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Inventory no. 45365 - Epact entry

Epact number: 21983

Astrolabe

Unsigned
Late 16th century; Flemish
Brass; 281 mm in diameter

Main text

Although unsigned, this astrolabe has many of the characteristics of instruments produced in the workshop begun in Louvain by Gemma Frisius and directed by Gualterus Arsenius. These include the pattern of tracery used in the rete and the inclusion of a 'quadratum nauticum' inside the mater. It may be by a slightly later maker from the same region, perhaps associated with the Louvain workshop at some time in his career, or perhaps simply copying the Arsenius style.



Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 45,365



Detailed text

The mater has the limb riveted to the back plate, shaped and pierced throne, shackle and suspension ring. The throne is held by 2 securing screws and a locating pin. The limb has an outer scale of hours marked with Roman numerals, 0 to 12 twice, divided to 1 hour, subdivided to 30 and to 15 minutes, numbered by 1 hour. Inside the mater is a 'QVADRATVM NAVTICVM', comprising a square with latitude and longitude scales, one on each half side, 0 to 90 degrees, divided to 10, subdivided to 2, numbered by 10, marked 'Longitudo Orientalis', 'Latitudo Borealis', &c. Latitude and longitude lines cross the square at 30-degree intervals. The cardinal points are marked 'SEPTENTRIO', 'ORIENS', 'MERIDIES' and 'OCCIDENS'. A circle inscribed in the square has names and directions of 32 winds: 'APARCTIAS', 'HYPERBOREUS', 'Boreas', 'Mesoboreas', 'Arctapeliotes', etc.

Three plates for latitudes 42° and 43°, 44° and 45°, and 46 and 48, with azimuths for every 3 degrees, numbered by 15, and almucantars for every degree, numbered by 10. Meridian and east-west line ('Horizon rectus'), circles for the tropics ('Tropicus Cancri', 'Tropicus Capricorni') and equator ('Æquinoctialis'), crepuscular line ('LINEA AVRORÆ'). The horizon is marked 'Horizon obliquus'. Beneath the horizon are lines of unequal hours, with Roman numerals; lines for the houses of heaven are numbered 1 to 12.

Rete of the Arsenius type for 48 named stars, the ecliptic circle with the names and symbols of the signs, each with a scale of 30 degrees, divided to 10, subdivided to 5 and to 1, numbered by 10.

The back has a an outer degree scale 90 to 0 to 90 to 0 to 90, divided to 10, subdivided to 5, to 1 and to |1/2|, numbered by 10. Inside this is a zodiacal scale with names and symbols of the signs, each with a 30-degree scale using the same divisions as the outer scale. Inside this is a calendar scale with the month names in Latin, each with a scale of days. divided to 10, subdivided to 1, numbered by 10 as appropriate; December is given 31|1/4| days. The first point of Aries is at 21 March. The upper half of the central area has a conversion diagram for equal and unequal hours, the semicircular scale of 'HORÆ INÆ: QVA: LES.' 1 to 12, divided to 1 hour, subdivided to 20 minutes and to 4 minutes, numbered by 1 hour, the lines got every hour and half-hour (marked by arrows) numbered by 1. One quadrant is marked 'Horæ ante meridiem', the other 'Horæ post meridiem'. The lower half has a double shadow square with scales 0 to 12 to 0 to 12 to 0, divided to 0.2, numbered by 1. The same scales are also marked 0 to 60 to 0 to 60 to 0, and are marked 'VMBRA VERSA', 'VMBRA RECTA', 'VMBRA RECTA', 'VMBRA VERSA'.

Counterchanges alidade with shaped ends, vanes with double pinhole sights, and a scale on each arm, 'Horæ ortus Solis', 0 to 10, subdivided to |1/2| and to |1/4|, numbered by 1, and 'Horæ occasus Solis', 0 to 12, subdivided to |1/2| and to |1/4|, numbered by 1. Screw, washer and shaped nut.

Jim Bennett

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