meteorite (meteor it)

[ in the matter was abandoned. There are now several col lections of meteorites, each of which contains specimens of between 300 and 400 different falls, and the whole number known is not far from 400, although it is by no means the case with all these occurrences that the specimens were seen to fall; many of them have been found on the earth's surface, but have been recognized as being extraterrestrial by their peculiar appearance and composition. The most important facts with regard to meteorites may be concisely stated as follows: They have not been found to contain any element not known to occur on the earth; they have furnished no evidence of the existence of life on the body or bodies of which they originally formed a part; they bear no indications of having been formed in the presence of water, or of the existence of water beyond the earth's atmosphere in the regions from which they came; they do exhibit abundant evidence of having had what geologists would call an "igneous origin"; they are never granitic in character, but resemble very closely certain volcanic rocks of not infrequent occurrence, with this difference, that in the case of the meteorites the iron a ociated with the silicated combinations exists in the me tallic form, while in the terrestrial volcanic rocks it is, with rare exceptions, oxidized. Furthermore, meteorites, almost without exception, show a certain family resemblance; so that it is nece ary to admit, either that they all originally formed a part of one celestial body, or else that, having come from various members of the solar system, or from other systems, these have a wonderful resemblance to each other and to the earth itself. The most obvious division of meteorites is into metallic and stony, but the pa age from one cla to the other is by no means an abrupt one. All metallic meteorites agree in that the predominating metal is iron, with which nickel is almost invariably a ociated; indeed, it has not been proved that there is any meteoric iron entirely free from that metal. With the nickel cobalt is almost always found, as is the case in terrestrial combinations. Tin and copper are also frequently found in meteorites in small quantity. The precious metals have not been detected in them. Meteorites com Meteoric Iron. posed almost entirely of metallic (nickeliferous) iron, forming a nearly homogeneous ma , have been denominated siderolites. These, however, almost always contain irregular nodular ma es of pyrrhotite, schreibersite (phosphuret of iron and nickel), either one or both, and occasionally of graphite. In a large proportion of the meteoric irons, etching the polished surface with an acid develops the so-called "Widmannstättian figures." The develop ment of these figures on the polished surface of a ma of iron found upon the earth's surface, and in regard to the time of whose fall nothing was known, was formerly considered to be sufficient evidence of the celestial origin of such a ma , especially if, in addition, the presence of nickel could be shown by chemical analysis. While most of the metallic ma es thus referred have almost certainly been correctly cla ed among the meteorites, there may be cases in which such reference has not been justifiable, since it is now known that all celestial irons do not give the Widmannstattian figures, while the iron found in large quantity and over a wide area, a ociated with and embedded in basalt, near Ovifak in Green land, contains nickel, and rives when chen stat tian, although other have etched, figures which have generally been nied that they could properly be so denominated. The terrestrial origin of the Ovifak iron is, however, now generally 3738 admitted, although for a considerable time after its discovery this was not the case. se. The wide extent of the area over which this iron occurs, and its peculiarly intimate a ociation with the minerals of which the basalt is made up, forbid the idea that the metal could have fallen from above into lava in proce of eruption, which was at first the favorite theory of its origin. Next in order to the siderolites come the palla sites, so named from the fact that a large meteorite of this cla was in 1772 discovered in Siberia by the distinguished traveler Pallas. Under the name of palla site are comprehended those meteorites which consist of a spongy or vesicular ma of iron, the cavities of which are in most cases partly or entirely filled with olivin, with which various other minerals are frequently a ociated, enstatite and bronzite being the most common, while chromite is of not infrequent occurrence. Both siderolites and palla sites belong to the cla of metallic meteorites. By far the larger part of the stony meteorites are included under the designation of chon drites. In these the iron is distributed in fine particles through a more or le intimate mixture of silicates, with which chromite and magnetic pyrites are frequently sociated, the silicates being chiefly olivin and bronzite. The name chondrite has reference to the fact that in this cla of meteorites the material of which they are composed occurs in the form of rounded grains (chondri). The chondritic meteorites have, however, a quite varied structure, in some few cases pa ing into a breccia; they have divided into numerous subgroups in accordance these structural variations. Most of the stony meteorites contain iron di eminated through their ma in grains or nodules; but there are a few which are destitute of such metallic particles. There are also a few stony meteorites which do not exhibit any traces of a chondritic structure: the minerals of which these are made up do not, however, differ very e entially from those occurring in the chondrites. There are also a few very anomalous meteorites which contain carbonaceous matter a ociated with the stony chondritic material. This carbon is not graphitic, but is combined with hydrogen and oxygen, the product resembling to a certain extent that resulting from the decay of organic matter, but no traces of vegetable ti ue have been discovered in these carbonaceous meteorites, which are only five or six in number. One or two interesting facts remain to be mentioned. The first is that since the phenomena of meteorites began to be observed and studied there have been extremely few falls of metallic meteorites. Of all the meteoric irons in the various collections, those of Hraschina in Austria (1751), of Dicks on county, Tenne ee (1855), of Braunau in Bohemia (1847), and a few others (in all probably about nine), are the only ones positively known to have fallen; all the others are considered meteoric on account of their peculiar appearance and chemical composition. The observed falls of stony meteorites, on the other hand, are numerous. Another remarkable fact is that all the meteorites which are known to have fallen are of infinitesimally small size as compared with the earth. In the fall of L'Aigle some 2,000 to 3,000 stones were estimated to have reached the earth, and of these the largest weighed only seven or eight pounds. The largest meteorites of which the fall was observed are that of Ensisheim (1492), which weighed about 280 pounds, that of Juvinas (1821), 242 pounds, and that of Emmett county, Iowa (1879), when a considerable number of stones fell, the largest of them weighing 437 pounds. Some ma es of iron believed to be meteorites, the date of whose fall is unknown, are much larger than this, but still utterly insignificant in size, not only as compared with the earth or its satellite, but even with the smallest celestial body of which anything is definitely known, namely the outer satellite of Mars, which has been estimated at from five to twenty miles in diameter. The ma of iron on the river Bendegó in Brazil has been variously estimated at from seven to ten tons in weight; that of Tucuman (Campo del Cielo) is said to weigh fifteen tons. The Santa Cater in a iron appears to be still larger, having been estimated at twenty five tons; but doubts have been expre ed as to whether this is really of celestial origin. - Neumann's lines, structural lines described by J. G. Neumann as occurring in the Braunau meteorite. meteoritic (mētē-ō-rit'ik), a. [ The bright lines from the interspaces, now at their minimum and containing vapours at a very high temperature, balance the absorption of the meteoritic nuclei. Nature , XXXVIII. 79. meteoroscope ors. This remarkable group of planetoidal or meteoroidal bodies forms a tolerably wide zone or ring between the orbits of Mars and Jupiter. Smithsonian Report , 1881, p. 29.