605 



METEORS* 



METEORS. 



606 



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. Bray ley. 



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 rrleteor 

 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 

 - ible distances from each other, continue to preserve, during their 

 glow and uniform ile-sceut 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 siiccession 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 spherules 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. 



The two great causes of all the phenomena now described, are 

 evidently the motion and the heat of the meteors. The origin of the 

 former u doubtless involved in that of the portions of matter con- 

 stituting the nuclei of the meteors themselves, a subject noticed 

 below. Dr. Chladni, the earliest philosophical investigator of the 

 subject of meteors and meteorites (as a whole), and in later times Sir 

 1 1 . 1 ).ivy , and Sir John F. W. Hcrschel, have ascribed the heat to the 

 compression and friction of the air, resulting from the enormous 

 Telocity, of from six to thirty miles in a second, or more, of the 

 meteors, supposed to be solid when they enter the atmosphere. Still 

 more recently, in a paper read before the lioyal Society on the 19th of 

 Jttne, 1856, Dr. Joule and Professor William Thomson have inferred 

 from their own experiments on the thermal effects of fluids in motion, 

 to which those pf solids carried through fluids must be equivalent, the 

 great probability that meteors really acquire all the heat they manifest 

 from the friction of the air. In a communication made by Dr. Joule 

 mi of Mathematics and Physics of the British Association, 

 in 1859, he affirms, reasoning from the concluding series of experiments 



These tiews of the physical constitution of meteors and their trails were in 

 nitatai ce originally staled by Mr. Braylcy, in a pnicr read in 1824 before the 

 Meteorological Society then recently formed, and published in the ' Philosophical 

 Magazine,' 1st aeries, vol. Uiv., p. 288, fee. With additions and modifications 

 required by the progress of science, they have been subsequently often rrj.i ;,;. <i 

 by him, in lectures delivered at the Koynl Institution, ar.d in several courses at 

 the London Institution. 



on the heat developed by friction in air, made by him and Professor 

 Thomson, that " there remains no doubt whatever as to the real nature 

 of ' shooting stars.' These," he says, " are small bodies which come 

 into the earth's atmosphere at velocities of perhaps twenty miles per 

 second. The instant they touch the atmosphere their surfaces are 

 immediately heated far beyond the point of fusion, or even of volatili- 

 sation, and the consequence is, that they are speedily and completely 

 burnt down and reduced to impalpable oxides." If this be true, the 

 persistent trails of igneous meteors, which are left in the sky equally 

 by the smaller as by the larger, (though continuing, with the former, 

 for a much shorter space of time,) will consist of the particles of these 

 oxides, or perhaps of particles condensed from the vapour into which 

 the oxides are first converted ; agreeably to the explanation of their 

 nature already given in this article, as derived long ago from applying 

 the facts made known by Davy, relative to combustion in rarefied air, 

 to the observed phenomena of meteors. 



In the present state of cosmical and meteorological science, it is 

 unnecessary to enter upon the question of the origin of meteors and 

 meteorites further than to urge, that, the computed enormous magni- 

 tude of the former, the actual diameter of the visible meteor, 

 however constituted, being often many hundred yards, while in some 

 instances its dimensions must probably be expressed in miles, their 

 planetary velocity and the pregnant fact that they give out a more 

 intense light than any objects in nature except the sun, (an 

 assemblage of characters explicitly claimed by the writer of this article 

 for the particular meteors from which meteorites have been observed 

 to descend, as well as for many, if not all of those from which then- 

 fall is not known), must at once disprove nearly all the hypotheses 

 which have been framed specifically to explain the origin of meteorites ; 

 and especially, among others, that of their projection from lunar 

 volcanoes. The cogency of this argument will remain essentially 

 unimpaired if it shall be found, according to recent suggestions, that 

 the actual magnitude of many of the meteors is considerably less than 

 that hitherto ascribed to them. The problem of their origin must 

 in fact, be regarded as the same with that of the origin of the greater 

 asteroids and planets themselves. 



It is right to state that Mr. R. P. Greg, F.G.S., who has given much 

 attention to the subject, is of opinion that there is a distinction between 

 luminous meteors and those from. which meteorites have fallen ; an 

 opinion which, so far as the (apparently) smaller meteors called shooting 

 stars are concerned, he shares with the American Professor Olmsted 

 and others. Mr. Greg is the author of a valuable essay on meteorites, 

 entitled ' Observations on Meteorolites or Aerolites, considered Geo- 

 graphically, Statistically, and CoBUiically ; accompanied by a complete 

 Catalogue of Meteoric Falls.' It was first published in the ' Philoso- 

 phical Magazine' for November and December, 1854, and in a separate 

 form in November of the following year. 



The views of the entire subject which have been enunciated in this 

 article, have resulted from long attention to it by the writer. Others 

 will be found, together with an invaluable ai-semblage of facts, in 

 Arago's 'Astronomic Populaire,' liv. xxvi. ; 'Meteores G'osmiques," 

 tome iv., p. 181-322 ; and also in the reports on meteors annually 

 communicated for some years past to the reports of the British Asso- 

 ciation by the late Professor the Rev. Baden Powell. 



The purely physical history of the subject having now been generally 

 considered, we may proceed to notice the manner in which the extra- 

 ordinary relations produced in former times, of the appearance in the 

 sky of blazing torches, sceptres, bundles of rods, fiery swords, trumpets, 

 and other objects, may be rationally interpreted, agreeably to our 

 present knowledge of meteoric phenomena. This subject belongs to a 

 field in the history of science and literature hitherto but little culti- 

 vated. It may be elucidated by examining the figures and accounts of 

 such appearances which are given in the works of old writers, especially 

 in those of Zahn, Conrad Wolfhart, and their contemporaries, and also 

 by Ambrose Parey, and comparing them with simikr phenomena as 

 witnessed in more modern tiiues, and depicted by observers whose only 

 object was to represent the actual configuration of the luminous 

 appearances. 



The circumstance that from the enormous rapidity of the meteors all 

 the visible phenomena (except the persistent trail) would have been 

 seen and have ceased to appear within the limits of a few seconds of 

 time (so that in all cases the figures must have been produced from 

 memory alone), which must have led to the representation of many 

 appearances as simultaneous that in reality occurred in succession, and 

 the manner in which, during the transit of the meteor, impressions on 

 the retina of past phenomena must have been mingled with those 

 actually present, have led to the production of many of the singular 

 representations that are extant. It would not be difficult to trace the 

 mental process by which natural objects, thus witnessed for a few 

 seconds only, would by uninformed observers, prepared to regard them 

 with superstition, be supposed to be really preternatural types of the 

 familiar objects to which the outlines of their forms were comparable ; 

 the meteors, thus supposed to be torches, swords, and the like, would 

 naturally be described and depicted with all the appendages and accom- 

 paniments of those objects. These accompaniments, however, were 

 not in all cases merely (suppositions, as may be evinced by reference to 

 the great meteor of 1758, which exemplified the ringed sceptre of the 

 mediaeval figures, the rings on the shaft being manifestly the smaller 



