Mr Townsend, Secondary Rontgen Rays. 



217 



Secondary Rontgen Rays. 

 Fellow of Trinity College. 



By John S. Townsend, M.A., 



[Received 1 December, 1899.] 



1. When Rontgen rays from a Crookes tube fall upon a 

 metal or other body a secondary radiation is given out which has 

 properties similar to the direct rays. The existence of this 

 secondary radiation was established by Sagnac 1 , who made a 

 series of experiments showing that the secondary radiation pro- 

 duces photographic effects and renders the air a conductor at a 

 distance of several centimetres from the radiating body. The 

 secondary radiation is weaker than the direct radiation from the 

 Crookes tube, both as regards its intensity and its power of 

 penetrating bodies. 



Sagnac contends that the surface effect noticed by Perrin' 2 

 was due to this secondary radiation, but it is difficult to reconcile 

 Perrin's results with this theory, without some modification. This 

 paper contains the results of some experiments made with a view 

 to finding how the two phenomena are connected. 



2. The apparatus shown in Figure 1 was used to determine 



Fig. l. 



the relative intensities of the secondary radiations given out by 



1 Sagnac, Journal de Physique, 3rd Series, vol. vm. Feb. 1899. 



2 Perrin, Comptes Rendus, vol. cxxiv. p. 455, 



