1896.] 



on Electric Shadows and Luminescence. 



211 



piece of metal — preferably platinum — wliich I term the antikatliode * 

 set obliquely opposite the kathode, and whicli serves as a radiating 

 surface from which the X-rays are emitted in all directions. When 

 experimenting with various forms of tube, I have spent much time in 

 watching, by aid of a fluorescent screen, their emissive activity during 

 the progress of exhaustion. As already mentioned. X-rays are not 

 emitted until the stage of minimum internal resistance has been 

 passed. As the exhaustion advances, while resistance rises and spark 

 length increases, there is noticed by aid of the screen a luminosity in 

 the bulb, which, faint at first, seems to come both from the front face 

 of the bit of platinum that serves as antikathode, and from the back 

 face ; an oblique dark line (Fig. 11), corresponding to the plane of 



Fig. 11. 



Fig. 12. 



the antikathode, being observed in the screen to separate the two 

 luminous regions. On slightly increasing the exhaustion the emis- 

 sion of X-rays from the back of the antikathode ceases while that 

 from the front greatly increases (Fig. 12), and is quite bright right 

 up to the angle delimited by the plane of the antikathode. There is 

 something mysterious, needing careful investigation, in this lateral 

 emission of X-rays under the impact of the kathode discharge. 



Of all the many forms of tube yet produced none has been found 

 to surpass the particular pattern devised by Mr. Sydney Jackson 



* Comptos Rendus, cxxii. p. 807. 



P 2 



