470 Dr. E. Goldstein on the Influence of the 



disk is manifest. If the exhaustion be carried further, the 

 dark semicircular lines move further apart ; and at a constant 

 density the distance between any two of the dark semicircles is 

 greater the further the pair in question lies from the centre. 

 This last behaviour manifests itself also if the phosphorescent 

 image is received on a plane surface parallel to the kathode 

 instead of upon a spherical wall. 



The phenomena described for plane disks lead to the follow- 

 ing conclusions: — 



(1) The different points of a plane kathode-surface are not 

 of equal value in the emission of kathode-rays, but the inten- 

 sity of the rays depends on the position of the elements by 

 which they are radiated with respect to the contour -line of 

 the kathode. 



(2) The rays of a plane kathode-plate do not in general form a 

 parallel pencil* ; but the inclination of the rays varies from 

 element to element, in accordance with the distance from the 

 contour-line of the plate. 



(3) The direction of the radiation from each separate ele- 

 ment varies moreover with the density of the gas. The smaller 

 the density becomes, the more does the direction of radiation 

 differ from the normal to the element ; and the direction of 

 deviation is always outwards. 



Whether any density exists at which there would be devia- 

 tion from the normal in the opposite direction (t. e. inwards), 

 at which therefore the rays Avould be convergent, is a question 

 to which an answer must for the present be deferred. The 

 deviations which make their appearance as the density dimi- 

 nishes are the more considerable the nearer the element in 

 question lies to the edge of the surface. 



11. Convex kathodes of regular outline also produce regular 

 phosphorescent images. 



Convex spherical forms, so far as I have observed, give the 

 same figures as plane kathodes of the same outline — only of 

 larger dimensions at an equal distance of wall, in consequence 

 of the stronger divergence of the rays. 



With cylindrical convex surfaces the figures obtained with 

 plane surfaces of similar outline are deformed, as might have 

 been expected ; the image is, cateris paribus, more expanded at 

 right angles to the axis of the cylinder than parallel to the 



* If we assume that each point of a kathode emits, not simply one ray, 

 but a small conical pencil of rays, then in the above proposition, instead 

 of " ray " we must read " axis of conical pencil of rays." I am still occu- 

 pied with experiments to determine the limit of aperture which we can 

 ascribe to the pencil of rays from a point of a surface. 



