dip, magnetic

A dip circle is used to measure the angle between the direction of the Earth's magnetic field and the horizontal at any point on the Earth's surface.

Angle at a particular point on the Earth's surface between the direction of the Earth's magnetic field and the horizontal. It is measured using a dip circle, which has a magnetized needle suspended so that it can turn freely in the vertical plane of the magnetic field. In the northern hemisphere the north-seeking end of the needle dips below the horizontal, pointing along the line of the magnetic field towards the Earth's magnetic north pole. At the magnetic north and south poles, the needle dips vertically and the angle of dip is 90°. See also angle of declination.