ON THE CALCULATION OF THE MACROSCOPIC RELAXATION-TIME FROM THE LANGEVIN EQUATION FOR A DIPOLE IN A CAVITY IN A DIELECTRIC MEDIUM

A generalisation of Onsager's theory of the static permittivity of a polar fluid to time-dependent fields is presented by direct averaging of the nonlinear Langevin equation involving the Onsager reaction field for the rotation of a dipole (excluding inertial effects) in a cavity in a dielectric medium. The complex dielectric permittivity calculated in a definite approximation differs from the results of earlier investigations but the equation so derived for the macroscopic relaxation time coincides with the Powles formula.