366 ELECTRICAL MEASUREMENTS 



As the currents have arrived at the steady state, 



/c N 



I* r~ M + Ro' 



Consequently 



IG IG N 



IP M + RG + N 



7P 7/1? , 

 + ^P^ - IGKG ~\ 



T 



and 



\ 7 



4 ft J IG 



where IQ is the galvanometer current when the circuit is in the 

 steady state. 



When e touches b, a varying current, i c , which finally becomes 

 zero, flows into the condenser and all the other currents are 

 temporarily altered. 



Let the alteration in I M be 81 M 

 in I N be 81 N 

 in IP be d! P 

 in I B be 81 B 

 in I G be 8I 



If Q G is the quantity of electricity displaced through the gal- 

 vanometer by the current 8I G at each contact of e and b and there 

 are n such contacts per second, the quantity per second so dis- 

 placed will be nQ G . 



Therefore, if the galvanometer stands at zero under the com- 

 bined action of I g and nQ G , 



IG + nQ = 

 and 



. (2) 



To find Q G , the quantity displaced through the galvanometer by 

 the variable current 8I when the condenser is charged, suppose 

 C to be discharged and the steady currents to be flowing as indi- 

 cated in Fig. 215. The potential differences between the ter- 

 minals of all the resistances will have definite values. As soon 



