PHYSICAL BASIS OF SOLAR CHEMISTRY. 341 



are in a state of volatilisation, each metallic vapour 

 would cut out a system of bands, corresponding ex- 

 actly in position with the bright bands of the same 

 metallic vapour. The light of our electric lamp shin- 

 ing through such a composite flame would give us a 

 spectrum cut up by dark lines, exactly as the solar 

 spectrum is cut up by the lines of Fraunhofer. 



Thus by the combination of the strictest reasoning 

 with the most conclusive experiment, we reach the 

 solution of one of the grandest of scientific problems 

 the constitution of the sun. The sun consists of a 

 nucleus surrounded by a flaming atmosphere. The 

 light of the nucleus would give us a continuous spec- 

 trum, like that of our common carbon-points; but hav- 

 ing to pass through the photosphere, as our beam had 

 to pass through the flame, those rays of the nucleus 

 which the photosphere can itself emit are absorbed, 

 and shaded spaces, corresponding to the particular rays 

 absorbed, occur in the spectrum. Abolish the solar 

 nucleus, and we should have a spectrum showing a 

 bright line in the place of every dark line of Fraun- 

 hofer. These lines are therefore not absolutely dark, 

 but dark by an amount corresponding to the difference 

 between the light of the nucleus intercepted by the 

 photosphere, and the light which issues from the latter. 



The man to whom we owe this noble generalisation 

 is Kirchhoff, Professor of Natural Philosophy in the 

 University of Heidelberg; * but, like every other great 

 discovery, it is compounded of various elements. Mr. 

 Talbot observed the bright lines in the spectra of 

 coloured flames. Sixteen years ago Dr. Miller gave 

 drawings and descriptions of the spectra of various 

 coloured flames. Wheatstone, with his accustomed in- 

 genuity, analysed the light of the electric spark, and 

 Now Professor in the University of Berlin. 



