Alternating Currents to Calibration of Capacity -boxes. 719 



in the arm R (see fio-. 2). We are now in a position to 

 dispense altogether with tlie steady currents in the inductance 



Fio-. 2. 





D C S^\,)>i^ 



measurement. The bridge is balanced with W and 30 or 

 40 ohms non-inductive resistance in the arm, but without the 

 condenser connected to the bridge. The switch is then rocked 

 over, the condenser connected, and the bridge again balanced 

 for C bj adjusting the resistance r. We found the experi- 

 ment hopeless with the air-leyden, r = and r = co giving 

 deflexions in the same direction. Obviously the capacity of 

 the air-leyden was too great. We therefore constructed a 

 rough air-condenser of two concentric tubes 34*4 cms. long, 

 the mean diameter being 6*3 cms. The tubes were separated 

 from one another by three small pieces of ebonite attached at 

 each end to the inner tube. The calculated capacity of this 

 condenser was 219 M.M.F.'s. On replacing the air-leyden by 

 this condenser we could easily measure the inductance^ and 

 the following results were obtained using the moving coil 0. 



Table YII. 



i c. 



1 



S. 



Q- 



P. 



r. 



L. 



r 



19-9 



1869-3 



4165-5 



240-7 



-000241 henries 



219 M.M.F.'s 1 



19-9 



984-7 



2112-7 



496-8 



-000244 „ 



f 

 1 



19-9 



1181-7 



2526-5 



415-2 



•0U0245 „ 



a B2 



