A Lathe and the Material Sphaera: Astronomical Technique at the Origins of the Cosmographical Handbook

Abstract

Even though cosmographers loved to drape their discipline in the ancient dignity of Ptolemy, actual manuals of cosmography often depended on Johannes de Sacrobosco's medieval introduction to spherical astronomy. In fact, certain strains of cosmography shared organization, principles, and even visual apparatus with Sacrobosco's Sphaera and its growing commentary tradition, to the extent that these cosmographies can be seen as themselves commenting on the Sphaera. This paper traces the origins of certain Renaissance cosmographical handbooks to the commentary on the Sphaera by Lefèvre d'Étaples and his colleagues at Paris around 1495. By focusing on the visual elements of this commentary, its instructions for calculating techniques, and the emergence of the "lathe" model of the "material sphere," this chapter argues that one of the mixed mathematical genres now seen as most characteristic of the Renaissance-cosmography-in fact was based on a medieval textbook. 1 I wish to thank Matteo Valleriani for helpful comments, the other contributors to this volume for stimulating conversation, and an anonymous reviewer for a useful suggestion.