1. Methods in astrodynamics and celestial mechanics,1966
2. Libration Clouds in the Earth-Moon System;Kordylewski;Intern. Astron. Union Circular 1760,1961
3. The Libration Clouds: A Status Report;Simpson;Rev. Popular Astron., 551: 10,1968
4. See also News Notes. Sky and Telescope, 31, 265.