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the secondary of a step-up transformer has an inductance which is 

 inconveniently large to measure directly, and the ratio of transforma- 

 tion circuit eliminates this necessity. The circuit used is practically 

 the same as that already described for measuring inductance balance, 

 the ratio of transformation being equal to the ratio of the resistance 

 arms of the bridge at balance. 



Capacitance. The direct comparison of capacitance is made in a 

 special bridge known as the Campbell ^-Colpitts ^ capacitance and 

 conductance bridge. The ratio arms, input and output circuits, and 

 the shielding are similar to the impedance bridge already described. 

 The unique feature of this bridge is the method of connecting the 

 standard air condenser to eliminate the dielectric loss in the measure- 

 ment of capacitance. The schematic diagram of the bridge is shown 

 in Fig. 7. Instead of connecting the standard condensers in the 



Fig. 7 — Schematic circuit of capacitance and conductance bridge 



arm AD as in the case of the impedance bridge already described, a 

 special switch is used to switch these condensers from AD to CD, 

 and in the case of the continuously variable condenser, the three-plate 

 construction is used, causing a decrease in the capacitance in CD as 

 the capacitance in AD is increased. 



The method of construction of the unit air condensers is shown in 



8G. A. Campbell, "The Shielded Balance," Electrical World and Engineer, 

 April 2, 1904, p. 647. 



9G. A. Campbell, "Measurement of Direct Capacities," Bell System Technical 

 Journal, July, 1922, p. 18. 



