370 
DR. J. HOPKINSON ON THE ELECTROSTATIC 
insulated cylinder could hang; three brass rods suspended the latter from an ebonite 
ring which rested on three legs rising from the outer cylinder of the annular vessel. 
The position of the insulated cylinder was geometrically determined by three brass 
stops (a, a, a) which abutted against the legs which carried the ring, six points being 
thus fixed. A dummy ebonite ring with three brass rods, but without the cylinder, 
was provided for the purpose of determining the capacity of all parts and connexions 
not immersed in fluid. 
Fig- *5 
Half full size. 
The condenser was balanced against a sliding condenser, first with air and then with 
fluid. 
The key which was used for experiments on plates was used here also, leaving the 
piece connected to the guard ring idle. 
The capacity of the sliding condenser was first tested with the result that to the 
reading of the slide 82'2 must be added to obtain the capacity in terms of the milli¬ 
meter divisions of the scale. The capacity of the fluid condenser empty, with its 
connexions, was 106'5 divisions. The capacity of the dummy and connexions was 7‘7, 
so that the nett capacity of the fluid condenser was 98'8. In all cases 1000 AgCl 
elements were tried, these being divided between the two condensers. 
The following tables give the results obtained :— 
Column I. is the number of elements charging the fluid condenser, the complement 
being used on the sliding condenser. 
Column II. the reading of the slide plus 8 2 “2 when a balance was obtained; this is 
the mean of two readings when the fluid condenser was respectively charged positive 
and negative. 
Column III. is the capacity calculated from the experiment. 
