1. McCracken, K. G., and Rao, U. R., Plan. Space Sci., 14, 649 (1966).
2. Kolomeets, E. V., Sergeeva, G. A., Nemolochnov, A. N., Chumbalova, R. A., and Zusmanovich, A. G., Proc. Ninth International Conference on Cosmic Rays, London, 1965, 1, 224 (The Institute of Physics and the Physical Society, London, 1966).
3. Parker, E. N., Plan. Space Sci., 12, 735 (1964).
4. Axford, W. I., Plan. Space Sci., 13, 115 (1965).