104 REPORT ISGl. 



In October 1859, Professor Kirchhoff of Hcitlclberg matic a comiminica- 

 tion to the Berlin Academj' on tlie snbjpct of Frauiiliofer's liiirs, wliicli, along 

 with Foucault's communication, has been inserted by Professor Stokes in the 

 * Philosophical Magazine ' for March 1860. Professor Kirchhoft' thus de- 

 scribes the result of his experiments : — 



" On the occasion of an examination of the spectra of coloured flames, not 

 yet published, conducted by Bunsen and myself in common, by which it has 

 become possible for us to recognize tiie qualitative composition of complicated 

 mixtures from the appearance of the spectrum of their blowpipe-flame, I 

 made some observations which disclose an unexpected explanation of the 

 origin of Fraunhofer's lines, and authorize conclusions therefrom respecting 

 the material constitution of the atmosphere of the sun, and perhaps also of 

 the brighter fixed stars. 



" Fraunhofer had remarked that in the spectrum of the flame of a candle 

 there appear two bright lines, which coincide with the two dark lines D of the 

 solar spectrum. The same bright lines are obtained of greater intensity from 

 a flame into which some common salt is put. I formed a solar spectrum by 

 projection, and allowed the solar rays concerned, before they fell on the slit, 

 to pass through a powerful salt-flame. If the sunlight were sufliciently re- 

 duced, there appeared in place of the two dark lines D two bright lines ; if, 

 on the other hand, its intensity surpassed a certain limit, the two dark lines 

 D showed themselves in much greater distinctness than without the employ- 

 ment of the salt-flame. 



" The spectrum of the Drummond light contains, as a general rule, the two 

 bright lines of sodium, if the luminous spot of the cylinder of lime has not 

 long been exposed to the white heat; if the cylinder remains unmoved these 

 lines become weaker, and finally vanish altogether. If they have vanished, 

 or only faintly appear, an alcohol flame into which salt has been put, and 

 which is placed between the cylinder of lime and the slit, (;auses two dark 

 lines of remarkable sharpness and fineness, which in that respect agree with 

 the lines D of the solar spectrum, to show themselves in their stead. Thus 

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

 which naturally they are not present. 



" If chloride of lithium is brought into the flame of Bunsen's gas-lamp, the 

 spectrum of the flame shows a very bright sharply defined line, which lies 

 midway between Fraunhofer's lines B and C. If, now, solar rays of moderate 

 intensity are allowed to fall through the flame on the slit, the line at the 

 place pointed out is seen bright on a darker ground ; but with greater strength 

 of sunlight there appears in its place a dark line, which has quite the same 

 character as Fraunhofer's lines. If the flame be taken away, the line disap- 

 pears, as far as I have been able to see, completely. 



" I concluded 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. I conclude 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 

 the same place 



<' The examination of the spectra of coloured flames has accordingly ac- 

 quired a new and high interest; I will carry it out in conjunction with Bunsen 

 as far as our means allow. In connexion therewith we will investigate the 



