PHYSICAL BASIS OF SOLAR CHEMISTRY 359 



spectrum extends over a sensible space, blending on one 

 side with the orange and on the other with the green. 

 The term "yellow band" is therefore somewhat indefinite. 

 This vagueness may be entirely removed. By dipping the 

 carbon-point used for the positive electrode into a solu- 

 tion of common salt, and replacing it in the lamp, the 

 bright yellow band produced by the sodium vapor stands 

 out from the spectrum. When the sodium flame is caused 

 to act upon the beam it is that particular yellow band that 

 is obliterated, an intensely black streak occupying its 

 place. 



An additional step of reasoning leads to the conclusion 

 that if, instead of the flame of sodium alone, we were to 

 introduce into the path of the beam a flame in which lith- 

 ium, strontium, magnesium, calcium, etc., are in a state 

 of volatilization, each metallic vapor would cut out a sys- 

 tem of bands, corresponding exactly in position with the 

 bright bands of the same metallic vapor. The light of our 

 electric lamp shining 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 constitu- 

 tion 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 photo- 

 sphere, 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 



