A compass depending for its directive force upon the attraction of the horizontal component of the earth’s magnetic field for a magnetized needle or sensing element free to turn in a horizon- tal direction.



Related Terms

VIBRATING NEEDLE

A magnetic needle used in compass adjustment to find the relative intensity of the horizontal components of the earth’s magnetic field and the magnetic field at the compass location. Also called HORIZONTAL FORCE INSTRUMENT.

DIRECTIVE FORCE

The force tending to cause the directive element of a compass to line up with the reference direction. Also, the value of this force. Of a magnetic compass, it is the intensity of the horizon- tal componen

COEFFICIENT A

A component of magnetic compass deviation of constant value with compass heading resulting from mistakes in calculations, compass and pelorus misalignment, and unsymmetrical arrangements of horizontal soft iron.

MAGNETIC MERIDIAN

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

COEFFICIENT C

A component of magnetic compass deviation, varying with the cosine function of the compas

COEFFICIENT E

A component of magnetic compass deviation varying with the cosine function of twice th

COEFFICIENT D

A component of magnetic compass deviation, varying with the sine function of twice th

HORIZONTAL MAGNETOMETER

A measuring instrument for ascertaining changes in the horizontal component of the magnetic field intensity.

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.

DIP NEEDLE

A magnetic needle suspended so as to be free to rotate about a horizontal axis. An instrument using such a needle to measure magnetic dip is called a DIP CIRCLE. A dip needle with a sliding weight that can be moved along one of its arms to balance the magnetic force is called a HEELING ADJUSTER.

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