Magnetometer

Instrument for measuring the intensity of a magnetic field. A simple form for detecting slight changes in the strength of the earth's magnetism consists of a bar magnet hung with a bifilar suspension, so turned that the bar is at rest in a position as nearly as po ible perpendicular to the earth's meridian. Changes in the direction of the force, if Unifilar Magnetometer, Kew Model. they be not over a few minutes of arc, will have no appreciable effect on the magnet, but a slight change of intensity will produce a corresponding change in its position of equilibrium. If the apparatus be so arranged as to produce a permanent record of the changes it indicates, it is called a magnetograph. Such a record may be made by reflecting a beam of light from the polished end of the magnet upon a sheet of photographic paper moved by clockwork.