This astrolabe was made by Thomas Gemini. On the front are the rete and the alidade. The mater carries the mariner's quadrant and the names of the winds in English, Greek, and Latin. The date is incomplete, but the three engraved digits (155) narrow the time frame for the instrument's construction to 1550-1559. On the back is a universal planisphere with another alidade fitted with a mobile perpendicular arm and a jointed index. The tympanums are missing. Provenance: Robert Dudley bequest to the Medici collections.