On the Reflection of Cathode Rays. 393 



The above are a few typical examples of a much larger number of 

 sets of observations, all giving similar results. On examination it will 

 be seen that in all, both in the cases when the reflector was moved so 

 as to reflect the cathode rays at different angles into the stationary 

 Faraday cylinder, and also when the reflector was stationary and the 

 field of reflected rays explored by moving the cylinder, the effects are 

 approximately similar. In each case the electric charge imparted to 

 the cylinder, as measured by the electrometer deflection, is greatest for 

 almost exactly those positions of reflector and cylinder relatively to the 

 primary cathode rays that would make the angle of reflection most nearly 

 equal to the angle of incidence, the electrometer deflections diminishing 

 gradually, though not at a uniform rate, the greater the departure from 

 this condition. Any slight discrepancies are readily accounted for by 

 the difficulties of maintaining a constant vacuum and uniform action of 

 the induction coil contact breaker, and are also possibly, in some in- 

 stances, due to electrostatic repulsion experienced by the reflected cathode 

 rays. It would, therefore, appear that the reflection of cathode rays 

 by a flat polished platinum surface is not altogether diffuse, but takes 

 place to some considerable extent in a more or less specular manner. 



As will be observed in several of the sets of observations, a small 

 reverse deflection of the electrometer, indicating a slight positive charge 

 of the cylinder, was obtained either at the end or beginning of a series, 

 when the relative positions of reflector, cylinder, and primary cathode 

 rays would allow of no reflected cathode rays entering the cylinder. 

 This curious fact requires further investigation. 



In order to ascertain whether the intensity of the reflected cathode 

 rays would increase as the incidence was made more slanting, several 

 series of observations were made, where both the reflector and cylinder 

 were moved, the latter at twice the rate of the former, in such a manner 

 as to measure the maximum intensity of the reflected rays for varying 

 angles of incidence. The following table (Table X) gives the mean 

 deflections obtained with four series, which appear to show that the 

 intensity of the reflected rays does increase as the incidence is more 

 slanting. The increase in the early stages is not, however, great; 

 while it is possible that in the latter stages some direct cathode rays 

 obtained access to the cylinder. 



Charge Imparted to the Reflector. 



Experiments were also made to ascertain whether the charge imparted 

 to the reflector varied with the angle of incidence of the primary 

 cathode rays. The results are given in Table XI, from which it will 

 be seen that the electrification of the reflector while strongly negative 

 for normal incidence of the cathode rays, becomes zero at an angle 

 between 130 and 135, and slightly and increasingly positive for still 

 larger angles. Comparing this result with that obtained in the pre- 



2 H 2 



