284 MEASUREMENT OF CURRENTS. 



Similarly, if we accentuate those letters which have an analogous 

 meaning, the electrodynamometer gives 



C T 

 1*0 = ^- '. 



SO 7T 



We deduce from these two equations 



C G T a' 

 "SliCT'TF a ' 

 S'H 2 G' T 2 a 2 



~~ * 



We may eliminate the constants of the electrodynamometer, by 

 observing the deflections 8 and 8', which the same current produces 

 in the galvanometer and in the electrodynamometer. We have, in 

 fact, 



H 2 C 



and therefore 



H T tan 2 8 a' 

 ~"GT~ a tan 8" 

 T 2 a 2 tan 8' 

 TrT' tari 2 8 a' 



The latter expression only contains experimental numbers, but 

 in general it will only give a rough valuation of the real duration of 

 the discharge ; for the supposition that the current is uniform is 

 often far from being true. 



899. SERIES OF DISCHARGES. BROKEN CURRENTS. It is 

 evident that a continuous series of discharges which are identical 

 with each other, and such that the sum of the duration of each 

 discharge and of the interval separating it from the next, is small 

 compared with the time of oscillation of the needle, will produce 

 in the galvanometer the same deflection as a current of constant 

 intensity which sets in motion the same quantity of electricity in 

 each unit of time. 



If N is the number of discharges per second, m the quantity 

 of electricity corresponding to each of them, we shall thus have 



TT 



/ = Nw = - tan 8. 

 G 



