PROF. INGOLD has introduced an important modification of Baeyer's strain theory, which brings the calculated ring strains into closer agreement with the thermal data of the cycloparaffins and with the general chemistry of the formation and decomposition of this series of saturated hydrocarbons (Trans. Chem. Soc., 119, 305, 1921). He has pointed out that the carbon atoms in a cycloparaffin are secondary and, by assuming that the carbon atoms attached to the central one occupy more of the surrounding space than the two hydrogen atoms, has calculated the angle (115.3°) between the carbon to carbon valencies from the atomic volumes of carbon and hydrogen.