Analysis of the theory of entropy and LA fluctuations in solids shows that the coupling to the dielectric constant is anisotropic. Scattered radiation therefore in general will change its state of polarization. Thus the observation of thermal Rayleigh and LA Brillouin scattering in solids is facilitated by detection of the depolarized component. The Landau-Placzek ratio strongly depends on polarization and scattering geometry. © 1977.