PHYSICAL BASIS OF SOLAR CHEMISTRY. 341 



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 spectrum, 

 like that of our common carbon-points ; but having 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 Fraunhofer. 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 ; l 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 

 ingenuity, analysed the Ii ht of the electric spark, and 

 showed that the metals between which the spark passed 

 determined the bright bands in the spectrum of the 

 spark. Masson published a prize essay on these bands; 

 Van der Willigen, and more recently Pliicker, have 

 given us beautiful drawings of the spectra, obtained 

 from the discharge of KuhmkorfPs coil. But none of 

 these distinguished men betrayed the least knowledge 

 of the connection between the bright bands of the 

 1 Now Professor in the University of Berlin. 



