116 Mr. J. Burke on the Luminescence 



receiver, articles such as glass bottles, vessels of sealing-wax, 

 &c, became luminous by ? be supposed, tbe violent dashing of 

 the external air on them ; the luminosity was most conspicuous 

 at the necks of the bottles or at the upper edges of the vessels. 

 As has already been remarked, Beccaria's researches appear 

 to have been forgotten for more than a century, and not until 

 quite recently has attention been drawn to them. This has 

 been done by Professor J. J. Thomson, who, in his ' Hecent 

 Researches in Electricity and Magnetism,' p. 119, recalls the 

 fact and indicates its possible close relationship to Mr. Crookes' 

 theory of the luminescence of the glass in Geissler's tubes : 

 that the bombardment of the glass by the particles of gas pro- 

 jected from the kathode is intense enough to cause the glass 

 to become luminous. Prof. Thomson quotes from Priestley's 

 ' History of Electricity' : — 



" Signor Beccaria observed that hollow glass vessels, of a certain 

 thinness, exhausted of air, gave a light when they were broken in 

 the dark. By a beautiful series of experiments, he found, at 

 length, that the luminous appearance was not occasioned by the 

 breaking of the glass but by the dashing of the external air against 

 the inside when they were broke. He covered one of those ex- 

 hausted vessels with a receiver, and letting the air suddenly on the 

 outside of it observed the very same light." 



That the light observed in both cases was the same, unless 

 the exhausted vessel, which had been covered by the receiver, 

 was broken by the dashing of the external air against it, is a 

 circumstance which, from considerations that shall presently 

 be adduced, I think we may be justified in questioning. 



Through the kindness of Prof. Fitz Gerald in extending to 

 me the facilities afforded in the Physical Laboratory of Trinity 

 College, Dublin, I have been enabled to experiment upon this 

 subject. It would be impossible for me to attempt to render 

 in detail the acknowledgment of what has been due to his 

 invaluable advice and suggestions. 



It must be mentioned at the outset that the present in- 

 vestigation has by no means been completed, yet, thus far, it 

 appears that some of Beccaria's results have not been wholly 

 of that degree of exactness which we should have hoped for. 

 It must, however, be borne in mind that scientific appliances 

 in his time were less perfect than they are to-day, and such 

 mperfection may account for much inaccuracy. 



A number of incandescent lamps of various sizes with 

 broken filaments w T ere procured. An observer who had been 

 hfteen or twenty minutes in the dark, whose sight had become 



