1. F. Verniani:Nuovo Cimento,26, 209 (1962).
2. E. J. öpik: Harvard Reprint SeriesI, no. 100 (1933).
3. A. F. Cook:Astron. Journ.,60, 156 (1955).
4. R. E. McCrosky andR. K. Soberman:Smith. Contr. Astrophys.,7, 199 (1963).
5. F. Verniani:Smith. Contr. Astrophys. (1964), in press; alsoSmith. Astrophys. Obs., Special Report no. 145 (1964).