266 Prof. Oliver Lodge on the Seat of the Electromotive 



V{t)=tf(t), .... (3; 



©a(0-®b(W"<0 W 



If, now, © is to be regarded as simple proportion, in accord- 

 ance with the results of Professor Tait, f" is a constant 

 depending on the two metals only ; 

 so 



f"(f) = c, 



f'(t) =! + <*, 



and 



/ (t) = a + bt + ict 2 , 



t meaning absolute temperature throughout. 



So far everything is unassailable, except by one who may 

 believe in some irreversible degradation of heat by conduction 

 or otherwise as necessarily accompanying the process, and so 

 deny the applicability of the second law altogether. Certainly 

 Ayrton and Perry are not thinking of doing this : they accept 

 the equations as they stand, and claim that their own are 

 identical with them. 



But now comes in the gratuitous assumption which causes 

 them to misunderstand the true physical meaning of these 

 equations, and which leads them into what seems to me error. 



I speak from my own point of view : I do wish to show that 

 their position is untenable, but I have no wish to dogmatize. 

 I use language which may serve to bring out the differences 

 between us plainly ; and while I am sure neither Prof. Ayrton 

 nor Prof. Perry, so I hope no one else, will misconstrue what 

 I say in any offensive or disrespectful sense. From my 

 standpoint their theory looks erroneous, and it is allowable to 

 say so. They will no doubt return the compliment. 



They beg the whole question by their interpretation off(t). 

 All that is certain about f(t) is that it is a potential function 

 characteristic of the two metals in contact. Ayrton and Perry 

 assume, without, so far as I can see, the slightest warrant for 

 their assumption, that /(f) is the " contact-difference of poten- 

 tials " which has been measured electrostatically as the Volta- 

 effect. 



Once grant this, and things begin to go their way : thermo- 

 electric force is a mere variation of Volta-effect with tempera- 

 ture ; Peltier generation of heat is proportional to the rate at 

 which Volta-effect changes per degree ; the E.M.F. of a cell 

 is due to differences of Volta-effects at the several junctions, 

 just as the E.M.F. of a thermopile is due to their variations 

 with temperature : and in general the Volta-effect, as observed 



