ABSTRACT
In birefringent prisms these two beams are conserved. In polarizing prisms only one beam is conserved; the other is eliminated by total reflection. The differences in the indices of refraction of ordinary and extraordinary vibrations propagating in transparent uniaxial crystals is put to use for separating the two polarized beams from a beam of natural light. A plane parallel plate of calcite or that of sodium nitrate natural rhombohedron of sufficient thickness permits the separation of two polarized beams provided that the incident beam of natural light is sufficiently narrow. The diverse polarizers differ from one another by the orientation of the parallelopiped with respect to the optic axis and by the nature of the dielectric. Fresnel's Parallelopiped plays the role of an achromatic quarter-wave plate. A circular polarizer transforms natural light into circularly polarized light.
