METEORS, IGNEOUS on LUMINOUS. The following is a con densed statement of the present condition of knowledge in the department of meteorology relating to these objects, which may now not improperly be termed meteoric astronomy, and which is con nected in a remarkable manner with cosmical science, and also with almost every branch of physics and of the study of inorganic nature.
The spaces through which the bodies of the solar system and the comets revolve about the sun, appear also to be traversed by celestial bodies comparatively minute, but in number incalculable ; which, in common with the smaller true planets of the system have received from certain astronomersand physicists the appellation of Asteroids, or star-like bodies—the word star being taken in its universal and ancient sense of any luminous object seen in the heavens.. (ASTEROIDS.] Zones of these bodies, consisting of countless myriads of them, we have much reason to infer, revolve about the sun in nearly their own planes, or in sonic plane which they include ; end certain astronomers consider that some of them have been proved to be minute satellites of the earth, as was believed, indeed, early in the scientific history of this subject.
These smaller asteroids, when they approach within a certain com paratively small distance from the earth, are, or subsequently become, the objects termed shooting-stars, fire-balls, and igneous meteors; new series of phenomena being eueeesaively presented by them as they come nearer to the earth's surface, and especially in many instances, in consequence of their finally passing through a great extent of the atmosphere in an oblique direction, so as to experience the effects of its increasing density, both physical and chemical, throughout a trajectory of great length. But in this general statement it is not pretended to deny that objects and phenomena very different in their origin and nature, as well from each other as from those now under review, may probably be included also under the popular or only half-scientific desig nations of meteors and shooting-stars.
The appearance of these meteors is in many cases attended or suc ceeded by the fall of eolid bodies, either stones or metallic iron, or in some cases both mingled together in the same block, forming a series of bodies collectively termed Meteorites (or AEROLITES, in NAT. Misr.
Dry.), consisting, mineralogieally, of two principal groups, graduating into each other, namely, meteoric stones, and meteoric iron ; and which have also received the appellation of Meteoric Rods in the classifi cation of the mineral aggregates to which the term rock has in modern science been extended.
The visible meteor, when observed at those distances which must be within the atmosphere, must consist of flame or gaseous matter in an ignited or incandescent state, and undergoing combustion ; but arising, as may be inferred from Sir II. Davy's researches on flame, not from the combustion of matter which under ordinary circumstances can exist in a gaseous state at the surface of the earth ; but from that of matter which is there solid, consisting, doubtless, of the metallic or other combustible bases which meteorites are found to contain. Among those, it may be remarked, are sulphur and phos phorus, both which Davy particularised as capable of combustion in air rarefied to a degree equal to that of the regions of the atmosphere in which meteors had been observed to display their phe nomena. No particular stress, however, can be laid upon this circumstance, as meteorites contain other combustible bases which very probably have the same property, including the metal magnesium, an element of almost every meteoric atone, in considerable proportions. The catraordinary intensity of light also which attends the combu.tion of magnesium in oxygen, may be connected with the brilliant pheno mena of the meteors.
The luminous extensions in the directions opposite to that of the meteor', =Alone, ordinarily called tails, as observed in many, if not in all igneous meteors, are manifestly referable to the elongation of the moos of flame constituting the visible meteor, by the resistance of the atmosphere to their progress through It with planetary velocity, as well as in some degree by the adhesion of the air to it; the passage from the intense white light of the head or body and proximate portions of tho tail, to the red light of the distant and extreme portions of the latter, being attributable to the cooling down of tho flame during its course, and in proportion to its distance from the most intensely heated part of the meteor.