On the Reflection of Cathode Rays. 383 



of and behind the anti-cathode, while the elongated patch, F, moved to 

 an extent that showed that the angular displacement of the reflected 

 beam of cathode rays that occasioned it was twice the angular dis- 

 placement of the reflecting surface. 



The patch E, and the ring GG', appear to be due to some description 

 of rays given off directly by the anti-cathode normally to its concave 

 and convex surfaces respectively, and independently of the position of 

 the anti- cathode on its axis. The exact nature of these normal anti- 

 cathode rays at present appears uncertain, and calls for further investi- 

 gation. 



The fluorescent patch F, from the manner in which both its move- 

 ments and form obey the usual laws of reflection, seems undoubtedly 

 to be due to cathode rays proceeding initially from the cathode C, and 

 reflected specularly by the concave surface of the anti-cathode. 



It should be mentioned that though, when obtained, the fluorescent 

 patches described above are most distinct and unmistakable, they are 

 not always obtained very readily. With the tube used, the patches 

 increased in brightness when the spark gap included in the circuit 

 between the coil and the anode of the tube was made fairly large. 

 The patch F was best obtained when the angle between the incident 

 and reflected beams is greater than 90 and less than 180. This patch 

 could not be obtained satisfactorily when the angle was much less than 

 90, possibly owing to the incident beam interfering with the reflected 

 beam. In order to obtain satisfactory patches, it was found that the 

 anti-cathode must not be used as anode, and must be connected to 

 earth ; that there must be at least one spark-gap in the circuit, and 

 that the anode must not be connected to earth. The patches are 

 generally somewhat unsteady as regards position, being apparently 

 affected by the varying electrification of the glass walls of the tube. 



The patches were best obtained with the tube exhausted to about 

 O000024: atmosphere, when the general green fluorescence over half 

 the bulb, due to diffusely reflected cathode rays, was but faintly 

 visible. When the degree of exhaustion was raised above that stated, 

 the patches became larger and fainter, and finally disappeared, merging 

 in the general fluorescence. 



Quantitative Results. 



Endeavours were next made to obtain accurate quantitative mea- 

 surements of the cathode rays reflected from a flat and highly polished 

 platinum surface by catching a definite portion of the reflected rays in 

 a movable Faraday cylinder connected to earth through a galvano- 

 meter, and noting the amount of charge imparted to the cylinder for 

 different angles both of incidence and reflection. 



The first tube constructed for this purpose is shown in fig. 5. Here 



