1. Abbot, Annals of the Astrophysical Observatory of the Smithsonian Institution 2: 174 (1908).
2. Pickering, W. H., Century Magazine 64:91 (1902).
3. A Comparison of the Features of the Earth and Moon;Smithsonian Contributions to Knowledge,1903
4. ASTROPHYSICAL J 8: 199 (1898).
5. Very F. W. Philosophical Magazine 6 16 : 478 (1908).