Accurate measurement of the refractive indices of solids and liquids by the double-layer interferometer

The rings of equal inclination of the double-layer interferometer disappear in their common center if a plane-parallel glass plate is rotated inside one of the interferometer gaps that is filled with a liquid. Knowledge of the ring count and the rotated angle allows the refractive indices of both the rotated plate and the liquid to be found from a new analytical formula accurate to ?0.0004. The experimental results for glass, distilled water, and methanol are fitted to the Sellmeier dispersion function to determine their quantum parameters such as the absorption wavelengths in the ultraviolet side of the spectrum and the atomic number densities contributing to these absorption bands.