Mr Orange, On certain phenomena of the kathode region. 221 



This would indicate that at this pressure the discharge is 

 taking place almost entirely from the corners of the kathode, the 

 probable explanation being that the electrostatic field at this 

 stage is somewhat similar to the simple field due to a charged 

 triangular conductor. If this is so, those portions of the sides of 

 the kathode which are free from dark space will correspond very 

 well with the regions of weakest electric intensity. But these 

 regions of low intensity are the places where the lines of force are 

 straightest. Hence, when the mean free path in the gas is suffi- 

 ciently great for the untrammelled formation of kathode rays, the 

 discharge will tend to occur to a greater extent than previously 

 from those parts (according to Prof. Thomson's view given above), 

 and the Crookes' dark space will surround the whole triangle, 

 although it will be somewhat narrower opposite these places. 

 [e.g. ctr. Figs. 1 and 2, PL IV.] 



In the next photograph, Fig. 2, PI. IV, the pressure is a little 

 lower and the kathode rays have become visible. They appear to 

 come off from practically the whole lengths of the sides of the 

 triangle, and show maxima of luminosity at certain places. It 

 seems only too probable, however, that the three connecting pins, 

 the ends of which appear in the photograph, play a large part in 

 determining the positions of these maxima. Notice in this and 

 the following photograph, Fig. 1, PI. V, the dimpled boundary of the 

 Crookes' dark space opposite each of the three sides of the triangle, 

 as referred to above. 



The next photograph. Fig. 2, PI. V, has a very vague appearance 

 because at this stage the kathode rays, although now past their 

 maximum of brightness, are still fairly active photographically, 

 by virtue of their bluish colour, whereas the canal rays, in spite 

 of their prominence visually, are inadequately recorded by the 

 camera owing to their reddish colour. We thus have a medley of 

 two kinds of rays which it would be difficult and unprofitable to 

 unravel at this stage. The beginning of the green phosphorescence 

 due to kathode rays is visible in this photograph in three patches 

 corresponding to the three sides of the triangle, but the next view. 

 Fig. 1, PI. VI, associated with an increased exhaustion, shows the 

 phosphorescence very well. The blaze of light which masks the 

 kathode in this case, represents the phosphorescence on the glass 

 wall nearest to the camera. The actual space within the vessel is 

 almost free from luminosity, but it is still possible to make out 

 the boundary of the Crookes' dark space and a few traces of the 

 rays. 



The last photograph of this set. Fig. 2, PI. VI, is certainly the 

 most interesting owing to the distinct appearance of the ' canal 

 rays ' [so-called by Goldstein*]. It corresponds very nearly to 



* E. Goldstein, Phil. Mag. March 1908, p. 378. 



