produced in Gases by Rontgen Rays tyc. 437 



to prevent inductive effects from the lamp. With the Rontgen 

 rays shining in between the insulated disk and the opposing 



Fig. 10. 



ELECTROMETER 



TINFQIL BQ* 



tinfoil wall so as to illuminate both, the following results were 

 obtained : — 



Difference of potential 

 between rays-zero 

 and metallic zero. 



+ 0-168 of a volt 

 + 0-179 „ 

 + 0-165 „ 

 + 0-165 „ 



Distance between 

 the surfaces. 



1*2 centim. 



2-2 „ 

 3-8 „ 

 6-0 .. 



With a polished zinc disk in place of the oxidized copper 

 disk we found :— 



0-580 of a volt 

 0-565 „ 

 ■0-580 „ 

 •0-640 „ 

 0-640 „ 



at 1 centim. distance. 

 J? 1'5 „ „ 

 » 3-0 „ „ 

 » 7-0 „ 

 ii 7*5 ,, ,, 



The effect of changing the distance between the opposed 

 surfaces is to vary the capacity of our arrangement. Had 

 the Rontgen rays given a charge to the insulated conductors 

 other than that necessary for the equalization of the volta 

 difference of the two mutually insulated conducting surfaces, 

 this would have been shown by a variation of the potential- 

 difference observed in the electrometer when the distances 

 were changed. We should not, however, be justified in con- 

 cluding that the difference between the rays-zero and the 

 metallic zero is the contact-difference between the electrically 

 effective surfaces of the mutually insulated conductors. 



We used the same arrangement with ultra-violet light, A 

 glance at fig. 10 will show how the light was placed so as 

 to fall on both surfaces. The insulated conductor employed 

 was the same oxidized copper disk as used in the Rontgen ray 

 experiments. The difference between the metallic zero and the 



