THE GROWTH OF OUR KNOWLEDGE OF HELIUM. 267 



But this was by no means all. The solar observations 

 had been made by eye, and referred therefore to the less 

 refrangible part of the spectrum, but I had obtained and 

 studied hundreds of stellar photographs, so I at once pro- 

 ceeded to photograph the gas and compare its more re- 

 frangible lines with stellar lines. 



Here, if possible, the result was still more marvellous. 

 In the few-lined stars by 6th May I had caught nearly all 

 the most important lines at the first casts of the spectroscopic 

 net. Fig. 1 5, which includes some later results, will give an 

 idea of the tremendous revelation which had been made as 

 to the chemistry of some of the stages of star-life. I 

 pointed out on 8th May that we had already "run home " 

 the most important lines in the spectra of Group III. in 

 which stars alone we find D 3 reversed. 



These results enabled us at once to understand how it 

 was that the "unknown lines" had been seen both in the 

 sun's chromosphere and some nebulae and stars. The gas 

 obtained from the minerals made its appearance in the 

 various heavenly bodies in which the conditions of the 

 highest temperatures were present ; and the more the work 

 goes on, we find that this gas is really the origin of most, 

 but certainly not of all, of the unknown lines which have 

 been teasing astronomical workers for the last quarter of a 

 century. 



THE FIRST INVESTIGATIONS OF THE SPECTRUM OF THE 



GAS FROM CLEVEITE. 



The dates of the papers communicated to the Royal 

 Society recording the observations of the lines in the gas 

 obtained from minerals which had been previously recorded 

 are as follows : — 



4026 



4922 



The lines at 667 and 5016 had been previously seen 

 by Thalen (Comptes Rendus, 16th April, 1895). 



