1881.] Discontinuous Pliosphorescent Spectra in High Vacua. 211 



Soda phosphoresces faintly yellow, and gives the yellow line in the 

 spectrum. 



Lithium carbonate gives a faint red phosphorescence. Examined in 

 the spectroscope, the red, orange, and blue lithium lines are seen. 



I have already said that the diamond phosphoresces with great 

 brilliancy. In this respect perfectly clear and colourless stones " of 

 the first water " are not the most striking, and they generally glow of 

 a blue colour. Diamonds, which in sunlight have a slight fluores- 

 cence disappearing when yellow glass is interposed, generally phos- 

 phoresce stronger than others, and the emitted light is of a pale 

 yellowish-green colour. 



Most diamonds which emit a very strong yellowish light in the 

 molecular discharge give a continuous spectrum, having bright lines 

 across it in the green and blue. A faint green line is seen at about 

 X 537 ; at A 513 a bright greenish-blue line is -seen, and a bright blue 

 line at X 503. A darkish space separating the last two lines. 



Diamonds which phosphoresce red generally show the yellow sodium 

 line superposed on a continuous spectrum. 



There is great difference in the degree of exhaustion at which 

 various substances begin to phosphoresce. Some refuse to glow until 

 the exhaustion is so great that the vacuum is nearly non-conducting, 

 whilst others commence to become luminous when the gauge is 5 or 

 10 millims. below the barometric level. The majority of bodies, how- 

 ever, do not phosphoresce till they are well within the negative dark 

 space. 



During the analysis of ^ome minerals containing the rarer earths 

 experimented on, certain anomalies have been met with, which seem 

 to indicate the possible presence of other unknown elements awaiting 

 detection. On several occasions an earthy precipitate has come down 

 where, chemically speaking, no such body was expected ; or, by frac- 

 tional precipitation and solution, from a supposed simple earth some- 

 thing has separated which, in its chemical characters, was not quite 

 identical with the larger portion ; or, the chemical characteristics of 

 an earth have agreed fairly well with those assigned to it in books, 

 but it deviated in some physical peculiarity. It has been my practice 

 to submit all these anomalous bodies to molecular bombardment, and 

 I have had the satisfaction of discovering a class of earthy bodies 

 which, whilst they phosphoresce strongly, also give spectra of remark- 

 able beauty. 



The spectrum seen most frequently is given by a pale yellowish 

 coloured earth. It consists of a red, orange, citron, and green band, 

 nearly equidistant, the citron being broader than the others and very 

 bright. Then comes a faint blue, and lastly two very strong blue- 

 violet bands. These bands, when seen at theii best, are on a per- 

 fectly black background ; but the parent earth gives a continuous 



