1. Adams, W. M. and Tang, F.: 1977, Solar Phys. 55, 499.
2. Belvedere, G., Godoli, E., Motta, S., Paterno, L., and Zappala, R. A.: 1977, Astrophys. J. 214, 91.
3. D'Azambuja, L. and D'Azambuja, M.: 1948, Ann. Obs. Paris 6, 1.
4. Gigolashvili, M. Sh. and Khutsishvili, E. V.: 1990, in T. D. Guyenne and J. J. Hunt (eds.), Plasma Astrophysics, A Joint Varenna-Abastumani-ESA-Nagoya-Potsdam Workshop 4?12 June, 1990, Telavi, Georgia, U.S.S.R., p. 35.
5. Glackin, D. L.: 1974, Solar Phys. 36, 51.