472 MEASUREMENT OF CAPACITY. DIELECTRICS. 



o 



The ratio may then be determined, either by the ratio of two 



P 

 successive currents I and / or I and /', or by the ratio of two 



simultaneous currents / and /"'. 



A galvanometer with two rectangular coils (854) interposed in 

 the two branches r and r' would give directly the ratio of the 

 currents / and /', and therefore 



The value of p would still be determined by the comparison of 

 the discharge current I, either with the principal current I , or with 



c 



one of the currents / and *'. If, for instance, we introduce a dif- 

 ferential galvanometer in the branch r', and in the wire connecting 

 one of the points P or N with the condenser, we may choose the 

 resistance r', so that the needle is at zero. The galvanometer being 

 adjusted, the condition I = /' gives 



1061. Let us assume that the capacity which can be discharged 

 is inserted between two points P and N on the branch b of a 

 Wheatstone's bridge (Fig. 224). 



The resistances a, a' and b', being adjusted so that there was 

 no current in the bridge during the alternating discharges of the 



