1. Helliwell, R. A., Stanford University Radio Propagation Report, A0110184 (1956).
2. Gallet, R. M., Proc. Inst. Roy. Eng., 47, 211 (1959).
3. Ellis, G. R. A., “Planetary and Space Science” (in the press).
4. Kolomenski, A. A., Dokl. Akad. Nauk, S.S.S.R., 106, (6), 982 (1956).
5. Ellis, G. R. A., Jour. Atmos. Terr. Phys., 10, 302, (1957).