Abstract

The Istituto e Museo di Storia della Scienza, Florence, Italy, possesses an astrolabe with five latitude plates that is now attributed to the Duisburg workshop of Gerard Mercator. Although it is known that Mercator made instruments, this is the first surviving example to be identified. Another latitude plate is shown to come from the workshop of the Florentine, Giovan Battista Giusti. A seventh plate, possibly engraved by Rumold Mercator, provides the only known Mercatorian polar stereographic projection. The role of Egnazio Danti, cosmographer to the Grand Duke of Tuscany, in the acquisition of the astrolabe in about 1570 is considered