magnetic compass
Device for determining the direction of the horizontal component of the Earth's magnetic field. It consists of a magnetized needle (a small bar magnet) with its north-seeking pole clearly indicated, pivoted so that it can turn freely in a plane parallel to the surface of the Earth (in a horizontal circle). The needle aligns itself with the lines of force of the Earth's magnetic field, turning so that its north-seeking pole points towards the Earth's magnetic north pole. See also compass.
Walkers, sailors, and other travellers use a magnetic compass to find their direction. The direction of the geographic, or true, North Pole is, however, slightly different from that of the magnetic north pole, and so the readings obtained from a compass of this sort must be adjusted using tables of magnetic corrections or information marked on local maps.
A magnetic compass can also be used to check the direction of the magnetic field around a wire with a current flowing through it.
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