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possible if the field energy is transferred only to a frRctlon of plasma particles~for instance to paltlcles matching some resonance condition similar to the static-corkscrew conditions; complications are introduced by field self-consistency and time dependence at the focus.Measurement of the tilt angle of the smectic C phase of terephthal-bis-(4-n-butylaniline) has been made using conoscopic observation and circularly polarized light. The new phenomenon of a smectic C phase with a temperature-dependent tilt angle is reported.Terephthal-his-(4-n-butylanaline) has nematic, smectic A, smectic C, and smectic J3 liquid-crystalline phases. The tilt angle of smectic C changes from 0 at the smectic-

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The cholesteric phase is associated with scattering effects that give rise to iridescent colors, the dominant wavelength being influenced by very small changes in temperature, which can be as large as 1000 A shift per degree. This unusually high temperature sensitivity has given rise to the use of the cholesteric phase as a sensitive thermometer and thermal mapping media. This paper reviews the optical effects in the cholesteric phase with some new additions that are particularly relevant to thermal mapping. An attempt has been made to give a complete picture of the cholesteric liquid crystal as applied to nondestructive testing, rather than to review the work actually being done in this field.

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.We have studied three compounds which exhibit a nematic phase and a single smectic phase of the type classified by Sackmann and Demus 1 as type C. The smectic phases classified by Sackmann and Demus correspond to different molecular arrangements and are separated from each other by first-order phase transitions.The nematic phase has a long-range order such that the long axes of the molecules are nearly parallel and the parallelism of the long axis generally varies continuously throughout the bulk of the liquid. Assuming a random arrangement of the center of mass and free rotation about the long molecular axis, nematic liquids would be uniaxial. All observations do show the nematic phase to be uniaxial. Smectic A is a system in which the molecules are arranged in layers with the long molecular axis perpendicular to the layer. 2 If the centers of mass within the layers are random and free rotation is assumed, then smectic A would be uniaxial. Experimentally, all smectic -A phases have been shown, in general, to be uniaxial. Smectic C is generally considered to have a structure such that the molecules are arranged in layers but with the long molecular axis tilted with respect to the layer normal. 2 In general, it has been assumed that all smectic phases including smectic C would show uniaxial character and, in fact, Friedel 3 argued that all smectic phases would be uniaxial.