MAG 



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Ai 



served, on Mount Ida, the attractive 

 power which the loadstone exercised upon 

 his iron crook. The most probable sup- 

 position, however, is that it took its name 

 from Magnesia, a country of Lydia, where 

 it was first discovered; and this con- 

 jecture is confirmed by the fact, that the 

 magnet was often called by the ancients 

 Lapi* Heracleus, from Heradea, the capital 

 of Magnesia. 



MAONET'IC COMPENSATOR. A contrivance 

 by Mr. Barlow, for eliminating the in- 

 fluence of a ship's guns and other iron- 

 Avork, in deranging the bearings of the 

 compass. 



MAGNET'IC NEEDLE. A slender piece 

 of steel, suspended on its centre, and 

 magnetised, which is free to turn, and 

 always settles in the magnetic meridian. 



MAGNETIC PYRITES. Native black 

 sulphate of iron. It attracts the needle. 



MAGNETISM. The power of the magnet. 

 2. That branch of physics which has 

 for its object the investigation of all mag- 

 netic phenomena (.whether natural, like 

 the loadstone, or artificial, like bars of 

 steel to which magnetism has been per- 

 manently communicated), of their re- 

 ciprocal action upon each other, of the 

 laws of the forces which they develope, 

 of the methods of making artificial 

 magnets, and other magnetic phenomena 

 exhibited by the globe which we inhabit. 

 For ANIMAL MAGNETISM, see MESMERISM. 

 For TEaRESTRiAL MAGNETISM, see TER- 

 RESTRIAL MAGNETISM. 



MAG'NETO-ELECTRIC'ITT. Electricity pro- 

 duced by magnetism. The phenomena of 

 electro-magnetism are produced by elec- 

 tricity in motion : accumulated electricity, 

 when not in motion, exerts no magnetic 

 effects. Dr. Faraday early felt convinced 

 that as every electric current is accom- 

 panied by a corresponding intensity of 

 magnetic action at right angles to the 

 current, good conductors of electricity, 

 when placed within the sphere of this 

 action, should have a current induced 

 through them, or some sensible effect pro- 

 duced, equivalent in force to such a cur- 

 rent- These considerations, with their 

 consequence, the hope of obtaining elec- 

 tricity from ordinary magnetism, stimu- 

 lated him to investigate the subject ex- 

 perimentally , and he was rewarded by 

 an affirmative answer to the question 

 proposed. Dr. Faraday not only suc- 

 ceeded in obtaining galvanometrical in- 

 dications of an electric current, but by a 

 modified apparatus, in which the electric 

 current was induced by an electro-magnet, 

 he actually succeeded in obtaining the 

 electric spark. The electric spark was 

 afterwards obtained from a common 

 magnet, by Nobili and Autinori, and in 

 this country by Professor Forbes. 



ftUojiETuJt'ETER. Ail instrument for 



measuring liie intensity oi tcrx 

 magnetism. 



MAONETOMO'TOR. A tern: applied to a 

 voltaic series, which, producing a great 

 quantity of electricity of low teiuion, 

 beautifully exhibits the phenomena cf 

 electro-magnetism. 



MAG.NIF'ICO. The title given by courtesy 

 to a nobleman of Venice. 



MAG'JUFIER, ) A convexo-convex 



MAO'NIFTING-GLASS. ) lens, which in- 

 creases the apparent size or magnitude 01 

 any body seen through it, by increasing 

 the angle under which it is seen. Magni- 

 fying power is the amount of apparent 

 enlargement of an object, by means of 

 such magnifier, or other optical instru- 

 ment, as the microscope. Magnify, from 

 magnus, great, and/aeio, to make. 



MAG'NITUDE denotes the extension of 

 anything whether it be in one direction, 

 as a line ; in two directions, as a surface ; 

 or in three directions, which constitute a 

 solid. Geometrical magnitudes may be 

 conceived to be generated by motion, as a 

 line by the motion of a point ; a surface, 

 by the motion of a line ; and a solid, by 

 the motion of a surface. 2. Apparent 

 magnitude is the angular space under 

 which a body appears when viewed from 

 a distance. The term is used chiefly In 

 astronomy and optics. 



MAGNO'LIA. The laurel-leaved tulip-tren, 

 a magnificent genus of trees and shrubs. 

 PolyandriaPolygynia. There are 17 spe- 

 cies ; but the M . grandifolia of the warm 

 parts of N. America is that most prized. 

 It is remarkable for its large evergreen, 

 leaves and splendid white flowers. Se- 

 veral of the other species are also culti- 

 vated for ornament : as the M. glauca, or 

 beaver- wood of America; the M. macro- 

 phylla, also of America ; and the M. con- 

 spicua, or youlan, a greenhouse shrub from 

 China. 



MAHA'BARATA. One of the great Indian 

 epic poems. 



MA'HALEB. (1.) A species of cherry cul- 

 tivated in our gardens. (2.) The fruit of 

 this shrub affords a violet dye, as well as 

 a fermented liquor like kirschwasser. 



MAHOG'AN*. The wood of the Swietenia 



nirt/jopam, a large tree which grows in the 

 West Indies and Central America. The 

 principal importations of mahogany into 

 Great Britain are made from Honduras 

 and Campeachy. 



MAHOMETANS, see MOHAMMEDANS. 



MAIDEN. An instrument formerly used 

 in Scotland for beheading criminals. It 

 was the prototype of the French guillo- 

 tine. 



MAIDEN ASSIZE. In law, an assize in 

 which no person is condemned to die. 



MAIDESHAIH-TREE. The Ginyko lilola, a 

 tree of China and Japan. Its fruit, about 

 the size of a damask plum, contains a 



