Until roughly a hundred and fifty years ago meteors and meteorites had the status of cosmic orphans, unacknowledged members of the astronomical family. Few persons doubted the existence of the fixed stars, the solar planets, comets, or even of “new stars” or novae, but they rejected a natural explanation for meteors and interpreted them as falling stars, flying dragons, or fountains of fire in the sky. Most astronomers as well as laymen laughed at the recurrent idea that “stones from heaven” could fall on the earth. Then in 1803 the French scientist J. B. Biot described an extraordinary rain of meteorites that fell at L’Aigle on April 26[V-3]; he convinced the French Academy of Sciences that the stones had indeed pelted from the sky during the great meteor display. Meteoritics is thus a relatively young science. Much remains to be learned about these cosmic visitors, but certain basic facts have been established[V-4]. Meteors enter the earth’s atmosphere continually, by day as well as by night, and they show great variety. Some are so brilliant that they are visible even in broad daylight. Some are so faint that even in darkness they can be seen only through a telescope. Others, still fainter, can be detected only by radar specially designed for this purpose. Because of the friction created when they penetrate the earth’s atmosphere, most meteors vaporize and vanish many miles above the ground. We see them as only bright streaks of light, quickly extinguished. If the meteoric body is large enough, has the right chemical constitution, and enters the atmosphere at a favorable angle and velocity, some of it may survive the journey and fall to the earth as a meteorite. A distinct odor sometimes accompanies the fall--the smell of sulphur, onions, or cyanide. About 40,000 tons of meteoritic material fall on the earth each day, most of it in the form of fine dust. The object may be a chunk of metal or stone the size of a pebble or a boulder, or it may be a mass weighing several tons, so enormous that it gouges out a crater at the place where it hits and comes to rest far beneath the earth’s surface. Some meteors, fortunately extremely rare, apparently can strike the earth and devastate a large area but, like the wind, leave behind no physical trace. According to present theory, members of a regular shower are probably remnants of comets, which have an icy structure, and the minute bits of frozen debris vaporize in a flash of light high in the atmosphere. Meteors that survive to reach the earth as meteorites are thought to be fragments of asteroids, or tiny planets. Meteorites vary so widely in their physical and chemical structure that they require a complex system of classification. Nevertheless the specialist can distinguish between a meteorite and earthly rocks and stones by laboratory tests[V-5]. _Meteor Streams and Showers_