1. Butt, E. P., Carruthers, R., Mitchell, J. T. D., Pease, R. S., Thonemann, P. C., Bird, M. A., Blears, J., and Hartill, E. R., Proc. Second Intern. Conf. Peaceful Uses of Atomic Energy, Geneva, 32, 42 (United Nations, Geneva, 1958).
2. Fawcett, B. C., Jones, B. B., and Wilson, R., Proc. Phys. Soc., 78, 1223 (1961).
3. Burton, W. M., and Wilson, R., Proc. Phys. Soc., 78, 1416 (1961).
4. Hobbs, G. D., McWhirter, R. W. P., Griffin, W. G., and Jones, T. J. L., Proc. Fifth Intern. Conf. loniz. Phen. in Gases, Munich, 1965 (North-Holland, 1961).
5. Jones, B. B., and Wilson, R., Nuclear Fusion, 1962 Supp., Part 3, 889.