Nicholas Jardine offers here an edition and the first translation into English of Johannes Kepler's A Defence of Tycho against Ursus. He accompanies this with essays on the provenance of the treatise - the circumstances which provoked Kepler to write it, an analysis of its strategy, style and historical sources and of the contents of Ursus' Treatise on Astronomical Hypotheses to which Kepler was replying. Dr Jardine also provides three extended interpretive essays on the intrinsic interest and historical significance of (...) the work. (shrink)

: We question the claim, common since Duhem, that sixteenth century astronomy, and especially the Wittenberg interpretation of Copernicus, was instrumentalistic rather than realistic. We identify a previously unrecognized Wittenberg astronomer, Edo Hildericus (Hilderich von Varel), who presents a detailed exposition of Copernicus's cosmology that is incompatible with instrumentalism. Quotations from other sixteenth century astronomers show that knowledge of the real configuration of the heavens was unattainable practically, rather than in principle. Astronomy was limited to quia demonstrations, although demonstration propter (...) quid remained the ideal. We suggest that Osiander's notorious preface to Copernicus expresses these sixteenth century commonplaces rather than twentieth century instrumentalism, and that neither `realism', nor `instrumentalism', in their modern meanings, apply to sixteenth century astronomy. (shrink)

Levi ben Gerson (1288–1344) was a medieval astronomer who responded in an unusual way to the Ptolemaic tradition. He significantly modified Ptolemy’s lunar and planetary theories, in part by appealing to physical reasoning. Moreover, he depended on his own observations, with instruments he invented, rather than on observations he found in literary sources. As a result of his close attention to the variation in apparent planetary sizes, a subject entirely absent from the Almagest, he discovered a new phenomenon of Mars (...) and noticed a serious flaw in Ptolemy’s treatment of the Moon. (shrink)

In 364 the German Schoolman, Henry Hembuche of Langenstein, or as he is more frequently called, Henry of Hesse, wrote an extremely odd treatise entitledOn the Reprobation of Eccentrics and Epicycles (De reprobatione ecentricorum et epiciclorum) in which he attempted to refute Ptolemaic astronomy. We can be confident of the date, 1364, since Henry himself tells us that he is writing in that year. At that time Langenstein had been an M.A. at Paris for about a year, and was teaching (...) in the arts faculty while pursuing the studies which were ultimately to bring him a doctorate in theology. (shrink)