~CALI QUSHJI AND REGIOMONTANUS: ECCENTRIC TRANSFORMATIONS AND COPERNICAN REVOLUTIONS

摘要

In 1973, Noel Swerdlow presented a new and significant reconstruction of how Copernicus arrived at the heliocentric theory. This reconstruction was based upon several bits of newly-interpreted information, most importantly a set of notes in Copernicus's hand contained in an Uppsala University manuscript. These notes provided compelling evidence that Copernicus had transformed Ptolemy's epicyclic models of the planets into eccentric models as a first step in developing a Sun-centred astronomy. But this transformation depended upon a general proposition that one could indeed convert all the epicycle models into eccentric ones. Curiously, Ptolemy denied this, claiming in Book Ⅻ of the Almagest that this was possible only for the outer planets (Mars, Jupiter, and Saturn) but not the inner ones (Mercury and Venus). From a modern perspective this seems odd, and it is not entirely clear why Ptolemy could not see that the epicycles of the inner planets, with a proper consideration of speeds, could also be converted into eccentrics. Indeed, Ptolemy's modern translator Gerald Toomer says: "I do not understand why Ptolemy does not recognize this."