The Story of Electricity

by John Munro

IV. MAGNETIC UNITS.—

UNIT MAGNETIC POLE is that which repels an equal and similar pole at unit distance with unit force in air.

STRENGTH OF MAGNETIC FIELD at any point is measured by the force which would act on a unit magnetic pole placed at that point.

UNIT INTENSITY OF FIELD is that intensity of field which acts on a unit pole with unit force.

MOMENT OF A MAGNET is the strength of either pole multiplied by the distance between the poles.

INTENSITY OF MAGNETISATION is the magnetic moment of a magnet divided by its volume.

MAGNETIC POTENTIAL.—The potential at a point due to a magnet is the work that must be done in removing a unit pole from that point to an infinite distance against the magnetic attraction, or in bringing up a unit pole from an infinite distance to that point against the magnetic repulsion.

UNIT DIFFERENCE OF MAGNETIC POTENTIAL.—Unit difference of magnetic potential exists between two points when it requires the expenditure of one erg of work to bring an (N. or S.) unit magnetic pole from one point to the other against the magnetic forces.