Phenomena in the Solar System. 445 



Other observations of a very different nature give a strong sup- 

 port to the conclusions of Leverrier ; the remarkable discoveries 

 of Kirchoff and Bunsen upon the dark lines in the solar spectrum, 

 have enabled us to submit the solar atmosphere to an optical 

 analysis which makes known its chemical composition, and shows 

 it to contain several alkaline metals, including sodium and cal- 

 cium, which can only exist there in the state of gas or vapor. 

 The discussion of this interesting subject belongs especially to 

 chemists and physicists, but geologists may be permitted to ex- 

 press their sympathy for that view which best accords with 

 the theory that forms the basis of their science, and is, moreover, 

 entitled to a certain authority among mathematicians and astrono- 

 mers, inasmuch as it bears the name of the illustrious Laplace. 



All modern geological theories implicitly admit the unity of 

 our planetary system, in so far as that they suppose the sun, the 

 planets and their satellites, to have been formed from one primi- 

 tive substance ; their very variable densities only show that the 

 constituent elements are grouped in varying proportions.^ It is 

 not necessary to suppose that each body of the system presents 

 exactly the same chemical combinations as are known on our globe, 

 for affinities will vary with the temperature and the densities of 

 the elements, but we may admit that a portion of any one of these 

 celestial bodies brought to the surface of our earth and there sub- 

 jected to terrestrial influences, would in obedience to the chemical 

 affinities which here prevail, be at length converted into a portion 

 of earth. 



This unity of origin once admitted there is no longer any rea- 

 son for denying the analogy if not the identity, of the phenomena 

 which have accompanied the formation of the sun and the planets, 

 at least of those whose density approaches the nearest to that of 

 the earth. All of them must have passed by cooling from a state 

 of igneous fluidity to a solid condition, and their present state will 

 depend upon the greater or less facility which their volume and 

 their composition will have offered to the passage of heat. The 

 chemical composition being the same, the duration of the geolo- 

 gical epochs upon each planet will have been nearly in a direct 

 ratio to its volume, setting aside certain corrections of which it is 

 not necessary at present to discuss the elements. The low density 

 of the sun, which is little greater than that of water (0*252 that 



[* Or in diflfereut degrees of condensation.— 2VansZa/or."| 



