Magdeburg Hemispheres
a celebrated invention designed to show atmospheric pressure. About 1650 Otto von Guericke, burgomaster of Magdeburg, prepared two hollow hemispheres of copper. Their edges were ground and polished, so that when placed together, oiled, and twisted slightly, they formed an air-tight globe. One of the hemispheres was fitted with a stopcock through which the inventor exhausted the air by means of an air-pump. He exhibited his apparatus before scientific men of the day and before the emperor, Ferdinand III, at the Diet of Ratisbon. When full of air the hemispheres fell apart of their own accord. When the air was exhausted they could not be pulled apart by two men. The experiment is still a familiar one in the school laboratory. The force with which the hemispheres are held together may be obtained readily. It is fifteen pounds for every square inch of the cross-section of the united hemispheres.
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Magenta
an Italian town, 18 miles W. of Milan. Here, on June 4, 1859, 55,000 French and Sardinians defeated 75,000 Austrians, the latter losing 10,000 (besides 7,000 prisoners), and the allies only 4,000. For this victory Macmahon received his dukedom.
DUC DE. See MACMAHON.
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Maggiore
LAGO, one of the largest lakes in Italy, the Lacus Verbanus of the Romans, situated for the most part in Italy, but also partly in the Swiss canton of Ticino; length 39 miles, breadth from 1/2 mile to 5½ miles; 646 feet above sea-level, with a maximum depth of 1,158 feet. The river Ticino flows through it. In a S. W. expansion of the lake are the BORROMEAN ISLANDS (q. v.). On the N. and W. it is surrounded by granitic mountains, 7,000 feet high, on the S. and E. by vineyard-covered hills.
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Maggot
larva of an insect; a grub.
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Magic Circle
a circle invented by Franklin, founded on the same principles and possessing similar properties with the magic square of squares.
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Magic Darts
The Laplanders, who passed at one time for great magicians, were said to launch lead darts, about a finger-length, against their absent enemies, believing that with the magic darts they were sending grevious pains and maladies. (See Magic.)
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Magical Union of Cologne
A society stated in a MS. of the Rosicrucians at Cologne to have been founded in that city in the year 1115. In the Rosenkreutzer in seiner blosse of Weise it is stated that the initiates wore a triangle as symbolising power, wisdom and love. The more exalted orders among them were called Magos, and these held the greater mysteries of the fraternity.
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Maginot, Adele
One of the mediums whose trance utterances have been recorded by the French spiritualist Alphonse Cahagnet, who published his Arcanes de la vie future devoilés in 1848. Her séances, of which Cahagnet strove to obtain a written account from as many as possible of those present, are among the most valuable evidence which spiritualism can produce. Her descriptions of absent or deceased friends of the sitters were singularly accurate, though her supposed conversations with their spirits would appear to be fictitious. At the least her séances are excellent examples of telepathic communication.
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Magnesia
in mineralogy, the same as periclase. Used as a drug, if administered in small doses, magnesia acts as an antacid; if in quantity beyond what is necessary to neutralize acids in the stomach, it passes undigested into the intestines, and may form concretions. The salts of magnesia are purgatives. It is given as a lithontriptic, from its power of dissolving uric acid, and in gouty diseases.
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Magnesian Limestone
a limestone composed of carbonate of lime and carbonate of magnesia, the proportion of the latter sometimes being nearly 50 per cent. It effervesces much more slowly with acids than common limestone (carbonate of lime). It is sometimes earthy, sometimes hard and compact. One variety of it is DOLOMITE (q. v.).
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Magnesite
a widely occurring mineral, consisting of magnesium carbonate, MgCO3. It is mined in California, British Columbia, New Jersey, New York, Washington, Quebec, India, Austria, and Greece. It occurs in three forms-crys- forms talline, massive, and earthy, the two latter being white in color and frequently mixed with other magnesium salts. Its principal use is in the manufacture of refractory linings for furnaces and retorts, and for this purpose it is of great value in the cement and metallurgical industries. It is also used in the preparation of Epsom salts (magnesium sulphate) and other salts of magnesium. A strong cement is made by mixing calcined magnesite with chloride of magnesium. Other uses are in the manufacture of paper and pigments and for heat insulation. MAGNESIUM (-ne'shium) (Latinized from Magnesia, a city in Asia Minor), in chemistry, a diatomic metallic element; symbol, Mg; at. wt. 24.4; sp. gr. 1.743. Fuses and volatilizes at a red heat. Magnesic sulphate (Epsom salts) was known in the middle of the 17th century, but the metal was first isolated by Davy. The compounds of magnesium are widely distributed in nature, occurring as magnesite, MgO"CO; ophite or serpentine, MgO"Si2O; talc, MgO" SisO6; dolomite, kainite, te, epsomite, etc.
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Magnet
There are two kinds of magnets-natural and artificial. The natural magnet is an iron ore which has the property of attracting to itself particles of iron or steel. If suspended, it takes a north and south direction, and it is from this particular leading property that it is called leadstone or loadstone. The magnet (magnes in Greek) is supposed to have received its name from Magnesia, in Asia Minor, where it was first discovered. See LOADSTONE. Magnetite is a magnetic iron ore, or oxidulated iron. It is one of the richest and most important ores of iron, and produces the finest brands of steel. It is found in almost all parts of the world, and occurs crystallized in iron in black octahedrons and dodecahedrons; also massive, as well as in the form of sand. See ORES.
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Magnetic Equator
a theoretical line drawn on the surface of the earth, connecting the points at which a dip ping needle assumes a horizontal posiis tion, and at which the magnetic dip is zero. MAGNETIC NEEDLE. See MAGNET- ISM. MAGNETIC POLES. See MAGNETISM.
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Magnetite
magnetic iron ore, also known as loadstone. It consists of black oxide of iron, FeO. Fe2O3, with small percentages of impurities. It contains approximately 72 cent. of iron, and is widely distributed. As found, it is free quently crystalline in character with a marked metallic luster, and can readily be recognized by the fact that small fragments are picked up by a weak magnet. It is mined in the Adirondacks, in Sweden, Norway, Lapland, and the Ural Mountains. MAGNETO. See MOTOR VEHICLE.
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