1887.] 



Specific Inductive Capacity. 



157 



of determinate and approximately equal capacity ; the other two, J, I, 

 were adjustable slides, the capacity of either condenser being varied 

 by the sliding part. The outer coatings of the condensers E, F, were 

 connected to the case of the quadrant electrometer, and to one pole of 

 the induction coil ; the outer coatings of the other pair, J, I, were 

 connected to the needle of the electrometer and to the other pole of 

 the induction coil. The inner coatings of the condensers J, F, were 

 connected to one quadrant, and I, E, to the other quadrant of the 

 electrometer. The slide of one or both condensers J, I, was adjusted 

 till upon exciting the induction coil no deflection was observed on the 

 electrometer. A dummy was provided with the fluid condenser, as 

 in my former experiments, to represent the necessary supports and 

 connexions outside of the liquid. Let now x be the reading of the 

 sliding condenser when no condenser for fluid is introduced, and a 

 balance is obtained. Let y be its reading when the condenser is 

 introduced fitted with its dummy, z when the .full condenser is charged 

 with air. Let z Y be the reading when the condenser charged with 

 fl uid is introduced, then will K, the specific inductive capacity of the 

 liquid, be equal to (y—^i)/(y—z). 



Three fluid condensers were employed, one was the same as in my 

 former experiments.* Another was a smaller one of the same type 

 arranged simply to contain a smaller quantity of fluid. The third 

 was of a different type designed to prove that by no chance did any- 

 thing depend on the type of condenser ; this done it was laid aside as 

 more complicated in use. 



To determine the capacity of a solid, the guard-ring condenser of 



Fig. 2. 



* ' Phil. Trans.,' 1881, Part II. 



