The index of refraction in the isotropic phase, n, and in the mesophase, n(o), for pure 5CB and 8CB liquid crystals, as well as their binary mixtures, were measured as a function of temperature. The related parameters, namely the orientational order parameter (S), relative polarizability anisotropy (zeta), and molecular length-to-breadth ratio (k), were calculated and compared for the mesophase of the considered samples. The order parameter and the relative polarizability anisotropy had maximum values for the binary mixture that had a eutectic composition. The low values observed for the (k), either for pure or mixed states, suggest the arrangement of parallel molecules within the nematic phase persists in group "swarms".