INDUCTANCE AND CAPACITY 381 



Assuming sinusoidal currents the capacity is 



If the applied e.m.f. is not sinusoidal, the harmonics will be 

 exaggerated in the current wave, for the current is 



- 6 ) 

 Using root-mean-square values, 



Therefore, 



Fi 2 



BRIDGE MEASUREMENTS OF CAPACITY AND INDUCTANCE 



As originally devised, many of the methods for comparing 

 capacities and for comparing inductances, as well as methods 

 for determining an inductance in terms of a capacity, depended 

 on the employment of variable currents. As the industrial 

 uses of alternating currents have developed, especially in connec- 

 tion with telephony, it has become important that tests be 

 made under conditions which are as nearly as possible those 

 pertaining to the ordinary use of the apparatus. Hence, 

 alternating currents have replaced the variable currents formerly 

 employed and the methods for capacity measurement have been 

 so modified that they give data of value, in addition to determining 

 the capacity of the condenser under measurement. 



Condition for Zero Indication of Detector. When variable 

 currents are used in balance methods for measuring inductance 

 and capacity, a long period galvanometer is employed as the 

 detector. The arrangement of the circuits is such that at balance 

 no permanent current flows through the instrument ; this being 

 so 



1. The deflection will certainly be zero if no current flows 

 through the galvanometer at any time during the establishment 

 of the permanent state of the circuit. 



2. Presumably the deflection will also be zero when the net 



