Any of several reversals in the polarity of the Earth's magnetic field (such that a compass points South) that have happened over geologic time.

(physics) the state of being a north pole or south pole; the magnetic equivalent of electric charge

(physics) The torque exerted on a magnet within a magnetic field; a vector, being the product of the strength of the magnet and the distance between its poles.

(physics) a measure of the magnetization of a material per unit of applied magnetic field

(physics) a thermometer whose operation is based upon Curie's law; typically used to measure temperatures below 1 K

(nautical, navigation) Directional bearing relative to the nearest magnetic pole, as shown by a compass.

(military) A mine which responds to the magnetic field of a target.

(military, nautical) An instrument containing a freely suspended magnetic element which displays the direction of the horizontal component of the Earth’s magnetic field at the point of observation.

The horizontal angle between magnetic north and true north at a given place.

(military, nautical, navigation) In navigation, at a given place and time, the horizontal angle between the true north and magnetic north measured east or west according to whether magnetic north lies east or west of true north.