[footnote] *'Relation Historique', t. i., p. 80, 213, 527. If in falling stars, as in comets, we distinguish between the head or nucleus and the tail, we shall find that the greater transparency of the atmosphere in tropical climates is evinced in the greater length and brilliancy of the tail which may be observed in those latitudes. The phenomenon is therefore not necessarily more frequent there, because it is oftener seen and continues longer visible. The influence exercised on shooting stars by the character of the atmosphere is shown occasionally even in our temperate zone, and at very small distances apart. Wartmann relates that on the occasion of a November phenomenon at two places lying very near each other, Geneva and Aux Planchettes, the number of the meteors counted were as 1 to 7. (Wartmann, 'Mém. sur les Etoiles filantes', p. 17.) The tail of a shooting star (or its 'train'), on the subject of which Brandes has made so many exact and delicate observations, is in no way to be ascribed to the continuance of the impression produced by light on the retina. It sometimes continues visible a whole minute, and in some rare instances longer than the light of the nucleus of the shooting star; in which case the luminous track remains motionless. (Gilb., 'Ann.', bd. xiv., s. 251.) This circumstance further indicates the analogy between large shooting stars and fire-balls. Admiral Krusenstern saw, in his voyage round the world, the train of a fire-ball shine for an hour after the lluminous body itself had disappeared, and scarcely move throughout the whole time. ('Reise', th. i., s. 58.) Sir Alexander Burnes gives a charming description of the transparency of the clear atmosphere of Bokhara, which was once so favorable to the pursuit of astronomical observations. Bokhara is situated in 39 degrees 48' north latitude, and at an elevation of 1280 feet above the level of the sea. "There is a constant serenity in its atmosphere, and an admirable clearness in the sky. At night, the stars have uncommon luster, and the Milky Way shines gloriously in the firmament. There is also a never-ceasing display of the most brilliant meteors, which dart like rockets in the sky; ten or twelve of them are sometimes seen in an hour, assuming every color — fiery red, blue, pale, and faint. It is a noble country for astronomical science, and great must have been the advantage enjoyed by the famed observatory of Samarkand." (Burnes, 'Travels into Bokhara', vol. ii. (1834), p. 158.) A mere traveler must not be reproached for calling ten or twelve shooting stars in an hour "many," since it is only recently that we have learned, from careful observations on this subject in Europe, that eight is the mean number which may be seen in an hour in the field of vision of one individual (Quetelet, 'Corresp. Mathém.', Novem., 1837, p. 447); this number is, however, limited to five or six by that diligent observer, Olbers. (Schum., 'Jahrb.', 1838, s. 325.)
p 114 Sir Alexander Burnes likewise extols as a consequence of the purity of the atmosphere in Bokhara the enchanting and constantly-recurring spectacle of variously-colored shooting stars.
The connection of meteoric stones with the grander phenomenon of fire-balls — the former being known to be projected from the latter with such force as to penetrate from ten to fifteen feet into the earth — has been proved, among many other instances, in the falls of azzzuerolites at Barbotan, in the Department des Landes (24th July, 1790), at Siena (16th June, 1794), at Weston, in Connecticut, U. S. (14th December, 1807), and at Juvenas in the Department of Ardèche (14th June, 1821). Meteoric stones are in some instances thrown from dark clouds suddenly formed in a clear sky, and fall with a noise resembling thunder. Whole districts have thus occasionally been covered with thousands of fragmentary masses, of uniform character but unequal magnitudes, that p 115 have been hurled from one of these moving clouds. In less frequent cases, as in that which occurred on the 16th of September, 1843, at Kleinwenden, near Mühilhausen, a large aërolite fell with a thundering crash while the sky was clear and cloudless. The intimate affinity between fire-balls and shooting stars is further proved by the fact that fire-balls, from which meteoric stones have been thrown have occasionally been found, as at Angers, on the 9th of June, 1822, having a diameter scarcely equal to that of the small fire-works called Roman candles.
The formative power, and the nature of the physical and chemical processes involved in these phenomena are questions all equally shrouded in mystery, and we are as yet ignorant whether the particles composing the dense mass of meteoric stones are originally, as in comets, separated from one another when they become luminous to our sight, or whether in the case of smaller shooting stars, any compace substance actually falls, or, finally, whether a meteor is composed only of a smoke-like dust, containing iron and nickel; while we are wholly ignorant of what takes place within the dark cloud from which a noise like thunder is often heard for many minutes before the stones fall.*
[footnote] *On 'méteoric dust', see Arago, in the 'Annuaire' for 1832, p. 254. I haave very recently endeavored to show, in another work ('Asie Centrale', t. i., p. 408). how the Scythian saga of the sacred gold, which fell burning from heaven, and remained in the possession of the Golden Horde of the Paralatæ (Herod., iv., 5-7), probably originated in the vague recollection of the fall of an aërolite. The ancients had also some strange fictions (Dio Cassius, lxxv., 1259) or silver which had fallen from heaven, and with which it had been attempted, under the Emperor Severus, to cover bronze coins; metallic iron was however, known to exist in meteoric stones. (Plin., ii., 56.) The frequently-recurring expression 'lapidibus pluit' must not always be understood to refer to falls of aërolites. In Liv., xxv., 7, it probably refers to pumice ('rapilli') ejected from the volcano, Mount Albanus (Monte Cavo), which was not wholly extinguished at the time. (See Heyne, 'Opuscula Acad.', t. iii., p. 261; and my 'Relation Hist.', t. i., p. 394.) The contest of Hercules with the Ligyans, on the road from the Caucasus to the Hesperides, belongs to a different sphere of ideas, being an attempt to explain mythically the origin of the round quartz blocks in the Ligyan field of stones at the mouth of the Rhone, which Aristotle supposes to have been ejected from a fissure during an earthquake, and Posidonius to have been caused by the force of the waves of an inland piece of water. In the fragments that we still possess of the play of Æschylus, the 'Prometheus Delivered', every thing proceeds, however, in part of the narration, as in a fall of aërolites, for Jupiter draws together a cloud, and causes the "district around to be covered by a shower of round stones". Posidonius even ventured to deride the geognostic myth of the blocks and stones. The Lygian field of stones was, however, very naturally and well described by the ancients. The district is now known as 'La Crau.' (See Guerin, 'Mesures Barométriques dans les Alpes, et Météorologie d'Avignon', 1829, chap. xii., p. 115.)
p 116 We can ascertain by measurement the enormous, wonderful, and wholly planetary velocity of shooting stars, fire-valls and meteoric stones, and we can gain a knowledge of what is the general and uniform character of the phenomenon, but not of the genetically cosmical process and the results of the metamorphoses. If meteoric stones while revolving in space are already consolidated into dense masses,* less dense, however, p 117 than the mean density of the earth, they must be very small nuclei, which surrounded by inflammable vapor or gas, form the innermost part of fire-balls, from the height and apparent diameter of which we may, in the case of the largest, estimate that the actual diameter varies from 500 to about 2800 feet.
[footnote] *The specific weight of aërolites varies from 1.9 (Alais) to 4.3 (Tabor). Their general density may be set down as 3, water being 1. As to what has been said in the text of the actual diameters of fire-balls, we must remark, that the numbers have been taken from the few measurements that can be relied upon as correct. These give for the fire-ball of Weston, Connecticut (14th December, 1807), only 500; for that observed by Le Roi (10th July, 1771) about 1000 and for that estimated by Sir Charles Blagden (18th January, 1783) 2600 feet in diameter. Brandes ('Unterhaltungen' bd.i., s. 42) ascribes a diameter varying from 80 to 120 feet to shooting stars, and a luminous train extending from 12 to 16 miles. There are, however, ample optical causes for supposing that the apparent diameter of fire-balls and shooting stars has been very much overrated. The volume of the largest fire-ball yet observed can not be compared with that of Ceres, estimating generally so exact and admirable treatise, 'On the Connection of the Physical Sciences', 1835, p. 411.) With the view of elucidating what has been stated in the text regarding the large zërolite that fell into the bed of the River Narni, but has not again been found, I will give the passage made known by Pertz, from the 'Chronicon Benedicti, Monachi Sancti Andreæ in Mont Soracte', a MS. belonging to the tenth century, and preserved in the Chigi Library at Rome. The Barbarous Latin of that age has been left unchanged. "Anno 921, temporibus domini Johannis Decimi pape, in anno pontificatus illius 7 visa sunt signa. Nam juxta urben Romam lapides plurimi de cælo cadere visi sunt. In civilate quæ vocatur Narnia tam diri ac tetri, ut nihil aliud credatur, quam de infernalibus locis deducti essent. Nam ita ex illis lapidibus unus omnium maximum est, ut decidens in flumen Narnus, ad mensuram unius cubiti super aquas fluminus usque hodie videretur. Nam et ignitæita ut pene terra contingeret. AliAnno 921, temporibus domini Johannis Decimi pape, in anno pontificatus illius 7 visa sunt signa. Nam juxta urben Romam lapides plurimi de cælo cadere visi sunt. In civilate quæ vocatur Narnia tam diri ac tetri, ut nihil aliud credatur, quam de infernalibus locis deducti essent. Nam ita ex illis lapidibus unus omnium maximum est, ut decidens in flumen Narnus, ad mensuram unius cubiti super aquas fluminus usque hodie videretur. Nam et ignitæ ita ut pene terra contingeret. Ali cadentes," etc. (Pertz, 'Monum. Germ. Hist. Scriptores', t. iii., p. 715.) On the aërolites of gos Potamus, which fell, according to the Parian Chroniccle, in the 78 1 Olympiad, see Böckh, 'Corp. Inscr. Graec', t. ii., p. 302, 320, 340; also Aristot., 'Meteor.', i., 7 (Ideler's 'Comm.', t. i., p. 404-407); Stob., 'Eel. Phys.', i., 25, p. 508 (Heeren); Plut., 'Lys.', c. 12; Diog. Laert., ii., 10; and see, also, subsequent notes in this work. According to a Mongolisn tradition, a black fragment of a rock, forty feet in height, fell from heaven on a plain near the source of the Great Yellow River in Western China. (Abel Rémusat, in Lamétherie, 'Jour. de Phys.', 1819, Mai p. 264.)
The largest meteoric masses as yet known are those of Otumpa, in Chaco, and of Bahia, in Brazil, described by Rubi de Celis as being from 7 to 7 1/2 feet in length. The meteoric stone of gos Potamos, celebrated in antiquity, and even mentioned in the Chronicle of the Parian Marbles, which fell about the year in which Socrates was born, has been described as of the size of two mill-stones, and equal in weight to a full wagon load. Notwithstanding the failure that has attended the efforts of the African traveler, Brown, I do not wholly relinquish the hope that, even after the lapse of 2312 years, this Thracian meteoric mass, which it would be so difficult to destroy, may be found, since the region in which it fell is now bcome so easy of access to European travelers. The huge aërolite which in the beginning of the tenth century fell into the river at Narni, projected between three and four feet above the surface of the water, as we learn from a document lately discovered by Pertz. It must be remarked that these meteoric bodies, whether in ancient or modern times can only be regarded as the principal fragments of masses that have been broken up by the explosion either of a fire-ball of a dark cloud.
On considering the enormous velocity with which, as has been mathematically proved, meteoric stones reach the earth from the extremest confines of the atmosphere, and the lengthened course traversed by fire-balls through the denser strata of the air, it seems more than improbable that these metalliferous stony masses, containing perfectly-formed crystals of olivine, labradorite, and pyroxene, should in so short a period of time has been converted from a vaporous condition to a solid nucleus. Moreover, that which falls from meteoric masses, even where the internal composition is chemically different, exhibits almost always the peculiar character of a fragment, being of a prismatic or truncated pyramidal form, with broad, somewhat curved faces, and rounded angles. But whence comes this form, which was first recognized by Schreiber as characteristic of the 'severed' part of a rotating planetary body? Here, as in the sphere of organic life, all that appertains to the history of development remains hidden in obscurity. Meteoric masses become luminous and kindle at heights which p 118 must be regarded as almost devoid of air, of occupied by an atmosphere that does not even contain 1/100000th part of oxygen. The recent investigations of Biot on the important phenomenon of twilight* have considerably lowered the lines which had, perhaps with some degree of temerity, been usually termed the boundaries of the atmosphere; but processes of light may be evolved independently of the presence of oxygen, and Poisson conjectured that aëroliteswere ignited far beyond the range of our atmosphere. Numerical calculation and geometrical measurement are the only means by which as in the case of the larger bodies of our solar system, we are enabled to impart a firm and safe basis to our investigations of meteoric stones.
[footnote] *Biot, 'Traité d'Astronomie Physique' (3ème éd.), 1841, t. i., p. 149, 177, 238, 312. My lamented friend Poisson endeavored, in a singular manner, to solve the difficulty attending an assumption of the spontaneous ignition of meteoric stones at an elevation where the density of the atmosphere is almost null. These are his words: "It is difficult to attribute, as is uaually done, the incandescence of aërolites to friction against the molecules of the atmosphere at an elevation above the earth where the density of the air is almost null. May we not suppose that the electric fluid, in a neutral condition, forms a kind of atmosphere, extending far beyond the mass of our atmosphere, yet subject to terrestrial attraction, although physically imponderable, and consequently following our globe in its motion? According to this hypothesis, the bodies of which we have been speaking would, on entering this imponderable atmosphere, decompose the neutral fluid by their unequal action on the two electricities, and they would thus be heated, and in a state of incandescence, by becoming electrified." (Poisson, 'Rech. sur la Probabilité des Jugements', 1837, p. 6.)