the Galvanic Current through Iron. 139 



work of the unit of heat, V the potential, for instance, of the 

 unit current on the magnet in reference to which work is per- 

 formed) is regarded as a new electromotive force which coun- 

 teracts the first. But I do not see why it is not also admissible 

 to write 



e 

 i== — — —j 

 iv + w A 



where iv A denotes a new resistance added to w in consequence 

 of the external work*. At all events it cannot be proved, as 

 Colleyf will have it, that the latter equation is false. Colley 

 thinks himself authorized to conclude as follows: — If Tand I v 

 denote the times necessary, with and without the performance 

 of work, to dissolve 1 gram of zinc in the galvanic series, then, 

 if iv varies, 



-T=-^-T + qT, (1) 



IV iv +• w A * 



where g signifies the work done in the unit of time. Now, 

 however, 



-T = — ^-T'; ...... (2) 



IV iv + iv A v 7 



consequently 



e = e+¥(w + iv A ), 



which is impossible. 



Equation (1) is true ; but equation (2) is as little applicable 

 as in the other case (where e is considered variable) the cor- 

 responding equation 



±T=—T, (2a) 



IV IV 



where e signifies the variation of e. Much rather are both 

 equations to be replaced by the common equation 



T=T', (3) 



which expresses that with i the evolution of heat has also di- 

 minished ; and this leads, in our case, to the very possible 

 equation 



iv iv 



+^ +? ' 



from which we get 



iv 2 q , . N 



tc A = Y (4a) 



A e 2 — u-q K ' 



* But compare Wiedemann, Galv. ii, 2, p. 521. 

 t Pogg. Ann. clvii. p. 370 (1876). 



