History of One Defeat: Reform of the Julian Calendar as Envisioned by Isaac Newton Ari Belenkiy  Mathematics Department, Bar-Ilan University, Israel Economics Department, College of Judea and Samaria at Ariel and Eduardo Vila Echagüe  IBM, Santiago, Chile Abstract Here we discuss a proposal for the reform of the Julian and Ecclesiastical calendars, found among Newton’s unpublished manuscripts, known among scholars as Yahuda MS 24. His calendar, if implemented, would have become for England a viable alternative to the Gregorian. We propose a reason for Newton’s failure to implement it. We also suggest tentative dating for several manuscripts of Yahuda MS 24. Introduction Circa 1700, England was one of many Protestant countries that did not join the calendar reform promulgated by Pope Gregory XIII in 1582. The resulting 10-day difference in dates caused problems in trade with the Continent. In 1700, the time disparity was expected to increase by a day due to the application of a Gregorian rule: that in years divisible by 100, but not by 400, a 29 th day should not be appended to the month of February. It is no surprise that Isaac Newton, then a Master of the Mint, c. 1699 foresaw the necessity for change and took it upon himself to propose a calendar that would be astronomically more sound than the Gregorian. He had every chance for success; astronomy had made great strides forward in the 118 years since implementation of the  belenka@mail.biu.ac.il  edovila@vtr.net