Inventory no. 63541 - Epact entry
Epact number: 40933
circa 1550; Flemish
Brass; 192 mm in diameter
Although this armillary sphere comprises a great many rings which move within each other in a complicated manner, it does not demonstrate anything more than the motions of the sun and the celestial sphere; there are, for example, no planets. The complexity is some indication of the sophistication of contemporary ideas about celestial motion and the challenge of making this accessible through an instrument. The motions include rotation about the poles of the equator and, independently, the poles of the ecliptic. In addition an oscillation of the ecliptic itself, known as 'trepidation' is provided for by the rotation of two discs which add a further motion to the innermost ecliptic ring.
All this 16th-century subtlety is set incongruously on a much later stand, the kneeling figure and the tiered structure beneath supported by satyrs representing a much more transparent effort at exotic composition.
Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 63,541
The later stand has a bronze figure of a kneeling man in a loincloth, supporting the sphere on his head and supported himself by a modern turned brass stand in two tiers, incorporating a magnetic compass and three feet ornamented with satyrs. Inscribed: 'SIC LVDITVR ASTRIS'.
Four brass quadrants of interwoven bands rise to support the horizon ring, with the four cardinal points names in Latin, a scale of dates and a zodiacal scale with symbols for the signs, each with a 30-degree scale. The first point of Aries is at March 11|1/2|.
The meridian ring is supported in two slots in the horizon ring and one at the top of the stand; one side has a degree scale, clockwise from the north pole 0 to 90 to 0, 90 to 0 to 90, divided to 10, subdivided to 5 and to 1, numbered by 10. At the north pole is a circle of hours 0 to 12 twice, and the mount for a quadrant arc with a degree scale slides on the meridian ring.
A celestial sphere comprising two meridian circles at right angles, equator, tropics, arctic and antarctic circles is pivoted at the poles on the meridian ring. The equator has a degree scale 0 to 360 from the spring equinox, the ecliptic has a zodiacal scale with symbols for the signs and a 30-degree scale for each. There are 16 pointers for named stars.
At the ecliptic pole is pivoted a sphere of three rings intersecting at right angles, and at two diametrically opposed intersections on the ecliptic are pivoted discs for effecting the adjustment for trepidation. Mounted on pivots that rotate with this disc is a further sphere of three rings. Both inner ecliptic rings, the one without and the one with the trepidation adjustment have zodiacal scales similar to the ecliptic ring on the outer celestial sphere Pivoted on the innermost ecliptic ring is a ring with a pair of fixed vanes with pinhole sights.