﻿Electrical Changes induced by Ultraviolet Light. 409 



in the dark, emits charged corpuscles deflectable by a 

 magnet; the amount of disintegration is very small, even 

 in the case of so active an element as sodium : so that 

 one would scarcely expect to be able to detect it in the case 

 of the less electropositive element. Nevertheless, in all pro- 

 bability the ultraviolet light, as suggested by Thomson, acts 

 as a detonator, bringing about the disintegration, otherwise 

 immeasurably slow, at an increased rate. The ultraviolet 

 light would therefore seem to act as an accelerator in the 

 breaking up of atoms. This idea seems to be confirmed by 

 the experiments of Strutt*, on the radioactivity of ordinary 

 materials. He obtained small discharges from plates of 

 various metals under ordinary conditions. These values, as 



Table VI. 



Element. 



Leak in dim per hour. 1 



Al 



1-4 

 1-2 

 2*2 

 2-3 

 (3-9—20) 



Zn 



Pb 



Cu 



Pt 





will be seen from Table VI., run parallel with the electro 

 potential of the elements ; aluminium is the only element 

 which is an exception to the series. Silver was also measured, 

 and gave a result which does not come into the series ; but 

 the silver was deposited on glass, and this may have modified 

 the result. Clearly, then, the action in our experiments and 

 those of Strutt is the same, the only difference being that we 

 have increased a small natural radiation by the use of ultra- 

 violet light. The experiments of Bumsteadf, although they 

 are in direct opposition to ours, do not of necessity prove 

 very much: they have in the first place only been carried out 

 for two elements, and in the second place, as pointed out by 

 the author himself, there are a great many sources of error. 

 "When palladium was charged wich either hydrogen or oxygen 

 very remarkable results were obtained : the value in both 

 Series A and B, Table V., places them between lead and 

 copper, a position in accordance with their place in electro- 



* Strutt, Phil. Mas. June 1903, p. 680. 

 f Bumstead, Phil. Mag. Feb. 1906, p. 292. 



