ize1 & 7 ak9 by _! prop]ties to !  
,x rays4  ,x 0 natural to ask "o's self 
if ! prop]ty discov]$ 9 salts ( uranium 
0 peculi> to ?is body1 or if x 7 n1 to a
 m or less degree1 a g5]al prop]ty (    
matt]4 ,madame ,curie & ,m4 ,s*midt1    
indep5d5tly ( ea* o!r1 made sy/ematic   
rese>*es 9 ord] to solve ! "q2 v>i\s    
comp\nds ( ne>ly all ! simple bodies at 
pres5t kn[n 7 ?us pass$ 9 review1 & x 0 
e/abli%$ t radioactivity 0 p>ticul>ly   
p]ceptible 9 ! comp\nds ( uranium &     
?orium1 & t x 0 an atomic prop]ty l9k$  
to ! matt] end[$ ) x1 & foll[+ x 9 all  

its comb9ations4 ,9 ! c\rse ( h]        
rese>*es ,madame ,curie obs]v$ t c]ta9  
pit*bl5des 7oxide ( uranium ore1 conta9+
 also b>ium1 bismu?1 etc47 7 f\r times m
 active 7activity be+ measur$ by !      
ph5om5on ( ! ionization ( ! air7 ?an    
metallic uranium4 ,n[1 no comp\nd       
conta9+ any o!r active metal ?an uranium
 or ?orium ought to %[ itself m active  
?an ^? metals !mselves1 s9ce ! prop]ty  
belongs to _! atoms4 ,x seem$1 !re=e1   
probable t !re exi/$ 9 pit*bl5des "s    
sub/ance yet unkn[n1 9 small quantities 
& m radioactive ?an uranium4  ,m4 &     
,madame ,curie !n comm5c$ ^? celebrat$  
exp]im5ts :i* br\ght !m to ! discov]y ( 
radium4 ,_! me?od ( rese>* has be5 ju/ly
 comp>$ 9 orig9ality & importance to !  
process ( spectrum analysis4 ,to isolate
 a radioactive sub/ance1 ! fir/ ?+ is to
 measure ! activity ( a c]ta9 comp\nd   
suspect$ ( conta9+ ?is sub/ance1 & ?is  
comp\nd is *emically sep>at$4 ,we !n    
aga9 take 9 h& all ! products obta9$1 & 
by measur+ _! activity anew1 x is       

asc]ta9$ :e!r ! sub/ance s\ght = has    
rema9$ 9 "o ( ^! products1 or is divid$ 
among !m1 & if s1 9 :at proportion4 ,!  
spectroscopic reaction :i* we may use 9 
! c\rse ( ?is sep>ation is a ?\s& times 
less s5sitive ?an obs]vation ( !        
activity by means ( ! electromet]4      
,?\gh ! pr9ciple on :i* ! op]ation ( !  
conc5tration ( ! radium re/s is         
admirable 9 its simplicity1 its         
application is nev]!less v labori\s4    
,tons ( uranium residues h to be treat$ 
9 ord] to obta9 a few decigrammes ( pure
 salts ( radium4 ,radium is *>act]is$ by
 a special spectrum1 & its atomic       
weight1 z det]m9$ by ,madame ,curie1 is 
#bbe2 x is consequ5tly ! high] homologue
 ( b>ium 9 "o ( ! gr\ps ( ,m5delef4     
,salts ( radium h 9 g5]al ! same *emical
 prop]ties z ! correspond+ salts (      
b>ium1 b are di/+ui%$ f !m by !         
diff]5ces ( solubility :i* all[ ( _!    
sep>ation1 & by _! enorm\s activity1 :i*
 is ab\t a hundr$ ?\s& times great] ?an 
t ( uranium4  ,radium produces v>i\s    

*emical & "s v int5se physiological     
reactions4 ,its salts are lum9\s 9 !    
d>k1 b ?is lum9osity1 at fir/ v bright1 
gradually dim9i%es z ! salts get old]4  
,we h "h to d ) a second>y reaction     
correlative to ! production ( !         
emanation1 aft] :i* radium und]goes !   
trans=mations :i* w be /udi$ lat] on4   
,! me?od ( analysis f\nd$ by ,m4 &      
,madame ,curie has enabl$ o!r bodies    
pres5t+ s5sible radioactivity to be     
discov]$4 ,! alkal9e metals appe> to    
possess ?is prop]ty 9 a slight degree4  
,rec5tly fall5 sn[ & m9]al wat]s manife/
 m>k$ action4 ,! ph5om5on may (t5 be    
due1 h[ev]1 to a radioactivity induc$ by
 radiations already exi/+ 9 ! atmosph]e4
 ,b ?is radioactivity h>dly atta9s !    
t5-?\s&? "p ( t pres5t$ by uranium1 or !
 t5-million? ( t app]ta9+ to radium4    
,two o!r bodies1 polonium & act9ium1 !  
"o *>act]is$ by ! special nature ( !    
radiations x emits & ! o!r by a p>ticul>
 spectrum1 seem likewise to exi/ 9      
pit*bl5de4 ,^! *emical prop]ties h n yet

 be5 p]fectly def9$2 ?us ,m4 ,debi]ne1  
:o discov]$ act9ium1 has be5 able to    
note ! active prop]ty :i* seems to      
belong to x1 sometimes 9 lan?anum1      
sometimes 9 neodynium4#cc ,x is prov$ t 
all extremely radioactive bodies are !  
seat ( incessant trans=mations1 & ev5 n[
 we _c /ate ! conditions "u :i* !y      
pres5t !mselves 9 a /rictly det]m9$ =m4 
,footnote #cc3 ,polonium has n[ be5 %[n 
to be no new elem5t1 b "o ( !           
trans=mation products ( radium4 ,radium 
itself is also ?\ght to be d]iv$ 9 "s   
mann]1 n yet asc]ta9$1 f uranium4 ,!    
same is ! case ) act9ium1 :i* is said to
 come 9 ! long run f uranium1 b n s     
directly z does radium4 ,all ?is is     
describ$ 9 ,pr(essor ,ru!r=d's          
,radioactive ,trans=mations 7,london1   
#aijf74--;,,ed4    #c4 ,,! ,,radiation  
,,( ,,! ,,radioactive ,,bodies ,,& ,,!  
,,emanation  ,to acquire exact notions z
 to ! nature ( ! rays emitt$ by !       
radioactive bodies1 x 0 necess>y to try 
to cause magnetic or electric =ces to   

act on !m s z to see :e!r !y behav$ 9 ! 
same way z light & ! ,x rays1 or :e!r l 
! ca?ode rays !y 7 deviat$ by a magnetic
 field4 ,?is "w 0 effect$ by ,pr(essor  
,giesel1 !n by ,m4 ,becqu]el1 ,pr(essor 
,ru!r=d1 & by _m o!r exp]im5t]s aft] !m4
 ,all ! me?ods :i* h already be5 m5tion$
 9 pr9ciple h be5 employ$ 9 ord] to     
discov] :e!r !y 7 electrifi$1 &1 if s1  
by electricity ( :at sign1 to measure _!
 spe$1 & to asc]ta9 _! degree (         
p5etration4  ,! g5]al result has be5 to 
di/+ui% ?ree sorts ( radiations1        
designat$ by ! lett]s alpha1 beta1      
gamma4  ,! alpha rays are positively    
*>g$1 & are project$ at a spe$ :i* may  
atta9 ! t5? ( t ( light2 ,m4,h4         
,becqu]el has %[n by ! aid ( photography
 t !y are deviat$ by a magnet1 &        
,pr(essor ,ru!r=d has1 on 8 side1 /udi$ 
?is deviation by ! electrical me?od4 ,! 
relation ( ! *>ge to ! mass is1 9 ! case
 ( ^! rays1 ( ! same ord] z 9 t ( ! ions
 ( electrolysis4 ,!y may !re=e be       
consid]$ z exactly analog\s to ! canal  

rays ( ,gold/e91 & we may attribute !m  
to a mat]ial transport ( corpuscles ( ! 
magnitude ( atoms4 ,! relatively        
consid]able size ( ^! corpuscles r5d]s  
!m v absorbable4 ,a flight ( a few      
millimetres 9 a gas suffices to r$uce _!
 numb] by "o-half4 ,!y h great ioniz+   
p[]4  ,! beta rays are on all po9ts     
simil> to ! ca?ode rays2 !y are1 z ,m4 &
 ,madame ,curie h %[n1 negatively *>g$1 
& ! *>ge !y c>ry is always ! same4 ,_!  
size is t ( ! electrons1 & _! velocity  
is g5]ally great] ?an t ( ! ca?ode rays1
 :ile x may become almo/ t ( light4 ,!y 
h ab\t a hundr$ times less ioniz+ p[]   
?an ! alpha rays4  ,! gamma rays 7      
discov]$ by ,m4 ,vill>d4#cd ,!y may be  
comp>$ to ! ,x rays2 l ! latt]1 !y are n
 deviat$ by ! magnetic field1 & are also
 extremely p5etrat+4 ,a /rip ( alum9ium 
five millimetres ?ick w /op ! o!r k9ds1 
b w all[ !m to pass4 ,on ! o!r h&1 _!   
ioniz+ p[] is #aj1jjj times less ?an t (
 ! alpha rays4  ,footnote #cd3 ,?is is  
admitt$ by ,pr(essor ,ru!r=d            

7,radio-,activity1 ,camb41 #aijd1 p4    
#ada7 & ,pr(essor ,soddy                
7,radio-,activity1 ,london1 #aijd1 p4   
#ff74 ,nei!r ,mr ,:e?am1 9 8 ,rec5t     
,developm5t ( ,physical ,sci5ce         
7,london1 #aijd7 nor ! ,hon4 ,r4,j4     
,/rutt 9 ,! ,becqu]el ,rays 7,london1   
same date71 bo? ( :om deal ) ! hi/orical
 side ( ! subject1 seem to h notic$ !   
fact4--,,ed4  ,to ^! radiations !re     
sometimes are add$ 9 ! c\rse ( exp]im5ts
 second>y radiations analog\s to ^? (   
,m4 ,sagnac1 & produc$ :5 ! alpha1 beta1
 or gamma rays meet v>i\s sub/ances4    
,?is complication has (t5 l$ to "s      
errors ( obs]vation4  ,phosphoresc5ce & 
fluoresc5ce seem especially to result f 
! alpha & beta rays1 p>ticul>ly f !     
alpha rays1 to :i* belongs ! mo/        
important "p ( ! total en]gy ( !        
radiation4 ,sir ,w4 ,crookes has inv5t$ 
a curi\s little app>atus1 ! sp9?>iscope1
 :i* enables u to exam9e !              
phosphoresc5ce ( ! bl5de excit$ by ^!   
rays4 ,by means ( a magnify+ glass1 a   

scre5 cov]$ ) sulphide ( z9c is kept "u 
obs]vation1 & 9 front ( x is dispos$1 at
 a di/ance ( ab\t half a millimetre1 a  
fragm5t ( "s salt ( radium4 ,we !n      
p]ceive multitudes ( brilliant po9ts on 
! scre51 :i* appe> & at once disappe>1  
produc+ a sc9tillat+ effect4 ,x seems   
probable t e p>ticle fall+ on ! scre5   
produces by its impact a di/urbance 9 ! 
neighb\r+ region1 & x is ?is di/urbance 
:i* ! eye p]ceives z a lum9\s po9t4     
,?us1 says ,sir ,w4 ,crookes1 ea* drop (
 ra9 fall+ on ! surface ( /ill wat] is n
 p]ceiv$ z a drop ( ra91 b by reason ( !
 slight spla% :i* x causes at ! mom5t ( 
impact1 & :i* is manife/$ by ridges &   
waves spread+ !mselves 9 circles4  ,!   
v>i\s radioactive sub/ances d n all give
 radiations ( id5tical con/itution4     
,radium & ?orium possess 9 some:at l>ge 
proportions ! ?ree k9ds ( rays1 & x is !
 same ) act9ium4 ,polonium conta9s      
especially alpha rays & a few gamma     
rays4#ce ,9 ! case ( uranium1 ! alpha   
rays h extremely slight p5etrat+ p[]1 & 

_c ev5 impress photographic plates4 ,b !
 wide/ diff]5ce betwe5 ! sub/ances      
proce$s f ! emanation4 ,radium1 9       
addition to ! ?ree gr\ps ( rays alpha1  
beta1 & gamma1 dis5gages cont9u\sly an  
extremely subtle emanation1 seem+ly     
almo/ impond]able1 b :i* may be1 = _m   
reasons1 look$ ^u z a vap\r ( :i* !     
ela/ic =ce is extremely feeble4         
,footnote #ce3 ,x has n[ be5 %[n t      
polonium :5 fre%ly sep>at$ emits beta   
rays also2 see ,dr ,logeman's pap] 9    
,proce$+s ( ! ,royal ,society1 ,a41 #f? 
,septemb] #aijf4--;,,ed4  ,m4 & ,madame 
,curie discov]$ z e>ly z #ahii t e      
sub/ance plac$ 9 ! neighb\rhood (       
radium1 itself acquir$ a radioactivity  
:i* p]si/$ = sev]al h\rs aft] ! removal 
( ! radium4 ,?is induc$ radioactivity   
seems to be c>ri$ to o!r bodies by !    
int]m$i>y ( a gas4 ,x goes r\nd         
ob/acles1 b !re mu/ exi/ betwe5 ! radium
 & ! sub/ance a free & cont9u\s space = 
! activation to take place2 x _c1 =     
in/ance1 d s ?r\gh a wall ( glass4  ,9 !

 case ( comp\nds ( ?orium ,pr(essor     
,ru!r=d discov]$ a simil> ph5om5on2 s9ce
 !n1 v>i\s physici/s1 ,pr(essor ,soddy1 
,miss ,brooks1 ,miss ,gates1 ,m4 ,danne1
 & o!rs1 h /udi$ ! prop]ties ( ^!       
emanations4  ,! sub/ance emanat$ c nei!r
 be weigh$ nor c its ela/ic =ce be      
asc]ta9$2 b its trans=mations may be    
foll[$1 z x is lum9\s1 & x is ev5 m     
c]ta9ly *>act]is$ by its ess5tial       
prop]ty1 i4e4 its radioactivity4 ,we    
also see t x c be decant$ l a gas1 t x w
 divide itself betwe5 two tubes (       
diff]5t capacity 9 ob$i5ce to ! law (   
,m>iotte1 & w cond5se 9 a refrig]at$    
tube 9 accordance ) ! pr9ciple ( ,watt1 
:ile x ev5 complies ) ! law (           
,gay-,lussac4  ,! activity ( ! emanation
 vani%es quickly1 & at ! end ( f\r days 
x has dim9i%$ by "o-half4 ,if a salt (  
radium is heat$1 ! emanation becomes m  
abundant1 & ! residue1 :i*1 h[ev]1 does 
n s5sibly dim9i% 9 weight1 w h lo/ all  
its radioactivity1 & w only recov] x by 
degrees4 ,pr(essor ,ru!r=d1 not)/&+ _m  

diff]5t attempts1 has be5 unable to make
 ?is emanation ent] into any *emical    
reaction4 ,if x be a gase\s body1 x mu/ 
=m "p ( ! argon gr\p1 &1 l its o!r      
memb]s1 be p]fectly in]t4  ,by /udy+ !  
spectrum ( ! gas dis5gag$ by a solution 
( salt ( radium1 ,sir ,william ,ramsay &
 ,pr(essor ,soddy rem>k$ t :5 ! gas is  
radioactive !re are fir/ obta9$ rays (  
gases belong+ to ! argon family1 !n by  
degrees1 z ! activity disappe>s1 !      
spectrum sl[ly *anges1 & f9ally pres5ts 
! *>act]i/ic aspect ( helium4  ,we "k t 
! exi/5ce ( ?is gas 0 fir/ discov]$ by  
spectrum analysis 9 ! sun4 ,lat] its    
pres5ce 0 not$ 9 our atmosph]e1 & 9 a   
few m9]als :i* happ5 to be ! v ones f   
:i* radium has be5 obta9$4 ,x might     
!re=e h be5 ! case t x pre-exi/$ 9 !    
gases extract$ f radium2 b a rem>kable  
exp]im5t by ,m4 ,curie & ,sir ,james    
,dew> seems to %[ conv9c+ly t ?is _c be 
s4 ,! spectrum ( helium nev] appe>s at  
fir/ 9 ! gas proce$+ f pure bromide (   
radium2 b x %[s itself1 on ! o!r h&1 v  

di/9ctly1 aft] ! radioactive            
trans=mations und]gone by ! salt4  ,all 
^! /range ph5om5a sugge/ bold hypo!ses1 
b to con/ruct !m ) any solidity !y mu/  
be support$ by ! greate/ possible numb] 
( facts4 ,be=e admitt+ a def9ite        
explanation ( ! ph5om5a :i* h _! seat 9 
! curi\s sub/ances discov]$ by !m1 ,m4 &
 ,madame ,curie consid]$1 ) a great deal
 ( reason1 t !y ought fir/ to enri* our 
k ) ! exact & precise facts relat+ to ^!
 bodies & to ! effects produc$ by !     
radiations !y emit4  ,?us ,m4 ,curie    
p>ticul>ly set himself to /udy ! mann] 9
 :i* ! radioactivity ( ! emanation is   
dissipat$1 & ! radioactivity t ?is      
emanation c induce on all bodies4 ,!    
radioactivity ( ! emanation dim9i%es 9  
accordance ) an expon5tial law4 ,!      
con/ant ( "t :i* *>act]ises ?is decrease
 is easily & exactly det]m9$1 & has a   
fix$ value1 indep5d5t ( ! conditions ( !
 exp]im5t z well z ( ! nature ( ! gas   
:i* is 9 contact ) ! radium & becomes   
*>g$ ) ! emanation4 ,! regul>ity ( !    

ph5om5on is s great t x c be us$ to     
measure "t3 9 #cihe seconds#cf !        
activity is always r$uc$ "o-half4       
,footnote #cf3 ,accord+ to ,pr(essor    
,ru!r=d1 9 #c4gg days4--,,ed            
,radioactivity induc$ on any body :i*   
has be5 = a long "t 9 pres5ce ( a salt (
 radium disappe>s m rapidly4 ,! ph5om5on
 appe>s1 moreov]1 m complex1 & ! =mula  
:i* expresses ! mann] 9 :i* ! activity  
dim9i%es mu/ conta9 two expon5tials4 ,to
 f9d x !oretically we h to imag9e t !   
emanation fir/ deposits on ! body 9 "q a
 sub/ance :i* is de/roy$ 9 giv+ bir? to 
a second1 ?is latt] disappe>+ 9 its turn
 by g5]at+ a ?ird4 ,! initial & f9al    
sub/ances w\ld be radioactive1 b !      
int]m$i>y "o1 n4 ,if1 moreov]1 ! bodies 
act$ on are br\ght to a temp]ature ( ov]
 #gjj1 !y appe> to lose by              
volatilisation c]ta9 sub/ances cond5s$ 9
 !m1 & at ! same "t _! activity         
disappe>s4  ,! o!r radioactive bodies   
behave 9 a simil> way4 ,bodies :i*      
conta9 act9ium are p>ticul>ly ri* 9     

emanations4 ,uranium1 on ! contr>y1 has 
none4#cg ,?is body1 nev]!less1 is ! seat
 ( trans=mations comp>able to ^? :i* !  
/udy ( emanations reveals 9 radium2 ,sir
 ,w4 ,crookes has sep>at$ f uranium a   
matt] :i* is n[ call$ uranium ,x4 ,?is  
matt] is at fir/ mu* m active ?an its   
p>5t1 b its activity dim9i%es rapidly1  
:ile ! ord9>y uranium1 :i* at ! "t ( !  
sep>ation loses its activity1 rega9s x  
by degrees4 ,9 ! same way1 ,pr(essors   
,ru!r=d & ,soddy h discov]$ a s-call$   
?orium ,x to be ! /age ?r\gh :i* ord9>y 
?orium has to pass 9 ord] to produce its
 emanation4#ch  ,footnote #cg3 ,pr(essor
 ,ru!r=d has lately /at$ t uranium may  
possibly produce an emanation1 b t its  
rate ( decay mu/ be too swift = its     
pres5ce to be v]ifi$ 7see ,radioactive  
,trans=mations1 p4 #afa74--;,,ed4       
,footnote #ch3 ,an act9ium ,x 0 also    
discov]$ by ,pr(essor ,giesel 7,jahrbu* 
d4 ,radioaktivitat1 i4 p4 #ceh1 #aijd74 
,s9ce ! above 0 writt51 ano!r product   
has be5 f\nd to int]v5e betwe5 ! ,x     

sub/ance & ! emanation 9 ! case (       
act9ium & ?orium4 ,!y h be5 nam$        
radio-act9ium & radio-?orium            
respectively4--,,ed4  ,x is n possible  
to give a complete table :i* %\ld1 z x  
71 repres5t ! g5ealogical tree ( ! v>i\s
 radioactive sub/ances4 ,sev]al au?ors h
 endeav\r$ to d s1 b 9 a premature      
mann]2 all ! affiliations are n at !    
pres5t "t yet p]fectly kn[n1 & x w no   
d\bt be ackn[l$g$ "s day t id5tical     
/ates h be5 describ$ "u diff]5t         
names4#ci  ,footnote #ci3 ,su* a table  
is giv5 on p4 #afi ( ,ru!r=d's          
,radioactive ,trans=mations4--,,ed4     
#d4 ,,! ,,disaggregation ,,( ,,matt] ,,&
 ,,atomic ,,en]gy  ,9 spite (           
unc]ta9ties :i* are n yet entirely      
remov$1 x _c be d5i$ t _m exp]im5ts r5d]
 x probable t 9 radioactive bodies we   
f9d ourselves witness+ v]itable         
trans=mations ( matt]4  ,pr(essor       
,ru!r=d1 ,pr(essor ,soddy1 & sev]al o!r 
physici/s1 h come to reg>d ^! ph5om5a 9 
! foll[+ way4 ,a radioactive body is    

compos$ ( atoms :i* h little /ability1 &
 are able to deta* !mselves spontane\sly
 f ! p>5t sub/ance1 & at ! same "t to   
divide !mselves into two ess5tial       
compon5t p>ts1 ! negative electron & its
 residue ! positive ion4 ,! fir/-nam$   
con/itutes ! beta1 & ! second ! alpha   
rays4  ,! emanation is c]ta9ly compos$ (
 alpha ions ) a few molecules agglom]at$
 r\nd !m4 ,pr(essor ,ru!r=d has1 9 fact1
 demon/rat$ t ! emanation is *>g$ )     
positive electricity2 & ?is emanation   
may1 9 turn1 be de/roy$ by giv+ bir? to 
new bodies4  ,aft] ! loss ( ! atoms :i* 
are c>ri$ (f by ! radiation1 ! rema9d] (
 ! body acquires new prop]ties1 b x may 
/ill be radioactive1 & aga9 lose atoms4 
,! v>i\s /ages t we meet ) 9 ! evolution
 ( ! radioactive sub/ance or ( its      
emanation1 correspond to ! v>i\s degrees
 ( atomic disaggregation4 ,pr(essors    
,ru!r=d & ,soddy h describ$ !m cle>ly 9 
! case ( uranium & radium4 ,z reg>ds    
?orium ! results are less satisfactory4 
,! evolution %\ld cont9ue until a /able 

atomic condition is f9ally rea*$1 :i*1  
because ( ?is /ability1 is no long]     
radioactive4 ,?us1 = in/ance1 radium    
w\ld f9ally be trans=m$ into helium4#dj 
,footnote #dj3 ,?is op9ion1 no d\bt =m$ 
:5 ,sir ,william ,ramsay's discov]y ( ! 
=mation ( helium f ! radium emanation 0 
fir/ made kn[n1 is n[ less t5able4 ,!   
late/ !ory is t ! alpha p>ticle is 9    
fact an atom ( helium1 & t ! f9al       
trans=mation product ( radium & ! o!r   
radioactive sub/ances is lead4 ,cf4     
,ru!r=d1 op4 cit4 passim4--,,ed4  ,x is 
possible1 by consid]ations analog\s to  
^? set =? above 9 o!r cases1 to arrive  
at an idea ( ! total numb] ( p>ticles p]
 second expell$ by "o gramme ( radium2  
,pr(essor ,ru!r=d 9 8 mo/ rec5t         
evaluation f9ds t ?is numb] approa*es   
#b4e x #ajaa4da ,by calculat+ f ! atomic
 weight ! numb] ( atoms probably conta9$
 9 ?is gramme ( radium1 & suppos+ ea*   
p>ticle lib]at$ to correspond to !      
de/ruction ( "o atom1 x is f\nd t "o    
half ( ! radium %\ld disappe> 9 #abhj   

ye>s2#db & f ?is we may conceive t x has
 n yet be5 possible to discov] any      
s5sible loss ( weight4 ,sir ,w4 ,ramsay 
& ,pr(essor ,soddy atta9$ a l result by 
endeav\r+ to e/imate ! mass ( !         
emanation by ! quantity ( helium        
produc$4  ,footnote #da3 ,see           
,radioactive ,trans=mations 7p4 #bea74  
,pr(essor ,ru!r=d says t ea* ( ! alpha  
ray products pres5t 9 "o gram ( radium  
product 7sic7 expels #f4b x #ajaj alpha 
p>ticles p] second4 ,he also rem>ks on !
 exp]im5tal difficulty ( accurately     
det]m9+ ! numb] ( alpha p>ticles expell$
 f radium p] second4--,,ed4  ,footnote  
#db3 ,see ,ru!r=d1 op4 cit4 p4          
#aej4--;,,ed4  ,if radium trans=ms      
itself 9 su* a way t its activity does n
 p]si/ ?r\gh\t ! ages1 x loses little by
 little ! provision ( en]gy x _h 9 !    
beg9n+1 & its prop]ties furni% no valid 
argum5t to oppose to ! pr9ciple ( !     
cons]vation ( en]gy4 ,to put ev]y?+ "r1 
we h only to recognise t radium possess$
 9 ! pot5tial /ate at its =mation a     

f9ite quantity ( en]gy :i* is consum$   
little by little4 ,9 ! same mann]1 a    
*emical sy/em compos$1 = in/ance1 ( z9c 
& sulphuric acid1 also conta9s 9 !      
pot5tial /ate en]gy :i*1 if we ret>d !  
reaction by any suitable arrangem5t--su*
 z by amalgamat+ ! z9c & by con/itut+ ) 
its elem5ts a batt]y :i* we cause to act
 on a resi/ance--may be made to exhau/  
itself z sl[ly z "o may desire4  ,!re c1
 !re=e1 be no?+ 9 any way surpris+ 9 !  
fact t a comb9ation :i*1 l ! atomic     
comb9ation ( radium1 is n /able--s9ce x 
disaggregates itself1--is capable (     
spontane\sly lib]at+ en]gy1 b :at may be
 a little a/oni%+1 at fir/ sight1 is !  
consid]able am\nt ( ?is en]gy4  ,m4     
,curie has calculat$ directly1 by ! aid 
( ! calorimet]1 ! quantity ( en]gy      
lib]at$1 measur+ x entirely 9 ! =m (    
heat4 ,! dis5gagem5t ( heat acc\nt$ = 9 
a gra9 ( radium is uni=m1 & am\nts to   
#ajj calories p] h\r4 ,x mu/ !re=e be   
admitt$ t an atom ( radium1 9           
disaggregat+ itself1 lib]ates #cj1jjj   

times m en]gy ?an a molecule ( hydrog5  
:5 ! latt] comb9es ) an atom ( oxyg5 to 
=m a molecule ( wat]4  ,we may ask      
ourselves h[ ! atomic edifice ( ! active
 body c be con/ruct$1 to conta9 s great 
a provision ( en]gy4 ,we w rem>k t su* a
 "q might be ask$ conc]n+ cases kn[n f !
 mo/ remote antiquity1 l t ( ! *emical  
sy/ems1 )\t any satisfactory answ] ev]  
be+ giv54 ,?is failure surprises no "o1 
= we get us$ to ev]y?+--ev5 to defeat4  
,:5 we come to deal ) a new problem we h
 really no "r to %[ ourselves m exact+2 
yet !re are f\nd p]sons :o refuse to    
admit ! hypo!sis ( ! atomic             
disaggregation ( radium because !y _c h 
set be=e !m a detail$ plan ( t complex  
:ole kn[n to u z an atom4  ,! mo/       
natural idea is p]haps ! "o sugge/$ by  
comp>ison ) ^? a/ronomical ph5om5a :]e  
our obs]vation mo/ readily all[s u to   
compreh5d ! laws ( motion4 ,x           
corresponds likewise to ! t5d5cy ev]    
pres5t 9 ! m9d ( man1 to comp>e !       
inf9itely small ) ! inf9itely great4 ,! 

atom may be reg>d$ z a sort ( sol> sy/em
 9 :i* electrons 9 consid]able numb]s   
gravitate r\nd ! sun =m$ by ! positive  
ion4 ,x may happ5 t c]ta9 ( ^! electrons
 are no long] reta9$ 9 _! orbit by !    
electric attraction ( ! re/ ( ! atom1 & 
may be project$ f x l a small planet or 
comet :i* escapes t[>ds ! /ell> spaces4 
,! ph5om5a ( ! emission ( light compels 
u to ?9k t ! corpuscles revolve r\nd !  
nucleus ) extreme velocities1 or at !   
rate ( ?\s&s ( billions ( evolutions p] 
second4 ,x is easy to conceive f ?is t1 
not)/&+ its lightness1 an atom ?us      
con/itut$ may possess an enorm\s        
en]gy4#dc  ,footnote #dc3 ,?is view ( ! 
case has be5 made v cle> by ,m4 ,gu/ave 
le ,bon 9 ,l'volution de la ,matire     
7,p>is1 #aijf74 ,see especially pp4     
#cf-eb1 :]e ! am\nt ( ! suppos$         
intra-atomic en]gy is calculat$4--,,ed4 
,o!r au?ors imag9e t ! en]gy ( !        
corpuscles is pr9cipally due to !       
extremely rapid rotations ( ^? elem5ts  
on _! own axes4 ,"l ,kelv9 lately drew  

up on ano!r model ! plan ( a radioactive
 atom capable ( eject+ an electron ) a  
consid]able vis viva4 ,he supposes a    
sph]ical atom =m$ ( conc5tric lay]s (   
positive & negative electricity dispos$ 
9 su* a way t its ext]nal action is     
null1 & t1 nev]!less1 ! =ce emanat$ f ! 
c5tre may be repell5t = c]ta9 values :5 
! electron is )9 x4  ,! mo/ prud5t      
physici/s & ^? mo/ respectful to        
e/abli%$ pr9ciples may1 )\t any         
scruples1 admit ! explanation ( !       
radioactivity ( radium by a dislocation 
( its molecul> edifice4 ,! matt] ( :i* x
 is con/itut$ evolves f an admitt$ly    
un/able initial /ate to ano!r /able "o4 
,x is1 9 a way1 a sl[ allotropic        
trans=mation :i* takes place by means ( 
a me*anism reg>d+ :i*1 9 %ort1 we h no m
 in=mation ?an we h reg>d+ o!r analog\s 
trans=mations4 ,! only a/oni%m5t we c   
legitimately feel is d]iv$ f ! ?\ght t  
we are sudd5ly & deeply p5etrat+ to ! v 
he>t ( ?+s4  ,b ^? p]sons :o h a little 
m h>dihood d n easily resi/ ! temptation

 ( =m+ d>+ g5]alisations4 ,?us x w occur
 to "s t ?is prop]ty1 already discov]$ 9
 _m sub/ances :]e x exi/s 9 m or less   
/rik+ degree1 is1 ) diff]5ces (         
int5sity1 common to all bodies1 & t we  
are ?us confront$ by a ph5om5on d]iv$ f 
an ess5tial quality ( matt]4 ,q rec5tly1
 ,pr(essor ,ru!r=d has demon/rat$ 9 a   
f9e s]ies ( exp]im5ts t ! alpha p>ticles
 ( radium cease to ionize gases :5 !y   
are made to lose _! velocity1 b t !y d n
 on t acc\nt cease to exi/4 ,x may foll[
 t _m bodies emit simil> p>ticles )\t   
be+ easily p]ceiv$ to d s2 s9ce !       
electric action1 by :i* ?is ph5om5on (  
radioactivity is g5]ally manife/$1 w\ld1
 9 ?is case1 be b v weak4  ,if we ?us   
believe radioactivity to be an          
absolutely g5]al ph5om5on1 we f9d       
ourselves face to face ) a new problem4 
,! trans=mation ( radioactive bodies c  
no long] be assimilat$ to allotropic    
trans=mations1 s9ce ?us no f9al =m c\ld 
ev] be atta9$1 & ! disaggregation w\ld  
cont9ue indef9itely up to ! complete    

dislocation ( ! atom4#dd ,! ph5om5on    
might1 x is true1 h a duration ( p]haps 
?\s&s ( millions ( c5turies1 b ?is      
duration is b a m9ute 9 ! inf9ity ( "t1 
& matt]s little4 ,our habits ( m9d1 if  
we adopt su* a conception1 w be none !  
less v deeply di/urb$4 ,we %all h to    
ab&on ! idea s in/9ctively de> to u t   
matt] is ! mo/ /able ?+ 9 ! univ]se1 &  
to admit1 on ! contr>y1 t all bodies    
:atev] are a k9d ( explosive decompos+ )
 extreme sl[ness4 ,!re is 9 ?is1 :atev] 
may h be5 said1 no?+ contr>y to any ( ! 
pr9ciples on :i* ! sci5ce ( en]getics   
re/s2 b an hypo!sis ( ?is nature c>ries 
) x consequ5ces :i* ought 9 ! highe/    
degree to int]e/ ! philosoph]1 & we all 
"k ) :at allur+ boldness ,m4 ,gu/ave ,le
 ,bon has develop$ all ^! consequ5ces 9 
8 "w on ! evolution ( matt]4#de         
,footnote #dd3 ,?is is ! ma9 cont5tion (
 ,m4 ,gu/ave ,le ,bon 9 8 "w la/        
quot$4--,,ed4  ,footnote #de3 ,see la/  
note4--,,ed4  ,!re is h>dly a physici/  
:o does n at ! pres5t day adopt 9 "o    

%ape or ano!r ! balli/ic hypo!sis4 ,all 
new facts are co-ord9at$ s happily by x1
 t x m & m satisfies our m9ds2 b x _c be
 ass]t$ t x =ces itself on our          
convictions ) irresi/ible weight4 ,ano!r
 po9t ( view appe>$ m plausible & simple
 at ! outset1 :5 !re seem$ reason to    
consid] ! en]gy radiat$ by radioactive  
bodies z inexhau/ible4 ,x 0 ?\ght t !   
s\rce ( ?is en]gy 0 to be look$ = )\t ! 
atom1 & ?is idea may p]fectly well he   
ma9ta9$ at ! pres5t day4  ,radium on ?is
 hypo!sis mu/ be consid]$ z a trans=m]  
borr[+ en]gy f ! ext]nal m$ium & return+
 x 9 ! =m ( radiation4 ,x is n          
impossible1 ev51 to admit t ! en]gy :i* 
! atom ( radium )draws f ! surr\nd+     
m$ium may s]ve to keep up1 n only ! heat
 emitt$ & its complex radiation1 b also 
! dissociation1 suppos$ to be endo!rmic1
 ( ?is atom4 ,su* seems to be ! idea (  
,m4 ,debi]ne & also ( ,m4 ,sagnac4 ,x   
does n seem to accord ) ! exp]im5ts t   
?is borr[$ en]gy c be a "p ( ! heat ( ! 
ambi5t m$ium2 &1 inde$1 su* a ph5om5on  

w\ld be contr>y to ! pr9ciple ( ,c>not  
if we wi%$ 7?\gh we h se5 h[ disputable 
is ?is ext5sion7 to ext5d ?is pr9ciple  
to ! ph5om5a :i* are produc$ 9 ! v bosom
 ( ! atom4  ,we may also address        
ourselves to a m noble =m ( en]gy1 & ask
 ourselves :e!r we are n1 = ! fir/ "t1 9
 pres5ce ( a trans=mation (             
gravitational en]gy4 ,x may be s+ul>1 b 
x is n absurd1 to suppose t ! unit (    
mass ( radium is n atta*$ to ! e>? ) !  
same int5sity z an in]t body4 ,m4       
,sagnac has comm5c$ "s exp]im5ts1 z yet 
unpubli%$1 9 ord] to /udy ! laws ( !    
fall ( a fragm5t ( radium4 ,!y are      
necess>ily v delicate1 & ! en]getic &   
+5i\s physici/ has n yet succe$$ 9 f9i%+
 !m4#df ,let u suppose t he succe$s 9   
demon/rat+ t ! int5sity ( gravity is    
less = radium ?an = ! plat9um or ! copp]
 ( :i* ! p5dulums us$ to illu/rate ! law
 ( ,newton are g5]ally made2 x w\ld !n  
be possible /ill to ?9k t ! laws (      
univ]sal attraction are p]fectly exact z
 reg>ds ! />s1 & t pond]ability is      

really a p>ticul> case ( univ]sal       
attraction1 :ile 9 ! case ( radioactive 
bodies "p ( ! gravitational en]gy is    
trans=m$ 9 ! c\rse ( its evolution &    
appe>s 9 ! =m ( active radiation4       
,footnote #df3 ,9 reality ,m4 ,sagnac   
op]at$ 9 ! conv]se mann]4 ,he took two  
equal weights ( a salt ( radium & a salt
 ( b>ium1 :i* he made oscillate "o aft] 
! o!r 9 a torsion balance4 ,_h !        
durations ( oscillation be5 diff]5t1 x  
might be conclud$ t ! me*anical mass is 
n ! same = radium z = b>ium4  ,b = ?is  
explanation to be admitt$1 x w\ld       
evid5tly ne$ to be support$ by v num]\s 
facts4 ,x might1 no d\bt1 appe> /ill m  
probable t ! en]gy borr[$ f ! ext]nal   
m$ium by radium is "o ( ^? /ill unkn[n  
to u1 b ( :i* a vague in/9ct causes u to
 suspect ! exi/5ce ar\nd u4 ,x is       
indisputable1 moreov]1 t ! atmosph]e 9  
all directions is furr[$ ) active       
radiations2 ^? ( radium may be second>y 
radiations reflect$ by a k9d ( resonance
 ph5om5on4  ,c]ta9 exp]im5ts by         

,pr(essors ,el/] & ,geitel1 h[ev]1 are n
 fav\rable to ?is po9t ( view4 ,if an   
active body be surr\nd$ by a radioactive
 envelope1 a scre5 %\ld prev5t ?is body 
f receiv+ any impression f outside1 &   
yet !re is no dim9ution app>5t 9 !      
activity pres5t$ by a c]ta9 quantity (  
radium :5 x is l[]$ to a dep? ( #hjj    
metres "u gr\nd1 9 a region conta9+ a   
notable quantity ( pit*bl5de4 ,^!       
negative results are1 on ! o!r h&1 s _m 
successes = ! p>tisans ( ! explanation (
 radioactivity by atomic en]gy4         
,,*apt] ,x  ,,! ,,e!r ,,& ,,matt]    #a4
 ,,! ,,relations ,,betwe5 ,,! ,,e!r ,,& 
,,matt]  ,= "s "t pa/ x has be5 ! m or  
less av[$ ambition ( physici/s to       
con/ruct ) ! p>ticles ( e!r all possible
 =ms ( corporeal exi/5ce2 b our k ( !   
inmo/ nature ( ?+s has hi!rto seem$ too 
limit$ = u to attempt su* an ent]prise )
 any *ance ( success4 ,! electronic     
hypo!sis1 h[ev]1 :i* has furni%$ a      
satisfactory image ( ! mo/ curi\s       
ph5om5a produc$ 9 ! bosom ( matt]1 has  

also l$ to a m complete electromagnetic 
!ory ( ! e!r ?an t ( ,maxwell1 & ?is    
tw(old result has giv5 bir? to ! hope ( 
arriv+ by means ( ?is hypo!sis at a     
complete co-ord9ation ( ! physical _w4  
,! ph5om5a ^: /udy may br+ u to ! v     
?re%old ( ! problem1 are ^? 9 :i* !     
connections betwe5 matt] & ! e!r appe>  
cle>ly & 9 a relatively simple mann]4   
,?us 9 ! ph5om5a ( emission1 pond]able  
matt] is se5 to give bir? to waves :i*  
are transmitt$ by ! e!r1 & by ! ph5om5a 
( absorption x is prov$ t ^! waves      
disappe> & excite modifications 9 !     
int]ior ( ! mat]ial bodies :i* receive  
!m4 ,we "h cat* 9 op]ation actual       
reciprocal actions & reactions betwe5 ! 
e!r & matt]4 ,if we c\ld ?or\ghly       
compreh5d ^! actions1 we %\ld no d\bt be
 9 a position to fill up ! gap :i*      
sep>ates ! two regions sep>ately conqu]$
 by physical sci5ce4  ,9 rec5t ye>s     
num]\s rese>*es h suppli$ valuable      
mat]ials :i* ought to be utiliz$ by ^?  
endeav\r+ to con/ruct a !ory (          

radiation4 ,we are1 p]haps1 /ill ill    
in=m$ z to ! ph5om5a ( lum9esc5ce 9 :i* 
undulations are produc$ 9 a complex     
mann]1 z 9 ! case ( a /ick ( moi/       
phosphorus :i* is lum9esc5t 9 ! d>k1 or 
9 t ( a fluoresc5t scre54 ,b we are v   
well acqua9t$ ) emission or absorption  
by inc&esc5ce1 :]e ! only trans=mation  
is t ( calorific into radiat+ en]gy1 or 
vice v]sa4 ,x is 9 ?is case alone t c be
 correctly appli$ ! celebrat$           
demon/ration by :i* ,kir*h(f e/abli%$1  
by consid]ations borr[$ f !rmodynamics1 
! proportional relations betwe5 ! p[] ( 
emission & t ( absorption4  ,9 treat+ ( 
! measurem5t ( temp]ature1 ,i h already 
po9t$ out ! exp]im5ts ( ,pr(essors      
,lumm] & ,pr+%eim & ! !oretical rese>*es
 ( ,/ephan & ,pr(essor ,wi54 ,we may    
consid] t at ! pres5t day ! laws ( !    
radiation ( d>k bodies are tol]ably well
 kn[n1 &1 9 p>ticul>1 ! mann] 9 :i* ea* 
elem5t>y radiation increases ) !        
temp]ature4 ,a few d\bts1 h[ev]1 subsi/ 
) respect to ! law ( ! di/ribution (    

en]gy 9 ! spectrum4 ,9 ! case ( real &  
solid bodies ! results are naturally    
less simple ?an 9 t ( d>k bodies4 ,"o   
side ( ! "q has be5 specially /udi$ on  
acc\nt ( its great practical int]e/1 t  
is to say1 ! fact t ! relation ( !      
lum9\s en]gy to ! total am\nt radiat$ by
 a body v>ies ) ! nature ( ?is la/2 & ! 
k ( ! conditions "u :i* ?is relation    
becomes mo/ consid]able l$ to ! discov]y
 ( inc&esc5t light+ by gas 9 !          
,au]-,welsba* mantle1 & to ! sub/itution
 = ! c>bon ?read 9 ! electric light bulb
 ( a filam5t ( osmium or a small rod (  
magnesium1 z 9 ! ,n]n/ lamp4 ,c>eful    
measurem5ts effect$ by ,m4 ,f]y h       
furni%$1 9 p>ticul>1 important in=mation
 on ! radiation ( ! :ite oxides2 b !    
ph5om5a notic$ h n yet f\nd a           
satisfactory int]pretation4 ,moreov]1 ! 
radiation ( calorific orig9 is "h       
accompani$ by a m or less important     
lum9esc5ce1 & ! problem becomes v       
complex4  ,9 ! same way t1 = ! purpose (
 kn[+ ! con/itution ( matt]1 x fir/     

occurr$ to u to inve/igate gases1 :i*   
appe> to be molecul> edifices built on a
 m simple & uni=m plan ?an solids1 we   
ought naturally to ?9k t an exam9ation (
 ! conditions 9 :i* emission &          
absorption are produc$ by gase\s bodies 
might be em95tly pr(itable1 & might     
p]haps reveal ! me*anism by :i* !       
relations betwe5 ! molecule ( ! e!r & ! 
molecule ( matt] might be e/abli%$4     
,un=tunately1 if a gas is n absolutely  
incapable ( emitt+ "s sort ( rays by    
simple heat1 ! radiation ?us produc$1 no
 d\bt by reason ( ! slightness ( ! mass 
9 play1 always rema9s ( mod]ate         
int5sity4 ,9 ne>ly all ! exp]im5ts1 new 
en]gies ( *emical or electrical orig9   
come into =ce4 ,on inc&esc5ce1          
lum9esc5ce is sup]pos$2 & ! advantage   
:i* might h be5 expect$ f ! simplicity (
 ! m$ium vani%es ?r\gh ! complication ( 
! circum/ances 9 :i* ! ph5om5on is      
produc$4  ,pr(essor ,pr+%eim has        
succe$$1 9 c]ta9 cases1 9 f9d+ ! divid+ 
l9e betwe5 ! ph5om5a ( lum9esc5ce & t ( 

inc&esc5ce4 ,?us ! =m] takes a pr$om9at+
 importance :5 ! gas is r5d]$ lum9\s by 
electrical dis*>ges1 & *emical          
trans=mations1 especially1 play a       
prepond]ant rle 9 ! emission ( !        
spectrum ( flames :i* conta9 a sal9e    
vap\r4 ,9 all ! ord9>y exp]im5ts (      
spectrum analysis ! laws ( ,kir*h(f _c  
!re=e be consid]$ z e/abli%$1 & yet !   
relation betwe5 emission & absorption is
 g5]ally tol]ably well v]ifi$4 ,no d\bt 
we are "h 9 pres5ce ( a k9d ( resonance 
ph5om5on1 ! gase\s atoms ent]+ into     
vibration :5 solicit$ by ! e!r by a     
motion id5tical ) ! "o !y are capable ( 
communicat+ to x4  ,if we are n yet v f>
 advanc$ 9 ! /udy ( ! me*anism ( !      
production ( ! spectrum1#dg we are1 on !
 o!r h&1 well acqua9t$ ) its            
con/itution4 ,! extreme confusion :i* ! 
spectra ( ! l9es ( ! gases seem$ to     
pres5t is n[1 9 great "p at lea/1 cle>$ 
up4 ,balm] gave "s "t s9ce1 9 ! case ( !
 hydrog5 spectrum1 an empirical =mula   
:i* enabl$ ! rays discov]$ lat] by an   

em95t a/ronom]1 ,m4 ,desl&res1 to be    
repres5t$2 b s9ce !n1 bo? 9 ! cases (   
l9e & b& spectra1 ! lab\rs ( ,pr(essor  
,rydb]g1 ( ,m4 ,desl&res1 ( ,pr(essors  
,kayz] & ,runge1 & ( ,m4 ,?iele1 h      
enabl$ u to compreh5d1 9 _! smalle/     
details1 ! laws ( ! di/ribution ( l9es &
 b&s4  ,footnote #dg3 ,_m !ories z to ! 
cause ( ! l9es & b&s ( ! spectrum h be5 
put =w>d s9ce ?is 0 writt51 among :i* t 
( ,pr(essor ,/>k 7= :i* see             
,physikalis*e ,zeits*rift = #aijf1      
passim7 is p]haps ! mo/ advanc$4 ,t (   
,m4 ,jean ,becqu]el1 :i* w\ld attribute 
x to ! vibration )9 ! atom ( bo?        
negative & positive electrons1 also     
des]ves notice4 ,a popul> acc\nt ( ?is  
is giv5 9 ! ,a!num ( #bj? ,april        
#aijg4--;,,ed4  ,^! laws are simple1 b  
some:at s+ul>4 ,! radiations emitt$ by a
 gas _c be comp>$ to ! notes to :i* a   
sonor\s body gives bir?1 nor ev5 to !   
mo/ complicat$ vibrations ( any ela/ic  
body4 ,! numb] ( vibrations ( ! diff]5t 
rays are n ! successive multiples ( "o &

 ! same numb]1 & x is n a "q ( a        
fundam5tal radiation & its h>monics1    
:ile--& ?is is an ess5tial diff]5ce--!  
numb] ( vibrations ( ! radiation t5d    
t[>ds a limit :5 ! p]iod dim9i%es       
inf9itely in/ead ( con/antly increas+1 z
 w\ld be ! case ) ! vibrations ( s\nd4  
,?us ! assimilation ( ! lum9\s to !     
ela/ic vibration is n correct4 ,once    
aga9 we f9d t ! e!r does n behave l     
matt] :i* obeys ! ord9>y laws (         
me*anics1 & e !ory mu/ take full acc\nt 
( ^! curi\s peculi>ities :i* exp]im5t   
reveals4  ,ano!r diff]5ce1 likewise v   
important1 betwe5 ! lum9\s & ! sonor\s  
vibrations1 :i* also po9ts out h[ little
 analog\s c be ! con/itutions ( ! m$ia  
:i* transmit ! vibrations1 appe>s 9 !   
ph5om5a ( disp]sion4 ,! spe$ (          
propagation1 :i*1 z we h se5 :5 discuss+
 ! measurem5t ( ! velocity ( s\nd1      
dep5ds v little on ! musical note1 is n 
at all ! same 9 ! case ( ! v>i\s        
radiations :i* c be propagat$ 9 ! same  
sub/ance4 ,! index ( refraction v>ies ) 

! duration ( ! p]iod1 or1 if y w1 ) !   
l5g? ( wave 9 vacuo :i* is proportion$  
to ?is duration1 s9ce 9 vacuo ! spe$ (  
propagation is entirely ! same = all    
vibrations4  ,cau*y 0 ! fir/ to propose 
a !ory on :i* o!r attempts h be5        
modell$2 = example1 ! v int]e/+ & simple
 "o ( ,briot4 ,?is la/-nam$ suppos$ t ! 
lum9\s vibration c\ld n p]ceptibly drag 
) x ! molecul> mat]ial ( ! m$ium across 
:i* x is propagat$1 b t matt]1          
nev]!less1 reacts on ! e!r ) an int5sity
 proportional to ! elongation1 9 su* a  
mann] z t5ds to br+ x back to its       
position ( equilibrium4 ,) ?is simple   
hypo!sis we c fairly well int]pret !    
ph5om5a ( ! disp]sion ( light 9 ! case (
 transp>5t sub/ances2 b f> f well1 z ,m4
 ,c>vallo has not$ 9 "s extremely c>eful
 exp]im5ts1 ! disp]sion ( ! infra-r$    
spectrum1 & n at all ! peculi>ities     
pres5t$ by absorb5t sub/ances4  ,m4     
,b\ss9esq arrives at almo/ simil>       
results1 by attribut+ disp]sion1 on !   
o!r h&1 to ! p>tial dragg+ along (      

pond]able matt] & to its action on !    
e!r4 ,by comb9+1 9 a measure1 z 0       
subsequ5tly done by ,m4 ,b\ss9esq1 ! two
 hypo!ses1 =mulas c be e/abli%$ f> bett]
 9 accord ) all ! kn[n facts4  ,^! facts
 are some:at complex4 ,x 0 at fir/ ?\ght
 t ! index always v>i$ 9 inv]se ratio to
 ! wave-l5g?1 b num]\s sub/ances h be5  
discov]$ :i* pres5t ! ph5om5on (        
abnormal disp]sion--t is to say1        
sub/ances 9 :i* c]ta9 radiations are    
propagat$1 on ! contr>y1 ! m quickly !  
%ort] _! p]iod4 ,?is is ! case ) gases  
!mselves1 z demon/rat$1 = example1 by a 
v elegant exp]im5t ( ,m4 ,becqu]el on ! 
disp]sion ( ! vap\r ( sodium4 ,moreov]1 
x may happ5 t yet m complications may be
 met )1 z no sub/ance is transp>5t = !  
:ole ext5t ( ! spectrum4 ,9 ! case (    
c]ta9 radiations ! spe$ ( propagation   
becomes nil1 & ! index %[s sometimes a  
maximum & sometimes a m9imum4 ,all ^?   
ph5om5a are 9 close relation ) ^? (     
absorption4  ,x is1 p]haps1 ! =mula     
propos$ by ,helmholtz :i* be/ acc\nts = 

all ^! peculi>ities4 ,helmholtz came to 
e/abli% ?is =mula by suppos+ t !re is a 
k9d ( friction betwe5 ! e!r & matt]1    
:i*1 l t ex]cis$ on a p5dulum1 "h       
produces a d\ble effect1 *ang+1 on ! "o 
h&1 ! duration ( ?is oscillation1 &1 on 
! o!r1 gradually damp+ x4 ,he fur!r     
suppos$ t pond]able matt] is act$ on by 
ela/ic =ces4 ,! !ory ( ,helmholtz has ! 
great advantage ( repres5t+1 n only !   
ph5om5a ( disp]sion1 b also1 z ,m4      
,c>vallo has po9t$ out1 ! laws (        
rotatory pol>ization1 its disp]sion &   
o!r ph5om5a1 among !m ! di*roism ( !    
rotatory m$ia discov]$ by ,m4 ,cotton4  
,9 ! e/abli%m5t ( ^! !ories1 ! language 
( ord9>y optics has always be5 employ$4 
,! ph5om5a are look$ ^u z due to        
me*anical de=mations or to movem5ts     
gov]n$ by c]ta9 =ces4 ,! electromagnetic
 !ory leads1 z we h se51 to ! employm5t 
( o!r images4 ,m4,h4 ,po9c>1 &1 aft]    
him1 ,helmholtz1 h bo? propos$          
electromagnetic !ories ( disp]sion4 ,on 
exam9+ ?+s closely1 x w be f\nd t !re   

are n1 9 tru?1 9 ! two ways ( reg>d+ !  
problem1 two equival5t translations (   
ext]ior reality4 ,! electrical !ory     
gives u to und]/&1 mu* bett] ?an !      
me*anical "o1 t 9 vacuo ! disp]sion     
ought to be /rictly null1 & ?is abs5ce (
 disp]sion appe>s to be confirm$ )      
extraord9>y precision by a/ronomical    
obs]vations4 ,?us ! obs]vation1 (t5     
repeat$1 & at diff]5t times ( ye>1      
proves t 9 ! case ( ! /> ,algol1 ! light
 ( :i* takes at lea/ f\r ye>s to rea* u1
 no s5sible diff]5ce 9 coloration       
accompanies ! *anges 9 brilliancy4      
#b4 ,,! ,,!ory ,,( ,,lor5tz  ,purely    
me*anical consid]ations h !re=e fail$ to
 give an entirely satisfactory          
int]pretation ( ! ph5om5a 9 :i* ev5 !   
simple/ relations betwe5 matt] & ! e!r  
appe>4 ,!y w\ld1 evid5tly1 be /ill m    
insuffici5t if us$ to expla9 c]ta9      
effects produc$ on matt] by light1 :i*  
c\ld n1 )\t grave difficulties1 be      
attribut$ to movem5t2 = in/ance1 !      
ph5om5a ( electrification "u ! influ5ce 

( c]ta9 radiations1 or1 aga91 *emical   
reactions su* z photographic            
impressions4  ,! problem _h to be       
approa*$ by ano!r road4 ,!              
electromagnetic !ory 0 a /ep 9 advance1 
b x comes to a /&/ill1 s to speak1 at ! 
mom5t :5 ! e!r p5etrates into matt]4 ,if
 we wi% to g deep] into ! inw>dness ( ! 
ph5om5a1 we mu/ foll[1 = example1       
,pr(essor ,lor5tz or ,dr ,l>mor1 & look 
) !m = a mode ( repres5tation :i*       
appe>s1 besides1 to be a natural        
consequ5ce ( ! fundam5tal ideas =m+ !   
basis ( ,h]tz's exp]im5ts4  ,! mom5t we 
look ^u a wave 9 ! e!r z an             
electromagnetic wave1 a molecule :i*    
emits light ought to be consid]$ z a k9d
 ( excitant4 ,we are ?us l$ to suppose t
 9 ea* radiat+ molecule !re are "o or   
sev]al electrifi$ p>ticles1 animat$ ) a 
to-&-fro movem5t r\nd _! positions (    
equilibrium1 & ^! p>ticles are c]ta9ly  
id5tical ) ^? electrons ! exi/5ce ( :i* 
we h already admitt$ = s _m o!r reasons4
  ,9 ! simple/ !ory1 we w imag9e an     

electron :i* may be displac$ f its      
position ( equilibrium 9 all directions1
 & is1 9 ?is displacem5t1 submitt$ to   
attractions :i* communicate to x a      
vibration l a p5dulum4 ,^! movem5ts are 
equival5t to t9y curr5ts1 & ! mobile    
electron1 :5 animat$ ) a consid]able    
velocity1 mu/ be s5sitive to ! action ( 
! magnet :i* modifies ! =m ( !          
trajectory & ! value ( ! p]iod4 ,?is    
almo/ direct consequ5ce 0 p]ceiv$ by    
,lor5tz1 & x l$ him to ! new idea t     
radiations emitt$ by a body ought to be 
modifi$ by ! action ( a /rong           
electromagnet4  ,an exp]im5t enabl$ ?is 
prevision to be v]ifi$4 ,x 0 made1 z is 
well kn[n1 z e>ly z #ahif by ,zeeman2 & 
! discov]y produc$ a legitimate         
s5sation4 ,:5 a flame is subject$ to !  
action ( a magnetic field1 a brilliant  
l9e is decompos$ 9 conditions m or less 
complex :i* an att5tive /udy1 h[ev]1    
all[s u to def9e4 ,accord+ to :e!r !    
obs]vation is made 9 a plane normal to !
 magnetic field or 9 ! same direction1 !

 l9e trans=ms itself into a triplet or  
d\blet1 & ! new l9es are pol>iz$        
rectil9e>ly or circul>ly4  ,^! are !    
precise ph5om5a :i* ! calculation       
=etells3 ! analysis ( ! modifications   
und]gone by ! light supplies1 moreov]1  
valuable in=mation on ! electron itself4
 ,f ! direction ( ! circul> vibrations (
 ! greate/ frequ5cy we c det]m9e ! sign 
( ! electric *>ge 9 motion & we f9d x to
 be negative4 ,b1 fur!r ?an ?is1 f !    
v>iation ( ! p]iod we c calculate !     
relation ( ! =ce act+ on ! electron to  
its mat]ial mass1 &1 9 addition1 !      
relation ( ! *>ge to ! mass4 ,we !n f9d 
= ?is relation precisely t value :i* we 
h already met ) s _m times4 ,su* a      
co9cid5ce _c be =tuit\s1 & we h ! "r to 
believe t ! electron reveal$ by ! lum9\s
 wave :i* emanates f x1 is really ! same
 z ! "o made kn[n to u by ! /udy ( !    
ca?ode rays & ( ! radioactive sub/ances4
  ,h[ev]1 ! elem5t>y !ory does n suffice
 to int]pret ! complications :i* lat]   
exp]im5ts h reveal$4 ,! physici/s mo/   

qualifi$ to effect measurem5ts 9 ^!     
delicate optical que/ions--,m4 ,cornu1  
,mr ,pre/on1 ,m4 ,cotton1 ,,mm4         
,becqu]el & ,desl&res1 ,m4 ,broca1      
,pr(essor ,mi*elson1 & o!rs--h po9t$ out
 "s rem>kable peculi>ities4 ,?us 9 "s   
cases ! numb] ( ! compon5t rays         
dissociat$ by ! magnetic field may be v 
consid]able4  ,! great modification     
br\ght to a radiation by ! ,zeeman      
effect may1 besides1 comb9e itself ) o!r
 ph5om5a1 & alt] ! light 9 a /ill m     
complicat$ mann]4 ,a p5cil ( pol>iz$    
light1 z demon/rat$ by ,signori         
,macaluzo & ,corb9o1 und]goes1 9 a      
magnetic field1 modifications ) reg>d to
 absorption & spe$ ( propagation4  ,"s  
+5i\s rese>*es by ,m4 ,becqu]el & ,m4   
,cotton h p]fectly elucidat$ all ^!     
complications f an exp]im5tal po9t (    
view4 ,x w\ld n be impossible to l9k    
toge!r all ^! ph5om5a )\t adopt+ !      
electronic hypo!sis1 by pres]v+ ! old   
optical equations z modifi$ by ! t]ms   
relat+ to ! action ( ! magnetic field4  

,?is has actually be5 done 9 "s v       
rem>kable "w by ,m4 ,voigt1 b we may    
also1 l ,pr(essor ,lor5tz1 look = m     
g5]al !ories1 9 :i* ! ess5tial image ( !
 electrons %all be pres]v$1 & :i* w all[
 all ! facts reveal$ by exp]im5t to be  
includ$4  ,we are ?us l$ to !           
supposition t !re is n 9 ! atom "o      
vibrat+ electron only1 b t !re is to be 
f\nd 9 x a dynamical sy/em compris+     
sev]al mat]ial po9ts :i* may be subject$
 to v>i$ movem5ts4 ,! neutral atom may  
!re=e be consid]$ z compos$ ( an        
immovable pr9cipal portion positively   
*>g$1 r\nd :i* move1 l satellites r\nd a
 planet1 sev]al negative electrons ( v  
inf]ior mass4 ,?is conclusion leads u to
 an int]pretation 9 agreem5t ) t :i* o!r
 ph5om5a h already sugge/$4  ,^!        
electrons1 :i* ?us h a v>iable velocity1
 g5]ate ar\nd !mselves a transv]se      
electromagnetic wave :i* is propagat$ ) 
! velocity ( light2 = ! *>g$ p>ticle    
becomes1 z soon z x exp]i5ces a *ange ( 
spe$1 ! c5tre ( a radiation4 ,?us is    

expla9$ ! ph5om5on ( ! emission (       
radiations4 ,9 ! same way1 ! movem5t (  
electrons may be excit$ or modifi$ by ! 
electrical =ces :i* exi/ 9 any p5cil (  
light !y receive1 & ?is p5cil may yield 
up to !m a "p ( ! en]gy x is c>ry+4 ,?is
 is ! ph5om5on ( absorption4  ,pr(essor 
,lor5tz has n cont5t$ himself ) ?us     
expla9+ all ! me*anism ( ! ph5om5a (    
emission & absorption4 ,he has endeav\r$
 to r$iscov]1 by />t+ ) ! fundam5tal    
hypo!sis1 ! quantitative laws discov]$  
by !rmodynamics4 ,he succe$s 9 %[+ t1   
agreeably to ! law ( ,kir*h(f1 !        
relation betwe5 ! emitt+ & ! absorb+ p[]
 mu/ be indep5d5t ( ! special prop]ties 
( ! body "u obs]vation1 & he ?us aga9   
meets ) ! laws ( ,planck & ( ,wi53      
un=tunately ! calculation c only be made
 9 ! case ( great wave-l5g?s1 & grave   
difficulties exi/4 ,?us x _c be v cle>ly
 expla9$ :y1 by heat+ a body1 !         
radiation is displac$ t[>ds ! side ( !  
%ort wave-l5g?s1 or1 if y w1 :y a body  
becomes lum9\s f ! mom5t its temp]ature 

has rea*$ a suffici5tly high degree4 ,on
 ! o!r h&1 by calculat+ ! en]gy ( !     
vibrat+ p>ticles we are aga9 l$ to      
attribute to ^! p>ticles ! same         
con/itution z t ( ! electrons4  ,x is 9 
! same way possible1 z ,pr(essor ,lor5tz
 has %[n1 to give a v satisfactory      
explanation ( ! !rmo-electric ph5om5a by
 suppos+ t ! numb] ( lib]at$ electrons  
:i* exi/ 9 a giv5 metal at a giv5       
temp]ature has a det]m9$ value v>y+ )   
ea* metal1 & is1 9 ! case ( ea* body1 a 
function ( ! temp]ature4 ,! =mula       
obta9$1 :i* is bas$ on ^! hypo!ses1     
agrees completely ) ! classic results ( 
,clausius & ( ,"l ,kelv94 ,f9ally1 if we
 recollect t ! ph5om5a ( electric &     
calorific conductivity are p]fectly     
int]pret$ by ! hypo!sis ( electrons1 x w
 no long] be possible to conte/ !       
importance ( a !ory :i* all[s u to gr\p 
toge!r 9 "o syn!sis s _m facts ( su*    
div]se orig9s4  ,if we /udy ! conditions
 "u :i* a wave excit$ by an electron's  
v>iations 9 spe$ c be transmitt$1 !y    

aga9 br+ u face to face1 & g5]ally1 ) ! 
results po9t$ out by ! ord9>y           
electromagnetic !ory4 ,c]ta9            
peculi>ities1 h[ev]1 are n absolutely ! 
same4 ,?us ! !ory ( ,lor5tz1 z well z t 
( ,maxwell1 leads u to =esee t if an    
insulat+ mass be caus$ to move 9 a      
magnetic field normally to its l9es (   
=ce1 a displacem5t w be produc$ 9 ?is   
mass analog\s to t ( :i* ,f>aday &      
,maxwell admitt$ ! exi/5ce 9 !          
dielectric ( a *>g$ cond5s]4 ,b ,m4,h4  
,po9c> has po9t$ out t1 accord+ z we    
adopt "o or o!r ( ^! au?ors' po9ts (    
view1 s ! value ( ! displacem5t diff]s4 
,?is rem>k is v important1 = x may lead 
to an exp]im5t :i* w\ld enable u to make
 a def9ite *oice betwe5 ! two !ories4   
,to obta9 ! displacem5t e/imat$ accord+ 
to ,lor5tz1 we mu/ multiply !           
displacem5t calculat$ accord+ to ,h]tz  
by a factor repres5t+ ! relation betwe5 
! diff]5ce ( ! specific inductive       
capacities ( ! dielectric & ( a vacuum1 
& ! fir/ ( ^! p[]s4 ,if !re=e we take z 

dielectric ! air ( :i* ! specific       
inductive capacity is p]ceptibly ! same 
z t ( a vacuum1 ! displacem5t1 accord+  
to ! idea ( ,lor5tz1 w be null2 :ile1 on
 ! contr>y1 accord+ to ,h]tz1 x w h a   
f9ite value4 ,m4 ,blondlot has made !   
exp]im5t4 ,he s5t a curr5t ( air into a 
cond5s] plac$ 9 a magnetic field1 & 0   
nev] able to notice ! slighte/ trace (  
electrification4 ,no displacem5t1 !re=e1
 is effect$ 9 ! dielectric4 ,! exp]im5t 
be+ a negative "o1 is evid5tly less     
conv9c+ ?an "o giv+ a positive result1 b
 x furni%es a v p[]ful argum5t 9 fav\r (
 ! !ory ( ,lor5tz4  ,?is !ory1 !re=e1   
appe>s v s$uctive1 yet x /ill raises    
objections on ! "p ( ^? :o oppose to x !
 pr9ciples ( ord9>y me*anics4 ,if we    
consid]1 = in/ance1 a radiation emitt$  
by an electron belong+ to "o mat]ial    
body1 b absorb$ by ano!r electron 9     
ano!r body1 we p]ceive imm$iately t1 !  
propagation n be+ in/antane\s1 !re c be 
no comp5sation betwe5 ! action & !      
reaction1 :i* are n simultane\s2 & !    

pr9ciple ( ,newton ?us seems to be      
attack$4 ,9 ord] to pres]ve its         
integrity1 x has to be admitt$ t !      
movem5ts 9 ! two mat]ial sub/ances are  
comp5sat$ by t ( ! e!r :i* sep>ates ^!  
sub/ances2 b ?is conception1 al?\gh 9   
tol]able agreem5t ) ! hypo!sis t ! e!r &
 matt] are n ( diff]5t ess5ce1 involves1
 on a clos] exam9ation1 suppositions    
h>dly satisfactory z to ! nature (      
movem5ts 9 ! e!r4  ,= a long "t         
physici/s h admitt$ t ! e!r z a :ole mu/
 be consid]$ z be+ immovable & capable (
 s]v+1 s to speak1 z a support = ! axes 
( ,galileo1 9 relation to :i* axes !    
pr9ciple ( in]tia is applicable1--or    
bett] /ill1 z ,m4 ,pa9lev has %[n1 !y   
alone all[ u to r5d] ob$i5ce to !       
pr9ciple ( causality4  ,b if x 7 s1 we  
might app>5tly hope1 by exp]im5ts 9     
electromagnetism1 to obta9 absolute     
motion1 & to place 9 evid5ce !          
translation ( ! e>? relatively to ! e!r4
 ,b all ! rese>*es attempt$ by ! mo/    
+5i\s physici/s t[>ds ?is end h always  

fail$1 & ?is t5ds t[>ds ! idea held by  
_m geometricians t ^! negative results  
are n due to imp]fections 9 ! exp]im5ts1
 b h a deep & g5]al cause4 ,n[ ,lor5tz  
has endeav\r$ to f9d ! conditions 9 :i* 
! electromagnetic !ory propos$ by him   
might agree ) ! po/ulate ( ! complete   
impossibility ( det]m9+ absolute motion4
 ,x is necess>y1 9 ord] to realise ?is  
concord1 to imag9e t a mobile sy/em     
contracts v slightly 9 ! direction ( its
 translation to a degree proportion$ to 
! squ>e ( ! ratio ( ! velocity (        
transport to t ( light4 ,! electrons    
!mselves d n escape ?is contraction1    
al?\gh ! obs]v]1 s9ce he p>ticipates 9 !
 same motion1 naturally _c notice x4    
,lor5tz supposes1 besides1 t all =ces1  
:atev] _! orig91 are affect$ by a       
translation 9 ! same way z              
electromagnetic =ces4 ,m4 ,langev9 & ,m4
 ,h4 ,po9c> h /udi$ ?is same "q & h not$
 ) precision v>i\s delicate consequ5ces 
( x4 ,! s+ul>ity ( ! hypo!ses :i* we are
 ?us l$ to con/ruct 9 no way con/itutes 

an argum5t aga9/ ! !ory ( ,lor5tz2 b x  
has1 we mu/ ackn[l$ge1 disc\rag$ "s ( ! 
m timid p>tisans ( ?is !ory4#dh         
,footnote #dh3 ,an objection n "h notic$
 has lately be5 =mulat$ ) mu* frankness 
by ,pr(essor ,lor5tz himself4 ,x is "o (
 ! pill>s ( 8 !ory t only ! negative    
electrons move :5 an electric curr5t    
passes ?r\gh a metal1 & t ! positive    
electrons 7if any su* !re be7 rema9     
motionless4 ,yet 9 ! exp]im5t kn[n z    
,hall's1 ! curr5t is deflect$ by !      
magnetic field to "o side ( ! /rip 9    
c]ta9 metals1 & to ! opposite side 9    
o!rs4 ,?is seems to %[ t 9 c]ta9 cases !
 positive electrons move in/ead ( !     
negative1 & ,pr(essor ,lor5tz confesses 
t up to ! pres5t he c f9d no valid      
argum5t aga9/ ?is4 ,see ,ar*ives        
,nerl&aises #aijf1 p>ts #a & #b4--;,,ed4
    #c4 ,,! ,,mass ,,( ,,electrons  ,o!r
 conceptions1 bold] /ill1 are sugge/$ by
 ! results ( c]ta9 int]e/+ exp]im5ts4 ,!
 electron af=ds u ! possibility (       
consid]+ in]tia & mass to be no long] a 

fundam5tal notion1 b a consequ5ce ( !   
electromagnetic ph5om5a4  ,pr(essor     
,j4,j4 ,?omson 0 ! fir/ to h ! cle> idea
 t a "p1 at lea/1 ( ! in]tia ( an       
electrifi$ body is due to its electric  
*>ge4 ,?is idea 0 tak5 up & precisely   
/at$ by ,pr(essor ,max ,abraham1 :o1 = !
 fir/ "t1 0 l$ to reg>d s]i\sly !       
seem+ly p>adoxical notion ( mass z a    
function ( velocity4 ,consid] a small   
p>ticle be>+ a giv5 electric *>ge1 & let
 u suppose t ?is p>ticle moves ?r\gh !  
e!r4 ,x is1 z we "k1 equival5t to a     
curr5t proportional to its velocity1 & x
 !re=e creates a magnetic field !       
int5sity ( :i* is likewise proportional 
to its velocity3 to set x 9 motion1     
!re=e1 !re mu/ be communicat$ to x ov] &
 above ! exp5diture correspond+ to !    
acquisition ( its ord9>y k9etic en]gy1 a
 quantity ( en]gy proportional to !     
squ>e ( its velocity4 ,ev]y?+1 !re=e1   
takes place z if1 by ! fact (           
electrification1 its capacity = k9etic  
en]gy & its mat]ial mass _h be5 increas$

 by a c]ta9 con/ant quantity4 ,to !     
ord9>y mass may be add$1 if y w1 an     
electromagnetic mass4  ,?is is ! /ate ( 
?+s s long z ! spe$ ( ! translation ( ! 
p>ticle is n v great1 b !y are no long] 
q ! same :5 ?is p>ticle is animat$ ) a  
movem5t ^: rapidity becomes comp>able to
 t ) :i* light is propagat$4  ,!        
magnetic field creat$ is !n no long] a  
field 9 repose1 b its en]gy dep5ds1 9 a 
complicat$ mann]1 on ! velocity1 & !    
app>5t increase 9 ! mass ( ! p>ticle    
itself becomes a function ( ! velocity4 
,m ?an ?is1 ?is increase may n be ! same
 = ! same velocity1 b v>ies accord+ to  
:e!r ! accel]ation is p>allel ) or      
p]p5dicul> to ! direction ( ?is         
velocity4 ,9 o!r words1 !re seems to be 
a longitud9al2 & a transv]sal mass :i*  
ne$ n be ! same4  ,all ^! results w\ld  
p]si/ ev5 if ! mat]ial mass 7 v small   
relatively to ! electromagnetic mass2 & 
! electron possesses "s in]tia ev5 if   
its ord9>y mass becomes slight] &       
slight]4 ,! app>5t mass1 x c be easily  

%[n1 increases indef9itely :5 ! velocity
 ) :i* ! electrifi$ p>ticle is animat$  
t5ds t[>ds ! velocity ( light1 & ?us !  
"w necess>y to communicate su* a        
velocity to an electron w\ld be inf9ite4
 ,x is 9 consequ5ce impossible t ! spe$ 
( an electron1 9 relation to ! e!r1 c   
ev] exce$1 or ev5 p]man5tly atta9 to1   
#cjj1jjj kilometres p] second4  ,all !  
facts ?us pr$ict$ by ! !ory are confirm$
 by exp]im5t4 ,!re is no kn[n process   
:i* p]mits ! direct measurem5t ( ! mass 
( an electron1 b x is possible1 z we h  
se51 to measure simultane\sly its       
velocity & ! relation ( ! electric *>ge 
to its mass4 ,9 ! case ( ! ca?ode rays  
emitt$ by radium1 ^! measurem5ts are    
p>ticul>ly int]e/+1 = ! reason t ! rays 
:i* compose a p5cil ( ca?ode rays are   
animat$ by v diff]5t spe$s1 z is %[n by 
! size ( ! /a9 produc$ on a photographic
 plate by a p5cil ( !m at fir/ v        
con/rict$ & subsequ5tly disp]s$ by !    
action ( an electric or magnetic field4 
,pr(essor ,kaufmann has effect$ "s v    

c>eful exp]im5ts by a me?od he t]ms !   
me?od ( cross$ spectra1 :i* consi/s 9   
sup]pos+ ! deviations produc$ by a      
magnetic & an electric field            
respectively act+ 9 directions at "r    
angles "o to ano!r4 ,he has ?us be5     
enabl$ by work+ 9 vacuo to regi/] ! v   
diff]5t velocities :i*1 />t+ 9 ! case ( 
c]ta9 rays f ab\t sev5-t5?s ( ! velocity
 ( light1 atta9 9 o!r cases to          
n9ety-five hundr$?s ( x4  ,x is ?us not$
 t ! ratio ( *>ge to mass--:i* = ord9>y 
spe$s is con/ant & equal to t already   
f\nd by s _m exp]im5ts--dim9i%es sl[ly  
at fir/1 & !n v rapidly :5 ! velocity ( 
! ray increases & approa*es t ( light4  
,if we repres5t ?is v>iation by a curve1
 ! %ape ( ?is curve incl9es u to ?9k t !
 ratio t5ds t[>d z]o :5 ! velocity t5ds 
t[>ds t ( light4  ,all ! e>li] exp]im5ts
 h l$ u to consid] t ! electric *>ge 0 !
 same = all electrons1 & x c h>dly be   
conceiv$ t ?is *>ge c v>y ) ! velocity4 
,= 9 ord] t ! relation1 ( :i* "o ( !    
t]ms rema9s fix$1 %\ld v>y1 ! o!r t]m   

necess>ily _c rema9 con/ant4 ,!         
exp]im5ts ( ,pr(essor ,kaufmann1 !re=e1 
confirm ! previsions ( ,max ,abraham's  
!ory3 ! mass dep5ds on ! velocity1 &    
increases indef9itely 9 proportion z ?is
 velocity approa*es t ( light4 ,^!      
exp]im5ts1 moreov]1 all[ ! num]ical     
results ( ! calculation to be comp>$ ) !
 values measur$4 ,?is v satisfactory    
comp>ison %[s t ! app>5t total mass is  
s5sibly equal to ! electromagnetic mass2
 ! mat]ial mass ( ! electron is !re=e   
nil1 & ! :ole ( its mass is             
electromagnetic4  ,?us ! electron mu/ be
 look$ ^u z a simple electric *>ge      
devoid ( matt]4 ,previ\s exam9ation has 
l$ u to attribute to x a mass a ?\s&    
times less t t ( ! atom ( hydrog51 & a m
 att5tive /udy %[s t ?is mass 0         
fictiti\s4 ,! electromagnetic ph5om5a   
:i* are produc$ :5 ! electron is set 9  
motion or a *ange effect$ 9 its         
velocity1 simply h ! effect1 z x 71 (   
simulat+ in]tia1 & x is ! in]tia due to 
! *>ge :i* has caus$ u to be ?us delud$4

  ,! electron is !re=e simply a small   
volume det]m9$ at a po9t 9 ! e!r1 &     
possess+ special prop]ties2#di ?is po9t 
is propagat$ ) a velocity :i* _c exce$ t
 ( light4 ,:5 ?is velocity is con/ant1 !
 electron creates ar\nd x 9 its passage 
an electric & a magnetic field2 r\nd ?is
 electrifi$ c5tre !re exi/s a k9d (     
wake1 :i* foll[s x ?r\gh ! e!r & does n 
become modifi$ s long z ! velocity      
rema9s inv>iable4 ,if o!r electrons     
foll[ ! fir/ )9 a wire1 _! passage along
 ! wire w be :at is call$ an electric   
curr5t4  ,footnote #di3 ,?is _c be said 
to be yet completely prov$4 ,cf4 ,sir   
,oliv] ,lodge1 ,electrons1 ,london1     
#aijf1 p4 #bjj4--;,,ed4  ,:5 ! electron 
is subject$ to an accel]ation1 a        
transv]se wave is produc$1 & an         
electromagnetic radiation is g5]at$1 (  
:i* ! "* may naturally *ange ) ! mann] 9
 :i* ! spe$ v>ies4 ,if ! electron has a 
suffici5tly rapid p]iodical movem5t1 ?is
 wave is a light wave2 :ile if !        
electron /ops sudd5ly1 a k9d ( pulsation

 is transmitt$ ?r\gh ! e!r1 & ?us we    
obta9 ,rntg5 rays4    #d4 ,,new ,,views 
,,on ,,! ,,con/itution ,,( ,,! ,,e!r ,,&
 ,,( ,,matt]  ,new & valuable in=mation 
is ?us af=d$ u reg>d+ ! prop]ties ( !   
e!r1 b w ?is enable u to con/ruct a     
mat]ial repres5tation ( ?is m$ium :i*   
fills ! univ]se1 & s to solve a problem 
:i* has baffl$1 z we h se51 ! prolong$  
ef=ts ( our pr$ecessors8  ,c]ta9 s*ol>s 
seem to h *]i%$ ?is hope4 ,dr4 ,l>mor 9 
p>ticul>1 z we h se51 has propos$ a mo/ 
+5i\s image1 b "o :i* is manife/ly      
insuffici5t4 ,! pres5t t5d5cy (         
physici/s r t5ds to ! opposite view2    
s9ce !y consid] matt] z a v complex     
object1 reg>d+ :i* we wrongly imag9e    
ourselves to be well in=m$ because we   
are s mu* accu/om$ to x1 & its s+ul>    
prop]ties end by seem+ natural to u4 ,b 
9 all probability ! e!r is1 9 its       
objective reality1 mu* m simple1 & has a
 bett] "r to be consid]$ z fundam5tal4  
,we _c !re=e1 )\t be+ v illogical1 def9e
 ! e!r by mat]ial prop]ties1 & x is     

useless lab\r1 condemn$ be=eh& to       
/]ility1 to endeav\r to det]m9e x by o!r
 qualities ?an ^? ( :i* exp]im5t gives u
 direct & exact k4  ,! e!r is def9$ :5  
we "k1 9 all its po9ts1 & 9 magnitude & 
9 direction1 ! two fields1 electric &   
magnetic1 :i* may exi/ 9 x4 ,^! two     
fields may v>y2 we speak f habit ( a    
movem5t propagat$ 9 ! e!r1 b ! ph5om5on 
)9 ! rea* ( exp]im5t is ! propagation ( 
^! v>iations4  ,s9ce ! electrons1       
consid]$ z a modification ( ! e!r       
symmetrically di/ribut$ r\nd a po9t1    
p]fectly c\nt]feit t in]tia :i* is !    
fundam5tal prop]ty ( matt]1 x becomes v 
tempt+ to suppose t matt] itself is     
compos$ ( a m or less complex assemblage
 ( electrifi$ c5tres 9 motion4  ,?is    
complexity is1 9 g5]al1 v great1 z is   
demon/rat$ by ! exam9ation ( ! lum9\s   
spectra produc$ by ! atoms1 & x is      
precisely because ( ! comp5sations      
produc$ betwe5 ! diff]5t movem5ts t !   
ess5tial prop]ties ( matt]--! law ( !   
cons]vation ( in]tia1 = example--are n  

contr>y to ! hypo!sis4  ,! =ces (       
cohesion ?us w\ld be due to ! mutual    
attractions :i* occur 9 ! electric &    
magnetic fields produc$ 9 ! int]ior (   
bodies2 & x is ev5 conceivable t !re may
 be produc$1 "u ! influ5ce ( ^! actions1
 a t5d5cy to det]m9e ori5tation1 t is to
 say1 t a reason c be se5 :y matt] may  
be cry/allis$4#ej  ,footnote #ej3 ,!    
read] %\ld1 h[ev]1 be w>n$ t a !ory has 
lately be5 put =? :i* attempts to acc\nt
 = cry/allisation on purely me*anical   
gr\nds4 ,see ,messrs ,b>l[ & ,pope's    
,developm5t ( ! ,atomic ,!ory 9 !       
,transactions ( ! ,*emical ,society1    
#aijf4--;,,ed4  ,all ! exp]im5ts effect$
 on ! conductivity ( gases or metals1 & 
on ! radiations ( active bodies1 h      
induc$ u to reg>d ! atom z be+ con/itut$
 by a positively *>g$ c5tre hav+        
practically ! same magnitude z ! atom   
itself1 r\nd :i* ! electrons gravitate2 
& x might evid5tly be suppos$ t ?is     
positive c5tre itself pres]ves !        
fundam5tal *>act]i/ics ( matt]1 & t x is

 ! electrons alone :i* no long] possess 
any b electromagnetic mass4  ,we h b    
little in=mation conc]n+ ^! positive    
p>ticles1 ?\gh !y are met ) 9 an isolat$
 condition1 z we h se51 9 ! canal rays  
or 9 ! ,x rays4#ea ,x has n hi!rto be5  
possible to /udy !m s successfully z !  
electrons !mselves2 b t _! magnitude    
causes !m to produce consid]able        
p]turbations 9 ! bodies on :i* !y fall  
is manife/ by ! second>y emissions :i*  
complicate & mask ! primitive ph5om5on4 
,!re are1 h[ev]1 /rong reasons = ?9k+ t 
^! positive c5tres are n simple4 ,?us   
,pr(essor ,/>k attributes to !m1 )      
exp]im5ts 9 pro( ( 8 op9ion1 ! emission 
( ! spectra ( ! rays 9 ,geissl] tubes1 &
 ! complexity ( ! spectrum discloses !  
complexity ( ! c5tre4 ,besides1 c]ta9   
peculi>ities 9 ! conductivity ( metals  
_c be expla9$ )\t a supposition ( ?is   
k9d4 ,s t ! atom1 depriv$ ( ! ca?ode    
corpuscle1 w\ld be /ill liable to       
decomposition into elem5ts analog\s to  
electrons & positively *>g$4            

,consequ5tly no?+ prev5ts u suppos+ t   
?is c5tre likewise simulates in]tia by  
its electromagnetic prop]ties1 & is b a 
condition localis$ 9 ! e!r4  ,footnote  
#ea3 ,!re is mu* reason = ?9k+ t ! canal
 rays d n conta9 positive p>ticles      
alone1 b are accompani$ by negative     
electrons ( sl[ velocity4 ,! ,x rays are
 ?\ght1 z has be5 said above1 to conta9 
nei!r negative nor positive p>ticles1 b 
to be m]ely pulses 9 ! e!r4--,,ed4      
,h[ev] ?is may be1 ! edifice ?us        
con/ruct$1 be+ compos$ ( electrons 9    
p]iodical motion1 necess>ily gr[s old4  
,! electrons become subject to          
accel]ations :i* produce a radiation    
t[>ds ! ext]ior ( ! atom2 & c]ta9 ( !m  
may leave ! body1 :ile ! primitive      
/ability is1 9 ! end1 no long] assur$1 &
 a new arrangem5t t5ds to be =m$4 ,matt]
 ?us seems to u to und]go ^?            
trans=mations ( :i* ! radio-active      
bodies h giv5 u su* rem>kable examples4 
,we h already _h1 9 fragm5ts1 ^! views  
on ! con/itution ( matt]2 a deep] /udy (

 ! electron ?us enables u to take up a  
position f :i* we obta9 a %>p1 cle>1 &  
compreh5sive grasp ( ! :ole & a glimpse 
( indef9ite horizons4  ,x w\ld be       
advantage\s1 h[ev]1 9 ord] to /r5g!n ?is
 position1 t a few objections :i* /ill  
m5ace x %\ld be remov$4 ,! in/ability ( 
! electron is n yet suffici5tly         
demon/rat$4 ,h[ is x t its *>ge does n  
wa/e itself away1 & :at bonds assure !  
p]man5ce ( its con/itution8  ,on ! o!r  
h&1 ! ph5om5a ( gravitation rema9 a     
my/]y4 ,lor5tz has endeav\r$ to build up
 a !ory 9 :i* he expla9s attraction by  
suppos+ t two *>ges ( simil> sign repel 
ea* o!r 9 a slightly less degree ?an t 9
 :i* two *>ges1 equal b ( contr>y sign1 
attract ea* o!r1 ! diff]5ce be+1 h[ev]1 
accord+ to ! calculation1 mu* too small 
to be directly obs]v$4 ,he has also     
s\ght to expla9 gravitation by connect+ 
x ) ! pressures :i* may be produc$ on   
bodies by ! vibratory movem5ts :i* =m v 
p5etrat+ rays4 ,rec5tly ,m4 ,su!rl& has 
imag9$ t attraction is due to ! diff]5ce

 ( action 9 ! convection curr5ts produc$
 by ! positive & negative corpuscles :i*
 con/itute ! atoms ( ! />s1 & are c>ri$ 
along by ! a/ronomical motions4 ,b ^!   
hypo!ses rema9 r vague1 & _m au?ors ?9k1
 l ,m4 ,langev91 t gravitation mu/      
result f "s mode ( activity ( ! e!r     
totally diff]5t f ! electromagnetic     
mode4     ,,*apt] ,,xi  ,,! ,,future ,,(
 ,,physics   ,x w\ld d\btless be        
exce$+ly ra%1 & c]ta9ly v presumptu\s1  
to seek to pr$ict ! future :i* may be   
res]v$ = physics4 ,! rle ( prophet is n 
a sci5tific "o1 & ! mo/ firmly e/abli%$ 
previsions ( to-day may be ov]?r[n by ! 
reality ( to-morr[4  ,nev]!less1 !      
physici/ does n %un an extrapolation (  
"s little scope :5 x is n too f> f !    
realms ( exp]im5t2 ! k ( ! evolution    
accompli%$ ( late ye>s au?orises a few  
suppositions z to ! direction 9 :i*     
progress may cont9ue4  ,! read] :o has  
deign$ to foll[ me 9 ! rapid excursion  
we h j made ?r\gh ! doma9 ( ! sci5ce (  
,nature1 w d\btless br+ back ) him f 8  

%ort j\rney ! g5]al impression t !      
anci5t limits to :i* ! classic treatises
 /ill delight 9 re/rict+ ! div]s *apt]s 
( physics1 are trampl$ d[n 9 all        
directions4  ,! f9e /raight roads trac$ 
out by ! ma/]s ( ! la/ c5tury1 & enl>g$ 
& levell$ by ! lab\r ( su* numb]s (     
workm51 are n[ jo9$ toge!r by a cr[d (  
small pa?s :i* furr[ ! field ( physics4 
,x is n only because !y cov] regions z  
yet little explor$ :]e discov]ies are m 
abundant & m easy1 t ^! cross-cuts are s
 frequ5t1 b also because a high] hope   
guides ! seek]s :o engage 9 ^! new      
r\tes4  ,9 spite ( ! repeat$ failures   
:i* h foll[$ ! num]\s attempts ( pa/    
times1 ! idea has n be5 ab&on$ ( "o day 
conqu]+ ! supreme pr9ciple :i* mu/ comm&
 ! :ole ( physics4  ,"s physici/s1 no   
d\bt1 ?9k su* a syn!sis to be impossible
 ( realisation1 & t ,nature is inf9itely
 complex2 b1 not)/&+ all ! res]ves !y   
may make1 f ! philosophical po9t ( view1
 z to ! legitimacy ( ! process1 !y d n  
hesitate to con/ruct g5]al hypo!ses :i*1

 9 default ( complete m5tal             
satisfaction1 at lea/ furni% !m ) a     
highly conv5i5t means ( gr\p+ an imm5se 
numb] ( facts till !n scatt]$ abroad4   
,_! error1 if error !re be1 is          
b5eficial1 = x is "o ( ^? t ,kant w\ld h
 class$ among ! fruitful illusions :i*  
eng5d] ! indef9ite progress ( sci5ce &  
lead to great & important co-ord9ations4
  ,x is1 naturally1 by ! /udy ( !       
relations exi/+ betwe5 ph5om5a app>5tly 
( v diff]5t ord]s t !re c be any hope ( 
rea*+ ! goal2 & x is ?is :i* ju/ifies ! 
peculi> int]e/ accord$ to rese>*es      
effect$ 9 ! debatable l& betwe5 doma9s  
hi!rto consid]$ z sep>ate4  ,among all !
 !ories lately propos$1 t ( ! ions has  
tak5 a prepond]ant place2 ill und]/ood  
at fir/ by "s1 appe>+ some:at s+ul>1 & 9
 any case useless1 to o!rs1 x met at its
 inception1 9 ,france at lea/1 ) only v 
mod]ate fav\r4  ,to-day ?+s h greatly   
*ang$1 & ^? ev5 :o ignor$ x h be5 s$uc$ 
by ! curi\s way 9 :i* x adapts itself to
 ! int]pretation ( ! mo/ rec5t exp]im5ts

 on v diff]5t subjects4 ,a v natural    
reaction has set 92 & ,i might almo/ say
 t a "q ( fa%ion has l$ to "s           
exagg]ations4  ,! electron has conqu]$  
physics1 & _m adore ! new idol r bl9dly4
 ,c]ta9ly we c only b[ be=e an hypo!sis 
:i* enables u to gr\p 9 ! same syn!sis  
all ! discov]ies on electric dis*>ges & 
on radioactive sub/ances1 & :i* leads to
 a satisfactory !ory ( optics & (       
electricity2 :ile by ! int]m$i>y (      
radiat+ heat x seems likely to embrace  
%ortly ! pr9ciples ( !rmodynamics also4 
,c]ta9ly "o mu/ admire ! p[] ( a cre$   
:i* p5etrates also into ! doma9 (       
me*anics & furni%es a simple            
repres5tation ( ! ess5tial prop]ties (  
matt]2 b x is "r n to lose sight ( !    
fact t an image may be a well-f\nd$     
appe>ance1 b may n be capable ( be+     
exactly sup]pos$ on ! objective reality4
  ,! conception ( ! atom ( electricity1 
! f\ndation ( ! mat]ial atoms1 evid5tly 
enables u to p5etrate fur!r into        
,nature's secrets ?an our pr$ecessors2 b

 we mu/ n be satisfi$ ) words1 & ! my/]y
 is n solv$ :51 by a legitimate         
artifice1 ! difficulty has simply be5   
?ru/ fur!r back4 ,we h transf]r$ to an  
elem5t ev] small] & small] ^? physical  
qualities :i* 9 antiquity 7 attribut$ to
 ! :ole ( a sub/ance2 & !n we %ift$ !m  
lat] to ^? *emical atoms :i*1 unit$     
toge!r1 con/itute ?is :ole4 ,to-day we  
pass !m on to ! electrons :i* compose ^!
 atoms4 ,! indivisible is ?us r5d]$1 9 a
 way1 small] & small]1 b we are /ill    
unacqua9t$ ) :at its sub/ance may be4 ,!
 notion ( an electric *>ge :i* we       
sub/itute = t ( a mat]ial mass w p]mit  
ph5om5a to be unit$ :i* we ?\ght        
sep>ate1 b x _c be consid]$ a def9ite   
explanation1 or z ! t]m at :i* sci5ce   
mu/ /op4 ,x is probable1 h[ev]1 t = a   
few ye>s /ill physics w n travel beyond 
x4 ,! pres5t hypo!sis suffices = gr\p+  
kn[n facts1 & x w d\btless enable _m m  
to be =ese51 :ile new successes w fur!r 
increase its possessions4  ,!n ! day w  
arrive :51 l all ^? :i* h %one be=e x1  

?is s$uctive hypo!sis w lead to m errors
 ?an discov]ies4 ,x w1 h[ev]1 h be5     
improv$1 & x w h become a v va/ & v     
complete edifice :i* "s w n will+ly     
ab&on2 = ^? :o h made to !mselves a     
com=table dwell+-place on ! ru9s (      
anci5t monum5ts are (t5 too lo? to leave
 x4  ,9 t day ! se>*]s :o 7 9 ! van ( ! 
m>* aft] tru? w be caught up & ev5 pass$
 by o!rs :o w h foll[$ a long]1 b p]haps
 sur] road4 ,we also h se5 at "w ^?     
prud5t physici/s :o dread$ too d>+      
cre$s1 & :o s\ght only to collect all ! 
docum5t>y evid5ce possible1 or only took
 = _! guide a few pr9ciples :i* 7 to !m 
a simple g5]alisation ( facts e/abli%$  
by exp]im5ts2 & we h be5 able to prove t
 !y also 7 effect+ good & highly useful 
"w4  ,nei!r ! =m] nor ! latt]1 h[ev]1   
c>ry out _! "w 9 an isolat$ way1 & x    
%\ld be not$ t mo/ ( ! rem>kable results
 ( ^! la/ ye>s are due to physici/s :o h
 kn[n h[ to comb9e _! ef=ts & to direct 
_! activity t[>ds a common object1 :ile 
p]haps x may n be useless to obs]ve also

 t progress has be5 9 proportion to !   
mat]ial res\rces ( our laboratories4  ,x
 is probable t 9 ! future1 z 9 ! pa/1 ! 
greate/ discov]ies1 ^? :i* w sudd5ly    
reveal totally unkn[n regions1 & op5 up 
entirely new horizons1 w be made by a   
few s*ol>s ( g5ius :o w c>ry on _!      
pati5t lab\r 9 solit>y m$itation1 & :o1 
9 ord] to v]ify _! bolde/ conceptions1 w
 no d\bt cont5t !mselves ) ! mo/ simple 
& lea/ co/ly exp]im5tal app>atus4 ,yet =
 _! discov]ies to yield _! full h>ve/1 =
 ! doma9 to be sy/ematically work$ &    
desirable results obta9$1 !re w be m & m
 requir$ ! association ( will+ m9ds1 !  
solid>ity ( intellig5t s*ol>s1 & x w be 
also necess>y = ^! la/ to h at _!       
disposal ! mo/ delicate z well z ! mo/  
p[]ful in/rum5ts4 ,^! are conditions    
p>am\nt at ! pres5t day = cont9u\s      
progress 9 exp]im5tal sci5ce4  ,if1 z   
has already happ5$1 un=tunately1 9 !    
hi/ory ( sci5ce1 ^! conditions are n    
compli$ )2 if ! fre$oms ( ! work]s are  
trammell$1 _! unity di/urb$1 & if       

mat]ial facilities are too p>simoni\sly 
af=d$ !m1--evolution1 at pres5t s rapid1
 may be ret>d$1 & ^? retrogressions :i*1
 by-!-by1 h be5 kn[n 9 all evolutions1  
may occur1 al?\gh ev5 !n hope 9 ! future
 w\ld n be aboli%$ = ev]4  ,!re are no  
limits to progress1 & ! field ( our     
inve/igations has no b\nd>ies4          
,evolution w cont9ue ) inv9cible =ce4   
,:at we to-day call ! unkn[able1 w      
retreat fur!r & fur!r be=e sci5ce1 :i* w
 nev] /ay h] onw>d m>*4 ,?us physics w  
give great] & increas+ satisfaction to !
 m9d by furni%+ new int]pretations (    
ph5om5a2 b x w accompli%1 = ! :ole (    
society1 m valuable "w /ill1 by r5d]+1  
by ! improvem5ts x sugge/s1 life e day m
 easy & m agreeable1 & by provid+ mank9d
 ) weapons aga9/ ! ho/ile =ces (        
,nature4