work; a stone completely buried itself in the highway at Kaba; one fell between two carters on the road at Charsonville, throwing the ground up to a height of 6 ft.; the Tourinnes-la-Grosse meteorite broke the pavement and was broken itself; the Krühenberg stone fell within a few paces of a little girl; the Angers stone fell close to a lady standing in her garden; the Braunau mass went through the roof of a cottage; at Macao, in Brazil, where there was a shower of stones, some oxen are said to have been killed; at Nedagolla, in India, a man was so near that he was stunned by the shock; while at Mhow, also in India, a man was killed in 1827 by a stone which is a true meteorite, and is represented by fragments in museum collections,
Though the surface of a meteoric stone becomes very hot during the early part of the flight through the air, it is cooled again during the later and slower part of the flight. Meteorites are generally found to be warm to the touch if immediately dug out; at the moment of their impact they are not hot enough to char woody fibre on which they chance to fall, nor is the surface then soft, for terrestrial matter with which the surface comes into contact makes no impression upon the meteorite. Where many stones fall at the same time they are generally distributed over a large area elongated in the direction of the flight of the luminous meteor, and the largest stones generally travel farthest. At Hessle, for instance, the stones were distributed over an area of 10 m. long and 3 m. broad.
Meteorites are almost invariably found to be completely covered with a thin crust such as would be caused by intense heating of the material for a short time; its thinness shows the slight depth to which the heat has had time to penetrate. They are presumably cold and invisible when they enter the earth’s atmosphere, and become heated and visible during their passage through the air; doubtless the greater part of the superficial material flicks off as the result of the sudden heating and is left behind floating in the air as the trail of the meteor. The crust varies in aspect with the mineral composition of the meteorite; it is generally black; it is in most cases dull but is sometimes lustrous; more rarely it is dark-grey in colour. Each stone of a shower is in general completely covered with crust; but occasionally, as in the case of the Butsura fall, stones found some miles apart fit each other closely and the fitting surfaces are uncrusted, showing that a meteorite may break up during a late and cool stage of the flight through the atmosphere. A meteorite is generally covered with pittings which have been compared in size and form to thumbmarks; the pittings are probably caused by the unequal conductivity, fusibility and frangibility of the superficial material. As picked up, complete and covered with crust, meteorites are always irregularly-shaped fragments, such as would be obtained on breaking up a rock presenting no regularity of structure.
About one-third, and those the most common, of the chemical elements at present recognized as constituents of the earth’s crust have been met with in meteorites; no new chemical element has been discovered. The most frequent or plentiful in their occurrence are: aluminium, calcium, carbon, iron, magnesium, nickel, oxygen, phosphorus, silicon and sulphur; while less frequently or in smaller quantities are found antimony, arsenic, chlorine, chromium, cobalt, copper, hydrogen, lithium, manganese, nitrogen, potassium, sodium, strontium, tin, titanium, vanadium. The existence of minute traces of several other elements has been announced; of these special mention may be made of gallium, gold, iridium, lead, platinum and silver. Iron occurs chiefly in combination with nickel, and phosphorus almost always in combination with both nickel and iron (schreibersite); carbon occurs both as indistinctly crystallized diamond and as graphitic carbon, the latter generally being amorphous, but occasionally having the forms of cubic crystals (cliftonite); free phosphorus has been found in one meteorite; free sulphur has also been observed but may have resulted from the decomposition of a sulphide since the fall of the stone.
Of the mineral constituents of meteorites, the following are by many mineralogists regarded as still unrepresented among native terrestrial products: cliftonite, a cubic form of graphitic carbon; phosphorus; various alloys of nickel and iron; moissanite, silicide of carbon; cohenite, carbide of iron and nickel (corresponding to cementite, carbide of iron, found in artificial iron); schreibersite, phosphide of iron and nickel; troilite, protosulphide of iron; oldhamite, sulphide of calcium: osbornite, oxysulphide of calcium and titanium or zirconium; daubréelite, sulphide of iron and chromium; lawrencite, protochloride of iron; asmanite, a species of silica; maskelynite, a singly refractive mineral with the chemical composition of labradorite; weinbergerite, a silicate intermediate in chemical composition to pyroxene and nepheline.
Of these troilite is perhaps identical with some varieties of terrestrial pyrrhotite; asmanite has characters which approach very closely to those of terrestrial tridymite; maskelynite, according to one view, is the result of fusion of labradorite, according to another view, is an independent species chemically related to leucite. Other compounds are present corresponding to the following terrestrial minerals: olivine and forsterite; enstatite and bronzite; diopside and augite; anorthite, labradorite and oligoclase; magnetite and chromite; pyrites; pyrrhotite; breunnerite. Quartz (silica), the most common of terrestrial minerals, is absent from the stony meteorites; but from the Toluca meteoric iron microscopic crystals have been obtained of which some have certain resemblances to quartz, and others to zircon. Free silica is present in the Breitenbach meteorite but as asmanite. In addition to the above there are several compounds or mixtures of which the nature has not yet been satisfactorily ascertained.
Meteorites are conveniently distributed into three classes, which pass more or less gradually into each other: the first (siderites or meteoric irons) includes all those which consist mainly of metallic iron alloyed with nickel; only nine of them have been actually seen to fall; the second (siderolites) includes those in which metallic iron (alloyed with nickel) and stony matter are present in large proportion; few of them have been seen to fall; those of the third class (aerolites or meteoric stones) consist almost entirely of stony matter; nearly all have been seen to fall.
In the meteoric irons the iron generally varies from 80 to 95% and the nickel from 6 to 10%; the latter is generally alloyed with the iron, and several alloys or mixtures have been distinguished by special names (kamacite, taenite, plessite). Troilite is frequently present as plates, veins or large nodules, sometimes surrounded by graphite; schreibersite is almost always present, and occasionally also daubréelite. The compositeness and the structure of meteoric iron are well shown by the figures generally called into existence when a polished surface is etched by means of acids or bromine-water; they are due to the inequality of the etching action on thick and thin plates of various constituents, the plates being composed chiefly of two nickel-iron materials (kamacite and taenite). A third nickel-iron material (plessite) fills up the spaces formed by the intersection of the joint plates of kamacite and taenite; it is probably not an independent substance but an intimate intergrowth of kamacite and taenite. The figures were first observed in 1808 and are generally termed “Widmanstätten figures” in honour of their discoverer; the plates which give rise to them are parallel to the faces of the regular octahedron, and such masses have therefore an octahedral structure. A small number of the remaining masses have cubic cleavage; instead of Widmanstätten figures they yield fine linear furrows when etched; the furrows were found by Neumann in 1848 to have directions such as would result from twinning of the cube about an octahedral face; they are known as “Neumann lines.” For meteoric irons of cubic structure the percentage of nickel is lower than 6 or 7; for those of octahedral structure it is higher than 6 or 7; the plates of kamacite are thinner, and the structure therefore finer the higher the percentage of that metal. A considerable number of meteoric irons, however, show no crystalline structure at all, and have percentages of nickel both below and above 7; it has been suggested that each of these masses may once have had crystalline structure and that it has disappeared as a result of prolonged heating throughout the mass while the meteorite has been passing near a star.
An investigation of the changes of the magnetic permeability of the Sacramento meteoric iron with changing temperature led Dr S. W. J. Smith to infer that the magnetic behaviour can only be explained by imagining the meteorite to consist
