434 



METEORIC STONES AND SHOOTING STARS. 



for the elements composing aerolites are not in a state of combination, but sim- 

 ply agglomerated and held together in juxtaposition. And yet, if they are not 

 subjected to any force, these little globuL-s ought to fall separately as they are 

 formed. It is in vain to object that they might be suspended, for more or less 

 time, by a cause analogous to that which, according to the ingenious opinion 

 of Volta, balances the particles of hail between two clouds, so as to give them 

 time to enlarge by the addition of new layers of ice. The fact still remains, 

 that these latter have never been seen to amount to several hundred weight, 

 though the elements that form hail are much more abundant in the air than those 

 of aerolites are supposed to be. Besides, in Volta's theory, the suspension of 

 hail in the atmosphere is attributed to the reciprocal action of electric clouds, 

 a cause which can not be in like manner adapted to the formation of aerolites, 

 since the meteors that carry them sometimes burst in the clearest weather. 



But even granting all this, and admitting the formation of aerolites in the at- 

 mosphere by some unknown agency, how shall we account for the circumstan- 

 ces attending their collision with the surface of the earth 1 According to this 

 theory, they would move to the surface of the earth by the operation of terres- 

 trial gravity alone, and would meet the earth with a velocity due to the height 

 from which they fell. Now the actual velocities with which they are known 

 to strike the earth could never be acquired under the mere agency of terrestrial 

 gravity, through any height within the ordinary limits of the air. 



But, if the velocity of the meteorites be incompatible with this theory, their 

 direction is still more so. Their obliquity could never be produced by any con- 

 ceivable atmospheric current. 



We may, therefore, safely pronounce the atmospheric theory to be incom- 

 patible with the ascertained circumstances of the phenomena, and to require 

 admissions inconsistent with the established principles of physics. 



The volcanic theory is subject to objections as decisive as that we have first 

 examined. The nature of the substances ejected from terrestrial volcanoes is 

 well known, and we do not find among them the substances which form the 

 constituents of meteorites ; besides this, it is found that meteoric stones fall on 

 parts of the earth so remote from volcanoes, and at times so distant from any 

 known extensive eruptions, that it is impossible to admit the supposition that 

 they have proceeded from this cause. For these and other reasons, needless 

 to dwell on, the volcanic hypothesis is set aside. 



The planetary hypothesis is subject to less difficulty, and is much more in 

 harmony with the phenomena. The velocity and direction of meteoric stones 

 when they strike the earth are quite in accordance with this theory, and the 

 existence in them of constituents like metallic iron and nickel, which have no 

 natural existence on the earth, is also explicable ; but these circumstances are 

 equally accounted for by all the extra terrestrial theories, and afford, therefore, 

 no more countenance to the planetary than to the lunar or nebular hypothesis. 

 On the other hand, a serious difficulty is presented in the uniform analysis of 

 the meteorites. How can it be supposed that all the various fragments of a 

 broken planet should consist of the same constituents in the very same propor- 

 tion ? If the earth were split in pieces by any cause internal or external, would 

 its fragments be so uniform in its constituents ? Assuredly not. We should 

 find fragments of very heterogeneous character. One would consist of a mass 

 of sandstone, another a lump of granite ; here would be an agglomerate of one 

 kind, there of another. It is, therefore, in the highest degree improbable that 

 the fragments of another planet should be uniform in their constituents, and this 

 improbability is rendered greater by the fact that the meteorites are composed 

 of heterogeneous materials, mechanically agglomerated, and not of a uniform 

 substance, composed of different elements, united like those of water or air. 



