MEASUREMENT OF CAPACITANCE 



421 



The present paper describes the adaptation of a bridge circuit due 

 to M. Wien/ together with apparatus and procedure, which permits a 

 measurement of capacitance in terms of resistance and frequency with 

 an accuracy comparable to that of the primary standards. To illus- 

 trate the possibilities of the method in practice the results of a specific 

 determination are included. Among its advantages over Maxwell's 

 method are the use of a single frequency voltage and the fact that there 

 is no general limitation placed on the type of condenser which may be 

 measured or on the frequency at which the measurement may be made. 



Fig. 1 



The method described is also generally applicable to the determina- 

 tion of inductance, since its unit, like that of capacitance, may be 

 derived from the units of resistance and frequency. The circuit and 

 procedure to be described may be used with a change of only minor 

 details. 



In its simplest form the bridge, as shown in Fig. 1, consists of two 

 equal resistance ratio arms, a third arm containing a capacitance and 

 a resistance in series, and a fourth arm containing a capacitance and 

 a resistance in parallel. A balance is easily made by varying any two 

 of the five variables, viz., the two capacitances, the two resistances as- 

 sociated with them, and the frequency. 



If, at balance, the frequency and any two of the other variables are 

 known, the remaining two can be determined. Thus if the frequency, 

 the resistance in the series arm, and the resistance in the parallel arm 

 are known, the magnitude of both capacitances can be determined. 

 However, the equations for balance, which are given below, are such 

 that if the ratio of the capacitances and the value of the frequency are 



* M. Wien, Weid. Ann., 1891, p. 689. 



