His progress to Jesus College, Cambridge, recommended by the Master of Derby School, was delayed by some years of chronic ill health. During those years, Flamsteed gave his father some help in his business, and from his father learnt arithmetic and the use of fractions, developing a keen interest in mathematics and astronomy. In July 1662, he was fascinated by the thirteenth-century work of Johannes de Sacrobosco, "De sphaera mundi", and on 12 September 1662 observed his first partial solar eclipse. Early in 1663, he read Thomas Fale's "Horologiographia: The Art of Dialling", which set off an interest in sundials. In the summer of 1663, he read Wingate's "Canon", William Oughtred's "Canon", and Thomas Stirrup's "Art of Dialling". At about the same time, he acquired Thomas Street's "Astronomia Carolina, or A New Theory of the Celestial Motions" ("Caroline Tables"). He associated himself with local gentlemen interested in astronomy, including William Litchford, whose library included the work of the astrologer John Gadbury which included astronomical tables by Jeremiah Horrocks, who had died in 1641 at the age of twenty-two. Flamsteed was greatly impressed (as Isaac Newton had been) by the work of Horrocks.