Volvelles Sebastian Münster (1489–1552)
Organum uranicum. Basle: Heinrich Petri, 1536; bound with Venerable Bede (673–735), Opuscula cumplura de temporum ratione. Cologne: Printed by Johannel Prael for Peter Quentel, 1537. PML 195039. Purchased as the gift of Rudy L. Ruggles, Jr., and on the Lathrop C. Harper Fund, 2008.

Two astronomical treatises are bound together in this volume, first a collection of tracts by the Venerable Bede on dating systems and calendar reform, second a mathematical account of planetary motions by Sebastian Münster. Readers could calculate the position of heavenly bodies by using Münster's elegantly designed and brilliantly colored volvelles, rotating dials and pointers calibrated like slide rules and attached by threads to the leaves, which contained the instructions. This copy was owned by two famous astronomers, Peter Crüger (1580–1639) and Johannes Hevelius (1611–1687), who built the most advanced observatory of his day and used it to make lunar maps of unprecedented detail and accuracy.