1. Van de Hulst, H. C.: 1953, in The Sun (ed. by G. Kuiper).
2. Allen, C. W.: 1954, Rep. Prog. Phys.
17, 135.
3. Evans, J. W.: 1961, The Solar Corona (IAU Symposium, 1961).
4. Seaton, M. J.: 1964, Plan. Space Sci.
12, 55.
5. Osterbrock, A.: 1961, Astrophys. J.
134, 347.