THE GROWTH OF OUR KNOWLEDGE OF HELIUM. 251 



this of course is not possible, as the ordinary spectrum of 

 the sun, with its tell-tale dark lines, is invisible because the 

 sun, as we ordinarily see it, is hidden by the moon. 



Working, then, under such very favourable conditions, it 

 was seen that there was certainly a red line given by this lower 



1 



I 



Fig. 3. — The exact coincidence of the red line with the dark line C. 



part of the solar atmosphere coincident with the very im- 

 portant line in the solar spectrum which we call C. 



Another part of the spectrum in the blue-green was 

 examined, and there again it was seen that the parts out- 

 side the sun gave us a bright line exactly in the position of 



> ii 1 1 1 11 1 1 1 1 1 1 I ■ 



Fig. 4. — The exact coincidence of the blue-green line with the dark line F. 



the obvious dark line in the solar spectrum which is called 

 F ; so that with regard to those two most important lines, 

 there was no doubt whatever that we were dealing with 

 the substance which produces these dark lines in the solar 

 spectrum. 



