1. Parson, J. D., Mol. Cryst. Liq. Cryss.31, 79 (1975).
2. Bouchiat, M., D. Langevin, Phys. Lett. A34, 331 (1971).
3. Friedel, G., Annales de Physique27, 405 (1922).
4. Rapini, A., L. Leger, A. Martinet, J. de Physique36, C-1 189 (1975).
5. Proust, J E., L. Ter-Minassian-Saraga, Colloid & Polymer Sci. (in press).