Inventory no. 40829 - Epact entry
Epact number: 82905
Astrolabe
Unsigned
Later 15th century ?; Italian
Brass; 59 mm in diameter
Main text
This is a very unusual astrolabe, and not only because it is very small. The limit of the projection is the equator, whereas it is usual for it to extend to the Tropic of Capricorn. Thus the ecliptic is only an arc that has to serve, by symmetry, for the whole year, instead of being represented as a full circle.
The engraved plate beneath the rete serves for a single latitude of about 38°.
This is one of the most modest astrolabes yet one of the most significant in the Oxford collection.
Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 40,829
Detailed text
There is no raised limb, the 'mater' being simply a flat plate with a degree scale 90 to 0 to 90 to 0 to 90, divided to 10, subdivided to 2, numbered by 10. Three-lobe throne (no shackle or ring). The central area of the plate is engraved with almucantars on both sides of the horizon, and with unequal hour lines on the lower part of the plate. Some crudely engraved lines have been added later.
The rete has a short index and four star pointers with trefoil of fleur-de-lis heads. A broad arc spanning one diameter of the rete has the abbreviated names of the zodiacal signs and an unnumbered scale. The rete is held in place by a rivet and there are do separate plates.
The back has a degree scale similar to the front, and two quadrants of the remaining space are occupied by an unequal hour diagram and a double shadow square with scales 0 to 12 to 0 to 12 to 0, divided to 3, subdivided to 1, numbered by 3. Alidade with pinhole sights.
See R. T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932), vol. 2, pp. 319-20.
Jim Bennett