Reflection of Electrical Rays. 451 



kathode impinge directly, become charged with negative elec- 

 tricity, which ^ reaches such a tension that they themselves 

 form a second kathode and radiate electric rays, which then 

 produce F ; or (b) that the rays which produce F are rays 

 from the kathode k, which suffer reflection when they fall 

 upon the solid wall. In this reflection, either the power of 

 producing phosphorescence of the rays becomes weakened 

 or their density, thus explaining the small intensity of light 

 emitted by F. 



The hypothesis («) may be excluded, as shown further on ; 

 for the phenomenon in question is not altered if the surface 

 upon which the kathode-rays impinge directly be metallic, 

 and if this metal surface be made the anode of the discharge. 

 If in accordance with this assumption we suppose that 

 reflection takes place, then again reflection according to the 

 optical law is at once to be excluded, since the position and 

 form of the surface F remain unchanged even when the angle 

 of the bend at x varies from 25° to 80°. Consequently the law 

 of the equality of the angles of incidence and reflection, or the 

 rule that when the reflecting surface is rotated while the inci- 

 dent ray preserves the same direction, the reflected ray rotates 

 through twice the angle, is not obeyed. 



We may, however, easily make numerous experiments 

 which agree in showing the presence of diffused reflection, in 

 consequence of which each point of the wall on which the rays 

 impinge directly diffuses rays in all directions. 



If diffuse reflection is proved, we have at once the explana- 

 tion of the small luminosity of F in comparison with portions 

 of the tube reached by the direct rays in the diminution in 

 density of the incident pencil of rays. 



In the next place, if we employ a vessel such as fig. 3, we 

 obtain phenomena corresponding to the surface F in the cylin- 

 ders Ci and C 2 at the same time. The rays which travel as 

 far as x nearly parallel to each other, therefore, after reflection, 

 follow at least two directions at right angles to each other. 



The following experiment forms an experimentum crucis: — 

 A chamber B was introduced between the portion of the tube 

 containing the kathode and the bend at x, which contained a 

 paper diaphragm which could be turned round the axis a, and 

 which had a slit cut in it about 1 millim. broad and parallel 

 to a. If the plane of the diaphragm falls along the axis r r, 

 its edge intercepts no perceptible portion of the pencil of rays 

 -which reaches the tube r from the kathode, and which is about 

 7 millim. across. But if, on the other hand, D is at right 

 angles to the axis of r, then only the portion of this pencil 

 which passes through the narrow slit can reach the bend x 



