258 Prof. H. E. Armstrong and Dr. T. M. Lowry. [June 11, 



"The Phenomena of Luminosity and their possible Correlation 

 with Radio-Activity." By HENRY E. ARMSTRONG, F.K.S., and 

 T. MARTIN LOWRY, D.Sc. Received June 11, Read June 18, 

 1903. 



[Dynamic isomerism in relation to luminous phenomena.] 



The possibility of regarding luminous inanifestaMons generally 

 including radio-activity as the outcome of oscillatory changes in 

 molecular structure has already been pointed out by one of us in a 

 communication made to the Society more than a year ago,* in which 

 the kind of change contemplated was exemplified by reference to the 

 case of nitrocamphor. As the phenomena of radio-activity are exciting 

 so much interest, it appears desirable to enter somewhat more fully 

 into an explanation of the argument underlying this conception of the 

 origin of luminous appearances. 



In the note referred to, it was suggested that tribo-himinescent sub- 

 stances, i.e., substances which become luminous at the moment of 

 crushing, might conceivably, at the same time, manifest radio-activity. 

 Sir William Crookes has recently examined saccharin from this point 

 of view, using freshly prepared crystals which one of us had placed 

 at his disposal. We are much indebted to him for the following account 

 of his observations : 



" The crystals of saccharin, when broken in the dark, gave off 

 flashes of light. 



(1) A sensitive photographic film was covered with a sheet of 

 aluminium foil, 0'04 mm. thick and some crystals were broken on the 

 foil. On development no darkening was seen. 



(2) A similar experiment, in which black paper was used instead of 

 aluminium foil, also gave negative results. 



(3) Some crystals of saccharin were broken close to the sensitive 

 surface of a photographic film. The flashes of light could be seen 

 through the film. On development some spots were seen on the film 

 which were caused probably by the light given off. 



(4) A crystal was broken near the surface of a barium platino- 

 cyanide screen. The screen glowed at the moment of the flash from 

 the crystal. 



(5) A crystal of saccharin was put on a hard surface and a screen 

 of barium platinocyanide was laid face upwards on it. By means 

 of pressure on the screen the crystal beneath was crushed, when a 



* Henry E. Armstrong : " The Conditions Determinative of Chemical Change 

 and of Electrical Conduction in Oases and on the Phenomena of Luminosity." 

 ' Boy. Soc. Proc.,' 1902, rol. 70, p. 99. 



