Luminescence of Glass due to Kathode-Rays. 115 



In group VII. the volume -heats are constant. 

 Several elements, of known atomic weight, offer no data 

 for both C and D, and are altogether omitted. 



The above tables make clear the following laws : — 



1. In each natural group of elements volume-heat varies 

 inversely as atomic volume. (Group IV. a is an exception as 

 far as available data go.) 



2. The variations of volume-heat become less and less as 

 valency for oxygen rises, until the seventh group is reached, 

 when it becomes constant. 



3. As atomic heat increases in some groups and decreases 

 hi others, with increase of atomic weight, whilst atomic 

 volume regularly increases, it is evident that the increase in 

 atomic volume proceeds at a higher ratio than the variation 

 in atomic heat. 



4. Atomic weight being a constant increment, it follows 

 from the preceding law that in any natural group specific 

 gravity varies more than specific heat. 



VII. On a Suggestion by Professor J. J. Thomson in 

 Connexion with the Luminescence of Glass due to Kathode- 

 Hays. By John Burke, B.A., Lecturer in Physics, Mason 

 College, Birmingham* . 



LAST August, at Oxford, I communicated a paper to the 

 British Association on a strange luminous phenomenon 

 which had been observed by Beccaria more than a hundred 

 years ago. It was there pointed out that although the 

 conclusions arrived at by the Italian physicist, if true, were 

 likely to lead to results of an extremely interesting character, 

 in connexion w T ith Mr. Crookes' important researches on the 

 luminescence of glass, &c, in vacuum-tubes, and although 

 the mysterious nature of the phenomenon was likely to 

 attract much attention, yet the subject was allowed to retain 

 its obscurity. Beccaria (' Artificial Electricity,' § 766) 

 observed that when vacuum-hulbs were broken in the dark a 

 light, consisting of a faint glow, was produced in the place 

 where the bulb lay. He attributed an electrical origin to the 

 phenomenon, owing to the manner in which certain substances 

 were supposed to behave in yielding the glow. He mentioned, 

 moreover, that the mere breaking of glass did not give rise to 

 the phenomenon, but that the presence of air was essential to 

 its production, and that when air was allowed to rush suddenly 

 into a vacuum by the bursting of a bladder at the mouth of a 



* Communicated bv the Physical Society : read November 9, 1894. 



12 



