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2. Whipple, F. L., J. Geophys. Res., 64, 1655 (1959).
3. Keipenheuer, K. O., “The Sun”, ed. G. P. Kuiper, 1, 449 (University of Chicago Press, 1953).
4. Shklovskii, I. S., Soviet Astronomy, 2, 516 (1958).
5. Quoted by Aller, L. H., in “Handbuch der Physik, Astrophysics II: Stellar Structure”, 52, 344 (Springer Verlag, Berlin, 1958).