Alan C. Bowen is Director of the Institute for Research in Classical Philosophy and Science, Princeton, and editor of several books including "Science and Philosophy in Classical Greece "(1991) and "Astronomy and Astrology from the Babylonians to Kepler "(2003). Robert B. Todd is Professor of Classics at the University of British Columbia; his publications include "Themistius on Aristotle on the Soul "(1996) and "Cleomedis Caelestia "(1990).