1. Avery, D. H., and Backofen, W. A., Fracture of Solids, edit. by Drucker, D. C., and Gilman, J. J., 339 (Gordon and Breach, New York, 1963).
2. Segall, R. L., Electron Microscopy and the Strength of Crystals, 515 (Interscience, New York, 1963).
3. Feltner, C. E., Phil. Mag., 12, 1229 (1965).
4. Broom, T., and Ham, R. K., Proc. Roy. Soc., A, 251, 186 (1959).
5. Laufer, E. E., and Roberts, W. N., Phil. Mag., 10, 883 (1964).