OF ARTS AND SCIENCES. 438 



Moreover, it is obvious that heat will be evolved at the surface B. 

 For the heat evolved when the surface contracts to nothing is due to the 

 disappearance of the energy of electrical separation; the electricity flow- 

 ing back in a direction opposite to that in which it was first separated. 



Consequently, if electricity is separated from platinum to acid, heat 

 will be evolved when it flows from acid to platinum. 



The energy of electrical separation that takes place at any instant 

 is 



The current strength into the electromotive force equals the electri- 

 cal energy, and this is maintained by a disappearance of heat which 

 must be proportional to 



dk 



d'l 



- dT%dm, 



1dm being the total quantity of electricity separated in unit time. 

 A current of unit strength would consequently absorb an amount of 

 heat : 



— ~ dTM=6dT. 

 a I 



The arrangement considered forms a reversible thermodynamic 

 engine. For small currents we can therefore consider the heat ab- 

 sorbed as proportional to the first power of the current strength. 



The heat absorbed by a current dm is 



edmdT. 

 The energy of the current must e<pial the heat absorbed : 



de . d7)i =^ 6 dm . d T, 



" dT—^— dT ^'^' 



From equation (c.) 



de 1 



dT——f(x) 



a 

 f 





For a cij'cuit in which the temperatures of the junctions differ by a 

 finite amount, 



-n- 



VOL. XX. (N. 8. XII. 28 



