Spatial dispersion in isotropic media caused by anisotropy fluctuations

It is demonstrated that taking into account the fluctuations of molecular orientations in an amorphous substance with anisotropic molecules leads to spatial dispersion of the permittivity. Expressions for the local field, polarization, and permittivity of an amorphous insulator are derived with allowance for the anisotropy fluctuations. The dispersion relation for the longitudinal electromagnetic waves in such a medium is discussed.