42 



THE CHEMISTRY OF THE SUN. 



[CHAP. 



gas is contained in a large glass tube closed at each end by a 

 flat glass plate. At one end of the tube is placed a lamp, and 

 at the other the spectroscope. 



LL. 



FIG. 21. Absorption spectrum of iodine (Thalen). 



We are now, then, in possession of the phenomena first 

 observed by Brewster arid Herschel, and of an easy means of 

 producing them for our own satisfaction. We must now pass 

 on to their applications. 



FIG. 22. Method of observing the absorption of a great thickness of vapour. 



Brewster at once applied this new knowledge to the sun. 

 He first of all endorsed Fraunbofer's view that the dark 



