BALANCE OF CAPACITIES. 



461 



traversed by a permanent current. The point P of the resistance AB 

 is sought at which, when the wire of the galvanometer G is attached 

 connecting P and D, the needle is stationary. The position of the 

 point P does not change when the current of the battery is reversed 

 by the commutator M. 



As the charge of the two condensers is the same, in consequence 

 of their being connected (85), and if V and V are the potentials 

 of the points A and B, and V l that of the external armatures, 



or 



C(V-V 1 ) = C(V 1 -V), 



V-V 1 _V 1 -V / 



On the other hand, if x be the potential at the point P, R and R' 

 the resistance AP and PB, we have also 



R 



R' 



In order that there be no current in the galvanometer, the 

 potentials x and Vj_ must be equal, which requires the condition 



.C = R' 

 C'~R' 



It is again advantageous to replace the galvanometer by an 

 electrometer, which makes it easier to find by trial the position 

 of equilibrium. 



This method is susceptible of great accuracy, and lends itself 

 very well to a verification of the standards of capacity. 



