An anomalous effect owing to electric fields has been found in the nematic phase of a liquid crystal exhibiting positive dielectric and negative conductivity anisotropies. The preferred direction for the long axes of the molecules is perpendicular to a dc or very low-frequency ac electric field but parallel to a field for frequencies of a few thousand Hz. A sizable change in the average value of the dielectric loss was observed at the nematic-liquid transition temperature. This is explained by assuming that the nematic phase, which is believed to be a doubly-hydrogen-bonded dimer, contains a small percentage of monomer or dimer with one hydrogen bond broken. A small change in the percentage of normal dimer at the transition temperature could account for the change in loss. The effect of magnetic fields up to 68 000 G on the molecular alignment in the smectic $C$ phase is discussed.

• Received 4 December 1972

DOI:https://doi.org/10.1103/PhysRevA.7.1639