Page:Collier's New Encyclopedia v. 06.djvu/107

LEFT MAGNETITE 81 MAGRUDEB netic poles do not coincide with the geo- graphical poles, the N. being 70° 5' N., and 96° 43' W. The S. is probably at 13V2° S. and 14%° E. There are two foci of maximum force in the Northern Hemi- sphere and two in the Southern. In the Northern Hemisphere the stronger focus is assumed to be in 52° N. and 90° W., and the weaker in 70° N. and 115° E. In the Southern Hemisphere the stronger focus is assumed to be in 65° S. and 140° E., and the weaker probably in 50° S. and 130° W. MAGNETITE, magnetic iron ore, also known as loadstone. It consists of black oxide of iron, FeO.Fe-Os, with small per- centages of impurities. It contains ap- proximately 72 per cent, of iron, and is widely distributed. As found, it is fre- quently crystalline in character with a marked metallic luster, and can readily be recognized by the fact that small frag- ments are picked up by a weak magnet. It is mined in the Adirondacks, in Swe- den, Norway, Lapland, and the Ural Mountains. MAGNETO. See MOTOR VEHICLE. MAGNETOGRAPH, an instrument for recording the fluctuation of the mag- netic field of the earth. The variations in strength only are recorded — the exact value at any given time is usually ob- tained by use of a magnetometer. The principle of operation most commonly used is the reflection of a ray of light from a mirror attached to a sus- pended or freely moving magnetic needle to a recording sheet of photographic paper which is attached to a drum actu- ated at a uniform speed by clockwork. When the instrument is to be used for recording the magnetic declination, the magnetic needle is usually suspended by a quartz fiber. When used to measure the vertical component, the needle is mounted on a knife edge so that its axis about which it may move is horizontal. Any movements of the needle, which should be of light weight in order that the inertia may be of a minimum, will cause a movement of the image reflected upon the recording paper, and a curve representing the relative changes of the magnetic is obtained. MAGNETOMETER, an instrument for measuring any of the magnetic elements, as the dip, inclination, and intensity. MAGNETS, this term, which was originally applied only to loadstone, or magnetite (Fe304), has come to include the various substances which have mag- netic properties. A magnet in the form of a needle (compass) or bar, when so suspended that it is free to move_ about a vertical axis, places itself in an approximately N. and S. direction. Portions of a magnet have the property of attracting iron, nickel, cobalt, and a few other substances, while some sub- stances are repelled. The substances which are atti'acted by a magnet are called magnetic substances. Those por- tions of the magnet which have the property of attracting or repelling are called the poles, and, in the case of a bar magnet, are usually located near the ends. Opposite magnet poles have the power of attracting each other; the like poles repel each other. A piece of iron or steel which has been stroked laterally with a magnet becomes magnetized, and forms a typical example of ferromagnetism. If a core of iron is wound with insulated wire, and an elec- tric current passed through the wire, the core takes on magnetic properties and becomes an electro-magnet, the direction of the electric current determining the polarity of the magnet. The latter method has by far the greater commercial appli- cation. MAGNIFICAT, the song of the Virgin Mary, which, in the Vulgate, begins with "Magnificat." See Breviary. MAGNOLIA [named after Pierre Mag- nol (1638-1715), Professor of Medicine at Montpellier, and author of several botanical works], the typical genus of the tribe Magnolicse and the order Mag- noliacese. Sepals three, deciduous; petals, six to nine; stamens and pistils many; carpels compacted in spikes or cones; seeds baccate, somewhat cordate, pendu- lous, with a long white umbilical thread. The species are trees or shrubs, with alternate leaves and large, terminal, odoriferous flowers. They are found in North America and Asia. M. grandiflora, the great-flowered magnolia, or laurel bay, is a fine evergreen tree, 70 feet high in America, and from 20 to 30 in foreign gardens. The species have large, beau- tiful, fragrant flowers. MAGPIE, a well-known bird of the family Corvidx. It is the Corvus pica of Linnaeus, Pioa oaudatu, melanoleuca, or i-ustioa of later ornithologists. It is an extremely beautiful bird, the pure white of its scapulars and inner web of the flight feathers contrasting vividly with the deep glossy black of the body and wings, while the long tail is lustrous with green, bronze, and purple reflections. MAGRUDER, JOHN BANKHEAD, an American military officer; born in Winchester co., Va., Aug. 15 1810. He was graduated at the United States