172 THE CHEMISTEY OF THE SUN. [CHAP. 



departure from the terrestrial distribution. But here again 

 the facts were all the other way. 



How came it that the total chemical composition of the 

 atmosphere of the sun, which we were taught to look upon as 

 the exemplar of what must have once existed in the case of 

 our own planet, varied so enormously from the composition of 

 the crust of our earth ? 



Among all the metalloids known to chemists only one of 

 them or one substance classed as such, hydrogen was present 

 in the solar atmosphere, and that in overwhelming quantity; 

 whereas the efforts of Angstrom, Kirchhoff, and others, could 

 not trace such substances as oxygen, chlorine, silicon, and 

 other common metalloidal constituents of the earth's crust. 

 It was difficult to imagine a stronger difference to exist 

 between any two masses of matter than that found between 

 the incandescent sun, and the earth which is now cooling. 



Even the elements in the sun were in an unnatural order 

 according to the received chemical views . To give an instance : 

 The layer produced by what was taken to be gaseous magne- 

 sium round the sun, a layer indicated by the brightest member 

 of the 5 group, was always higher always gave us longer lines 

 than that other layer which was brought under our ken by the 

 bright line D seen in the spectrum of sodium. Here was a distinct 

 inversion of the chemical order. The atomic weight of sodium 

 being 23, and of magnesium 24, the sodium ought to have been 

 higher than the magnesium ; but the contrary was the fact, and 

 that fact has been established by twelve years of observation. 



3. The Chemical Nature of the Sun unlike that of many 

 of the Stars. 



If then the sun and earth were chemically unlike, it was of 

 the highest importance to learn how the facts stood in the case 

 of the stars a point of view very soon forced upon solar 



