[ 370 ] 



XLIX. On a Method of Comparing the Electrical Capacities 

 of two Condensers. By R. T. Glazebrook, M.A., Fellow 

 of Trinity College, and Demonstrator of Experimental Physics 

 at the Cavendish Laboratory, Cambridge *. 



THE following is a well-known method of comparing the 

 capacities of two condensers : — 

 Let A, A / be the outer coatings, B, B' the inner of two con- 

 densers. Connect A A' together, and to one pole of a 

 battery. Connect B to a resistance R and to one pole of a 



B - 1 A 



galvanometer, B' to another resistance R/ and to the other 

 pole of the galvanometer. Connect the other ends of R R / 

 together and to a key K, and let the second screw of the key 

 be in connexion with the other pole of the battery. Let C C / 

 be the capacities of the condensers. On depressing the key 

 the condensers are charged; and it is easy to show that, if 

 CR=C / R / , no current passes through the galvanometer. 



If, then, we adjust R until no current is observed on making 

 contact, W remaining unaltered, we can find the ratio of C to C 



I propose to discuss the more general problem of finding 

 the current through the galvanometer when the equation 

 CR=C / R / is not fulfilled, and hence to obtain the conditions 

 of sensibility. 



Let Vj be the potential of A, V 2 of the other pole of the 

 battery, V of B, V' of B', at time t. Let G be the galvano- 

 meter resistance. 



Let 



,/ 



h = 



current in R ; 



current into condenser A ; 



T) , 



current through galvanometer ; 

 the quantities in the condensers. 



* Communicated by the Physical Society, having been read at the 

 Meeting- on January 22. 





