1. NATURE, 133, 759, May 19, 1934.
2. NATURE, 133, 948, June 23, 1934.
3. NATURE, 120, 602, Oct. 22, 1927. This table has been checked and republished by Mittelstaedt (Phys. Z., 30, 165; 1929).
4. Annual Report of Director, Mount Wilson Observatory, 1930–31, p. 218; 1931–32, p, 170; 1932–33, p. 164. See also NATURE, 133, 169, Feb. 3, 1934.
5. The first three columns of this table differ from the data already published by de Bray3 and by Mittelstaedt3 only in the use of 10 in place of 20 km./sec., for the probable error of Mittelstaedt's own work (Ann. Phys., 2, 285; 1929). He states explicitly on p. 310 of his paper that 20 km./sec. is his limit of error.