It would appear, both from theory and observation, that the figure of the meteors must approach in their course more or leas closely to that of the solid of least resistance. The meteorites which fall, or are cast down from them, when unbroken, especially those consisting of metallic iron, retain approximately the form which had thus been imparted to the meteors of which they were the nuclei, by the resist ance of the air,—a form resembling that of the more perfect volcanic bombs, and which they have received from the same cause. These effects of the resistance of the atmosphere to the meteor's motion were first pointed out by Mr. Brayley.
The persistent track or trail of less vivid light often continuing to be seen for several minutes, or for a considerable fraction of an hour, or even for more than an hour, after the disappearance of the Meteor itself, must be attributed to the deposition in the atmosphere, in the meteor's path, of a kind of beam of finely-divided solid matter, mingled probably with vapour, and no doubt in part produced by the conden sation of vapour resulting from the combustion proceeding in the meteor, and the particles of which, being originally deposited at insensible distances from each other, continue to preserve, during their slow and uniform descent in the tranquil regions of the air where they originate, the aggregate form in which they were deposited; while the low conducting power for heat of the rare atmosphere permits them to retain their high temperature and consequent luminosity for a comparatively long period of time. The continued action of gravity, and the disturbing agency of currents in the lower regions of the atmosphere will, however, eventually convert the at first rectilinear beam into a more or less curved and waved figure, and at length produce the serpent of fire of the superstitious ages, accurately repro duced in the case of the meteor of the 7th January, 1856, as witnessed at Tunbridge Wells, and represented by a correspondent of the ' Illustrated London News,' of the 12th. These views are supported by reference to telescopic observations of the trails, particularly by those of the late Professor Pictet, of that left visible for seven or eight minutes by the meteor seen in France and Switzerland on the 15th of May, 1811, the most luminous part of which " did not appear to be continuous, but composed of distinct and separate particles."
The production, continuance, gradual change of form and descent, and final dissolution of these trails, may be familiarly, but correctly, illustrated by comparison with the similar succession of phenomena characterising the trail of smoke and soot issuing from the funnel of a steam ship during its progress on its course, in which also a rectilinear beam of finely divided solid matter separated from flame and smoke, and often several miles in length, becomes a persistent trail, and gradually changes into a waved or serpentine form. In many cases the trail of a meteor must have been originally a cylindrical beam, con stituted as now explained, having a diameter of many hundred yards (equal to or greater than that of the meteor itself), and a length of many miles, deposited in an inclined direction, at heights of some miles above the earth's surface.* An objection founded on the assumed solidity of the particles, and the considerable specific gravity which must be attributed to them as results of the combustion going on within the meteors, which, it might be inferred are inconsistent with their long suspension in the manner supposed, is at once obviated by applying to the subject the results of Professor Stokes's researches on the effects of the internal friction of fluids as applied by himself to the suspension of fine powders in a fluid of widely different specific gravity, and to that of the suspension in the air of the minute globules of water constituting the clouds. [CLouDs.] The trails of meteors are suspended like the clouds, though, at first, probably, in higher regions of the atmosphere, and like them they consist of excessively minute particles, which, as in all probability their dimensions will be very nearly the same in all directions, may be regarded as spherulcs also, and will consequently be suspended temporarily, like the globules of the clouds, by the resistance to their downward motion arising from the internal friction of the air. The degree in which they partake of the projectile motion of the meteor itself, will also tend to their longer suspension, by con verting the perpendicular fall which the mere action of gravity would cause into an oblique curvilinear descent.