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 is 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 11. Davy, and Sir John F. W. Herschel, have ascribed the heat to the compression and friction of the air, resulting from the enormous velocity, 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 Royal Society on the 19th of Jtine, 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 to the Section of Mathematics and Physics of the British Association, in 1859, he affirms, reasoning from the concluding series of experiments 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, 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 their 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 game 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 A8rolites, considered Geo graphically, Statistically, and Cosmically ; 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 assemblage of facts, in Arago's 'Astronomic Populaire; liv. xxvi.; Mdtedres Cosmiques,' tome iv., p. 181-322 ; and also in the reports on meteors annually communicated for some years past to the reports of the British AkS0 elation 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 arc 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 similar phenomena as witnessed in more modern times, 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 eases 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 meteors, the production of which is the first visible result of the ex. r(luaioo, aeon as irojected upon the tail of the parent meteor ; either tic use, as is evidently the fact In many instmeea, they were really enreloned in the flames composing it, or on account of the blending on the retina of the observer of past and actual appearances. The fiery sword dipped in blood in the meteor in its normal form, at the middle of its visible course, the distant part of the tail shining with red light, being cooled down to the temperature of simple ignition, as already indicated. In a similar manner, the bull's heads, flying eagles, and other monstrous appearances, may be consistently explained, care being taken, when the authorities permit, to identify them with the actual meteor otherwise recorded. The blazing and interlaced serixelts moving in the air may be explained by reference to the actual pheno mena of the psnsistent tracks or trails already described, as in various eases Ly Pieta and others, as well as by the published representations of the meteor of January 7th. 1350. One instance may be cited, in which a large and beautitul luminous serpentine tram continued for soma minutes after the disappearance of n meteor which threw down a Atone at Angers. in 1822. The emsonguinel tresses attached to blazing stars are evidently the trails under another phase, and in their Liter condition, emitting red light only, but retaining their linear or band-like form. The Lomprolat rultodes and Droroncs of former ages may be similarly understood, by reference to other characters and phenomena of meteors; one of the contemporary figures of the fire-ball seen in London on November 13th, 1803 (described under phases by Dr. in the ' Philosophical Magazine' for the following year). exemplifies the particular configuration of the meteors to which the latter appellation was given : it is contained in Nieholson's ' Philosophical Journal' for 1801.
merilioNIC ACID (C,II,S,0,„. 2 HO ), Disulplionvfltofic Arid. This acid is obtained by heating cyanide of methyl with concentrated sulphuric acid : C,B,Cy s(s0, = SRO SO, Cy- nide of Inethionte acid. Sulphate of methyl. ammonia.
It is only of theoretical importance.