METEORITES, also called AbOUTE METEORS and METEORIC STONES, are bodies enter the earth's atmosphere from without anc being intensely heated by impact with the ar are partially consumed before reaching ground. If the fall occurs at niflit meteorite is seen as a ball of fire passing (we' the heavens and frequently leaving a brilliare train of material behind it; usually sparlo fragments are thrown off from the head. sometimes this bursts in pieces with a 1c5 explosion and finally reaches the ground ?* hundreds, or even thousands, of pieces. If nr too far away from the observer, its pascap through the air may be heard as a continuer roaring sound accompanied by frequent de., tonauons of great volume; if a final, louder explosion is both seen and heard, the distance from the observer to the meteorite at the time may be very accurately determined by the con sideration, that sound travels but 1,040 feet a second while the transmission of light is practically instantaneous. The reader who is fortunate enough to witness a meteoric fall should therefore take means to estimate the number of seconds which elapse between when the explosion is seen and when the sound reaches him. This is usually done by beginning to count, or to repeat the letters of the alphabet, or some piece of doggerel at the first instant and breaking off at the second By a repeti tion immediately afterward, winch is rimed by a watch, a quite accurate approximation will be obtained. If in addition the apparent position of the meteor among the stars is noticed at the beginning and end of its appearance or if the phenomenon is witnessed In the daytime) if the approximate 1,( arilpz and elevation aboye the ground are noted at the two instants, the time being also stated, at least approximately, the observer will have secured a record which will be of real scientific value.
Meteorites are of two classes — the stony meteorites and the iron meteorites. The former are about 10 times more numerous than the latter. In the iron meteorites iron usually forms more than 90 per cent of the entire mass, but it is almost invariably alloyed with nickel. In the stony meteorites mineral combinations occur which are peculiar to these bodies, and serve as one of the ear marks by which they may be recognized when they were not seen at the time of their fall.
Other distinguishing marks of meteorites are found in their physical appearance and struc ture. They are covered with a blackish crust formed by surface melting during their passage through the air. This crust consists mainly of oxide of iron, and is magnetic. Pits and hollows are formed in the surface of a mete orite by the fusing of the less refractory min erals and these are a characteristic feature.
When a portion of the surface of an iron meteorite is polished and then etched with acid peculiar markings, called from the name of their discoverer Widmannstatten figures, make their appearance. These are among the most trust worthy criteria of the meteoritic origin of sus pected masses of native iron.
About one-third of the chemical elements known in the laboratory have been found in meteorites. But no new element has ever yet been discovered in them. The following ele ments occur, in greatly varying quantity, some times a mere trace being present : As the true nature of shooting stars was not understood until after the investigation that fol lowed the great shower of 1833, so the true nature of meteorites was recognized only after a remarkable fall of those bodies which oc curred at L'Aigle in France about noon on 26 April 1800. Nine years before, in 1794, Chladni, a German physicist, had formulated the theory that meteorites before encountering the earth traveled in independent orbits in space, but his conclusions were not generally accepted until the occurrence at L'Aigle had focused the atten tion of men of science. On that occasion be tween 2,000 and 3,000 meteoric stones were scattered over an area about nine miles long by three miles wide. The French astronomer, J. B. Biot, visited L'Aigle, carefully examined the fallen stones and collected and discussed the evidence of eye witnesses. Thereafter the old idea that meteors and meteorites were sim ply atmospheric phenomena was abandoned, and the fact of their extra-terrestrial origin was generally recognized. It is now perfectly cer tain that meteorites cannot have originated in volcanic eruptions on the earth or on the moon, as some have supposed, but that they came from remote parts of our solar system, or, more probably, from beyond its borders, or even from the region of the stars. That this is so is definitely proved from the velocities (many times observed), with which they encounter the earth. It is found that before the collision they must have been falling toward the sun along such elongated paths that upon reaching the earth's orbit their velocity of motion was very approximately 26 miles a second. This is the velocity which a body would acquire in falling to this distance from the sun from an infinitely great distance away, and leaves no room for doubt that each of these bodies was pursuing its own independent orbit about the sun before it suffered collision with the earth.