The ability to retain magnetism after removal of the magnetizing force.



Related Terms

BLUE MAGNETISM

The magnetism displayed by the south-seeking end of a freely suspended magnet. This i

ELECTROMAGNETISM

  1. Magnetism produced by an electric current. 2. The science dealing with the physical relations between electricity and magnetism.

GAUSSIN ERROR

Deviation of a magnetic compass due to transient magnetism caused by eddy currents set up by a changing number of lines of force through soft iron as the ship changes heading. Due to these eddy currents, the induced magnetism on a given heading does not arrive at its normal value until about 2 minutes after change to the heading. This error should not be confused with RETENTIVE ERROR.

HARD IRON

Iron or steel which is not readily magnetized by induction, but which retains a high percentage of the magnetism acquired

INDUCED MAGNETISM

The magnetism acquired by soft iron while it is in a magnetic field. Soft iron will lose its induced magnetism when it is removed from a magnetic field. The strength and polarity of the induced magnetism will alter immediately as its magnetic latitude, or its orientation in a magnetic field, is changed. The induced mag- netism has an immediate effect upon the magnetic compass as the magnetic latitude or heading of a craft changes.

MAGNETISM

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.

PARAMETER

  1. A quantity which remains constant within the limits of a given case or situation. 2. One of the components into which a craft’s magnetic field is assumed to be resolved for the purpose of compass adjustment. The field caused by permanent magnetism is resolved into orthogonal components or parameters: Parameter P, Parameter Q, and Parameter R. The field caused by induced magnetism is resolved into that magnetism induced in 9 imaginary soft iron bars or rods. With respect to the axis of a craft, these parameters lie in a fore-and-aft direction, an athwart ships direction, and in a vertical direction.

QUADRANTAL DEVIATION

Deviation which changes its sign (E or W) approximately each 90° change of heading. It is caused by induced magnetism in horizontal soft iron.

RED MAGNETISM

The magnetism of the northseeking end of a freely suspended magnet. This is the magnetism of the earth’s south magnetic pole.

REMANENCE

Ability to retain magnetism after removal of the magnetizing force.

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