A new form of the Gans phenomenological dielectric anisotropy fluctuation theory of the Kerr electro-optic effect in non-dipolar liquids is derived in terms of the anisotropic part of the light-scattering Rayleigh ratio Ran. Molecular theories developed for light scattering are thus also applicable to the Kerr effect, this being illustrated by a simple re-derivation of Vuks' expression for the Kerr constant. Measurements of the Kerr constant and relative permittivity have been made for some liquid n-alkanes over the temperature range 10–90°C, and values of the mean second molecular hyperpolarizability have been derived by comparing this measured Kerr constant with that calculated from the old and new Gans formulae. Temperature dependences of depolarization ratios calculated from measured Kerr constants exhibit fair agreement with light-scattering measurements.