THE SMITHSONIAN INSTITUTION. 165 



meteorites more strongly than any other, it is the freedom of the masses 

 of iron from oxydation except on tlie surface. But a still more re- 

 markable abstinence from oxydation would be the ascent of the parti- 

 cles of phosphorus to form the Schreibersite traceable in so many me- 

 teorites. 



Having noticed the prominent objections to this hypothesis, I pass 

 on to consider, in as few words as possible, the other two suppositions. 



The most generally adopted theory of the origin of meteoric bodies 

 is that they are small planetary bodies revolving around the sun, one 

 portion of their orbit approaching or crossing that of the earth ; and 

 from the various disturbing causes to which these small bodies must 

 necessarily be subjected, their orbits are constantly undergoing more 

 or less variation, until intersected by our atmosphere, when they meet 

 with resistance and fall to the earth's surface in whole or in part ; 

 this may not occur in their first encounter of the atmosphere, but re- 

 peated obstructions in this medium at different times must ultimately 

 bring about the result. In this theory their origin is supposed to be 

 the same as that of other planetary bodies, and they are regarded as 

 always having had an individual cosmical existence. Now, however 

 reasonable the admission of this orbital motion immediately before and 

 for some time previous to their contact with the earth, the assumption 

 of their original cosmical origin would appear to have no support in 

 the many cTiaracteristics of meteoric bodies as enumerated before. The 

 form alone of these bodies is anything but what ought to be expected 

 from a gradual condensation and consolidation ; all the chemical and 

 mineralogical characters are opposed to this supposition. If the ad- 

 vocates of this hypothesis do not insist on the last feature of it, then 

 it amounts to but little else than a statement that meteoric stones fall 

 to us from space while having an orbital motion. In order to entitle 

 this planetary liypothesis to any weight it must be shown how bodies, 

 formed and constructed as these are, could be other than fragments of 

 some very much larger mass. 



As to the existence of meteoric stones in space travelling in a special 

 orbit prior to their fall, there can be but little doubt, when we con- 

 sider their direction and velocity ; their composition proving them to 

 be of extra-terrestrial origin. This, however, only conducts in part 

 to their origin, and those who examine them chemically will be con- 

 vinced that the earth is not the first great mass that metoric stones 

 have been in contact with, and this conviction is strengthened when 

 we reflect on the strong marks of community of origin so fully dwelt 

 upon. 



It is, then, with the consideration of what was the connexion of these 

 bodies prior to their having an independent motion of their own, 

 that this lecture will be concluded. 



It only remains to bring forward the facts already developed to ex- 

 hibit the plausibility of the hypothesis of the lunar origin of meteoric 

 stones. 



It was originally proposed as early as 1660, by an Italian phi- 

 losopher, Terzago, and advanced by Olbers in 1*795, without any 

 knowledge of its having been before suggested ; it was sustained by 

 Laplace, with all his mathematical skill, from the time of its adoption 



