Apparatus of the Faraday type to measure crystal magnetic susceptibilities is described in conjunction with the method of analysis to deduce the anisotropic molecular magnetic susceptibilities. The relative merits of the Faraday and torsion methods to measure anisotropic susceptibilities are discussed. The principal molecular susceptibilities*which were determined at 293 K for the cesium, potassium, and ammonium copper Tutton's salts indicate orthorhombic distortion in the crystal fields around the copper ion.