.CHAPTEE IV.. 



BREWSTER, HERSCHEL AND FORBES ; BECQUEREL AND DRAPER. 



18221843. 



THE work of Wollaston and Fraunhofer then, and the im- 

 provements in the methods of observation which they effected, 

 taught us that the quality of the sun's light was very special and 

 that the solar spectrum was a thing per se. Fraunhofer, as we 

 have seen, was firmly of opinion that the special quality was 

 imparted at the siin itself. 



"We learnt from both of them, moreover, that while sunlight, 

 on the one hand, differed from ordinary white light in having 

 a spectrum of dark lines ; coloured light, on the other hand, 

 differed from the same white light, in having a spectrum in 

 which bright lines are seen. 



It is in Sir David Brewster's work that we find the next 

 important development. 



Like his predecessors, he too made a map of the solar spec- 

 trum, and, like them too, he was the first to open out a branch 

 of research on which our present knowledge of solar chemistry 

 is based. 



In 1822 he laid before the Koyal Society of Edinburgh 1 

 the results of experiments he had performed, with the view of 



1 Edin. Phil. Trans, vol. ix. 1823, p. 433 



