VOL TAIC GENERA TORS. 2 9 



kind in our Expose des applications de F&ectridte, tome /, p. 

 207, et tome V., p. 392. 



There are two important elements to be considered in a 

 battery its electro-motive force and its resistance. We have 

 at the beginning of this work defined what is to be under- 

 stood by these two expressions. The laws of electric currents 

 have been based on the constancy of those two elements, 

 and hence the name of voltaic constants which has been given 

 to them ; but as a matter of fact, on account of the secondary 

 reactions which show themselves, and of which polarization 

 eifects are the principal, this is far from being the case. 

 Nevertheless, as the values of these constants must be known 

 approximately for all the oVher electric applications, it has 

 been necessary to calculate them, and I have indicated, in 

 tome /. of my Expose des applications de Felectricite, pp. 171 

 e?4$6, those which have been obtained by various physicists. 

 As in the present work we have hardly more than one form 

 of battery to consider, we shall merely state that the electro- 

 motive force of the Bunsen cell represents in units of electro- 

 motive force or in volts from i v '888 to 1^964; and its ratio 

 to the electro-motive force of the Daniell cell is from 1749 

 to 1-820. The resistance of the same cell (average form), 

 which is composed of that of the liquid interposed between 

 the polar electrodes, and that of the porous vessel and of the 

 gaseous deposits produced by electrolytic action and polariza- 

 tion, varies from 50 to 150 metres of telegraph wire, accord- 

 ing to the resistance of the external circuit. I say varies, 

 because figures which are deduced from experiment appear 

 to prove that this variation exists ; but as this results from 

 the effects of the polarization of the electrodes, and as it 

 affects the resistance of the cell only because the rest of the 

 circuit is discharged from it, it may quite as well be referred 

 to the whole circuit as to one of its parts. However, as a 

 resistance other than that which it really possesses cannot 

 be given to the metallic circuit, it is convenient to attribute 

 to that of the Bunsen cell the value of 50 metres when the 



