CH. xxxiv. TffZ SOLAR SPECTRUM. 341 



He repeated the experiment with other burning metals, 

 such as potassium and strontium, and always with the same 

 result. Each incandescent gas absorbed out oj white light 

 exactly those rays which it gave out itself when glowing. 



The black lines in the solar spectrum were now explained, 

 for each one of them must imply that some particular ray of 

 sunlight has been absorbed by a gas between the sun and 

 us, and it must have been absorbed near the sun, as Fraun- 

 hofer had pointed out, because the lines are different in 

 light which comes from the stars, showing that in that case 

 it has passed through other kinds of gases. Therefore 

 Kirchhoff concluded that round the solid or liquid body of 

 the sun, which gives out white light, and would of itself pro- 

 duce a continuous spectrum, there must be an atmosphere 

 of gases of different kinds, which absorb or destroy particular 

 rays of light, and prevent them reaching us. 



If this is the case, it is clear that we can tell from the 

 lines in the spectrum what gases and vapours there are in 

 this solar atmosphere. For example, there must be sodium 

 which cuts off the rays which ought to come to D, and there 

 must be also iron, magnesium, calcium, chromium, potas- 

 sium, rubidium, nickel, barium, lead, copper, zinc, strontium, 

 cadmium, cobalt, uranium, cerium, vanadium, palladium, 

 aluminium, titanium, hydrogen, and carbon, for the bright 

 lines of all these metals are wanting in the solar spectrum, 

 showing that the white light from the body of the sun 

 must have passed through their gases. Sir W. Herschel 

 had supposed the sun to be a dark body surrounded by a 

 luminous atmosphere. But we see that spectrum analysis 

 shows just the opposite to be true. The body of the sun 

 must be an intensely heated body giving out light, and if 

 it is composed of gas it must be so dense as to act as a 

 liquid and give a continuous spectrum. This body is called 

 \h& photosphere^ or light-giving sphere; and around it lies the 



