240 



Mr.'E. C. Rimington on 



where p is the internal resistance and E the E.M.F. of the 

 testing battery. 



lfg=0, 



Ki_C 

 K 2 ~B* 



If a key be also put in the galvanometer- circuit, and the 

 battery-key be first depressed and then, after a certain interval 

 of time, the galvanometer-key, 

 we have Gott's method of com- 

 paring capacities. This allows 

 the condenser longer time to 

 charge ; and if the galvano- - 

 meter when its key is depressed 

 shows no throw, it indicates 

 that the potentials t\ and v 2 

 are equal, and that therefore 



K 1= C 



as before. 2 



If, however, either of the condensers has an appreciable 

 'leakage, the result will be false by this method. 



Suppose the condenser K 2 has an insulation-resistance R, 

 that of Kj being infinite. On depressing the battery-key, as 

 the condensers are in series, they take initial charges each 

 equal to Q. 



Q=(V 1 -« 1 )K 1 = (r 1 -V 2 )K 2 =(V 1 -V 2 )j&. 2 . 



Let an interval of time t elapse before the galvanometer-key 

 is depressed, and at the end of it let Q ll and Q 2 be the charges 

 on Kj and K 2 respectively, and v the value of v x . Then 



t_ 



Q 2 = Q e *,*, where <? = 2"718, 



and 



Q^V.-V,)-^ 



K i K 2 --E5 



K, 



Q 1 = (V,-t.)K 1 ={(V x -V,)-(i;-V,)K 1 

 = {(V:-V 2 )-|}K J( 



