432 Drs. Beattie and De Sniolan on the Conductance 



The curves for air, oxygen, and hydrogen, given in fig. 8, 

 were obtained by taking the atmospheric pressure in millim. 

 as abscissa and the leakage per minute for four volts as 

 ordinate. 



Fig. 8. 



> 



^ 100 



# 



50 100 150 200 250 



AtrnospLeric pressure in inillims. 



§ 7. Measurement of the Difference of Potential between 

 wires of one metal connected with two mutually insulated 

 metals when. the air between them is rendered conductive by 

 Rontgen rays, by ultra-violet light, and by uranium. 



The fact that gases are made conductive by Rontgen rays, 

 by ultra-violet light, and by uranium supplies us with a 

 means of measuring the difference of potential between wires 

 of one metal connected with two mutually insulated con- 

 ductors. This method has already been used by Righi. 

 He determined the difference of potential of wires of one 

 metal connected to two mutually insulated conductors 

 by rendering the air between them conductive under the 

 influence of ultra-violet light. Minchin, Righi, and Murray 

 have made experiments of a similar kind with Rontgen rays. 



In our experiments to measure this difference of potential 

 between wires of one metal connected to two mutually 

 insulated conductors by rendering the air between two 

 mutually insulated conductors conductive by means of 

 Rontgen rays, we used a cylinder of unpolished aluminium 

 connected to the case of the electrometer. Along the axis of 

 this a conductor was placed, supported by its ends on small 

 blocks of paraffin. This insulated conductor was connected 



