464 Dr. E. Goldstein on the Influence of the 



from the intersection of the rays emitted by one half of the 

 cross with those from the other half, was shown to be probable 

 by the experiments already described with stars of an uneven 

 number of arms. This may, however, be better shown by 

 experiments with screens arranged to throw shadows, which 

 also prove the same thing for kathodes with an even number 

 of arms. 



If we arrange (fig. 18 a) a screen of paper or of mica in front 

 of the kathode, and at a distance from its centre less than the 

 radius of curvature, so that, for example, the lower half of the 

 kathode-cross is covered, then in the phosphorescent image it 

 is the upper half of the cross which is wanting (fig. 18 L). 



Since at a certain density these images formed on the wall 

 at the distance 2 p from the kathode possess nearly the same 

 dimensions as the kathode itself, it follows that the rays which 

 produce the images, at least for the most part, are under these 

 circumstances at right angles to the surface from which they 

 are emitted, assuming, of course, that their course till they 

 strike upon the walls of the tube is rectilinear. 



(Exactly similar experiments show that the images of ordi- 

 narv polygonal kathodes observed at small pressures are 

 formed by the intersection of the rays which issue from points 

 situated symmetrically with reference to the centre of the 

 kathode.) 



As with the figure of the kathode-cross, so also in the con- 

 tour of the square (fig. 12 b) which appears surrounding the 

 figure of the cross as the density decreases, each side is formed 

 by rays which come from the opposite side of the kathode. 



We may obtain a more satisfactory explanation of the figures 

 of kathode-crosses which appear at small densities ; we only 

 need to place a screen P(fig. 19 a) between two of the arms 

 of a cross, so that it projects beyond the kathode on the con- 

 ca\e side. The screen may be rectangular, and the edge 

 which faces towards the image may be called its front edge. 

 1 anticipated, and the anticipation was verified by experiment, 

 that the figures which correspond to the higher degrees of 

 exhaustion are formed by the rays emitted by one arm of the 

 kathode suffering a repulsion by the neighbouring arm, of the 

 same or a similar kind to that described in my work on ka- 

 thodic deflection. This deflection cannot take place through a 

 solid plate. 



If now, at high exhaustion, we obtain repeatedly the figure 

 with the dark cross so often mentioned, then, when the plate 

 is introduced, we obtain the figure 10 6; or, if the plate 

 does not project so far beyond the kathode, we obtain 1!» c. 



We have therefore, in the first case, only the left bounding 



