266 SCIENCE PROGRESS. 



way that Dr. Hillebrand had done in 1888. The gas 

 obtained as Dr. Hillebrand had obtained it was eventually- 

 submitted to a spectroscopic test, following Dr. Hillebrand's 

 example. But here a noteworthy thing comes in. 



It so happened that the pressure and electrical conditions 

 employed by Professor Ramsay were so different from those 

 used by Dr. Hillebrand that, although nitrogen was un- 

 doubtedly present, the fluted spectrum which, as I have 

 previously stated, floods the orange part of the spectrum 

 with luminous details, was absent. But still there was 

 something there. 



Judge of Professor Ramsay's surprise when he found 

 that he got a bright orange line ; that was the chief thing, 

 and not the strong suggestion of the spectrum of nitrogen. 

 Careful measurements indicated that the twenty-six-year- 

 old helium had at last been run to earth, D 3 was at last 

 visible in a laboratory. Professor Ramsay was good enough 

 to send specimens of the tubes containing this gas round 

 to other people, and he sent one of them to me. 



I received Professor Ramsay's tube on 28th March, but 

 it was not suitable for the experiments I wished to make. 



On 29th March, therefore, as Professor Ramsay was 

 absent from England, in order not to lose time I determined 

 to see whether the gas which had been obtained by chemical 

 processes would not come over by heating in vacuo, after the 

 manner described by me to the Royal Society in 1879/and Mr. 

 L. Fletcher was kind enough to give me some particles of 

 uraninite (broggerite) to enable me to make the experiment. 



This I did on 30th March, and it succeeded ; the gas 

 giving the yellow line came over, associated with hydrogen, 

 in good quantity. 



From 30th March onwards my assistants and myself 

 had a very exciting time. One by one the unknown lines 

 I had observed in the sun in 1868 were found to belong to 

 the gas I was distilling from broggerite ; not only D 3 but 

 4923, 5017, 4471 (Lorenzoni's/), 6677 (the B C of Fig. 7), 

 referred to previously, and many other solar lines, were all 

 caught in a few weeks. 



1 Roy. Soc. Proc, vol. xxix., p. 266. 



