1. Rothwell, P., and Quenby, J., Proc. Varenna Conf. (June 1957).
2. Storey, J. R., Fenton, A. G., and McCracken, K. G., Nature, 181, 1155 (1958).
3. Katz, L., Meyer, P., and Simpson, J. A., Proc. Varenna Conf. (June 1957).
4. Kodama, M., and Miyazaki, Y., Rep. Ionosph. Res., Japan, 11, 99 (1957).
5. Alexander, N. S., and Onwumechilli, C. A., Nature, 180, 191 (1957).