1887.] On the Crimson Line of Phosphoresce?it Alumina. 25 



M = -43429 44819 03251 82765 11289 18916 60508 22943 97005 80366 



65661 14453 78316 58646 49208 87077 47292 24949 33843 17483 



18706 10674 47663 03733 64167 92871 58963 90656 92210 64662 



81226 58521 27086 56867 03295 93370 86965 88266 88331 16360 



77384 90514 28443 48666 76864 65860 85135 56148 21234 87653 

 43543 43573 17253 83562 21868 25 



which is true, certainly to 272 and probably to 273 places of 

 decimals. 



IV. " On the Crimson Line of Phosphorescent Alumina." By 

 William Crookes, F.R.S., V.P.C.S. Received December 

 30, 1886. 



Id a paper which 1 had the honour of communicating to the Royal 

 Society* in March, 1879, I described the phosphorescence of alumina 

 and its various forms when under the influence of the electrical dis- 

 charge in vacuOy in the following words : — " Next to the diamond, 

 alumina in the form of ruby is perhaps the most strikingly phosphor- 

 escent stone I have examined. It glows with a rich, full red ; and a 

 remarkable feature is that it is of little consequence what degree of 

 colour the earth or stone possesses naturally, the colour of the phos- 

 phorescence is nearly the same in all cases ; chemically precipitated 

 amorphous alumina, rubies of a pale reddish-yellow, and gems of the 

 prized ' pigeon's blood ' colour, glowing alike in the vacuum, thus cor- 

 roborating E. Becquerel'sf results on the action of light on alumina 

 and its compounds in the phosphoroscope The appear- 

 ance of the alumina glow in the spectroscope is remarkable. There is 

 a faint continuous spectrum ending in the red somewhere near the 

 line B ; then a black space, and next an intensely brilliant and sharp 

 red line, to which nearly the whole of the intensity of the coloured 



glow is due This line coincides with the one described 



by E. Becquerel as being the most brilliant of the lines in the spec- 

 trum of the light of alumina, in its various forms, when glowing in 

 the phosphoroscope." 



In 1881J I again returned to the subject, describing a large 

 number of fresh experiments ; and I may add that the red glow of 

 alumina has been, off and on, a subject of examination with me since 

 the year first named down to the present time. 



In the papers above quoted I gave as accurate measurements of 

 the alumina line as my instrumental means would then permit. I 

 have recently had occasion to go over these measurements again in a 



* ' Phil. Trans./ Part 2, 1879, pp. 660, 661. 



f 1 Annales de Chimie et de Physique,' vol. 57, 1859, p. 50. 



% 1 Boy. Soc. Proc.,' vol. 32, pp. 206—208. 



