1. Groves, G. V., Proc. Roy. Soc., A, 263, 212 (1961).
2. Jacchia, L. G., Space Research II, 747 (North-Holland Publ. Co., Amsterdam, 1961).
3. Jacchia, L. G., and Slowey, J., Smithsonian Astrophys. Obs. Spec. Rep. No. 100 (1962).
4. Kallmann-Bijl, H. K., J. Atmos. Terr. Phys., 24, 831 (1962).
5. King-Hele, D. G., and Walker, D. M. C., Space Research II, 918 (Amsterdam, 1961).