384 



ELECTRICAL MEASUREMENTS 



The potential difference between b and c is 



bc = r- i M dt 



and between d and c it is. 



i 



V dc =-- ~ i N dt. 



Vbc must equal Vdc since at no time during the establishment of 

 the steady state does any current flow through G. Then 



R N 



.*. CY = 



FIG. 225. Mesh diagram for De Sauty method for comparing capacities. 



r 



[ition I i ( 

 Jo 



If the condition I iodt = Q G = be applied, the demonstration 



is more complicated, since the expression for Q G must first be 

 deduced and then the condition found which renders it zero. 

 Consider that the bridge is arranged as in Fig. 225. 



Assume that during the time of charging the condensers, that 

 is, until the steady state has been established, the meshes are 

 traversed by the variable currents x, x + y, and i Bt which 

 finally become zero. 



Taking the mesh abd, 



x(R M + Ro + RN) + Lo - - (x + y) Ro - L + 



- i B R N = 



