Radioluminescence 413 



lent me for the purpose of these experiments." Then follows the 

 statement that diamond and beryl luminescence (from cathode rays) 

 is not polarized, but light (the extraordinary rays of higher velocity) 

 from emerald, sapphire, ruby, and tinstone is completely polarized, 

 with luminescence colors— crimson red, blue grey, red, and yellow, 

 respectively. In hyacinth, luminescence of the ordinary ray depends 

 on the variety— pink in some specimens and yellow in others, while 

 the extraordinary ray luminescence is lavender blue in the first 

 type and deep violet in the second type. Such observations indi- 

 cate the complicated phenomena to be encountered in study of 

 cathodoluminescence. 



" Crookes tubes " or " radiant matter tubes " became famous. 

 Crookes' earliest work in 1863-1864 and 1872 had been on the rare 

 earths and his later experiments (1874-1879) on the mechanical 

 effects of light, during which period he developed the radiometer. 

 What more appropriate subject for his experimentation than the 

 mysterious cathode rays, which did excite the most characteristic 

 luminescence of rare-earth compounds. For completeness and perti- 

 nent observation, the 1879 papers of Crookes on cathodolumi- 

 nescence are to be compared with the 1852 paper of Stokes on 

 fluorescence. 



In addition to exciting luminescence, Crookes also demonstrated 

 that the rays heated substances they struck, and could move a rotat- 

 ing vane mounted in their path; also that t^vo beams of rays moving 

 side by side repelled and were deflected from each other. These 

 observations supported the particle nature of cathode rays, a stand 

 fully vindicated by later work. 



Crookes continued his luminescence investigation in 1881, the 

 year after E. Wiedemann (1880) observed polarized light from 

 double salts of platinum when struck by cathode rays. In general 

 Crookes (1883-1888) found that cathodoluminescence spectra were 

 usually continuous but in some cases made up of rather narrow 

 bands, which turned out to be connected with the presence of rare 

 earths. " Radiant matter spectroscopy " was actively pursued during 

 the 1880's and 1890's by Crookes* himself, and by E. Wiedemann 

 (1880, 1889) , E. Becquerel (1885) , Francois Lecoq de Boisbaudran 

 (1885-1893) and others too numerous to mention.^ These men all 

 added new cathodoluminescent materials ^° to the growing list and 



* Several of Crookes' papers (1887) dealt with study of the after-glow, using a 

 phosphoroscope of his own design. Papers on Cathode ray spectra of rare earths 

 appeared from 1879 to 1899, the most important in 1883 and 1885. 



«See the dissertation of W. Arnold (1897) and also E. Goldstein (1900) . 



^"^ An English patent was granted to Rankin Kennedy in 1882 for a vacuum bulb 

 with electrodes coated with phosphorescent material which glowed when hit by 

 cathode rays. 



