A body which produces a magnetic field around itself. It has the property of attracting certain materials capable of being magnetized. A magnet occurring in nature is called a natural magnet in contrast with a man-made artificial magnet.

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The phenomena associated with magnetic fields and their effects upon magnetic materials, notably iron and steel. The magnetism of the north-seeking end of a freely suspended magnet is called red magnetism; the magnetism of the south-seeking end is called blue magnetism. Magnetism acquired by a piece of magnetic material while it is in a magnetic field is called induced magnetism. Permanent magnetism is retained for long periods without appreciable reduction, unless the magnet is subjected to a demagnetizing force. The magnetism in the intermediate iron of a ship which tends to change as the result of vibration, aging, or cruising in the same direction for a long period but does not alter immediately so as to be properly termed induced magnetism is called sub permanent magnetism. Magnetism which remains after removal of the magne- tizing force may be called residual magnetism. The magnetism of the earth is called terrestrial magnetism or geomagnetism.


An instrument that measures the magnetic intensity of a natural magnet or electromagnet.


A gaussmeter that consists of a thin piece of silicon or other semiconductor material which is inserted between the poles of a magnet to measure the magnetic field strength by means of the Hall effect.


A temporary magnet made of a ferromagnetic core wound with insulated wire through which is passed an electric current. The current flow through the windings causes a magnetic field to build that will attract magnetic material.


A detector that gives an electric signal whose magnitude and phase are proportional to the magnitude and direction of the external magnetic field acting along its axis; used to indicate the direction of the terrestrial magnetic field.


A magnetometer for determining the gradient of a magnetic field by measuring the difference in reading from two magnetometers placed at different positions.


  1. Either of the two places on the surface of the earth where the magnetic dip is 90°, that in the Northern Hemisphere being designated north magnetic pole, and that in the Southern Hemisphere being designated south magnetic pole. Also called MAGNETIC DIP POLE. See also MAGNETIC LATITUDE, GEOMAGNETIC POLE, MAGNETIC LATITUDE. 2. Either of those two points of a magnet where the magnetic force is greatest.


Neutralization of the strength of the magnetic field of a vessel, using electric coils permanently installed in the vessel.


A magnet occurring in nature.


A permanent magnet placed vertically in a tube under the center of a marine magnetic compass, to correct for heeling error.

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