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Inventory no. 42143 - Epact entry

Epact number: 74519

Nocturnal and Sundial

Signed by Antonius Geminus
Dated 1589; Rome
Brass; 110 mm in diameter

Main text

This instrument tells the time by day or night anywhere in the world. The combination for this purpose of a nocturnal and an unusual type of altitude sundial is the same as that on the instrument made in Antwerp by Michiel Coignet at a similar period.

These Italian and Flemish instruments can be linked with practical mathematics in France, as the standard account of the dial was published by Oronce Fine of Paris.

Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 42,143

Detailed text

The nocturnal side has a zodiacal calendar on the base plate, with the names and symbols of the zodiacal constellations, each with a scale of 30 degrees, divided to 10, subdivided to 5 and to 1, numbered by 10; the month names in Latin, with scales of days, divided to 10, subdivided to 5 and to 1, numbering to 10 adjusted for each month; the first point of Aries is at 21 March. The first moving plate has an hour scale for the nocturnal, divided to single hours with Roman numerals, each marked by a point, and a 1 to 29 lunar scale for the lunar volvelle. There is a pointed engraved with a sun at the 12 o'clock / zero position for setting these scales on the zodiacal calendar. A second moveable plate has a diagram of planetary aspects, an aperture to reveal the lunar phase, and an index arm with an engraved moon and stars, for observing with the nocturnal and for reading off the moon's position in the zodiac.

The arm is signed: 'Ants Geminus f: Romæ. 1589'. There is a pierced, decorated handle with a suspension ring.

The reverse side has the 'organum Ptolemai' form of altitude sundial; Oronce Fine calls it 'horologium generale'. The base plate has a latitude scale 0 to 90 degrees to 0, divided to 10, subdivided to 5 and to 1, numbered by 10. This is for setting, by a short index point, a rotating disc with a central Rojas-type projection comprising straight right ascension lines (three for each sign) with zodiac symbols, crossed by curved hour lines numbered 1 to 11 'HORÆ ANTE MERIDIEM' and 11 to 1, 'HORÆ PEST MERIDIEM'. The projected scales are subdivided by dots, but not consistently. Pivoting at the centre is an alidade and rule with a scale between the vanes, 9 to 66, divided to 10, subdivided to 5 and to 1, numbered by 10. Rising from the alidade are two curved bands, meeting in the suspension point for the plumb-line (missing) on the circular limit of the projection (hour line 12) subtending a right angle with the alidade at the pivot.

The edge of the rotating plate is marked for the 8 Mediterranean winds: 'OSTRO', 'Gaybino', PON|Ebar|T|Ebar|', 'Maestro', 'TRAMONTANA', 'Greco', 'LEV|Abar|TE' and 'Sciyocco'. Each name is broken by a sun symbol, but the half-cardinal points, as well as having lower case letters, have the symbol placed close to the limiting circle, so that only half is present. On the edge of the base plate is a form of solar declination scale, where each degree is numbered, running from 1 to 23 in each quadrant, reaching 23|1/2| for the quadrant. The graduations are drawn parallel to the equator, or line joining the zero points, i.e. they do not radiate from the centre. This scale may be for laying out an equivalent projection to a larger radius.

Jim Bennett

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