THE SMITHSONIAN INSTITUTION. 157 



sphere, whicli tliey do at a very great velocity ; heat is developed in 

 them by their friction against the air; the iron they contain is .sub- 

 ject to combustion, which is augmented by the condensed condition 

 of the atmosphere before the object wliile in rapid motion. All this 

 suffices for the production of the light exhibited. Light does not 

 always accompany the fall of these bodies — a fact which, it is reason- 

 able to suppose, belongs especially to the masses of iron, which, from 

 the compact nature of their structure, and their great conductibility, 

 cannot become so readily heated on the surface as to reach the point of 

 incandescence. The noise is produced by their rapid motion through 

 the air, and their bursting by the combined effects of irregular expan- 

 sion by heat, and certrifugal force produced by irregular resistance of 

 the atmosphere ; the latter being alone sufficient to bring about such 

 a result, as is shown by the shooting of stone balls from a cannon. 

 The velocity of these bodies will be discussed in another part of this 

 lecture. 



The lessons to be learned from meteorites, both stony and metallic, 

 are probably not as much appreciated as they ought to be ; we are 

 usually satisfied with an analysis of them and surmises as_ to their 

 origin', without due consideration of their physical and chemical char- 

 acteristics. 



The great end of science is to deduce general principles from parti- 

 cular facts. Thus terrestrial gravitation has been extended to the 

 whole solar system, and, indeed, to the whole visible universe. The 

 astronomer, however, has only proved the universality of this one law, 

 and has found no evidence that any other force observed at the surface 

 of the earth displays itself in any other sphere. However probable it 

 may appear that the same laws affect terrestrial and celestial matter, 

 it is none the less interesting to extend our proofs of this assumption, 

 and meteorites, when looked upon in this light, acquire additional in- 

 terest. 



First. They lead us to the inference that the materials of the earth 

 are exact representatives of those of our system, for up to the present 

 time no element has been found in a meteorite that has not its coun- 

 terpart on the earth ; or if we are not warranted in making such a 

 broad assumption, we certainly have the proof, as far as we may ever 

 expect to get it, that some materials of other portions of the universe 

 are identical with those of our earth. 



Second. They show that the laws of crystallization in bodies foreign 

 to the earth are the same as those affecting terrestrial matter, and in 

 this connexion we may instance pyroxene, olivine and chrome iron, 

 affording, in their chrystalline form, angles identical with those of 

 terrestrial origin. 



Third. The most interesting fact developed by meteorites is the 

 universality of the laws of chemical affinity, or the truth, that 

 the laws of chemical combination and atomic constitution are to be 

 equally well seen in extra-terrestrial and terrestrial matter ; so that 

 were Dalton or Berzelius to seek for the atomic weights of iron, 

 silica or magnesia, they might learn them as well from meteoric 

 minerals as from those taken from the bowels of the earth. The 



