L 



METEORIC STONES AND SHOOTING STABS. 



tended that, even though the air were not to become luminous, it might, never- 

 theless, be raised to such a temperature by compression as, by contact with 

 the meteorite, might render the latter luminous ; but, even admitting the possi- 

 bility of this supposition, as applied to the air contiguous to the earth, or even 

 at any moderate elevation, an almost insuperable difficulty arises from the vavt 

 height at which meteorites have been visible. By barometric experiments and 

 observations made on the duration of the morning and evening twilight, it may 

 be considered as proved, that beyond the elevation of thirty miles there exists 

 no atmosphere possessing any sensible mechanical properties. We may safely 

 conclude that at such elevations the air, if any really exists there, must be so 

 infinitely attenuated as to be divested of all sensible resistance or inertia. The 

 space there must, for example, be a more absolute vacuum than any which 

 could be produced under the receiver of the most perfect philosophical air- 

 pump ; how, then, can we imagine such a compression of that fluid to be pro- 

 duced, as would be necessary to evolve the enormous temperature requisite to 

 render luminous the matter composing meteoric stones ? still less to become lu- 

 minous itself. 



In short, it must be admitted that none of these theories afford a satisfactory 

 explanation of the luminous appearances which accompany these meteors. Let 

 us, however, examine these theories respectively, and see how far they \vill 

 bear a further comparison with the actual circumstances of the phenomena. 



The atmospheric hypothesis is subject to objections so unanswerable, that it 

 may be considered as altogether set aside. In order to suppose it probable that 

 aerolites could be formed in the atmosphere, we must show that their constituent 

 elements can exist there. We know that hail and snow can be formed in the 

 air, because it can be proved that aqueous vapor is suspended there,, ajid that a 

 temperature is sometimes produced there so low as to convert tha,t vapor, first, 

 into a liquid, and then into the solid form of snow or hail. But th,e most rigor- 

 ous analysis has never detected in the atmosphere any of the constituents of 

 meteoric stones, nor is there any proof that the constituent principles of the air 

 could dissolve, evaporate, or sublimate such substances. Nor can it be said 

 that, although the atmosphere which immediately surrounds us may not have 

 such properties, yet, that at the great elevations in which meteorites are formed, 

 the air may consist of different constituents, for, besides the fact that it has been } 

 ascertained by direct analysis that the atmosphere, at all elevations to which * 

 man has ever yet attained, consists of exactly the same constituents, in exactly < 

 the same proportions, there is a general law, which prevails among all gaseous j 

 substances, that when different gases are superposed they will, notwithstanding { 

 their different degrees of levity, ultimately mingle so as to forrn a uniform ( . 

 mass ; thus, if we could imagine for a moment a stratum of air to exist near the 

 top of the atmosphere, having constituents different from those around us, such. 

 stratum would gradually intermingle with the strata below it, until the whole- 

 would acquire a uniform quality. It is, therefore, physically impossible thav 

 there can exist in any elevated region of the air any substances capable of dis- 

 solving or sublimating the matter of meteoric stones. 



To these objections we may add others. Although it may be admitted, as Ala- 

 go argues, that the constituent principles of aerolites should really exist in the 

 atmosphere at all heights, and that they only escape analysis because of ikeir 

 extreme minuteness, it would still be necessary to explain with such feeble and 

 such dispersed elements a sudden precipitation, yielding stones of several hun- 

 dred weight, such as those preserved at Ensenheim, in Alsace, or 3,000 or 4,000 

 stones of various dimensions, like those which were separated and shot off by 

 the Laigle meteor. It would be necessary to assign the cause that combines 

 the scattered molecules, and forms them into a single mass. It is not affinity, 



as 



