Radioluminescence 417 



nescence of the screen has a far greater action on the plate than that 

 of X-rays alone and hence reduces the exposure time and helps 

 prevent injury to tissue. 



In addition to the radioluminescence of barium-platinum cyanide. 

 Roentgen, in his first paper, noted that calcium sulphide, uranium 

 glass, Iceland spar, and rock salt also luminesced. It was not long 

 before a systematic study of the ability of these X-rays to excite 

 fluorescence of various compounds was undertaken.^* An editor's 

 article in the Electrical Review for 1896 (38: 508) on " The Roent- 

 gen Rays " stated that T. A. Edison had tested a large number 

 of compounds and found that it was not necessarily dense sub- 

 stances but some relatively light ones, such as ammonium salicylate, 

 which phosphoresce in X-rays. A. Winkelmann and R. Straubel in 

 1896 observed a marked fluorescence with fluorspar and zircon, 

 while many other minerals sho^ved little effect. W. Arnold and 

 also J. Precht in 1897 discovered the bright fluorescence of sheelite 

 (calcium tungstate) and of many artificial preparations (tungstates 

 and platinum cyanides) , although some common phosphors fre- 

 quently showed no effect. Arnold also noticed that certain ma- 

 terials excited to luminesce by cathode rays were inert to X-rays. 

 The search for radioluminescence of minerals and other substances 

 was continued in America by J. E. Burbank (1898) and J. Trow- 

 bridge and J. E. Burbank (1898) and in France by H. Becquerel 

 (1899) . For many years the use of barium platinocyanide and 

 calcium tungstate screens with no phosphorescent afterglow was 

 standard, but the development in recent years of high intensity 

 zinc sulphide screens with practically no persistence has so reduced 

 the exposure time that X-ray moving pictures can be made. 



FROM RADIUM RAYS 



Discovery of the natural radioactivity of uranium, which led to 

 the isolation of radium, was made in 1896. Like the discovery of 

 X-rays, knowledge of radio-activity is connected with luminescence ^^ 



^* A book by Edward P. Thompson appeared as early as 1896, Roentgen rays and 

 phenomena of the anode and cathode (190 pp., New York, 1896) , which described in 

 detail a large number of luminescent effects. Other popular works were Light, visible 

 and invisible (New York, 1897) by Silvanus P. Thompson, and Radiation (London 

 and New York, 1898) by H. H. F. Hyndman, both paying considerable attention to 

 luminescence. 



^^ The various luminescent phenomena connected with radioactivity greatly stimu- 

 lated the general interest in cold light. In addition to a paper by W. Arnold (1897) , 

 several popular books appeared in the early twentieth century, for example, Radium 

 and other radioactive substances, etc. (New York, 1903) , by W. J. Hammer, in which 

 chapters were devoted to phosphorescence and fluorescence. Hammer, a consulting 

 electrical engineer, lectured before a joint meeting of the American Institute of Elec- 



