MAG 



MAG 



producing magnesia, or oxide of magne- 

 sium, which is white, inodorous, and 

 forms an ingredient in many rocks, to 

 ■which it usually communicates a soapy 

 or greasy feel. 



MAGNET. Magnets are substances 

 which attract certain metals; which dis- 

 play towards one another a force partly 

 attractive and partly repulsive; and, 

 lastly, which exhibit a tendency to ar- 

 range their mass in a certain direction 

 (seePoZe). The term is probably derived 

 from Magnesia, owing to the native iron 

 ore, or loadstone, having been found in 

 abundance near that city. 



I. Magnet, Natural and Artificial. 1. 

 The natural magnet, or loadstone, is a 

 chemical combination of the oxide and 

 the suboxide of iron. It occurs in the 

 northern parts of the world, where it 

 forms entire mountains. 2. Artificial 

 magnets are commonly of steel, to which 

 the magnet^ properties are communi- 

 cated by a particular process. They are 

 of various forms : if cylinders or parallel- 

 epipeds, they are called bar magnets ; if 

 curved in the middle, so as to bring the 

 two ends near together, they form horse- 

 shoe magnets ; when several bars or horse- 

 shoes are combined, the apparatus is 

 called a compound magnet, or a magnetic 

 battery, or, more simply, a bundle of mag- 

 nets. Those artificial magnets which are 

 constructed so as to move freely, and 

 which will then invariably assume a 

 certain definite position with respect to 

 the earth, are called needles. 



2. Magnetic North. A term applied 

 to the direction of the magnetic needle, 

 which, though commonly said to point to 

 the north, usually points some degrees 

 from it, one way or the other. For in- 

 stance, all along the line which passes 

 through the Cape de Verd Islands, the 

 magnetic north is 1 5° west of the true 

 meridian; and hence, a ship on this line, 

 wanting to sail any particular course, 

 steers 15° wrong by her compass to be 

 right by the meridian. 



3. Magnetic Indifference, Point of. 

 That point of a magnet, somewhere 

 about midway between the two extre- 

 mities, where the attractive force, after 

 continually diminishing as we proceed 

 from either pole, ceases altogether. 



4. Magnetic Fluid. The hypothetical 

 agent, to which the phenomena of mag- 

 netism have been referred. Some have 

 supposed two such fluids,— a boreal or 

 northern, and an austral or southern. 

 The former of these is also distinguished as 



206 



positive, the latter as negative magnetism, 

 neither of which, however, is found singly 

 combined with the particles of matter, 

 but always both together. 



5. Magnetic Curves. The curved lines 

 into which iron-filings arrange them- 

 selves when dropped gently on a plate of 

 glass having a magnet beneath it. The 

 filings will be found to accumulate most 

 perceptibly about the poles of the magnet, 

 and to arrange themselves in curved lines 

 extending from one pole to the other. 



6. Magnetic Induction. That property 

 by which each pole of a magnet excites 

 magnetism in any magnetizable body 

 within a certain distance of itself, im- 

 parting an opposite polarity to its own to 

 the contiguous end of such a body, and 

 similar polarity to its remote end. The 

 range within which the magnet exerts an 

 influence is termed its circle of magnetic 

 influence, or its magnetic atmosphere. 



7. Magnetic Points of Convergence. 

 The name given to two points, near to 

 the north and south poles of our planet, 

 around which are drawn the isogonic 

 lines, or lines of equal declination. The 

 two points are also called the magnetic 

 poles of the earth. 



8. Magnetic Equator. The name of an 

 irregular curve in the neighbourhood of 

 the terrestrial equator, where a needle 

 balances itself perfectly horizontally. It 

 is also called the aclinic line. 



9. Magneto-electrical Rotatory Machine. 

 An apparatus for rendering the magneto- 

 electric induction currents continuous, 

 and for converting their alternating di- 

 rection into a constant one. Such a 

 machine may be employed as a substitute 

 in part for a common electrical machine, 

 and in part also for a voltaic pile, as it is 

 capable of producing electric sparks, in- 

 candescence and fusion of wire, intense 

 light at charcoal points, physiological 

 effects, chemical decomposition, and 

 magnetic action of many kinds. 



MAGNET, ARSENICAL. A corro- 

 sive preparation of equal parts of sulphur, 

 white arsenic, and common antimony, 

 mixed by fusion. 



MAGNE'TIC PYRI'TES. Native 

 black sulphuret of iron. It attracts the 

 magnetic needle. 



MA'GNETISM. A term expressing 

 the peculiar property occasionally pos- 

 sessed by certain bodies, more especially 

 by iron and some of its compounds, by 

 which, under certain circumstances, they 

 mutually attract or repel one another, ac- 

 cording to determinate laws. See Magnet, 



