THE GROWTH OF OUR KNOWLEDGE OF HELIUM. 271 



others ; in /3 Lyrae and other bright line stars ; and as a 

 dark line in such stars as Bellatrix, by Mr. Fowler, Pro- 

 fessor Campbell and Professor Keeler. In all these cases 

 it is associated with other lines, which, as I shall show pre- 

 sently, are associated with it in the spectra of the new gases. 



The Blue Line, A 4471*8. — A provisional determination 

 on 2nd April of the wave-length of a bright blue line, seen 

 in the spectrum of the gases obtained from a specimen of 

 cleveite, showed that it approximated very closely to a 

 chromospheric line, the frequency of which is stated as 100 

 by Young. 



This line was also seen very brilliantly in the tube 

 supplied to me by Professor Ramsay on 1st May, and on 

 6th May it was compared directly with the chromosphere 

 line by Mr. Fowler. The second order grating spectrum 

 was employed. The observations in this region were not 

 so easy as in the case of D 3 , but with the dispersion em- 

 ployed, the gas line was found to be coincident with the 

 chromospheric one. In this case also, the chromosphere 

 was observed at the sun's poles, in order to eliminate the 

 effects due to the sun's rotation. 



Besides appearing in the spectrum of the chromosphere, 

 the line in question is one of the first importance in the 

 spectra of nebulae, bright line stars, and of the white stars 

 such as Bellatrix and Rigel. 



The Infra-red Line, \ 7065*5. — In addition to D 3 and 

 the line at 447 1 '8, there is a chromospheric line in the infra- 

 red which also has a frequency of 100, according to Young. 

 On 28th May I communicated a note to the Royal Society 

 stating that this line had been observed in the spectrum of 

 the gases obtained from broggerite and euxenite {Roy. Soc. 

 Proc, vol. lviii., p. 192), solar comparisons having con- 

 vinced me that the wave-length of the gas line corresponded 

 with that given by Young ; and I added : " It follows, there- 

 fore, that besides the hydrogen lines all three chromospheric 

 lines in Young's list which have a frequency of 100 have 

 now been recorded in the spectra of the new gas or gases 

 obtained from minerals by the distillation method ". 



M. Deslandres, of the Paris Observatory, has also 



