The History of Science in the Post-Classical Period (Astronomy, Optics, Life Sciences, and Mathematics)

Rationalist Sciences II

Medieval Muslim intellectuals found themselves presented with the daunting task of reconciling two of the leading scientific figures from the Hellenistic world: Aristotle in physics and Ptolemy in astronomy. Aristotle had argued that all celestial bodies undergo uniform circular motion around the earth as center; however, in order to bring the then best astronomical model in line with empirical observation, Ptolemy had a number of celestial bodies move uniformly around a purely theoretical point other than the center, called the equant. Something that became increasingly clear by the end of the classical period in the Islamic world and then began to take on serious urgency in the post-classical period was that, in light of the best (Aristotelian) physics of the time, Ptolemy’s equant represented a “physical impossibility”. George Saliba, Professor of Arabic and Islamic Science, Columbia University, has shown us that during the post-classical period, Muslim astronomers and natural philosophers developed extremely sophisticated geometrical models—such as the Tusi Couple and the ‘Urdi Lemma—with an eye to ridding Ptolemy’s system of the equant and so bring it into line with Aristotelian physics, while retaining the same predictive capacity as Ptolemy’s system. It was in fact on the edifice of these major mathematical discoveries—which in fact appear in Copernicus’ monumental De Revolutionibus orbium coelestium—that the Copernican Revolution was built. Similar examples can be found in the life sciences, and in particular, the attempts of medieval Arabic-speaking physicians and philosophers to reconcile Galen and Aristotle concerning the nature of the mind.  Seminar Two will take up topics and disciplines in the history of science as its subject of inquiry.