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 largely of plates of nickel-iron containing about 7% of nickel (kamacite), separated from each other by thin plates of a nickel-iron constituent (taenite), containing about 27% of nickel and having different thermomagnetic characters from those of kamacite; he suggests, however, that taenite is not a definite chemical compound but a eutectic mixture of kamacite and a nickel-iron compound containing not less than 37% of nickel.

About eleven out of every twelve of the known meteoric stones belong to a division to which Rose gave the name “chondritic” (, a grain); they present a very fine-grained but crystalline matrix or paste, consisting of olivine and enstatite or bronzite, with more or less nickel-iron, troilite, chromite, augite and triclinic feldspar; through this paste are disseminated round chondrules of various sizes and generally with the same mineral composition as the matrix; in some cases the chondrules consist wholly or in great part of glass. Some meteorites consist almost solely of chondrules; others contain only few; in some cases the chondrules are easily separable from the surrounding material. In mineral composition chondritic meteorites approximate more or less to terrestrial lherzolites.

A few meteorites belonging to the chondritic division are remarkable as containing carbon in combination with hydrogen and oxygen; those of Alais and Cold Bokkeveld are good examples.

The remaining meteoric stones are without chondrules and contain little or no nickel-iron; of these the following may be mentioned as illustrative of the varieties of mineral composition: Juvinas, consisting essentially of anorthite and augite; Petersburg, of anorthite, augite and olivine, with a little chromite and nickel-iron (both Juvinas and Petersburg may be compared to terrestrial basalt); Sherghotty, chiefly of augite and maskelynite; Angra dos Reis, almost wholly of augite, but olivine is present in small proportion; Bustee, of diopside, enstatite and a little triclinic feldspar, with some nickel-iron, oldhamite and osbornite; Bishopville, of enstatite and triclinic feldspar, with occasional augite, nickel-iron, troilite and chromite; Roda, of olivine and bronzite; and Chassigny, consisting of olivine with enclosed chromite, and thus mineralogically identical with terrestrial dunite.

Almost all meteoric stones appear to be made up of irregular angular fragments, and some of them bear a close resemblance to volcanic tuffs. In the large group of chondritic stones, chondrules or spherules, some of which can only be seen under the microscope while others reach the size of a walnut, are embedded in a matrix apparently made up of minute splinters such as might result from the fracture of the chondrules themselves. In fact, until recently it was thought by some mineralogists that the chondrules owe their form, not to crystallization, but to friction, and that the matrix was actually produced by the wearing down of the chondrules through frequent collision with each other as oscillating components of a comet or during repeated ejection from a volcanic vent of some small celestial body. Chondrules have been observed, however, presenting forms and crystalline surfaces incompatible with such a mode of formation, and others have been described which exhibit features resulting from mutual interference during their growth. The chondritic structure is different from anything which has yet been observed in terrestrial rocks, and the chondrules are distinct in character from those observed in perlite and obsidian. It is now generally believed that the structural features of meteoric stones are the result of hurried crystallization.

No organized matter has been found in meteorites and they have brought us, therefore, no evidence of the existence of living beings outside our own world.

.—The literature consists chiefly of memoirs dispersed through the journals of scientific societies. The following separate works may be consulted: A. Brezina, ''Die Meteoriten-Sammlung d. k-k. min. Hofkabinetes in Wien (Vienna, 1896); A. Brezina u. E. Cohen, Die Structur und die Zusammensetzung der Meteoriten (Stuttgart, 1886–1887); P. S. Bigot de Morogues, Mémoire historique et physique sur les chutes des pierres (Orléans, 1812); Chladni, Ueber den Ursprung der von Pallas gefundenen und anderer ihr ähnlicher Eisenmassen (Riga, 1794), and Ueber Feuer-Meteore, und über die mit denselben herabgefallenen Massen (Vienna, 1819); E. Cohen, Meteoritenkunde (Stuttgart, 1894–1905); L. Fletcher, An Introduction to the Study of Meteorites'', 10th ed. (London, 1908); E. King. Remarks concerning Stones said to have fallen from the Clouds both in these Days and in Ancient Times (London, 1796); S. Meunier, Météorites (Paris, 1884); C. Rammelsberg, Die chemische Natur der Meteoriten (Berlin, 1870–1879); G. Rose, Beschreibung und Eintheilung der Meteoriten (Berlin, 1864); G. Tschermak, Die mikroskopische Beschaffenheit der Meteoriten (Stuttgart, 1883–1885); E. A. Wülfing, Die Meteoriten in Sammlungen und ihre Literatur (Tübingen, 1897).

METEOROLOGY (Gr. , and  , i.e. the science of things in the air), the modern study of all the phenomena of the atmosphere of gases, vapours and dust that surrounds the earth and extends to that unknown outer surface which marks the beginning of the so-called interstellar space. These phenomena may be studied either individually or collectively. The collective study has to do with statistics and general average conditions, sometimes called normal values, and is generally known as Climatology (see, where the whole subject of regional Climatology is dealt with). The study of the individual items may be either descriptive, explanatory, physical or theoretical. Physical meteorology is again subdivided according as we consider either the changes that depend upon the motions of masses of air or those that depend upon the motions of the gaseous molecules; the former belong to hydrodynamics, and the; latter are mostly comprised under thermodynamics, optics and electricity.

History.—The historical development of meteorology from the most ancient times is well presented by the quotations from classic authors compiled by Julius Ludwig Ideler (Meteorologia veterum graecorum et romanorum, Berlin, 1832). We owe to the Arabian philosophers some slight advance on the knowledge of the Greeks and Romans; especially as to the optical phenomena of the atmosphere. The Meteorologia of Aristotle (see Zeller, Phil. der Griechen) accords entirely with the Philosophica of Thomas Aquinas, the poetic songs of the troubadours, and the writings of Dante (see Kuhn’s Treatment of Nature in Dante’s Divina Commedia; London, 1897). Dante’s work completed the passage from the ancient mythological treatment of nature to the more rational recognition of one creator and lawgiver that pervades modern science. The progress of meteorology has been coincident with the progress of physics and chemistry in general, as is shown by considering the works of Alhazen (1050) on twilight, Vitellio (1250) on the rainbow, Galileo (1607) on the thermometer and on the laws of inertia, on attractions and on the weight of the air, Toricelli (1642) on the barometer, Boyle (1659) on the elastic pressure of the air in all directions, Newton (1673) on optics; Cavendish (1760), elastic pressure of aqueous vapour; Black (1752), separation of carbonic acid gas from ordinary air; Rutherford (1772), separation of nitrogen; Priestley and Scheele (1775) and Cavendish (1777), separation of oxygen; Lavoisier (1783), general establishment of the character of the atmosphere as a simple mixture of gases and vapour; De Saussure’s measurement of relative humidity by the accurate hair hygrometer (1780), Dalton’s measurement of vapour tension at various temperatures (1800), Regnault’s and Magnus’s revision of Dalton’s tension of water vapour (1840), Marvin’s and Juhlins’s measurements of tension of ice vapour (1891), and the isolation of argon by Rayleigh and Ramsay (1894).

Theoretical meteorology has been, and always must be, wholly dependent on our knowledge of thermodynamics and on mathematical methods of dealing with the forces that produce the motions within the atmosphere. Progress has been due to the most eminent mathematicians at the following approximate dates: Sir Isaac Newton (1670), Leonhard Euler (1736), Pierre Simon Laplace (1780), Jean Baptiste Joseph Fourier (1785), Simon Denis Poisson (1815), Sir George Gabriel Stokes (1851), Hermann von Helmholtz (1857), Lord Kelvin (1860), C. A. Bjerknes (1868), V. Bjerknes (1906), and to their many distinguished followers.

The earliest systematic daily record of local weather phenomena that has survived is that kept by William Merle, rector of Driby, during seven years 1331–1338: the manuscript is preserved in the Digby MS., Merton College, Oxford, and