118 



Mr. J. Burke on the Luminescence 



^>e 



d 



Various gases were made to take the 

 place of air. Fig. 1 represents the appa- Fig. *• 



ratus employed for this purpose, a is a 

 glass receiver ; the strong glass ring Z>, the 

 opening of which was covered by a piece of 

 thin glass c, rested on the mouth of the 

 receiver a, and served to support a long 

 glass tube d, at the upper end of which, 

 being closed, there was an arrangement e 

 by which a weight / was supported and 

 allowed to fall by turning the handle h 

 and thus break the glass c and open free 

 communication between the gas in the tube 

 d and that in the receiver a. 



The joining between d and a was made 

 complely air-tight so that no leakage oc- 

 curred. The tube d was then filled with 

 carbon dioxide or oxygen, and the air in 

 the receiver a exhausted until a vacuum 

 of about 20 millim. was obtained. The 

 weight / was made to fall and break the glass c, so that the 

 gas in d might enter violently into the vacuum. The same 

 luminous phenomenon was observed as on previous occasions 

 when air was employed, with no perceptible difference as 

 regards colour, intensity, or the general appearance of the 

 glow and luminous spots. 



When the gases in both a and d were exhausted and the 

 glass c broken as before, no luminosity whatsoever was 

 observed, thereby showing that the mere breaking of glass 

 did not suffice to produce the phenomenon ; but that the 

 presence of a gas was essential, though any gas was sufficient 

 to produce the effect — that is, that some function performed 

 by a gas in rushing into a vacuum was the cause or a circum- 

 stance invariably connected with the phenomenon. 



The three following hypotheses seemed possible : — 



(].) The violent dashing or bombardment of the molecules 

 of air against the glass might have caused the latter to emit 

 light, 



(2) It might have been a sort of miniature meteorite phe- 

 nomenon, caused by the collisions of the fragments of glass 

 with the interior of the receiver and with each other ; the 

 intense bombardment of the larger fragments by the minute 

 dust particles giving rise to the luminous spots. 



(3) It might have been an electrical phenomenon caused 

 by the rubbing of air against glass ; somewhat resembling 



