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Inventory no. 48140 - Epact entry

Epact number: 65261

Nocturnal and Sundial

Dated 1578; Rome
Gilt copper; 83 mm in diameter

Main text

The use in this nocturnal and sundial of gilt copper is unusual for the period, except for the work of Erasmus Habermel.

Another unexpected feature is the reversible plate on the sundial face, which has been given a raised rim to accommodate it. The angle measuring scales on the reverse of this plate could have been uses with the sights of the 'trigonus' from the sundial, and the instrument can be taken apart and re-assembled for this purpose. Ingenuity and diversity were prized features of mathematical instruments.

Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 48,140

Detailed text

On the sundial face, the base plate has a raised edge with a degree scale for latitude adjustment, 90 to 0 to 90 to 0 to 90, divided to 10, subdivided to 5 and to 1, numbered by 10. Inside this edge fits a reversible circular plate, one side of which has the Rojas projection for the 'organum Ptolemai' form of altitude sundial, which is complete with its pierced and decorated 'trigonis' with sights and plumb-rule. The central line of the projection is marked 'Meridianus mobilis', and at either end 'Polus Arcticus' and 'Polus Antarcticus'. The sodiacal scales on either side of the projection are marked 'Austratia Signa' and 'Borealia Signa'. The hour lines are numbered [0] to 12, 'HORÆ ANTE MERIDIEM', and 12 to [0], , 'HORÆ POLS MERIDIEM'.

The reverse of this disc has a double shadow square divided 0 to 12 to 0 to 12 to 0, subdivided to 3, to 1 and to 0.5, numbered by 3, marked 'Umb: Recta', 'Umbra Versa', 'Vm: Recta'. The upper half of the disc has a degree scale 0 to 90 to 0, divided to 10, subdivided to 5 and to 1, numbered by 10, marked 'Ad Solis & stellaru altitudines dimetiendas. ROMÆ. ao. 1578'. The remainder of the disc has foliate decoration.

The nocturnal face has a zodiacal calendar, with the constellation names and symbols, each with a scale 0 to 30 divided to 10, subdivided to 1, numbered by 10; the months names and divided to 10 and to 1 day, numbered by 10 as appropriate to each month. The hour disc is divided to 1 hour, subdivided to |1/4|, the hours 4 to 12 to 9 numbered by Roman numerals; each hour indicated by a point, the midnight point extended to the zodiac scale. Index arm; the are and central area of the hour disc with scrollwork and foliate decoration.

The base plate has a shaped and pierced handle and suspension ring. The whole assembly is held together by a threaded tube attached to the trigonus and a wing nut.

Jim Bennett

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