1905.] the Beta and Gamma Rays of Radii' m .- \ ] 



"Phosphorescence caused by the Beta and Gamma Rays O f 

 Radium.-Part II." By G. T. BEILKY. Communicated by 

 Professor J. LARMOR, Sec. R.S. Received February 9 Read 

 February 23, 1905. 



19. By the study of the case of barium platino-cyanide, it has been 

 shown that certain forms of phosphorescence or luminescence are due 

 to change of physical state e.g., to the passage from the crystalline 

 to the amorphous state, or from one amorphous state to another. The 

 molecular movement required to bring about these changes may be 

 caused (1) by disintegration produced by mechanical means, as in the 

 crushing or flowing of crystals ; (2) by the expulsion of a volatile con- 

 stituent, as in the dehydration of crystals, the molecular movement 

 which necessarily occurs at the moment of expulsion being taken advan- 

 tage of by the forces of cohesion to establish new arrangements of the 

 molecules either crystalline or amorphous; and (3) by a condition 

 of excessive vibration and ultimate overstrain set up by a stream of 

 electrons, as in the radium or the cathode rays. 



20. After due allowance has been made for the element of physical 

 change, there remains a large class of phosphorescent phenomena which 

 cannot be thus explained ; but I believe that the clear recognition of 

 the part played by physical change at once makes the consideration of 

 the latter class much simpler. 



21. Even in the case of platino-cyanide, where it is seen that physical 

 changes play so large a part in the phosphorescent phenomena, there 

 remains a certain residuum of phosphorescent effect which appears to 

 be independent of the physical condition of the substance. Platino- 

 cyanide itself, therefore, opens the way to a further study of the pheno- 

 mena of phosphorescence ; but other substances in which the physical 

 state plays a less important part are better suited for this study. 



22. Throughout this paper the different phases of luminescence are 

 referred to as : primary phosphorescence, or the luminescence produced 

 under the direct influence of a stimulus, e.g., the /3 rays or the cathode 

 rays ; secondary phosphorescence, or the luminescence which continues 

 after the direct stimulation has ceased ; revived phosphorescence, or the 

 luminescence revived by heat after the secondary phosphorescence has 

 diminished or ceased altogether. 



23. It has been shown that primary phosphorescence is exhibited 

 under various forms of stimulation and under conditions in which the 

 elastic vibration of molecules or molecular aggregates might alone 

 account for the generation of light waves. But when the secondary 

 and the revived forms of phosphorescence appear, it becomes necessary 

 to suppose that these effects are due to some more intimate changes 

 among the atoms themselves ; in other words, to the play of chemical 



VOL. LXXIV. 2 P 



