1. Gold, T., Nature, 218, 731 (1968); ibid., 221, 25 (1969).
2. Armstrong, T. P., and Krimigis, S. M., J. Geophys. Res., 73, 143 (1968).
3. Waddington, C. J., Scuola Internationale Enrico Fermi, Varenna, 135 (1963).
4. Jelley, J. V., Prog. Elementary Particles and Cosmic Rays, 9, 41 (John, Wiley, New York, 1967).