1. Dyson, E. D., and Whitehouse, W. J., Nature, 217, 576 (1968).
2. Dyson, E. D., and Whitehouse, W. J., Proc. Symp. Ossium Europ. Assoc. Radiology (in the press).
3. Sikorski, J., Moss, J. S., Newman, P. H., and Buckley, T., J. Sci. Instrum., 1, 29 (1968).
4. Chayes, F., Petrographic Modal Analysis (Wiley, New York, 1956).
5. Hennig, A., Zeiss Werkz., 30, 78 (1958).