Abstract: The method for the differential measurement of an angle of incidence of a luminous beam uses a polarized light beam which is passed twice through a birefringent plate followed by a polarizing analyzer in order to obtain a succession of interference fringes. The orientation or the mutual spacing between the crests of said fringes, which are a direct function of the measured angle (.gamma.), are analyzed by means of a suitable detector and of an electronic analyzing circuit. The measuring device comprises a single polarizing analyzer, a birefringent plate which is followed by a mirror in order to reflect the light beam through said birefringent plate a second time, and means for detecting the variations of the luminous intensity including an electronic analyzing circuit.