1897.] Mr New all, On Luminosity attending Compression. 295 



(2) On Luminosity attending the compression of certain 

 rarifiecl gases. By H. F. Newall, M.A., Trinity College. 



1. Morrem (Pogg. Ann. 1862, Vol. 115, pp. 350—2, and 1865, 

 Vol. 126, pp. 643—654) and Sarasin (Pogg. Ann. 1870, Vol. 140, 

 p. 425) have given accounts of phosphorescence produced in 

 rarified gases by the passage of electrical discharges. The pheno- 

 menon itself was recognized in the earliest days of vacuum tubes. 



Morrem and Sarasin agreed in thinking that no pure single 

 gas (as distinct from a mixture of gases) exhibits phosphorescence. 

 Morrem found the phosphorescence very strong in a mixture of 

 gases containing 200 parts of Oxygen, 100 parts of Nitrogen, and 

 150 parts of S0 2 . Sarasin regards the presence of oxygen as 

 essential to the production of phosphorescence. J. J. Thomson 

 (Recent Researches, 1893, p. 184) has described observations of 

 such phosphorescence and has explained it in accordance with 

 his view that the conduction of electricity by a gas is associated 

 with decomposition. He states, " I have never detected any glow 

 in a single gas (as distinct from a mixture) unless that gas was 

 one which formed polymeric modifications, but all the gases I have 

 examined which do polymerize have shown the afterglow." 



2. In the course of an investigation of the spectra of rarified 

 gases rendered luminous by electrodeless discharges by Prof. J. J. 

 Thomson's method, I was dealing with the case of mixtures of 

 Oxygen with other gases, chiefly Nitrogen and Carbonic Oxide 

 in different proportions, and frequently obtained mixtures which 

 at certain exhaustions phosphoresced so brilliantly that I was 

 induced to devote some time to the study of the phenomena, in 

 particular by means of the spectroscope. 



3. A description of the apparatus used will make the con- 

 ditions clearer. 



A glass tube, in which electrodeless discharges were to be 

 passed, was connected with a Hagen-Tbpler mercury-pump, fused 

 glass joints being used throughout. There was also attached 

 to the pump a graduated tube in which mixtures of gases could 

 be made in any desired proportions, and which served as a 

 reservoir of such mixtures. Samples of the mixtures could be 

 let into the pump by an arrangement very similar to that figured 

 by Salet in his Traite de Spectroscopic (Masson, Paris, 1883), 

 p. 209. In most of the experiments the electrodeless discharge 

 was produced near the middle of a large tube, about 2 inches 

 in diameter and 6 feet long. In a tube like this the phos- 

 phorescence begins near the bright discharge and spreads along 

 VOL. IX. pt. vi. 24 



