﻿for Measurement of Resistances and Capacities. 299 



axle. In general the reversals of the battery commutator 

 produce an alternating current in the arms of the bridge, 

 which gives rise to a direct current through the galvanometer 

 in consequence of the second set of reversals. The general 



Fijr. 1. 



theory of the bridge shows that the alternating current in the 

 arm B C, and with it the direct current through the galvano- 

 meter, will vanish when P, Q, R, and H are adjusted so that 

 the double equality is satisfied, 



? = ? = ? (1) 



Thus if any two of these four variables, say Q and H, be 

 fixed arbitrarily, an adjustment of both P and 11 is required 

 to effect a complete balance and determine S and K. P and 

 R are taken throughout in this paper as the adjustable 

 variables. 



Incomplete Balances. — The use of the secohmmeter presents 

 at the outset an effect which does not exist in the telephone 

 methods in the fact that, besides the complete balance, an 

 infinite number of balances may be obtained which are 

 characterized by zero galvanometer deflexion. In fact, 

 generally, R being given any value, P may always be adjusted 

 so as to bring the galvanometer-needle to zero. The following 

 pairs of values of R and P taken with the battery and 

 galvanometer reversed simultaneously are examples of this 

 effect. 



