Optical Rotatory Dispersion of $\alpha$-quartz

It is shown that some formulae describing optical rotatory dispersion of $\alpha$-quartz with the aid of two Drude’s terms reduce to the combined formula containing one Drude’s and one Chandrasekhar’s term. Comparison of various formulae describing the experimental data of $\alpha$-quartz leads to the conclusion that the optical activity of this crystal is due to its crystal structure only, that means the optical activity is not of molecular origin. Further the rotatory strengths are discussed with the regard to coupled oscillator model and to the structure of $\alpha$-quartz.