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Convergent light observations have been made on three liquid crystalline substances with nematic and smectic phases. The nematic phase was observed to be uniaxial as expected, but smectic C was found to be biaxial. The optic axial angle 2V for smectic C was found to be on the order of 20^ for all three compounds. Also, the tilt angle for smectic C is nearly 45^ for all three liquid-crystal systems. Anisotropy of the degrees of order is suggested as a partial explanation for the biaxial character of smectic C.
Taylor et al. (Mon,) studied this question.