Of the many who contend for the atmospheric for mation of meteorites, scarcely any two agree in regard to the manner in which such FOrmation is effected. • Mnschenbroeck, in one part of his writings, ascribes the descent of stones from the air to earthquakes and volcanic eruptions ; an opinion which later observations have disproved. In other passages, however, he leans to a modification of the atmospheric hypotheses, and attributes the origin of shooting stare to the accumula tion of volatile matters suspended in the air. Whatever relation may subsist between shooting stars and fiery meteors, the former seem to move at a much greater distance from the earth than the latter, and occasion only a transient luminous appearance, in their passage through the upper regions of the atmosphere. The Dutch phi losopher, however, adopts the common notion of their falling to the ground, and seems to confound their residue with tremella nostoc.
The late ingenious, but fanciful Patrin, who was so licitous to extend and illustrate his favourite doctrine of a regular circulation of gaseous fluids between the schis tose strata of the globe and its surrounding atmosphere, very confidently deduced from this fancied circulation the occasional ignition and concretion of portions of these fluids in the higher regions of the air. But it is a suffi cient confutation or his theory, that it rests on assumed and very improbable foundations.
In aid of the same cause, M. Salverte had recourse to a very liberal exhibition of hydrogen gas, kindled by electricity during thunder storms. But we have shown that thunder and meteors are distinct phenome na ; and this gentleman's magazines of hydrogen remain to be proved.
His countryman, M. Izarn, has dragged his readers into a tedious and somewhat obscure exposition of his own sentiments, founded on the principles of chemical combination ; but we are not certain that we perfectly comprehend his meaning; and, at any rate, his infer ences depend on admissions of gaseous substances, ar ranged in spherical masses in the superior regions of the air, and occasionally detached from their insulating medium, and brought into one capable of combining with them ; a disposition of things which may, or which may not exist, but of which we are entirely ig norant, M. Seguin thinks it not improbable that the constitu went principles of meteorites being transported by che mical or mechanical means into the upper portions of the atmosphere, where a vacuum, the cause of the noise of thunder, is produced, there remain suspended by so lution or otherwise ; but, although disseminated, being pressed by the external strata which fill the vacuum, they unite, conglomerate, and form a mass, the more considerable in proportion to the quantity of materials which it encounters in this place. Now, granting to
this philosopher his conjectural premises, we have again to repeat, that the fall of meteorites is independent of thunder, and that the noise of the explosion, which so much resembles thunder as to have been often confounded with it, is posterior to the consolidation of the mass.
In the 75 h volume of the ?liznales de Chimie, M. Marcel de Serrcs enters into the of the origin of meteorites: but much of his paper is occupied with a very rapid and imperfect recapitulation of the in stances of their occurrence, and incidental notices of showers of sand, &c. His decided bias, however, is to the generation of these bodies in the atmosphere, from the contact of all the matters carried up by the evapo ration, and the formation of metallic particles during the ignition. Y• t, his solution of the problem is, on the whole, far from luminous ; nor is he altogether insensi ble to the difficulties with which it is encompassed. The total absence of oxygen in the Lissa stone, in par ticular, strikes him very forcibly. It is, besides, ex tremely difficult to conceive the machinery by which an immense field of gaseous, or highly attenuated !natter in the air, can be instantaneously reduced into the com pass and consistency of a solid compact mass, of very moderate dimensions, and suspended in the air, as if by enchantment, until it explodes, and is precipitated to the earth.
Dr. Reynolds' Outline of the Theory of Meteors does not very materially differ from some of those to which we have just alluded ; for it proceeds on the supposi tion that minute portions of the earthy and metallic compounds of the surface of the globe, being exposed to the sun's influence, will be volatilized by the absorp tion of heat, and thereby assuming the state of elastic fluids, will ascend, until they arrive at media of their own density, where, congregating into immense and highly concentrated volumes, they will explode, and ex hibit all the appearances of meteoric stones and showers. But the elevation of particles of stone and iron, how ever much attenuated, to the enormous height of a hun dred miles above the earth's surface, is scarcely con ceivable on any principle with which we are acquainted ; and their combustion and explosion, in such a lofty and frigid medium, arc alike unsusceptible of satisfactory explanation.