 The oscillations of the differential susceptibility when plotted against formula_7, have a period formula_8 (in teslas−1) that is inversely proportional to the area formula_9 of the external orbit of the Fermi surface (m−2), in the direction of the applied field, that is

where formula_11 is Planck constant and formula_12 is the elementary charge.The modern formulation allows the experimental determination of the Fermi surface of a metal from measurements performed with different orientations of the magnetic field around the sample.Experimentally it was discovered in 1930 by W.J.