Rotation of the plane of polarization of a beam of linearly polarized light when the light passes through matter in the direction of the lines of force of an applied magnetic field. Discovered by M. Faraday in 1846, the effect is often called magnetic rotation. The magnitude α of the rotation depends on the strength of the magnetic field H, the nature of the transmitting substance, the frequency v of the light, the temperature, and other parameters. In general, α = VxH, where x is the length of the light path in the magnetized substance and V the so-called Verdet constant. The constant V is a property of the transmitting substance, its temperature, and the frequency of the light.