1. Thomas, H. A., and Burgess, R. E., D.S.I.R. Radio Res. Spec. Rep., No. 15 (1947).
2. W.M.O., Bull. VII, 14 (1959).
3. C.C.I.R. Rep. No. 65, ITU, Geneva (1957).
4. C.C.I.R., Tenth Plenary Assembly, Resolution 51 (1961).
5. Hill, E. L., Proc. Inst. Radio Eng., 45, 775 (1957).