1. C. W. Allen, Astrophysical Quantities, 3rd ed. (Athlone, London, 1973; Mir,Moscow, 1977).
2. W. De la Rue, B. Stewart, and B. Loewy, Phil. Trans. 160, 389 (1870).
3. M. N. Gnevyshev, Tsirk. Gl. Astron. Obs. 24, 37 (1938).
4. M. N. Gnevyshev, Yu. A. Nagovitsin, and E. Yu. Nagovitsin, Soln. Dannye 2, 72 (1985).
5. M. N. Gnevyshev, Yu. A. Nagovitsin, and E. Yu. Nagovitsin, Soln. Dannye 3, 57 (1986).