This astrolabe, made by Johann Richter, is missing its rete, an alidade, a rule, and several tympanums (there is only one for latitudes 53° and 57°, corresponding to Great Britain). On the back, at the center, are marked the main religious feasts, the zodiacal calendar, and the leading saints. The shadow square frames a finely etched rural scene. Provenance: Medici collections.