686. Molecular polarisability. The C–C, C–O, CO, C–Cl, C–Br, and C–I link polarisabilities, and the conformations of cyclopentane, of cyclohexyl chloride, bromide, and iodide, and of cyclopentanone, cyclohexanone, cyclohexane-1 : 4-dione, comphor, paraldehyde, and tetrahydrofuran