512 Mr. G. T. Beilby. Phosphorescence caused by [Feb. 9, 



affinity. The association of phosphorescence with certain forms of slow 

 oxidation was early recognised, and possibly for this reason there has 

 sometimes been a tendency to limit the chemical view to this type of 

 action. But from the observations which follow it will be seen that 

 with many substances the chemical actions which occur must neces- 

 sarily be self-contained and independent of atmospheric or other 

 surroundings. 



24. The chemical action of the rays from radio-active substances has 

 been recognised from the first. Among the most prominent examples 

 of this action are the reduction of sensitive silver salts in photographic 

 films which led to the original discovery of the rays by M. Becquerel ; the 

 coloration of glass, first observed by M. and Madame Curie, and after- 

 wards attributed by Elster and Geitel and other observers to the 

 reduction and separation of the alkali metals in a state of solid solution ; 

 the electrolysis of water ; and the separation of iodine from iodof orm, 

 observed by W. B. Hardy and Miss Willcox in the liquid state, and 

 more recently by van Aubel in the solid state. Some of these actions 

 have been recognised by direct chemical tests, while others have been 

 inferred from the colour changes occurring in the substances exposed 

 to the rays. 



25. So far as I can learn, no systematic attempt has yet been made 

 to trace the connection between the chemical, the coloration, and the 

 luminescent effects of the /3 rays. The observations which follow are 

 to some extent a repetition of the experiments of previous workers on 

 the subject, but they have been extended in particular directions with 

 the express object of throwing light on the problems of secondary and 

 revived phosphorescence. 



In these observations, as in those recorded in the first part of the 

 paper, the substances under examination were exposed to the ft and y 

 rays only (see paragraph 3). 



26. A polished lens of rock crystal, after exposure to the rays for 

 four days, showed a patch of dark brown coloration at the spot where 

 the rays had entered. On removal from the radium, the coloured patch 

 phosphoresced faintly. This could only be seen in complete darkness. 

 After an interval of six weeks the lens showed no trace of phosphores- 

 cence at the ordinary temperature, but on heating it on a hot plate to 

 rather over 100 the coloured patch glowed so brightly that it lighted 

 up the rough edges of the lens and showed its complete outline quite 

 distinctly. On raising the lens to a considerably higher temperature, 

 probably over 250, it glowed more brightly, and then the glow ceased 

 altogether. The brown coloration had now completely disappeared. 



27. A colourless crystal of calcspar, measuring roughly 17x12 

 x 6 mm., was exposed to the rays for six days. A faint yellow colora- 

 tion marked the spot where the rays had entered. The coloration had 

 penetrated about 2 mm. below the surface. When the crystal was first 



