

KIRCHHOFFS RESEARCHES. 



55 



Thus the lines D of the solar spectrum are artificially evoked in a 

 spectrum in which naturally they are not present. . . . 



" I conclude from these observations, that coloured flames in the 

 spectra of which bright sharp lines present themselves so weaken rays 

 of the colour of these lines, when such rays pass through the flames, 

 that in place of the bright lines dark ones appear as soon as there is 

 brought behind the flame a source of light of sufficient intensity, in 

 the spectrum of which these lines are otherwise wanting. / con- 

 dude further, that the dark lines of the solar spectrum which are 

 not evoked by the atmosphere of the earth exist in consequence of 

 the presence, in the incandescent atmosphere of the sun, of those 

 substances which in the spectrum of a flame produce bright lines 

 at t/ie same place. We may assume that the bright lines agreeing 



FIG. 24. Diagram showing the solar spectrum and th& bright double line D of 



sodium. 



with D in the spectrum of a flame always arise from sodium contained 

 in it ; the dark line D in the solar spectrum allows us, therefore, to 

 conclude that there exists sodium in the sun's atmosphere. . . . 



" In the course of the experiments which have at present been 

 instituted by us . . . . a fact has already shown itself which 

 seems to us to be of great importance. The Drummond light 

 requires, in order that the lines D should come out in it dark, a 

 salt flame of lower temperature. The flame of alcohol containing 

 water is fitted for this, but the flame of Bunsen's gas lamp is not. 

 With the latter the smallest mixture of common salt, as soon as it 

 makes itself generally perceptible, causes the bright lines of sodium 

 to show themselves " 



The point marked with italics is the most important part of 



