 Celestial Spheres: Dynamics of the celestial spheres, Plato, Eudoxus of Cnidus, Aristotle, Ptolemy, Nicolaus Copernicus, Moon, Mercury (planet), Venus, ... Saturn, Axial precession (astronomy)
 Eudoxus of Cnidus: An entry from Gale's <i>Science and Its Times</i> by Judson Knight, 2001
 Proportionality Mathematics: Proportionality Mathematics, Mathematics, Quantity, Mathematical Constant, Multiple, Ratio, Proportionality, Correlation and Dependence, Eudoxus of Cnidus
 Callipus: An entry from Gale's <i>Science and Its Times</i> by Stephen D. Norton, 2001
 The Republic (Optimized for Kindle) by Plato, 20080312
 Two Studies in the Early Academy by R. M. Dancy, 19910806
