1. Billings, D. E.: 1966, A Guide to the Solar Corona, Academic Press, New-York.
2. Bohlin, J. D.: 1970a, Solar Phys. 12, 240.
3. Bohlin, J. D.: 1970b, Solar Phys. 13, 153.
4. Boischot, A.: 1958, Ann. Astrophys. 21, 273.
5. Bougeret, J. L., Caroubalos, C., Mercier, C., and Pick, M.: 1970, Astron. Astrophys. 6, 406.