The Hohendorff Almagest: A rediscovered case study in early modern ptolemaic astronomy

The Austrian National Library houses a heavily annotated copy of the 1515 printed edition of the Almagest (shelfmark: 80.O.11 Alt Rara), once part of Georg Wilhelm von Hohendorff's (1670-1719) library. The marginalia, including illustrations and diagrams, can be traced to sixteenth-century editions, translations, and commentaries on the Almagest. This article presents the first study of these annotations, highlighting two key aspects: (1) a comparative approach to the Latin editions, constructing a kind of synoptic Almagest, and (2) the reformulation of Ptolemy's procedure for calculating chords into verbally expressed arithmetical rules. Although the annotator remains unidentified, evidence suggests a late sixteenth-century origin. If so, these notes provide a rare glimpse into the early post-Copernican assimilation of the Almagest, offering insights into evolving mathematical practices in early modern astronomy. An Appendix details the main marginalia of the first book and their sources.