262 AXNTJAL OF SCIENTIFIC DISCOVERY. 



cussions upon the nature of the sun, -which seem to merit the attention 

 of geologists. The opinion hitherto generally adopted is founded upon 

 the view suggested by Arago from his observations concerning the spots 

 upon the sun. This great astronomer conceived that by admitting 

 a dark nucleus surrounded by a luminous atmosphere or photosphere, 

 it would be easy to explain the luminous phenomena presented by 

 the sun. On the other hand, Leverrier, from the observations made 

 in Algiers by the scientific commission from the Paris Observatory, 

 maintains that the sun is luminous from the incandescence of its nu- 

 cleus, and that the variations in the intensity of the light at its sur- 

 face may be explained by atmospheric perturbations similar to those 

 of our own atmosphere. M. Leverrier is led to admit for the sun at 

 least two atmospheres, different in nature and in density, and it is prin- 

 cipally with regard to the external envelope, or rose-colored atmos- 

 phere, which gives rise to the flames or luminous protuberances, that 

 there exists a difference of opinion among observers. 



Other observations of a very different nature give a strong support 

 to the conclusions of Leverrier ; the remarkable discoveries of Kirch- 

 hoff and Bunsen upon the dark lines in the solar spectrum have en- 

 abled us to submit the solar atmosphere to an optical analysis, which 

 makes known its chemical composition, and shows it to contain sev- 

 eral alkali-metals, including sodium and calcium, which can only 

 exist there in the state of gas or vapor. The discussion of this inter- 

 esting subject belongs especially to chemists and physicists, but geolo- 

 gists may be permitted to express their sympathy for that view which 

 accords the best with the theory that forms the basis of their science, 

 and is, moreover, entitled to a certain authority among mathemati- 

 cians and astronomers, 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 primitive sub- 

 stance ; 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 subjected to terrestrial influ- 

 ences, would, in obedience to the chemical affinities which here pre- 

 vail, be at length converted into a portion of earth. 



This unity of origin once admitted, there is no longer any reason 

 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 flu- 

 idity 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 geological epochs upon each planet 

 will have been nearly in a direct ratio to its volume, setting aside cer- 

 tain corrections, of which it is not necessary at present to discuss the 



