and the Double Refraction of Insulating Fluids. 3 
discharged while in the insulating fluid or in air by a sensitive 
multiplier, the ratio of the deflections of the multiplier gave 
the ratio of the capacities of the condenser, or the dielectricity- 
constant K. 
Finally the upper condenser-plate was removed, and replaced 
by a plate of equal dimensions with a short vertical metal tube 
in the centre, which was connected with a sulphide-of-carbon 
manometer and a long tube of caoutchouc furnished with a 
cock. 
While both plates of the condenser were conducted to earth, 
dry air was blown through the caoutchouc tube into the space 
between the condenser-plates, and a flattened air-bubble pro- 
duced, touching the plates in two equal surfaces of from 2 to 
5 centim. diameter. Then, with the cock closed, the separa- 
ting fluid showed in the two legs of the manometer a differ- 
ence of heights that was constantly less than 1 centim. and 
depended on the hydrostatic and capillary pressure of the 
fluid upon the air-bubble. 
If the two plates were now brought to the difference of 
electric potentials for which the weights Gri and Grn had been 
determined, the electrical transverse pressure in the interior 
of the fluid counteracted the electrical transverse pressure in 
the interior of the air-bubble, and the difference of heights of 
the fluid in the manometer received an increment Ji. This 
increase was independent of the diameter of the air-bubble, 
and proportional to the square of the electric potential-differ- 
ence. It varied, with the different fluids, between Olo and 
1 centim. 
If a denotes the specific gravity of the separating fluid, the 
difference of the electric transverse pressures upon unit sur- 
face in the interior of the fluid and of the air-bubble is 
07T or v J 
For the same potential-difference P and the same distance 
a of the plates of the condenser from the surface 0, the pulling 
force parallel to the lines of electric force in the interior of the 
fluid, for the unit of surface, had been found, 
Gn_Kp P 2 
_ 8tt a 2 ' (o) 
or, by division of both equations, 
K I= ^.K P (4) 
B2 
