THE SPECIFIC INDUCTIVE CAPACITY OF A DIELECTRIC. 
13 
clamped to a support about 18 inches above the surface of the liquid; so that the 
quadrants touched nothing except the liquid and this perfectly insulating support. 
The needle was suspended by a fine wire from the same height so as to oscillate under 
torsion. 
The hollow top of the water bath had seven holes through it, as shown in the 
figure. Through the outside four passed, without touching, the rods supporting the 
quadrants, through the centre one hung the needle, and through the two next the 
centre thermometers could be inserted. This top was permanently fixed to the 
support of the needle and quadrants; and the lower part of the bath containing the 
liquid was moved up on a smooth sliding arrangement into contact with the top so as 
to immerse the needle and quadrants. Above the fixed top of the bath was a box 
with a window on one side, through which the movements of the needle and mirror 
were read by a scale and telescope. The deflections of the needle were observed when 
connected first to one pair of quadrants and then to the other pair. 
As the needle and quadrants were parts of cylinders between three and four inches 
diameter and about a quarter of an inch apart, a large electromotive force was required 
to produce a deflection. The electromotive force had also to be rapidly reversed in 
direction to avoid as far as possible polarisation, convection, &c., in the liquid, The 
electromotive force was obtained from a Rulimkorff coil without a condenser, and 
with a high resistance between the terminals to prevent sparking. This high 
resistance consisted of a wdde glass tube, about 6 inches long, filled with distilled 
water, and having a thick copper wire sliding through a cork at each end. By 
altering the distance of the ends of the copper wires in the water the resistance could 
be adjusted and the deflection controlled as desired. The coil was worked by a 
current from the storage cells in the Laboratory. 
As the electromotive force given by this arrangement was variable, and also the 
loss of electromotive force by conduction was different for each liquid and for each 
temperature, it was necessary to be independent of such changes. Accordingly a 
second electrometer was placed between the terminals just outside the liquid one, 
which being always in the same state gave the comparative values of the electromotive 
force. This second electrometer was an Elliott’s lecture-room pattern with two 
quadrants removed and the needle connected to one of the remaining quadrants. 
The advantage of this form for the present purpose was that by moving the needle 
up from the quadrants the deflection could be diminished to any desired extent. 
Then the quotient of the deflection of the liquid electrometer by the deflection of the 
second electrometer was proportional to the specific inductive capacity of the liquid. 
For every deflection of the liquid electrometer a pair of deflections of the second 
electrometer were taken with the needle connected first to one pair of quadrants and 
then to the other. The general arrangement of the apparatus is shown in the figure. 
The liquids experimented upon were turpentine, carbon bisulphide, glycerine, 
benzene, benzylene, olive oil, and paraffin oil.* Methylated spirit was also tried; but 
