1. Akimov, A. A.: 1965, V?stnik Kharkov Univ. No. 4, 43?61.
2. Barabashev, N. P. and Ezersky, V. I.: 1965, V?stnik Kharkov Univ. No. 4.
3. Fedoretz, V. A.: 1952, Uch. Zap. Kharkovsk. Gos. Univ.42, 49.
4. Gehrels, T., Coffeen, T., and Owings, D.: 1964,Astron. J. 69, 826?852.
5. Hapke, B. W.: 1963,J. Geophys. Res. 68, 4571?4586.