438 Drs. Beattie and De Smolan on the Conductance 



ultra-violet-light-zero was found to depend on the distance 

 between the two surfaces. This will be seen from the follow- 

 ing table : — 



Difference of potential between 



ultra-violet-light-zero 



and metallic zero. 



Distance between 

 the surfaces. 



+ 0-615 of a volt. 



0*6 centim. 



+ 0-730 „ 



1 



»> 



+ 0-805 „ 



2 



»? 



+ 0-955 



3 



»i 



+ 1-205 ., 



4 



55 



+ 1-07 „ 



4-3 



51 



+ 1-15 



5-0 



»5 



+ 1-42 



7-0 



It 



The fact that the ultra-violet-light-zero depends on the 

 distance between the two mutually insulated conductors was 

 first observed by Righi. We have here something in reality 

 much greater than a mere equalization of the volta difference 

 between the two surfaces, and we cannot say that the differ- 

 ence of potential between the ultra-violet-light-zero and the 

 metallic zero at any arbitrary distance is the volta difference 

 between the electrically effective surfaces of the two metals. 



To observe the uranium-conductance-zero at different dis- 

 tances an aluminium box connected to the case of the electro- 

 meter was substituted for the tinfoil one. The insulated 

 metal was again oxidized copper — not, however, the same 

 specimen as was used with ultra-violet light and with Rontgen 

 rays. The uranium was placed outside the aluminium box 

 about 5 millim. from the end, to which the oxidized copper 

 was kept parallel. 



Potential-difference between 



Distance between 



uranium-conductance-zero 



the mutually 



and metallic zero. 



insulated surfaces. 



+ 0-96 of a volt. 



0-5 



centim. 



+ 0-97 „ 



1-5 



?> 



+ 0-95 „ 



2-0 



»? 



+ 0-98 „ 



4-0 



?» 



+ 1-03 „ 



8-0 



>? 



We see that the potential-difference does not depend on 

 the distance. We cannot, however, infer that therefore the 

 difference between the conductance- zero and the metallic zero 

 is the contact -difference between the electrically effective 

 surfaces of the mutually insulated conductors. 



§ 9. Difference of Potential due to Uranium in different 

 Gases at different pressures. 



