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Inventory no. 41468 - Epact entry

Epact number: 99166


Mid 16th century; Italian
Brass; 152 mm in diameter

Main text

This astrolabe, with its elegantly designed rete and precise engraving has been lettered throughout in the Lombardic style. This helps to locate its origins, but the accompanying plates cover a wide range of latitudes from 41 to 53 degrees. One interesting feature of the rete is the way the central meridian bar is drawn aside into a semicircle to make way for the projected position of the star Vega.

The astrolabe is very similar to another in the Museum of the History of Science, Oxford: Epact 12610.

Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 41,468

Detailed text

Limb attached to base plate to form mater, the shaped throne with circle decoration and suspension shackle. Degree scale on limb 0 to 360, divided to 5, subdivided to 1, 0 to 245 numbered by 5, 255 to 360 by 15.

Rete for 27 stars, pattern modified from the 'Y' type, with the tropic of capricorn terminated by a dragon's hear and tail. The ecliptic has abbreviated names for the zodiacal signs, each with a 30-degree scale on the bevelled edge, divided to 5, subdivided to 1, not numbered. Diametric bar counterchanged twice. There are two characters on the verso of the rete.

There are 4 plates, engraved for latitudes 41 and 48, 45 (verso blank), 50 and 51, 52 and 53 degrees. Each has azimuths every 15 degrees and almucantars every three degrees, unnumbered. Each has meridian and east-west lines, lines for the tropic of cancer and the equator, and lines of unequal hours, numbered on only 5 of the projections.

On the back is a degree scale 90 (at the throne) to 0 to 90 to 0 to 90, divided to 5, subdivided to 1, numbered by 5. The same divisions serve for a zodiacal scale, marked on the inside with the signs, each 0 to 30, divided to 5, subdivided to 1, numbered by 5. Within this scale is an eccentric date scale, with abbreviated month names, each with a scale of days, divined to 5, subdivided to 1, numbered by 10 adjusted to each month. The vernal equinox is at 12|1/2| March. In the centre is a double shadow square, each quadrant with scales 0 to 12 to 0, divided to 2, subdivided to 1, numbered by 2.

Counterchanged alidade with pinhole sights, pin, counterchanged rule and wedge all modern.

Jim Bennett

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