382 THE ELECTRIC TELEGRAPH. 



point a (Fig. 176), are connected by means of a contact key, 

 K, with a battery, E. The other end of the coil g',. goes to 

 one side of a condenser, (/, or to the interior of the standard 

 piece of cable; the other end of g to the interior of the 

 cable whose charge is to be measured. Part of the current 

 of the coil g is shunted by means of an adjustable resistance, 

 r. When the key is pressed down, the current divides itself 

 at #, part i', passing through the coil g, to the unit jar c', 

 and the remainder i, passing through the parallel circuit 



Q/j* 



a and r, whose combined resistance is - , into the 



g + r 

 cable c. 



Let the intensities in g and r be expressed by i and i lt and at 

 the moment of closing the circuit, let the needle be unaffected 

 by the currents, then 



I' m' = i m 



m 

 From the law of branch circuits, 



therefore 



m' I r I m g -\- r 



m g + r V m r 



and since the intensities of the charge currents at the mo- 

 ment of closing the battery circuit are proportional to the 

 capacities of the jars, or 



JL 



i' " a 



m 



For simplicity, to save measuring the constant of the 



m 



galvanometer, Mr. Yarley makes the coils g and g> of his 



