747 



that the electromotive force would have to increase with the square 

 of the intensity of the tiekl. On introduction of the values for iron 



;. = 29 X 10--^ e.m.e. d = 7.9 



we get for 



//= 10000 Gauss i;= 1.46 X 10~' ^olt. 



In Bucherer's experiment the intensity of the field was 1200, if 

 the induction B had had the same value, the electromotive force would 

 have been 2.1 X 10—' Volts. As this amount is much less than the 

 smallest value which Bucherer could measure (10- -^ Volts), its negative 

 result cannot be considered in conflict with the theoretical result. 



The results of the other investigators, who worked with acids as 

 electrolytes, are not at all in agreement with formula (3), in fact 

 they could iiardly be so, as (8) rests on the supposition of a neutral 

 iron solution. 



As the case that the electrolyte is a dilute solution of the metal 

 of electrodes, which is assumed to be equal for the two electrodes, 

 is the only one that is liable to exact thermodynamic treatment, 1 

 have calculated the value of the potential difference for this case in 

 what follows. Further 1 have communicated the results of experiments 

 made on this subject. 



2. Let us now consider ^) an arbitrary system in which also 

 electric currents and magnetic fields can be present. As variables in 

 this system we choose the temperature 7". further a number of 

 geometrical quantities a^, a.^ . . ., and finally the magnetic induction "O; 

 when the last quantity is knowMi everywhere, then, besides the 

 magnetic field, the electrical current is also determined everywhere. 

 The external forces exerted by the system, are the components of 

 force A^, A^ . . . corresponding to the geometi'ical quantities, besides 

 the external electromotive forces ^%. In order to be justified in leaving 

 Joulk's heat out of consideration we shall assume that the conductors, 

 for so far as a current passes through them, possess no resistance. 

 We shall further assume that the system loses no energy by electro- 

 motive radiation and we exclude currents of displacement. 



If the system undergoes an infinitely small virtual variation, we 

 first inquire into the work performed by the system on its surround- 

 ings. If the variations of the geometrical quantities are rffr,, cfff, . . ., 

 the corresponding work can be expressed by 



1) The train of reasoning on which the general method of treatment followed 

 here is based, was suggested to me by Prof. Dr. H. A. Lorentz, for which I will 

 express here my heartfelt thanks 



