Using the small angle prism technique refractive indices are measured at different temperatures in the nematic phase of (i) two nematogenic compounds, viz., hexylbenzoic acid (HBA) and diheptyl azoxybenzene (DHAB), and (ii) binary mixtures of HBA and octylbenzoic acid(OBA) (Mixture-I), and DHAB and nonylbenzoic acid (NBA) (Mixture-II). From the measured refractive index data and employing Neugebauer relations, anisotropy of Lorentz field factors and orientational order parameter have been estimated. The higher order parameter has also been computed using the Humphries-James-Luckhurst model and is compare i with that of Maier-Saupe model.