LETTERS TO THE EDITOR Frequency dependence of the relative permittivity of polar substances

A study of the Brownian motion of a dipolar molecule surrounded by a dispersive dielectric medium has resulted in the following generalization of Onsager's equation ( - ∞)(2* + ∞)(2 + 1)/3(2* + 1) = (4πNμ2/3kTV)((∞ + 2)2/9)(1/(1+iωτμ')) where τμ' is a microscopic relaxation time which includes the effect of dipole-dipole coupling.