1. Ginsburg, V. L., and Zeleznyakov, V. V., Sov. Astro., 3, 235 (1959).
2. Ellis, G. R. A., and McCulloch, P. M., Austral. J. Phys., 16, 380 (1963).
3. Ellis, G. R. A., Rad. Sci., 69D, 1513 (1965).
4. Fung, P. C. W., and Yip, W. K., Austral. J. Phys. (in the press).
5. Fung, P. C. W., and Yip, W. K., Plan. Space Sci. (in the press).