1905.] the Beta and Gamma Rays of Radium. 517 



1. Certain types of phosphorescence are due to the molecular move- 

 ment or displacement which is produced by heat, by mechanically 

 applied stresses, or by radiant energy. 



2. Certain other types of phosphorescence are distinguished by their 

 appearance in three stages, called here primary, secondary, and 

 revived phosphorescence. These can be explained as due to atomic 

 changes in which chemical affinity is the controlling factor. 



3. The phenomena of this type appear to support the view that a 

 species of electrolysis occurs in solids exposed to the ft or cathode 

 rays ; that the products of electrolytic dissociation are insulated or 

 partly insulated from each other by the neutral molecules, as in a 

 viscous electrolyte ; and that it is the breaking-down of this insulation 

 and the recombination of the ions which causes revived phosphor- 

 escence. 



[Added February 22, 1905. The following experiments have been 

 made at a temperature of about - 100 : 



44. Calcspar crushed to powder, and exposed to the radium rays for 

 an hour at this temperature, showed the usual primary and secondary 

 phosphorescence. On emptying the salt from the cold tube upon a 

 metal plate at the ordinary temperature, the glow increased con- 

 siderably as the temperature of the salt rose; but this revived 

 phosphorescence was not so vivid as that observed between 15 and 

 100 (see paragraph 35). 



45. Potassium chloride exposed to the rays for an hour at - 100 

 showed well-marked violet coloration. The primary and secondary 

 phosphorescence were brighter than at the ordinary temperature (see 

 paragraph 32). When the cooled salt was emptied on the metal plate 

 it glowed with a brilliant pink phosphorescence, which died down in 

 less than a minute. On returning the salt to the cold tube, the 

 phosphorescence completely ceased. 



46. Potassium bromide treated in the same way was coloured 

 greenish blue in one and a half hours. It showed distinct primary, 

 but no secondary, phosphorescence. Emptied on the metal plate, it 

 glowed with a brilliant greenish phosphorescence, which quickly died 

 down, and entirely ceased when the salt was returned to the cold tube 

 (see paragraph 33). 



47. Barium platino-cyanide in yellow crystals exposed to the rays 

 at - 100 turned red more slowly than at the ordinary temperature. 

 After five hours' exposure the primary phosphorescence had fallen 

 to 33 per cent, of its former value. There was still no secondary 

 phosphorescence, but, when emptied on the metal plate, the salt 

 glowed brilliantly for a few seconds. To make sure that this revived 

 phosphorescence was not due to the purely physical effect of cooling 

 and heating, another portion of yellow crystals was cooled under 

 identical conditions, except that the radium was absent. The crystals 



VOL. LXXIV. 2 Q 



