Electric-field-induced critical phenomena at the nematic-isotropic transition and the nematic-isotropic critical point

A convenient method for measuring the dc Kerr effect on the stage of a polarizing microscope is described. Two novel illustrations of this technique are presented: a low-field determination of the pretransitional Kerr effect in the isotropic phase of a nematic having a negative dielectric anisotropy and measurements of the birefringence on both sides of the nematic-isotropic ($N-I$) phase boundary as the $N-I$ critical point is approached by applying very high electric fields to a nematic with positive dielectric anisotropy.