A magnetometer measuring the horizontal component, H, of the total intensity F of the magnetic field. A magnet suspended horizontally is set to swinging and its period of oscillation is measured. The period is a function of the intensity M x H at the magnet, where M is the magnetic dipole moment. The suspended magnet is then taken down and placed near a suspended, standard magnet of the same kind. Interaction of the two magnets causes one of them to turn by an amount proportional to M/H. The value of H can then be calculated from the two sets of measurements.