Formuhc used in Inductance Measurements. 797 



A balancing inductance, L 2 =^L', is inserted in the arm 

 A 2 B. This evidently cancels out with I/, and we are left 



with L = ( 1 + - 1 -) M. The most convenient ratio for — is 



either 9 or 99, the appropriate balancing coil being ac- 



T ' L' 

 eordingly -j or ^ . 



When used with equal arms for small self-inductances the 

 secondary of M is divided, half being in each of the arms 

 AjB and A 2 B. The vector diagram becomes slightly 



altered, as PB is now equal to c 2 L 2 cb + — — ^ and 



BQ to — — -^ , half of the mutual inductances being 



in each arm. [The connexions, of course, are such that when 

 the E.M.F. induced in the lower arm is in the direction 

 A^, that in the upper is in the direction BA 2 .] The 

 equations remain as before, and since the value of L' is the 

 same in each arm this cancels, so we get L = 2M where L is 

 the self -inductance to be measured, and, as before, forms 

 part of the arm A 2 B. 



Comparison of Two Capacities [De Sauty's Method] . 



Fisr.4 



Circuit Diagram 



Vector Diaqram 



^ The argument is identical with that for self-inductances. 

 The upper vector diagram refers to the case of condensers 

 which are perfectly free from either dielectric hysteresis or 

 leakage, so that the currents through them are in exact 

 quadrature with the P.D.'s across their terminals. 



