Birefringence a Nichol prism

The properties of isotropic media (including optical properties) are identical in aU directions. Nearly all gases and liquids and highly symmetric crystals with cubic and, in part, hexagonal structure (see Chapter 9.1) are referred to as isotropic ones. With anisotropic crystals light interacts differently than with isotropic media. 

Because the light speed o in a substance depends on the dielectric permeability g, the given scheme also represents a diagram of the dependence of n on the crystal direction. In this case this figure is called an indicatrix of speeds. Since the light speed does not depend on direction in isotropic media, the indicatrix is represented by a spherical surface. In anisotropic crystals, the properties of which depend on direction, the indicatrix differs from a spherical one. Moreover, they can differ for ordinary and extraordinary 

Solution (1) An optically active medium rotates a polarization plane at an 

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