272 Mr Kaye, The Emission of Rontgen Rays, etc. 



In these preliminary experiments, aluminium, copper, gold 

 and platinum leaf were used for anticathodes. A few typical 

 measurements of the ratio R of the intensity of the emergent to 

 the incident radiation are appended. Platinum behaves like gold 

 in the values that it yields for the ratio under different conditions. 

 The speed of the cathode rays, being dependent on the potential 

 between the cathode and anode, is sufficiently indicated by the 

 length of the alternative spark gap (between large brass balls). 



These and other results indicate the following points: — 



1. Generally speaking the emergence Rontgen radiation from 

 a thin metal anticathode exceeds the incidence in intensity. This 

 is most marked in the case of aluminium. Furthermore, as evi- 

 denced by the phosphorescence of the glass walls of the tube, the 

 accompanying emergence secondai-y cathode radiation from the 

 anticathode is more intense than the incidence cathode radiation. 

 As far as could be judged " R " for the cathode rays seems to 

 follow any variation of " R " for the X rays. Madsen's results 

 (above) for /3 rays may be noted. 



2. With heterogeneous cathode rays the incidence beam of 

 Rontgen rays is softer than the emergence. 



3. The ratio {R) of the emergence intensity to the incidence, 

 increases with the speed of the impinging cathode rays, provided 

 the anticathode is thick enough. This is shown both by increasing 

 the potential on the tube, and by sifting out (with screens) the 

 softer X rays produced by the more slowly moving constituents of 

 the heterogeneous bundle of cathode rays. 



4. For each thickness of anticathode there is a certain speed 

 of cathode ray which gives a maximum value to the ratio R. The 

 ratio drops in amount for greater or less speeds than this. 



5. As the thickness of anticathode increases, the emergence 

 intensity (for the same speed of cathode ray) first increases to a 

 maximum and then dies away ; the incidence intensity meanwhile 

 gradually increases to a constant value. The resemblance to 

 Madsen's results for ^ rays (above) will again be noticed. 



A discussion of the results is reserved until the measurements 

 are concluded. 



I wish to thank Sir J. J. Thomson for his interest in these 

 experiments. 



