﻿402 Sir W. Ramsay and Dr. Spencer on Chemical and 



1. The work communicated in this paper was undertaken 

 with the object of repeating some experiments of Le Bon, 

 described in several papers published in the Comptes rendus, 

 and afterwards in greater detail in his treatise & evolution de 

 la Matiere. It will be remembered that Le Bon, by 

 allowing ultraviolet light to fall upon clean metallic surfaces 

 raised to a high potential, caused them to give up their 

 charges. He also showed that when ultraviolet light 

 fell on a metal plate placed above, and at an angle of 45° 

 to the cap of a positively charged electroscope, it caused the 

 discharge of the electroscope. This he found was also 

 the case when the electroscope cap was completely covered 

 by an earth- connected aluminium screen. The discharge 

 likewise takes place when the electroscope is charged 

 negatively, although with greatly diminished rapidity. Le 

 Bon concluded, from these experiments, that disintegration is 

 effected by the action of light on the surface of the metal, and 

 that this consists in the expulsion of charged particles capable 

 of penetrating metallic screens. It is not proposed to discuss 

 here the literature on this subject, but it may be mentioned 

 that previous to Le Bon's publications some of his results 

 had been anticipated, among others by Elster and Geitel, 

 Hoor, Stoletow, Wiedemann and Ebert, Hallwachs, Righi, 

 and Branley. 



Fig. 1. Fig. 2. 



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2. In our first experiments an iron arc served as the 

 source of ultraviolet light, but it was discarded because of 

 the great difficulty experienced in maintaining its intensity 

 constant. An electroscope of very small capacity was used 

 as the measuring instrument in all the experiments to be 

 described. It consisted of a very thin brass plate X (figs. 1 

 and 2) connected to a thin rod which also carried the cap of 



