English: Field vectors (E,D,B,H) and propagation directions (ray and wave-normal) for linear-polarized plane electromagnetic waves in a non-magnetic birefringent crystal. The plane of vibration, containing both electric vectors (E & D) and both propagation vectors, is sometimes called the "plane of polarization" by modern authors. Fresnel's "plane of polarization", traditionally used in optics, is the one containing the magnetic vectors (B & H) and the wave-normal. Malus's original "plane of polarization" was the one containing the magnetic vectors and the ray.