Mr Orange, On certain 'phenomena, of the kathode region. 217 



On certain phenomena of the kathode region. By J. A. Okange, 

 B.A., Major .Scholar of Trinity College. [Communicated by 

 Professor Sir J. J. Thomson.] 



[Bead 17 May 1909.] 



(Plates IV— IX.) 



In the discharge through rarefied gases, the appearances 

 surrounding the kathode seem to be quite independent of the 

 form and situation of the anode, and also of the shape of the 

 containing vessel, provided that the latter does not approach too 

 near to the kathode. For instance, if one arranges any kind of 

 kathode, of linear dimensions up to about 4 cms., in the middle 

 of a glass bulb of about 10 cms. diameter, the various luminous 

 effects associated with the kathode and known as glows and rays 

 (together with the secondary effect of phosphorescence on the 

 walls of the vessel) appear to have no relation to the position of 

 the side tube which contains the anode, but are determined solely 

 by the characteristics of the kathode, the intensity of the discharge, 

 and the pressure of the gas through which it passes. 



Throughout the whole range of what are termed low pressures 

 (pressures less than 1 mm. of mercury, say) the surface of demar- 

 cation between the Crookes' dark space and the negative glow is 

 one of the most conspicuous features of the region and, moreover, 

 its form is of considerable theoretical interest. The rajs which 

 have been observed in the neighbourhood of the kathode fall into 

 two classes, the first, which is now fairly well defined, consisting of 

 the kathode rays, rays that are twisted readily by the application 

 of a weak magnetic field, while the second consists of a number 

 of rather indefinite radiations to which Goldstein* has applied the 

 name of ' The Canal Ray Group.' 



Both classes of rays are in a sense more difficult of treatment 

 than the glows and dark spaces, for there is no one characteristic 

 by which a radiation may be apprehended, throughout the whole 

 range of pressures at which it undoubtedly exists. For example, 

 kathode rays have a maximum of luminosity at a certain pressure. 

 If the exhaustion is carried further the rays gradually become less 

 luminous, but at the same time another property is coming into 

 evidence, namely, the power of producing phosphorescence on the 

 glass, until finally we have quite invisible rays manifested solely 

 by the vivid phosphorescence at their termination. The canal 

 ray group shows luminosity within a still more restricted range of 

 pressure and gives rise to much inferior phosphorescent effects. 

 By piecing together the rather fragmentary evidences of the 



* E. Goldstein, Verhandl. d. D. Physik. Gesellsch. (iv), p. 228, 1902; Phil. Blag. 

 March 1908, p. 372. 



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