1. Scott, G. D., Nature, 188, 908 (1960).
2. Fraser, H. J., J. Geology (Chicago), 43, 910 (1935).
3. Verman, L. C., and Banerjee, S., Nature, 157, 584 (1946).
4. Zenz, F. A., and Othmer, D. F., Fluidization and Fluid-Particle Systems, 142 (New York, 1960).
5. Brown, R. L., and Hawksley, P. G. W., Nature, 157, 585 (1946).