A range oriented in a given magnetic direction and used to assist in the determination of the deviation of a magnetic compass.



Related Terms

SUBPERMANENT MAGNETISM

The magnetism in the intermediate iron of a ship which tends to change as a 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. This magnetism is the principal cause of deviation changes of a magnetic compass. At any instant this magnetism is recognized as part of the ship’s permanent magnetism, and consequently must be corrected as such by means of permanent magnet correctors.

MAGNETIC DIRECTION

Horizontal direction expressed as angular distance from magnetic north. magnetic diurnal variation. Oscillations of the earth’s magnetic field which have a periodicity of about a day and which depend to a close approximation only on local time and geographic latitude. Also called MAGNETIC DAILY VARIATION.

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.

LINE OF FORCE

A line indicating the direction in which a force acts, as in a magnetic field

SHADOW PIN

A small rod or pin used to cast a shadow on an instrument, such as a magnetic compass or sun compass, to determine the direction of the luminary; a GNOMON.

MAGNETIC LINES OF FORCE

Closed lines indicating by their direction the direction of magnetic influence.

ELECTROMAGNETIC WAVES

Waves of associated electric and magnetic fields characterized by variations of the fields. The electric and magnetic fields are at right angles to each other and to the direction of propagation. The waves are propagated at the speed of light and are known as radio (Hertzian) waves, infrared rays, light, ultraviolet rays, X-rays, etc., depending on their frequencies.

MAGNETIC MERIDIAN

A line of horizontal magnetic force of the earth. A compass needle without deviation lies in the magnetic meridian.

REVERSING FALLS

Falls which flow alternately in opposite directions in a narrow channel in the St. John River, New Brunswick, Canada, due to the large range of tide and a constriction in the river. The direction of flow is upstream or downstream according to whether it is high or low water on the outside, the falls disappearing at the half- tide level.

FLINDERS BAR

A bar of soft unmagnetized iron placed vertically near a magnetic compass to counteract deviation caused by magnetic induction in vertical soft iron of the craft

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