MEASUREMENT OF CAPACITANCE 425 



As mentioned above the method of this paper may obviously be 

 extended to the measurement of inductance in terms of resistance and 

 frequency. If in the circuit of Fig, 1, Ci is replaced by an inductance 

 L\ and C by an inductance L, at balance 



If as before Z-i is known in terms of L, i.e,, if 



Lx = AL, 

 Li can be eliminated from (4) and 



Expressing the relation (5) in terms of K, as in (3) above, 



This formula neglects the effective resistance of Li, The accuracy 

 with which the value of K can be determined will in practice probably 

 depend upon the accuracy with which the effective resistance of the 

 inductance Li can be determined, which in general will be somewhat 

 less than the accuracy of determining the conductance of the cor- 

 responding capacitance. 



Description of Apparatus 



The bridge equipment was a completely shielded equal-ratio bridge 

 built for the comparison of capacitance and including standard con- 

 densers in the bridge itself. In its adaptation to the Wien circuit the 

 standard condensers were cut out leaving a pair of equal-ratio resistance 

 arms, properly shielded. The two additional arms were made up of 

 external resistances and the condensers being measured. 



A description of the arrangement of the standards in the capacitance 

 bridge, however, is necessary to explain the means of obtaining the 

 precise value of the ratio of any two capacitances. The capacitance 

 standards, self-contained in the bridge, are variable from to 1 ;u/ and 

 are arranged in decade form, first an air condenser with a range of 

 slightly more than IOai/i/, then fixed condensers up to 1 ^t/ in 5 addi- 

 tional decades, each consisting of unit condensers controlled by 10 

 point switches. An external capacitance is measured by turning the 



