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[141] Ap. J., 29, 100, 1909.

[142] Ap. J., 60, 1, 1924.

[143] Atlas, p. 85, 1892.

[144] Wright, Nature, 109, 810, 1920.

[145] Chapter III, [p. 43].

[146] Pub. A. S. P., 32, 155, 1920.

[147] Mitchell, Ap. J., 38, 431, 1913.

[148] Phil. Trans., 197A, 381, 1901.

[149] C. R., 114, 578, 1892.