122 Prof. Arthur Smithells on the 



bardment of the dust particles against the surfaces of these 

 larger fragments. 



A large quantity of fragments of cast-iron, steel, ebonite, 

 sealing-wax, bone, &c, were tried as well as glass, but the 

 attempt to obtain a luminous effect by the above method proved 

 fruitless. 



If metallic dust should produce a luminous effect when 

 made to bombard the surface of glass, and if different effects 

 should be produced by lead glass and German glass, the 

 theory that solid particles emitted from the kathode would 

 give rise to luminescence of the glass would be justified. The 

 above experiments, however, do not seem to throw much light 

 on Mr. Oookes' theory of luminescence due to the emitted 

 particles of gas. 



In the earlier stage of the investigation hypothesis (3) 

 appeared plausible enough. Any experiments, however, 

 that were made in connexion with it did not lead to results 

 of an interesting character. 



Whatever may be the real value of these experiments, it 

 cannot be doubted that the inquiry into the cause of such a 

 phenomenon as that noticed by Beccaria must prove of the 

 greatest interest : firstly, on account of the obscurity enve- 

 loping the subject, and, secondly, on account of the interest 

 attached to the artificial production (though on a small scale) 

 of met'oric phenomena in the laboratory. 



VIII. The Luminosity of Gases. 

 By Arthur Smithells', B.Sc* 



[Continued from vol. xxxvii. p. 259.] 



[Plate IV.] 



Part III. — Experiments on the Flame-Spectra of Salts of 



Copper and Gold. 



IN his well-known memoir on the spectra of coloured flames 

 Grouy (Ann, Chim.Phys. xviii. p. 5, 1879) draws attention 

 to the fact that different spectral effects are obtainable from 

 different parts of the flame of a Bunsen-burner. From his 

 observations Gouy concludes that the inner cone of a Bunsen- 

 flame must be hotter than the outer one, and he remarks that, 

 though this is in some respects in accord with theory, the 

 mechanism of the phenomenon presents serious difficulties and 

 demands fresh researches. 



The mechanism alluded to by Gouy has, I think, been 

 explained by recent investigations on the " Structure and 



* Communicated bv the Author, 



