1. Paetzold, H. K., and Zschörner, H., Space Res. II, 958 (North-Holland Publishing Co., Amsterdam, 1961).
2. Harris, I., and Priester, W., J. Geophys. Res., 67, 4585 (1962).
3. Jacchia, L. G., Space Res. II, 747 (North-Holland Publishing Co., Amsterdam, 1961).
4. Jacchia, L. G., Space Res. III, 3 (North-Holland Publishing Co., Amsterdam, 1963).
5. Jacchia, L. G., Smithsonian Astrophys. Obs. Spec. Rep., No. 150 (1964).