1. Wilson, C. G., J. Less Common Metals (in the press).
2. Cahn, R. W. (private communication).
3. Cahn, R. W., Adv. Phys., 3, 433 (1954).
4. Thomas, L. A., and Wooster, W. A., Proc. Roy. Soc., A, 208, 43 (1951).
5. Erny, M., C.R. Acad. Sci. Paris, 242, 2698 (1956).