1. Orowan, E., Nature, 154, 341 (1944).
2. Gurney, C., and Pearson, S., Proc. Phys. Soc., B, 62, 469 (1949).
3. Zapffe, C. A., and Moore, G. A., Trans. Amer. Inst. Min. Met. Eng., 154, 335 (1943).
4. Seabrook, J. B., Grant, N. J., and Carney, D., J. Metals, 188, 1317 (1950).
5. Bastien, P., and Azou, P., C.R. Acad. Sci., Paris, 232, 69 (1951).