1. Bray, R. J.: 1964, Z. Astrophys. 60, 207.
2. Chapman, G. A.: 1971, Paper presented at the meeting of the Astronomical Society of the Pacific, 22?25 June 1971, Wailua, Kauai, Hawaii.
3. d'Azambuja, L. and d'Azambuja, M.: 1938, Bull. Astron. 11, 349.
4. Giovanelli, R. G., Hall, D. N. B., and Harvey, J. W.: 1972, Solar Phys. 22, 53.
5. Harvey, J. and Hall, D.: 1971, in R. Howard (ed.), ?Solar Magnetic Fields?, IAU. Symp. 43, 279.