with Mercury contained in Tubes. 533 



from between the violet and blue to beyond the green. 

 When the pressure is allowed to rise to that of the atmosphere 

 in both bottles, the glow gives a shorter continuous spectrum 

 and the violet line 4047 is no longer visible. 



Attempts to obtain the green glow in glass capillary tubes 

 by heating have been unsuccessful. 



Phosphorescence of Fused Quartz. 



A very interesting phenomenon exhibited by the quartz 

 lamps described in this paper is the remarkably bright phos- 

 phorescence which is observed on switching off the current. 

 The phosphorescent light is generally of a faint green tint, 

 but one specimen gave a yellowish light. The light is often 

 bright enough to be detected in a well-lighted laboratory, and 

 in the dark may be visible for more than a minute after 

 turning off the current. The quartz, after having lost its 

 phosphorescence, may be made to glow again by heating. 

 This heating will cause the renewal of the luminosity even 

 after the quartz has been kept in the dark for several 

 months. 



This phosphoresoence can be produced by exposing fused 

 quartz to the light from any of the lamps described in this 

 paper. Crystalline quartz does not exhibit this effect. The 

 phosphorescence of fused quartz is not a noticeable feature of 

 quartz vacuum lamps. This is probably owing to the intensity 

 of the radiation in the particular region of the spectrum 

 required to produce the phosphorescence being greater when 

 the pressure of the mercury vapour is increased. Mr. H. G. 

 Lacell informs me that he has noticed this phosphorescence 

 in connexion with the lamp described at the beginning of the 

 section on the ribbon effect. 



Conclusion. 



Many of the phenomena described in this paper require 

 further study with the help of the spectrograph, the oscillo- 

 graph, and the photometer. Much of the work should be 

 capable of repetition, using conductors other than mercury. 



The best thanks of the author are due to Professor 

 Sir J. J. Thomson, F.R.S., for valuable advice during the 

 progress of the work ; to Mr. C. Dearing, B.Sc, for aid in 

 some of the experiments ; to Mr. S. Lawrance for assistance 

 throughout the research; and to Mr. H. G. Lacell and the 

 Silica Syndicate, who have kindly provided the quartz 

 apparatus. 



L.C.C. Paddington Technical Institute. 

 Phil. Mag. S. 6. Vol. 22. No. 130. Oct. 1911. 2 N 



