The birefringence and refractive indices of several liquid crystalline structures were measured throughout the visible wavelength region (400-900 nm) at different temperatures. Mixtures composed of members of the same homologous series were used in order to achieve the nematic phase at room temperature. Data on 28 mixtures, mainly with cyclohexane - phenyl and biphenyl cores, are presented. The set includes widely used structures as well as newly synthesized. Some details of experimental methods, formulas for interpolation of the results and observed regularities are briefly discussed.