174 Scientific Proceedings, Royal Dublin Society. 



connected to the Kelvin electrometer. The capacity of the electro- 

 meter, the condenser as arranged (fig. 2), and joining wires is 

 determined by comparing it with a standard capacity of '001 

 microfarad. 



A careful series of observations is then taken, with cd in its 

 above position, using a suitable quantity of uranium nitrate. 



Fig. 2. 



Then the tube cd is moved 8*01 cms. further into AB, care being 

 taken not to displace AB or ab. A vernier was attached to cd 

 working in a slot in abf&o that the distance through which cd was 

 displaced could be accurately measured. A second series of 

 observations was then made with cd in the new position, keeping 

 the same uranium as before. "We have thus the data for deducing 

 from the experiments the increase of capacity produced by the 

 movement of cd. This increase of capacity can also be accurately 

 calculated from the formula 



/ 



2 log J 



since the effects of the ends are eliminated by the arrangement 



used, / being the distance cd is moved, and r\ and r 2 the radii of 



AB and cd respectively. We can thus estimate the value of the 



method for measuring very small capacities. 



The numbers observed were as follows : — 



(1) Finding the capacity C made up of the condenser described 



(fig. 2), the electrometer, and connections, 



-ooi + G 



100 divisions in 397" 50 divisions in 117-8" 



100 divisions in 39-6" 50 divisions in 118-1" 



100 divisions in 39-5" 50 divisions in 117-8" 



Mean, 39-6" Mean, 117-9" 



mi . C+-001 235-8 



Therefore, ___=___; 



or, C = -000201 microfarad ; 



or, C = 201 micro-microfarads. 



