1897.] the compression of certain rarified Gases. 297 



7. The spectroscopic study of the phosphorescence itself has 

 then given no evidence of its chemical origin. But the fact that 

 a continuous spectrum is visible in a gaseous mixture of such 

 tenuity as that dealt with (about mm '3 — mm- l pressure) is 

 noteworthy. I was unable to detect diffuse bands or a maximum 

 of brightness though the difference of the colours of the phos- 

 phorescent hazes in different mixtures of gas would lead one to 

 expect the existence of such bands. 



8. The spectrum of the bright discharge which precedes the 

 phosphorescence has only given results difficult to interpret when 

 taken in connection with one's knowledge of the care that has 

 been taken in preparing the gases. 



For instance, a bulb had been carefully filled with electrolytic 

 oxygen, after ' rinsing ' the pump and tubes out with the gas, 

 and after heating the tubes several times at very low pressure, 

 and after leaving the pump and tubes exhausted for two or three 

 days. The bright discharge gave only the band spectra of nitrogen 

 and cyanogen, and it was only after continued sparking that the 

 oxygen spectrum asserted itself. 



It seems to me that the spectrum of the bright discharge 

 possibly affords no more certain evidence of the chemical origin 

 of the phosphorescence than of the nature of the mixture of gases 

 in which the discharge takes place. 



9. The appearance of the phosphorescent gas led me to apply 

 a test, which Sir G. G. Stokes has described as affording proof of 

 the existence of solid particles in the flame of a candle. A beam 

 of sunlight was concentrated by means of a lens upon the phos- 

 phorescent gas : and the track of the beam in the gas, as also the 

 scattering of polarized light, were looked for. But no evidence 

 could be obtained that supports the idea that we might have to 

 deal with the phosphorescence of solid particles momentarily set 

 free by decomposition accompanying the bright discharge. 



10. In the course of my work with electrodeless discharges I 

 have frequently found black or brown deposits on the inside of 

 the glass tubes. In one or two cases the deposit has been thick 

 enough to form a film which could be detached from the glass ; 

 the film was translucent and had a highly offensive smell. The 

 formation of this film is a proof that permanent chemical changes 

 are brought about by the discharge ; and there can be little doubt 

 but that the phosphorescence is a sign that temporary chemical 

 changes are also produced. 



11. Taking into account the difference in the colour of 

 different phosphorescent hazes and the difference in the condi- 

 tions of their appearance, but setting only small weight on the 



24—2 



