756 



the value of satnralion, so thai this term — whicli far exceeds the 



other "magnetic" term — will increase oiilj" al)Oiit linearly with 



the external inlensity of the field. The sense of the electromotive 



force determined by the first term is directed inside the solution 



from the non-magnetized towards the magnetized electrode. The 



second {)art of the expression becomes equal to zero for c\ =: c.^ ; 



with neglect of the contraction which the solution undergoes on 



concentration, this expression agrees with the potential difference 



calculated by Helmhoi,tz ^), between two electrodes which are in 



solutions of different concentrations. 



If we assume Cj = i\, and neglect the terms which depend on 



the susceptibility of the solution, the following form holds for not 



too great intensities of the field (in which f* is still to be considered 



as very great) 



X.W 

 E^ (26) 



If we use electromagnetic nnities, this becomes; 



E: 



which agrees with (3). 



In order to simplify onr considerations we have disregarded the 

 transition layers between iron and electrolyte; in them phenomena 

 will namely take i)lace which cannot be examined in detail. It now 

 remains to prove that in the calculation of the free energy the in- 

 fluence of these transition layers may be neglected. For this purpose 

 it is necessary to assume that the thickness of the transition layers 

 is of the order of magnitude /, when / represents so small a quantity 

 that we may assume that inside the thickness / the liquid is in 

 equilibrium with the electrode. We shall furtlier assume the limits 

 of these transition layers on one side inside the iron, on the other 

 side inside the solution. Let the quantity of electricity e, which we 

 have passed through the solution, be of the order of magnitude §; the 

 same thing will be the case with the thickness of the iron layer, 

 which has dissolved at the anode, deposited at the cathode. This 

 iron layer may be infinitely thin with respect to the thickness of the 

 transition layer, and entirely fall within it. 



We have already taken into account the change of the "magnetic 

 part" of the free energy, which is the consequence of the displacement 

 of the iron and the dissolved substance. Now we have still to take 

 into account the change of the state of the transition layers, which 



1) H. Helmholtz. Wied. Ann. 3 p. 201, 1878. 



