466 Dr. E. Goldstein on the Influence of the 



to decrease, but so that the two systems of rays still intersect 

 each other (at x, in fig. 22). 



If now a plate capable of phosphorescing move at right 

 angles to the plane of the drawing in the space free from rays 

 between the points of intersection x and o, a dark space will 

 be seen on it, bounded by its luminous intersection with the 

 repelled systems of rays; thus the upper arm of the dark cross 

 is bounded by its two luminous curves. As the density of 

 the gas decreases, the repulsion increases; the convergence 

 of the two pencils of rays will therefore be still further di- 

 minished; the point of intersection, x, moves further away 

 from the kathode; and the plate may now be further off from 

 the kathode and still show the dark cross. As we saw already, 

 in examining deflection, the rays further off from the repelling 

 surface are carried with those which are nearer to it, but are 

 not deflected through so great an angle; the deflected rays are 

 therefore compressed together on the side turned towards the 

 repelling surfaces; hence the greater brilliancy of the narrow 

 contour-line immediately bounding the dark arms. 



If the phosphorescent plate moves away from o beyond x, 

 the dark cross on it must of course disappear, since the plate 

 comes into a space occupied by rays. We must therefore 

 have a bright field on the plate opposite o, the outer contour 

 of which is again formed by the intersection of the plate with 

 bounding surface of the deflected system of rays. 



If we take account of the fact that, according to the form of 

 the dark cross, the curved surfaces of these systems of rays 

 have their convex sides turned towards each other before the 

 intersection, we see that beyond x they will have their concave 

 sides towards each other, and will thus form the " curved 

 points," which observation shows to exist. 



Consequently the upper " curved point " (fig. 23) is not 

 formed, as we should have expected at first, by rays from the 

 upper arm of the kathode, but it is formed by rays from the 

 two horizontal arms of the kathode — the left-hand half, and in 

 particular the contour-line I, being formed by rays from the 

 right-hand arm E, and the right-hand half by rays from the 

 arm L. 



If this is the right way of regarding the curved points, 

 we ought to find it confirmed by experiments in which 

 shadows are thrown. This is, in fact, the case. 



If we put a plate as a screen close in front of the kathode, 

 so that, as in fig. 24 a, it covers one half of the kathode ob- 

 liquely, then at the density at which the curved points appear 

 we observe the phosphorescent figure 24 6. The bounding 

 curves shown in dotted lines are now wanting. The phe- 



