316 Intelligence and Miscellaneous Articles. 



fact these dark lines generally disappeared when the sun rose, and 

 there were no appreciable traces when the sun passed the meridian. 



Subsequently, a direct experiment, in which Messrs. Brewster and 

 Gladstone endeavoured to reproduce the gaps in the solar spectrum 

 by analyzing at a great distance an artificial light with a continuous 

 spectrum, did not give a satisfactory result (Philosophical Transac- 

 tions, 1860). 



The question of the origin of the dark lines and bands of the solar 

 spectrum was not then resolved ; but Brewster's beautiful researches 

 had nevertheless introduced into science very important ideas, and 

 facts which were to serve as the basis of ulterior studies. 



A short time afterthe publication of the important memoirof Messrs. 

 Brewster and Gladstone, a memoir which epitomizes the labours of 

 these gentlemen on this question, M. Kirchhoff published his beau- 

 tiful investigations on the solar spectrum. The result of these in- 

 vestigations is well known. The origin of spectral lines was referred 

 to an atmosphere surrounding the sun ; and the investigation of these 

 lines revealed the chemical composition of this atmosphere. The 

 general results of this theory will be a permanent acquisition to 

 science ; but the object was even exceeded. Between Brewster's 

 ideas seeking to explain the solar spectrum by the action of the 

 earth's atmosphere, and those of M. Kirchhoff assigning its origin to 

 a solar atmosphere, there was place for a doctrine less exclusive and 

 more complete, which will take into account the two causes, and de- 

 monstrate the twofold origin of the lines which Wollaston and Fraun- 

 hofer had discovered in the prismatic image of the sun. 



The solar origin of a portion of the lines of the spectrum of this 

 star being demonstrated, the action of our atmosphere remained to 

 be proved by completing the researches of Messrs. Brewster and 

 Gladstone, Piazzi Smyth, &c. That is the object of the investiga- 

 tions I have been engaged on since 1862. 



By new optical arrangements I first established the fact that Brew- 

 ster's bands were formed of a number of fine lines resembling the 

 solar lines properly so called. Further, the study of these lines has 

 shown that they were constant in the spectrum, although incessantly 

 variable in their intensity with the height of the sun, that is to say, 

 with the thickness of our atmosphere traversed by the lines of this 

 star. These results demonstrated the action of our atmosphere. To 

 corroborate them, I have investigated the spectrum on a high moun- 

 tain (the Faulhorn), September 1864. There I observed that the 

 lines of terrestrial origin grew weaker in proportion as I ascended — 

 that is, in proportion as the solar lines traversed a smaller thickness 

 of the terrestrial atmosphere. Lastly, in an experiment made on the 

 Lake of Geneva (October 1864), I was able artificially to reproduce 

 the same lines. The flame of a large log of spruce-fir, which gives 

 scarcely any line but the brilliant one of sodium, exhibited, at a dis- 

 tance of 21 kilometres, the atmospheric lines of the solar spectrum. 

 This accumulation of proofs showed, then, obviously the action of our 

 atmosphere, and the twofold origin of the lines of the solar spectrum. 

 I may add that this atmosphere, in spite of its small height and the 



