176 



Almy — Discharge-current from a 



p. The cork, S, which closed the upper end of the cylinder, was 

 coated with sealing-wax, surface-leakage, even when the glass 

 tube became coated with moisture, being thus prevented. 



The electric connections are sketched in fig. 2. W, a Wims- 

 hurst machine, was driven by a small motor. A galvanometer 

 (D'Arsonval), G, measured the discharge current ; potential dif- 

 ferences between wire and cylinder were read on a 'Braun,' — 

 later a Kelvin, l vertical,' voltmeter, V. Potential differences 

 were regulated by a fine discharge-point shunting the poles of 

 the Wimshurst. 



As air, which was the gas used throughout the first portion 

 of the observations, shows some deterioration with use, when 

 the discharge current attains to a measurable value (by 

 u deterioration " is meant a decrease of its capacity to carry 

 on the discharge), fresh, dried, gas was continuously drawn 

 through the discharge apparatus. 



As only relativity was wished for, the voltmeter and galva- 

 nometer were not standardized; nor were the variations of 

 atmospheric pressure, from day to day, noted. 



Observations. 

 3. First, the proportionality of total discharge to length of 

 the discharge wire was tested. It was found, that so long as 



tfcnB.-. 



% 



the length of wire is greater than the diameter of the cylinder, 

 and with the paraffin discs restricting the volume of the gas 

 which takes part in the discharge to the solid cylinder of the 

 length of the wire, the current is directly proportional to the 

 length of the wire, with a given applied potential, and the 

 minimum potential difference that will produce measurable 

 discharge current is independent of the length of the wire. 

 In case short lengths (as compared to cylinder diameter) 



