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Sundials have survived in a wonderful diversity of species. In this intriguing book, Catherine Eagleton examines the navicula de Venetiis, a late-medieval variety once thought to be exceedingly rare. The 'little ship from Venice' is an ingenious portable, palm-sized, ship-shaped sundial designed for a wide range of latitudes ('universal'). Its 'hull' circumscribes about two thirds of a circle (roughly five centimetres in diameter). Fore and aft are longitudinal peep sights (for the sun). The 'mast', which pivots about the centre of the circle and extends about ten centimetres above the 'deck', bears a latitude scale (roughly 15-65°) with a sliding marker equipped with a thread that bears a sliding pearl. The lower portion of the mast, mostly hidden between the parallel plates that form the hull, sticks out below it to mark the Sun's place on a zodiac engraved on the keel. The hull exhibits parallel vertical hour lines and a calendar scale (port), and a shadow square and an unequal hours diagram (starboard). To determine the hour, one first sets the sliding mast marker to the observer's latitude, and tilts the mast to mark the Sun's position in the zodiac. One then slides the pearl on the taut thread to match the observation date on the calendar. After aligning the peep sights with the Sun, the vertically...