The Sun 



mine the elements composing it, its form and 

 dimensions. 



The spectroscope gives an immediate answer 

 to the first question; it is enough to determine 

 the position of the bright lines emitted by the 

 chromosphere and try to identify them with 

 the lines of known bodies. Now, the character- 

 istic lines of hydrogen are recognised without 

 hesitation; their brightness and constant 

 presence prove hydrogen to be the fundamental 

 element of the chromosphere. To it this gaseous 

 layer owes the red colour which suggested 

 its name, and whose influence is visible in the 

 reddish colouring of the sun's rim. But this 

 influence affects the entire surface of the orb; 

 the chromosphere resembles a red veil stretched 

 over its disc. If we could tear it off and uncover 

 the photosphere we should see that the latter 

 is blue. 1 In addition to hydrogen the chromo- 

 sphere is shot through, but in a more irregular 



1 It is known, as a matter of fact, that the colour of in- 

 candescent bodies changes from red to white, and then to blue, 

 as their temperature increases ; thus the electric arc at 4000 

 centigrade is already distinctly bluish. This blue colour 

 must be even more marked in the case of the photosphere, 

 whose temperature reaches 7000. 



179 



