Epact Scientific Instruments of Medieval and Renaissance Europe

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Navicula Dial
Unsigned
15th century ?; origin unknown
Brass; 82 mm in width

The front has a rectilinear altitude sundial, with one set of hour-lines marked twice, [0] to 12 and 12 to [0], with intermediate lines for half-hours. A zodiac arc with the names of the constellations is beneath the hour-lines and serves to adjust the angle of the mast for the date. The mast has a sliding suspension point for a plumb-line (missing) adjustable against a scale of latitudes 20 to 65, divided by 5, the 35 to 65 section subdivided to 1, numbered by 5. There is an unmarked and unnumbered declination scale to the side of the hour-lines, for adjusting the position of the bead that would have been on the plumb-line.

The back has a shadow-square with scales on two sides 0 to 12 to 0, divided to 3, subdivided to 1, numbered by 1. Also on the back is a unequal hour quadrant for converting time in equal hours found by the sundial into unequal or planetary hours.

The castellated ship decks each incorporate double pinhole sights. A suspension hook it attached to the top of the mast.

Jim Bennett

Museum of the History of Science, Oxford
Inventory number 54358

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