460 Dr. E. Goldstein on the Influence of the 



following general rules (4—7), however, hold good for all the 

 kathode-forms mentioned. 



4. At constant density of gas, the forms of the phospho- 

 rescent images (not only their absolute dimensions) alter when 

 the distance of the kathode from the wall of the vessel is 

 made to change; as the distance of the wall decreases, the same 

 figures appear, in the same order, as when the distance of the 

 wall remains constant and the density of gas decreases. 



Instead of altering the distance of the wall by displacing 

 the kathode, we may, as in the vessel represented in fig. 17, 

 displace the wall which receives the rays with reference to the 

 kathode. 



If we experiment with varying distance of wall, and also 

 with varying density of gas at the same time, then, in order to 

 pass from one given figure to another of the same series, the 

 wall must be displaced through a greater distance the smaller 

 the density of gas is. 



This shows that all the figures which a kathode can call 

 forth upon a fixed wall as the density of gas decreases, do at 

 any fixed density of gas already exist in space one behind 

 the other at the same time, and that the different figures are 

 produced by the rays intersecting each other in various ways 

 at different points of space. As the density of gas decreases, 

 the images move further apart and further away from the 

 kathode, no doubt because the rays which first converge 

 become less convergent, and then, when after intersection 

 they diverge, their divergence is decreased. 



The influence of the distance of wall thus described would 

 lead us to expect that the series of images given in figs. 12 and 

 15 as examples obtained with a kathode at a distance equal to 

 twice the radius of curvature, would not include all the forms 

 which the particular kathode is capable of producing, but that 

 a diminution of the distance of the wall at the highest obtain- 

 able exhaustion would in general give other figures besides 

 these. This conclusion is found to be confirmed by ex- 

 perience, although the forms thus obtained are not for the 

 most part so striking as those previously described. It may, 

 however, be mentioned at this stage as worthy of consideration 

 further on, that upon diminishing the distance of the wall the 

 dark arms of the cross in fig. 11 e increase considerably in 

 width. 



5. If we take similar plane figures, and then bend them into 

 portions of spheres of different radii, p 1} p 2 , p 3 , and place 

 them as kathodes in similar vessels with equal distance of 

 wall, then at equal density their images represent different 

 phases of the series of figures obtained from a single such 



