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Armillary Sphere
Signed by Carlo Plato
Dated 1588; Rome
Brass; 390 mm in height

Three scroll legs support a turned base within which sits a turned upright sleeve and pivot for the vertical spindle carrying the armillary sphere. This spindle has a screw thread at its lower end, where it is secured to the stand by a wing nut.

Four quadrants of brass rise from the top end of the spindle to carry the horizon ring, whose rim is marked with the name of eight winds. The upper surface has 12 stars marked in their ecliptic positions with their names in Latin and Greek. Within this are scales for the date and the zodiac (the first point of Aries in at 201/2 March). An innermost degree scale 0 to 90 to 0 to 90 to 0, serves also for the 30-degree scales for the zodiacal signs, successive 30-degree sections being distinguished by the presence and absence of alternate hatching. The underneath of the horizon ring is signed: 'Rom? Anno Domini 1588 Ca: l'plat. f:'. There are three clamping screws for the meridian ring: one at its lowest point, two on the horizon ring.

The meridian ring has a degree scale for declination 0 to 90 to 0 to 90 to 0, divided to 10, subdivided to 5 and to 1 with alternate hatching, numbered by 10. There is a repair at the south pole. At the north pole is an hour circle; a round handle above is for rotating the sphere, but no time index is extant. On the poles rotates the sphere composed of 2 meridian circles, equator, tropics, arctic and antarctic circles and a band for the ecliptic. The equator has a degree scale 0 to 360, divided to 10, subdivided to 5 and to 1, numbered by 10, with alternate 30-degree portions having alternate hatching. The symbols, representations and Latin names of the zodiacal signs are on the ecliptic band, each with a 30-degree scale, divided to 10, subdivided to 5 and to 1, numbered by 10. The ecliptic scale is counterchanged with each new sign, and alternate signs have alternate hatching. The arctic circle has a scale of hours 1 to 24. A number of stars are named on the ecliptic, and there are pointers for 8 other named stars.

Within the sphere for the stars is the sun, the moon and the earth. The earth is mounted at the centre on a rod rising from the south pole. The sun and moon are carried by rotatable quadrants of brass pivoted at the north ecliptic pole. The moon symbol crescent is carried on an epicycle.

Jim Bennett

Museum of the History of Science, Oxford
Inventory number 45453

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