Abstract: A gas cell, preferably in the shape of a hemi-sphere, forms a transparent enclosure for helium or an alkali metal vapour. A coil forms an A.C. magnetic field H.sub.1 in the enclosure, the magnetic field having multi-directional field lines. A lamp or lamps, comprising either helium or alkali metal vapour, direct circularly polarized resonance radiation at the enclosure such that the radiation rays travelling through the enclosure are multi-directional. A photodetector or photodetectors detect the radiation rays after they have passed through the gas cell. The multi-directionality of the radiation rays and the A.C. magnetic field H.sub.1 ensures that the magnetometer will not possess dead-zones.