1. Adams, W. S.: 1911, Rotation Period of the Sun by Spectroscopic Methods, Carnegie Institution of Washington, Washington, D.C.
2. Bhatnagar, A.: 1971, this issue, page 40.
3. Bumba, V., Howard, R., and Smith, S. F.: 1964, Annual Report of the Director, Mount Wilson and Palomar Observatories, p. 6, Carnegie Institution of Washington, Washington, D.C.
4. Gopasyuk, S. I.: 1968, Izv. Krymsk. Astrofiz. Observ. 38, 65.
5. Hart, A. B.: 1954, Monthly Roy. Astron. Soc. 114, 17.