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Instrument type

circa 1570; French
Brass; 232 mm in diameter

The mater has a squat throne, shackle and suspension ring, and the back plate secured by rivets. The limb has the French names of 16 compass points, hour divisions 0 to 12 twice, by 1 with Roman numerals, and a degree scale from the east point 0 to 360, divided to 10, subdivided to 5 and to 1, numbered by 10. Inside the mater is a latitude projection for 43 degrees with azimuths every 5 degrees, numbered by 5 within the equator, and almucantars every 2 degrees, numbered by 4. There are meridian and east-west lines, equator, tropics and divisions of the 12 houses marked 'I DOMVS', 'II DOMVS' etc. from the eastern horizon.

Rete of the Arsenius type in tracery with a tulip motif, with 25 named stars. The ecliptic circle has the names and symbols of the zodiacal signs, each with a scale of 30 degrees, divided to 5, subdivided to 1, numbered by 10. The back of the ecliptic circle is also divided, but nor named or numbered.

There are two latitude plates for 45 and 47?, and for 48?. They are similar to the projection on the mater, but the azimuths and almucantars are numbered by 10. On the other side of the projection for 48 degrees is a universal projection of the Gemma Frisius type with lines of right ascension and declination every 2 degrees, and hour lines marked and introduced as required. Named stars are marked and ecliptic marked, and the outer degree scale is 90 to 0 to 90 to 0 to 90, divided to 5, subdivided to 1, numbered by 10.

The back has an outer degree scale, whose divisions are also used for a zodiacal scale with the names and symbols of the signs. A calendar scale has the names of the months in Latin, each with a scale of days divided to 5, subdivided to 1, numbered as appropriate by 10. The first point of Aries is at 101/2 March. The central area has a double shadow square and a conversion diagram between equal and unequal hours.

There is a rule with shaped ends and attached pin, with a linear scale 0 to 90 to 270 to 360 beginning and ending at the centre, divided to 10, subdivided to 2, numbered by 10, and marked with the signs of the zodiac. The counterchanged alidade has a scale of hours on one arm. The pin engages with a sliding washer.

Jim Bennett

Museum of the History of Science, Oxford
Inventory number 49726

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