746 



Gauss; on further strengthening of the field this amount did not 

 change. Also Hurmucescu ^) found the electromotive force in the same 

 sense, when diluted acetic acid or oxalic acid was used as electro- 

 lyte. In a field of 7300 Gauss the electromotive force amounted to 

 14 millivolts. Finally Bucherer") has occupied himself with this 

 question. His result is in so far entirely negati\e that he finds no 

 electromotive force which would reach the value of 10-^ Volts for 

 neutral solutions of ferro salts in the case of magnetisation of the 

 electrode in a field of 1200 Gauss. He further pronounces the opinion 

 that the electromotiAe forces found by Rowi,and are caused by 

 mechanical disturbances of the equilibrium ("Erschiitterungen"), whicii 

 w^ould be the consequence of the origin of the magnetic field. Then 

 Blcherer compares Hurmucescu's results with what has been theoreti- 

 cally derived by Duh'km''), and concludes that no concordance exists 

 between them. Duhem arrives at the formula: 



E= (1) 



in which I represents the magnetisation of the electrode, / the electro- 

 chemical equivalent of the iron, y. the susceptibility, and d the 

 density, the electromotive force E being taken positive, when the 

 magnetized electrode is cathode. When we eliminate ///,/, and x by 

 the aid of the relations : 



B = Hi + 4rr / B = (i .Hi I=x. Hi 



we get instead of (1) 



B' .X / 1 \ 

 E = 1 (2) 



It has appeared to me that in consequence of an inaccurate expres- 

 sion for the energy of a magnetic field, this value of E is about ft 

 times too small, so that we may write by approximation because \i 

 has a large value : 



B"" .X 



E = -E-—, (3) 



ö.T . a 



which expression, however, only holds when the electrolyte is a 

 neutral iron solution. 



When the experiment is arranged in such a way that B may be 

 put equal to the external intensity of the tield H, we see from (3) 



1) Hurmucescu. Eclair. Electr. Nr. 6 and 7, 1895. 



2) A. H. Bucherer. Wied. Ann. 58 p. 564, 1896 ; 59 p. 735, 1896 ; 61 p. 807, 1897. 

 ^) P. Duhem. Ann. de la Fac. des Sciences de Toulouse. 1888 — 89. Wied.. Ann. 



Beibl. 13 p. 101, 1889. 



