290 History of Luminescence 



covery of cathode rays and Roentgen rays, radioactivity, and the 

 many luminescent effects connected with them, described in Chapter 

 XII on radioluminescence. 



Other experiments of the same type were made by John Canton 

 (1718-1772) , whose interest in luminescence also extended to dead 

 fish and phosphors. Like Grummert (1745), he noticed (1753) the 

 light which appeared spontaneously in a sealed evacuated tube which 

 was brought near and then removed from the neighborhood of a 

 charged Leyden phial. The glow darted from one end of the tube 

 to the other at uncertain intervals for nearly a quarter of an hour 

 and imitated the appearance of an auroral display. In fact Canton 

 (1753) asked, " Is not the aurora borealis the flashing of electrical 

 fire from positive toward negative clouds at a great distance through 

 the upper part of the atmosphere where the resistance is least? " 



Benjamin Wilson (1759) continued the studies on electricity in a 

 vacuum, calling attention to differences in appearance of electric 

 light at the two poles. Using the double barometer of Cavendish, 

 Wilson broke the column of mercury on one side by letting in a 

 little air, thus separating the column into separate cylinders of mer- 

 cury, and he connected the other cup of the barometer to the earth. 

 When electrified by a rotating cylinder of glass, light appeared in 

 the vacuum of the tube but was always brighter in the upper sur- 

 faces of the mercury, whereas when electrified by a rotating cylinder 

 of rosin, the bright regions were on the lower surfaces of mercury 

 column. Wilson inferred from this that glass electrified positively 

 and rosin negatively, " depriving them of part of the electric fluid 

 which they naturally had." 



THE RELATION OF THE " ELECTRIC LIGHT " TO OTHER LUMINESCENCES 



In later years, both Canton (1768) and Wilson; (1775) became 

 students of luminescence in general. For example, Canton noted 

 that electric sparks were particularly good exciters of his newly pre- 

 pared phosphor and Wilson wrote a book on phosphors (see Chap- 

 ter VIII) , but neither attempted to relate the electric light to other 

 types of luminescence, except by comparison with the aurora 

 borealis. 



A somewhat different attitude was taken by Father Giovanni Bat- 

 tista (Giambattista) Beccaria (1716-1781) of Turin, a member of 

 the religious order of the Pious Schools, an astronomer and ingenious 

 experimenter, who had supported Franklin in his controversy with 

 Nollet. He was especially interested in atmospheric electricity, and 

 like many others, compared the electric light in vacuo to the north- 

 ern lights. He published a number of papers in the Phil. Trans. 



