92 ELECTROLYSIS. 



The maximum of this equation will occur when 



n 



that is to say, when the resistance of the entire battery is 

 equal to the external resistance.* 



The quantities R, n, and r being known, it is easy to 

 determine p, and arrange the battery with a view to obtain a 

 maximum capacity. 



ELECTROMOTIVE FORCE OF DYNAMO-ELECTRIC MACHINES. 

 The electromotive force of dynamo-electric machines depends 

 on the length of the induced wire, on the speed, on the strength 

 of the magnetic field, on the internal and external resistance of 

 the circuit. 



For a given machine it is sensibly proportional to its speed 

 of rotation, when the inductor is a permanent magnet, or if the 

 excitation is produced by an independent current. With a 

 machine having electro-magnets in circuit, this proportion is 

 not quite so exact. 



In order to illustrate the variations of electromotive force 

 obtained from variations of speed, we have carried out two 

 series of experiments on two Gramme machines, one with 

 permanent magnets, the other with electro-magnets; the 

 results are shown in the following tables : 



1. MACHINE WITH PERMANENT MAGNET. 



* The demonstration of this proposition requires some rather too elaborate 

 calculations to find room in a work which is especially intended for manufacturers. 



