1 6 DISCOVERIES WITH THE SPECTROSCOPE. 



formed is in exactly the same place as the dark line in the yellow 



Kirt of the solar spectrum, which Fraunhofer indicated by the letter 

 . Hence the conclusion is arrived at, that the light produced by 

 sodium burning in the sun is the cause of the appearance of this line 

 in the solar spectrum. Similarly, potassium gives a dull spectrum 

 with all the colours, but has a brilliant red line in the extreme end of 

 the red portion, which corresponds with the dark line in that position 

 called by Fraunhofer A ; and there is a second line for this substance 

 at the extreme end of the violet part of the spectrum. Iron when 

 burnt in the electric light yields about seventy bright lines. On 

 this kind of evidence about eighteen common metals, metalloids, 

 and gases have been identified as contributing by their incandescent 

 vapours to produce the sun's atmosphere. Among these substances are 

 sodium, calcium, magnesium, iron, nickel, copper, zinc, cobalt, man- 

 ganese, aluminium, barium, chromium, strontium, cadmium, titanium, 

 hydrogen, and oxygen. Hereafter many other elements may be found. 1 

 When a metal is burned on the earth, it enters into combinations 

 with gases and becomes an earthy or mineral substance. Hence, it is 

 probable that the combustion now going on in the sun, which illumi- 

 nates the whole solar system, will form in that star rock-substances 

 not unlike those which constitute the earth ; and we are led to infer 

 that at some far-distant time the earth itself may have been incan 

 descent at its surface, as the sun now is, and that the chemical com 

 binations of elements which form its rocks can thus be accounted for 

 as products of combustion. 



It has also been shown that the vast outer enveloping portion of 

 the sun's atmosphere is formed of the gas hydrogen in a burning state. 

 There is every reason to believe that hydrogen burns there as on the 

 earth, by combining with oxygen gas. The product of this combustion 

 is vapour, which must ultimately condense into water when the heat is 

 less, and, dissolving soluble salts, accumulate eventually in depressions on 

 the sun's surface so as to form oceans and seas. It is at least probable 

 that the earth has passed through a phase of this kind, and that all the 

 water on its surface was produced just as water may now be produced 

 artificially, by the combustion of hydrogen in oxygen gas. This conclu- 

 sion is the more likely since the earth's atmosphere is merely a 

 mechanical mixture of oxygen and nitrogen, as though it were the in- 

 combustible residue of gases left after the combustible materials on its 

 surface had burnt themselves out. The other planets are apparently 

 more or less like the earth in possessing atmospheres and seas ; and 

 Mars so far resembles the earth as to display white snow-capped poles ; 

 and both that planet and Jupiter exhibit changing shapes of clouds, 

 which in Mars frequently assume similar outlines over large portions of 

 its surface, as though land and water were grouped into large masses. 

 If the moon has neither atmosphere nor oceans, it may well be that 

 the atmosphere of gases was small while it was undergoing combustion, 

 and that they were entirely combined with the burning elements. 

 The phenomena produced by combustion must, at the smallest 

 1 Roscoe, "Spectrum Analysis." 



