1. Adams, W. S.: 1934, Annual Kept. Mt. Wilson Obs., C.I.W. Yearbook, p. 138.
2. Adams, W. S.: 1949, Annual Rept. Mt. Wilson Obs., C.I.W. Yearbook, p. 12.
3. Alfven, H.: 1967, Bjerkeland Symposium, Sandefjord, Norge, Stockholm.
4. Babcock, H. D.: 1948, Publ. Astron. Soc. Pacific
60, 244.
5. Babcock, H. D.: 1969, Astrophys. J.
130, 364.