

INDUCTANCE AND CAPACITY 387 



L x = L P |^. (15) 



r> 



Several trials with various values of ^ may be necessary before 



the proper ratio is found. 



In this and other methods where the balance is independent 

 of the frequency, a " buzzer" operating through a telephone in- 

 duction coil is often a convenient source of supply for the inter- 

 rupted current, the detector being a telephone. 



To prove the relation (15) the first condition stated on page 

 381 may be imposed. After the adjustment is complete no 

 current passes through the detector at any time, so for all values 

 oil, 



V bc = V dc 



v ab = v ad 



IM = ix 



iff = IP 



i_M_ _ RN __ ^x_ 



Iff t\>M 1p 



Therefore 



D i T ^ lx ; ( u u\ _i_ T p 



Ixtix i Lix ~j^~ = lp\lip ~\~ ti) ~r Lp rr 



so 



which must be true for all values of t. 



T M 

 Lip j^-i 



and . 



R> 



In order to balance the bridge when all four of the arms are 

 inductive, three instead of two conditions must be satisfied, as 

 will be seen from the following. 



