Gemma Frisius: A Convinced Copernican in 1555

Abstract

Gemma Frisius (1508–1555), who worked at the university of Louvain, heard about the Copernican system already around 1530 and afterwards was a careful reader of the Narratio prima and the De Revolutionibus. The article argues that his posthumous preface to the Ephemerides (1556) by his pupil Stadius expresses his ultimate opinion on the system of the world. Moreover, it is also the only text where he tackles the epistemological problems of the question. A careful analysis of this preface shows that at the end of his life, on the ground of observations as well as philosophical demands, he admitted at least the first two movements ascribed to the earth by Copernicus.