502 OHM ON THE GALVANIC CIRCUIT. 



38. We have lastly to determine the alteration in the ten- 

 sion of the circuit, which is produced by the chemical altera- 

 tion of the extent, which has hitherto been considered. For 

 this purpose we assume, till experience shall have taught us 

 better, the position, that the magnitude of the electric tension 

 between two bodies is proportional, first to the difference of 

 their latent clectroscopic forces, and secondly to a function, 

 which we will term the coefficient of the tension, dependent on 

 the size, position and form of the particles which act on each 

 other at the place of contact. Not only from this hypothesis 

 may be deduced the law which the tensions of the metals ob- 

 serve inter se, — nothing further being requisite than to assume 

 the same coefficient of tension between all metals placed under 

 similar circumstances, — but it likewise affords an explanation 

 of the phaenomenon, in accordance with which the electric 

 tension does not merely depend on the chemical antagonism of 

 the two bodies, but also on their relative density, and can for 

 this reason exhibit themselves differently, even in different tem- 

 peratures. For the same reasons which we have already men- 

 tioned in § 34 on the determination of the coherence which 

 occurs between the two constituents of a mixed body, we shall 

 likewise admit here, in the circumference of the chemically 

 variable extent as constant, the unknown function dependent 

 on the size, form and position of the particles in contact, and 

 designate it by <^'. Since now the latent clectroscopic force in 

 the disc M, to which the abscissa ic belongs, is expressed by 



n+ [m — n) z, 



and that in the disc M', to which the abscissa x + dx belongs, 



by 



n + (m — n)z + {m — n) d z, 

 the tension originating between the discs M and M' is 



— ^' [ill — n) d z ; 



consequently the sum of all the tensions produced through- 

 out a portion exposed to chemical change 



-^'{m-n){z"-z'), 



Avhen z' and z" represent those values of z, which belong to the 

 commencement and end of the extent in question. 



But the tension of the circuit undergoes, besides the change 

 just explained, a second one, from the extremities of the che 



