1. For example, Nature, 157, 469 (1946).
2. Hanson, D., Amer. Inst. Mining and Met. Eng. Tech. Pub. No. 1071.
3. Tapsell, H. J., and Remfry, J., D.S.I.R. Engineering Research Special Report No. 15 (1929).
4. For example, Bristol Conference Report, Physical Society (in the press).
5. Andrade, E. N. DA C., and Chalmers, B., Proc. Roy. Soc., A, 138, 348 (1932).