[63] Ap. J., 59, 197, 1924.

[64] St. John and Babcock, Ap. J., 60, 32, 1924.

[65] M. N. R. A. S., 82, 394, 1922.

[66] King, Ap. J., 41, 110, 1915.

[67] King, Ap. J., 48, 32, 1918.

[68] Saunders, quoted by Russell and Stewart, Ap. J., 59, 197, 1924.

[69] Payne, H. C. 256, 1924.

[70] A. Fowler, M. N. R. A. S., 80, 692, 1920.

[71] Stewart, Ap. J., in press.

[72] Ap. J., 59, 197, 1924.