Abstract Summary
Before 1332 in Paris, John of Genoa elaborated an original table of Lunar and Solar hourly velocities combined with a table of the radii of the Sun, the Moon and the shadow of the earth, including a column for the variation of the shadow of the earth – variatio umbre – used as a function of the motion in anomaly. This table was probably composed for renewing two tables embedded in John of Lingères’s set of tables (1321). It is the starting point of a whole project focused on eclipse theories and calculations. Indeed, John of Genoa wrote a canon associated with his table, and then eclipse canons entitled Canones eclipsium (1332). The climax of his work was a thorough computation of the solar eclipse of the 3rd March 1337. It is the most detailed calculation of the late Middle Ages. Three manuscripts contained this work, which is an important witness for the history of calculation practices. In this paper, I will compare the calculation provided for the 3rd March 1337 with the methods for establishing a calculation of eclipse that John of Genoa described in his Canones eclipsium. With this analysis, I will consider the link between theoretical knowledge and a real practice of computation.
