1. J�ger, F. W. and Oetken, L.: 1963, Publ. Astrophys. Potsdam 31, No. 103, H. 1.
2. Makita, M.: 1970, Ann. Tokyo Astron. Obs. XII, 139.
3. Serkowski, K.: 1960, Bull. Lowell Obs. 17, 216.
4. Shurcliff, W. A.: 1962, Polarized Light, Harvard Univ. Press, Cambridge.
5. Stepanov, V. E.: 1966, in M. Cimino (ed.), Proceeding of the Meeting on Solar Magnetic Fields, G. Barbera, Firence, p. 149.