  Newton's initial education at Cambridge was classical, focusing (primarily through secondary sources) on Aristotlean rhetoric, logic, ethics, and physics. By 1664, Newton had begun reaching beyond the standard curriculum, reading, for example, the 1656 Latin edition of Descartes's Opera philosophica, which included the Meditations, Discourse on Method, the Dioptrics, and the Principles of Philosophy. By early 1664 he had also begun teaching himself mathematics, taking notes on works by Oughtred, Viète, Wallis, and Descartes — the latter via van Schooten's Latin translation, with commentary, of the Géométrie. Newton spent all but three months from the summer of 1665 until the spring of 1667 at home in Woolsthorpe when the university was closed because of the plague.  This period was his so-called annus mirabilis. During it, he made his initial experimental discoveries in optics and developed (independently of Huygens's treatment of 1659) the mathematical theory of uniform circular motion, in the process noting the relationship between the inverse-square and Kepler's rule relating the square of the planetary periods to the cube of their mean distance from the Sun. Even more impressively, by late 1666 he had become de facto the leading mathematician in the world, having extended his earlier examination of cutting-edge problems into the discovery of the calculus, as presented in his tract of October 1666. He returned to Trinity as a Fellow in 1667, where he continued his research in optics, constructing his first reflecting telescope in 1669, and wrote a more extended tract on the calculus “De Analysi per Æquations Numero Terminorum Infinitas” incorporating new work on infinite series. On the basis of this tract Isaac Barrow recommended Newton as his replacement as Lucasian Professor of Mathematics, a position he assumed in October 1669, four and a half years after he had received his Bachelor of Arts.