1. Hey, J. S., Nature, 157, 47 (1946).
2. Hagen, John P. NRL Report No. 3504 (July 1949).
3. Hagen, John P., Astrophys. J., 113, 547 (1951).
4. Wild, J. P., and McCready, L. L., Aust. J. Sci. Research, A, 3, 387 (1950).
5. Wild, J. P., Aust. J. Sci. Research, A, 3, 399 (1950).