466 



MEASUREMENT OF CAPACITY. DIELECTRICS. 



remains at rest. If they are unequal, equilibrium may be established 

 either by a variable capacity, or by a convenient shunt added to one 

 of the coils of the galvanometer. 



If G and G' are the constants of the two coils, m the multiplying 

 power of the shunt in the first, C and C' the corresponding capa- 

 cities, we have 



C G 

 C 



- = G'C, 

 m 



or = 



The use of shunts is then allowable, provided the discharges are 

 of the same duration. This is the weak point of the method devised 

 by Varley.* 



1055. INTERMITTENT CURRENTS. A capacity may be evalu- 

 ated by a series of discharges in the same direction, succeeding at 



Fig. 220. 



very short intervals in reference to the time of oscillation of the 

 needle of a galvanometer, on which they produce the same effect as 

 a continuous current. 



Figs. 220, 221, give two arrangements used by Werner Siemens.! 

 A and B are the two armatures of a condenser, L a vibrating plate 



Fig. 221. 



between two contacts C and D, and P the charging battery. When 

 the plate vibrates, the galvanometer is traversed in the first pface by 



* L. CLA&K and R. SABINE. Electrical Tables and Formula, p. 63, 1871. 

 t Pogg. Annakn, Vol. en., p. 66, 1857. 



