304 History of Luminescence 



phorescence under the direct influence of the [electric] stream, but 

 a phosphorescence from the stream induced catliode rays." 



When the pressure in an evacuated tube reaches 0.01 mm Hg or 

 less, the Crookes dark space practically fills the tube. Faint bluish 

 cathode ray streamers can be detected and a brilliant fluorescence 

 of the glass walls of the tube where the cathode rays strike. The 

 conditions are now ripe for the emission of X-rays, discovered by 

 W. K. Roentgen in 1895. 



The many luminescence effects resulting from cathode rays, anode 

 rays and X-rays are described in the chapter on radioluminescence, 

 while phosphorescence and fluorescence from ultraviolet light pro- 

 duced by electroluminescence are considered in corresponding chap- 

 ters on these subjects. 



SURVEY 



Nearly three hundred years have elapsed since von Guericke 

 observed light on a sulphur ball, and nearly 250 years since the light 

 in Hauksbee's evacuated glass globes astonished the members of the 

 Royal Society. From so humble a beginning has come a highly 

 popular method of advertising, the neon sign, and in combination 

 with fluorescence, the predominant means of illumination at the 

 present day. The so-called " electric light " of the eighteenth cen- 

 tury was not the " electric light " of Edison and the late nineteenth 

 century. It was in fact more literally an electric light than the high 

 temperature incandescence of a filament, and it is interesting to 

 note that gas discharge lamps represent a return to the original 

 meaning of the words. 



Electrical discharge lamps for illumination are associated with the 

 names of D. McFarlane Moore in the eighteen-nineties, and Georges 

 Claude around 1900. The earliest practical suggestion the author 

 can find for use as an illuminant appeared as a short note by J. P. 

 Gassiot (1860) in the Proceedings of the Royal Society. The paper 

 contains a figure of a flat glass coil with enlarged electrodes at the 

 end which could be connected with a Ruhmkorff coil. When filled 

 with carbon dioxide at low pressure and the current from the coil 

 passed through, " the spiral becomes intensely luminous exhibiting 

 a brilliant white light." It was demonstrated at one of the meetings. 

 Thus over forty years passed before commercial development became 

 practical. 



