44 THE CHEMISTRY OF THE SUN. [CHAP. 



the want of variation among the other lines he saw an 

 indication 



" That the apparent body of the sun is not a flame in the ordinary 

 sense of the word, but a solid body or coating raised by intense heat 

 to a state of brilliant incandescence." 1 



It will be seen, then, that the study of the sun was now 

 (1833) in full swing. We had at length, after waiting some 

 centuries, a method of observing a spectrum ; we had, further, 

 the fact that there were dark lines in the solar spectrum ; that 

 coloured flames gave us bright lines ; that certain substances 

 stopped some of the light which passed through them, thus 

 producing dark lines. Hence that the solar lines might be 

 produced in the same way. 



We next come to Forbes, whose manner of work was interest- 

 ing, though it led him to a conclusion which we now know 

 to be erroneous. 



We have seen that both Fraunhofer and Brewster were 

 firmly of opinion that the dark lines were produced by some 

 action at the sun. Brewster was more definite, and said some 

 absorption at the sun. 



The next point investigated was this. It seemed obvious that 

 if Brewster's view were true there should be a difference between 

 the spectrum of the sun's centre and the sun's limb or edge, 

 because the light passing to the eye from the latter would have 

 to traverse a greater thickness of the sun's atmosphere. It did 

 not strike anybody at first to throw an image of the sun on 

 the slit of a spectroscope and see if there were a difference ; the 

 inquiry was, however, made in another way. 



In 1836, Professor Forbes began it by taking advantage of an 

 annular eclipse of the sun at Edinburgh, during which, of course, 

 only the light from the edge reached us, the centre being cut off 

 by the dark moon. 



1 Loc. cit. p. 529. 



