Mr Whiddington, Specific Inductive Capacities of Liquids 445 



A Laboratory Valve method for determining the Specific Inductive 

 Capacities of Liquids. By R. Whiddington, M.A. 



[Received 30 July 1921.] 



The method outhned below has been used successfully by students 

 as a laboratory exercise in the Physics Laboratories of Leeds Uni- 

 versity. 



The method employs alternating electro-motive forces of low 

 frequency generated by a thermionic valve linked with the usual 

 reacting circuits. 



The apparatus is shown diagrammatically below. On the left 

 is shown a standard circuit generating oscillations in the closed 

 circuit A consisting of a fixed condenser of about -5 m.f.d. and a 

 large air core coil. The natural frequency of this circuit is about 1000. 



Very loosely hnked to this circuit is a similar one B also comprising 

 an air core coil and condenser box, but in parallel with the latter 

 is arranged a small variable condenser C and a mercury cup switch 

 S so that an additional small condenser D can be switched in at will, 

 C is a moving vane air condenser fitted with pointer and scale, D is 

 a small parallel plate condenser the dielectric medium of which 

 can be easily changed without altering the distance between the 

 plates. Included in the anode circuit of this arrangement is a con- 

 denser shunted, and an aperiodic needle galvanometer G connected 

 as shown to a potentiometer P to balance the steady current flowing. 



