1. Van Allen, J. A., Ludwig, G. H., and Ray, E. C., Jet Propulsion, 28, No. 9 (1958).
2. Vernon, S. N., and Chudakov, A. Ye, communication presented to the Tenth General Assembly of the International Astronomical Union, Moscow (1958).
3. Van Allen, J. A., Proc. U.S. Nat. Acad. Sci., 43, No. 1 (1957).
4. Winckler, J. R., Peterson, L., Arnoldy, R., and Hoffman, R., Phys. Rev., 110, 1221 (1558).
5. Kellogg, P. J., Nuovo Cimento (in the press).