1. Rochester and Butler, Nature, 160, 855 (1947).
2. See discussion, Bagnères Conf. Report (1953).
3. Barker, Proc. Roy. Soc., A, 221, 328 (1954).
4. Thompson, Buskirk, Cohn, Karzmark and Rediker, Bagnères Conf. Report, p. 30 (1953).
5. See discussion, Bagnères Conf. Report (1953).