1. d'Azambuja, L. and d'Azambuja, M.: 1948, Ann. Obs. Paris-Meudon bd6, 1.
2. Billings, D. E.: 1966, A Guide to the Solar Corona, Academic Press, New York.
3. Chapman, S. and Ferraro, V. C. A.: 1931, Terrest. Magn. 36, 77.
4. DeMastus, H. L., Wagner, W. J., and Robinson, R. D.: 1973, Solar Phys. 31, 449.
5. Eddy, J. A.: 1974, Astron. Astrophys. 34, 235.