1) Theories of the nature of optical rotatory power are reviewed, with special reference to that of Kuhn. The phenomena of optical rotatory dispersion and corralation between molecular structure and optical rotatory power from ultraviolet absorption data are discussed. Analysis of rotatory dispersion data on the basis of the Drude equation, and some effects of temperature and solvents on rotatory power are reviewed. 2) The preparation of d1 2-thienyl-methyl carbinol is described, and its resolution as the brucine salt of its hydrogen phthalic ester. The rotatory dispersions of the optically active alcohol and its solutions in various solvents are recorded, and shown to be simple in the visible spectrum. The dispersions are discussed in relation to the ultraviolet absorption of the alcohol and conclusions are drawn regarding the type of Drude equation that would be required to cover the complete spectrum, and the most likely chromophoric groups in the molecule. Optical data are recorded for the hydrogen phthalic ester, and alkyl-oxygen fission in this compound has been demonstrated. 3) The preparation of d1 apicolyl-methylcarbinol and a method for its resolution as the brucine salt of its hydrogen phthalic ester are described. The rotatory dispersion of the active alcohol in twelve solvents has been examined in the visible spectrum and found to be simple in associating solvents, but complex and anomalous in non-polar media. The dispersive powers of the hydrogen phthalic and acetate esters and of the p-xenyl urethane are also recorded. A possible explanation of the dispersion phenomena in different solvents and the types of Drude equation required to predict the dispersions are discussed in relation to the ultraviolet absorption of the alcohol.