FOOTNOTES:
[412] Adams and Kohlschütter, Mt. W. Contr. 89, 1914.
[413] B. A. N. 19, 1922.
[414] Milne, Phil. Mag., 47, 209, 1924.
[415] Pannekoek, B. A. N. 19, 1922.
[416] Pop. Ast., 31, 88, 1923.
[417] Pop. Ast., in press.
[418] B. A. N. 19, 1922.
[419] In Pannekoek’s notation, a is surface brightness,
