74 



Prof. Thomson, On the Conductivity of Gases 



On the Conductivity of Gases exposed to Entladungsstrahlen. By 

 Professor J. J. Thomson. 



[Communicated February 20, 1899. MS. received March 20, 1899.] 



Professor E. Wiedemann discovered that many bodies became 

 thermo-luminescent when placed near an electric spark or to 

 the electric discharge in a vacuum tube. He attributed this 

 effect to the emission from the region through which the discharge 

 was passing of a kind of radiation, to which he gave the name 

 Entladungsstrahlen. The properties of this effect have been 

 investigated by E. Wiedemann and by Hoffmann ( Wied. Ann. lx. 

 269). They found that the effect was propagated in straight lines, 

 was not deflected by a magnet, and was stopped by solids or liquids 

 and even by some gases such as carbonic acid gas. 



The object of the following experiments was to see if the 

 effect which produced the thermo-luminescence affected the 

 electrical properties of the gas through which it passed. 



The apparatus used is represented in Fig. 1. The discharge 



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Fig. 1. 



takes place between the electrodes ef in the horizontal tube AB ; 

 these electrodes can be moved along the tube, the distance 

 between them remaining constant. In this way different portions 

 of the discharge can be brought over the mouth of the vertical 

 tube CD. In this tube, which is fused on to AB, two well in- 

 sulated aluminium cylinders are placed; one of them faces the 

 discharge, the other is placed in a side tube nearer to the dis- 

 charge but so that no -rectilinear radiation from the discharge 

 can reach it. Along the axis of each of these is a well-insulated 

 wire. The outer cylinders and the wires are well insulated from 



