312 Professor Thomson, On negative electricity etc. 



Experiment to show that negative electricity is given off by a 

 metal exposed to Rontgen Rays. By Professor J. J. Thomson. 



[Read 23 November 1903.] 



Dorn as well as Curie and Sagnac have in different ways shown 

 that a metal exposed to Rontgen rays gives out cathode rays : this 

 I find can be shown very simply by mounting a small gold-leaf 

 electroscope on a quartz support in a vessel in which a very good 

 vacuum can be produced ; when the vessel is exhausted and the 

 gold leaves exposed to Rontgen rays they diverge and on testing 

 they are found to have a charge of positive electricity. If before 

 exposure to the rays the leaves are charged negatively then when 

 the rays are applied the leaves at first collapse and then diverge, 

 while if the initial charge is positive the divergence of the leaves 

 increases from the time of putting on the rays. In this way we 

 get a very direct proof that the gold leaves when exposed to the 

 rays acquire positive and lose negative electricity. 



