TECHNICAL INDEX AND GLOSSARY 



Low Temperature Researches. The work of Rumford, Davy, 

 and Young, and later by Sir James Dewar and his associates in 

 reducing gases, even hydrogen itself, to a liquid state, is de- 

 scribed in "The Royal Institution and the Low Temperature 

 Researches," Vol. V, p. 29. 



Magdeburg Hemispheres. The name given two hollow brass 

 hemispheres with tightly-fitting surfaces which, when approx- 

 imated, and after the air had been exhausted, could not be pulled 

 apart by teams of horses. With these Otto von Guericke, in the 

 seventeenth century, demonstrated atmospheric pressure. See 

 Vol. II, p. 2ii ; Vol. VI, p. 66. 



Magnet. A body which possesses the property of attracting 

 fragments of iron or steel. The loadstone is a natural magnet. 

 It is the native magnetic oxide of iron, Fe s O. See "Electricity," 

 and "Electro-magnetism" of the present index. 



Magnetism. The property possessed by certain bodies whereby 

 they naturally attract or repel one another. See "Faraday ana 

 Electro-magnetic Induction," Vol. Ill, p. 240. Also "Electricity," 

 and "Electro-magnetism" of the present index. 



Magnetized Needle. A magnet in the form of a needle sus- 

 pended at its center of gravity, which places itself naturally in 

 a position with its long axis nearly north and south, with one 

 end inclining downward. See "Electricity and Magnetism," Vol. 

 Ill, p. 236. Also "The Mariner's Compass," Vol. VII, p. 7. 



Mammalia (mammiferous animals, mammals). All those ani- 

 mals which suckle their young, and no others. Thus, whales, 

 although fish-like in habits, are mammals quite as much as 

 horses or cattle. For studies of fossil mammals, see "The New 

 Science of Paleontology," Vol. Ill, p. 74; and "The Origin and 

 Development of Modern Geology," Vol. Ill, p. 116. 



Mantle, Gas. A porous, hollow cone, or bag-shaped structure, 

 composed of the oxides of thoria, alumina, magnesia, etc., which 

 when placed so that a mixture of air and illuminating gas passes 

 through it, and is ignited, becomes brilliantly luminous. See 

 "Gas Lighting," Vol. VI, p. 207. 



Mariner's Compass. An instrument, apparently invented and 

 used by the Chinese before the Christian era, in which a mag- 

 netized needle suspended at its center of gravity above a disk, 

 is used for determining directions at sea. The short-needle 

 compass, now used universally, was invented by Lord Kelvin 

 about 1875. See "The Mariner's Compass," Vol. VII. p. 7- 



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