The outside of the upper leaf has a rotating pierced lunar volvelle with an aspectarium in the centre. The aperture shows the phases of the moon engraved on an underlying silver plate. On the limb of the rotating volvelle are engraved two rings with hours, the outer one with hours numbered from 5 to 12 to 7 anticlockwise, with star symbols for the half-hours, and the inner one with hours numbered 1 to 12 twice, clockwise. There are external teeth at each hour, and on the 12 hour the two pins are slightly bigger and engraved 'L' and '[star] [star]'. The external ring is cut and shows a scale of days from 1 to 29 for the moon's age. Around it is a scale of degrees, divided to ten, subdivided to two by alternate shading, numbered by ten from 10 to 30 or 31 or 28 as appropriate. Engraved around the degree scale are the names of the months in French. The circular compass cover intersects the calendar scale and carries the inscription for 'April'. Surrounding the names of the months are common hours numbered from IIII to XII to VIII, with star symbols for the half-hours and divided to the quarter hour by alternate shading. On the ring is the inscription 'HEVRES [star] [star] [star] SOLAIRES [star]'. The centre has a recess for a pin gnomon, which is now missing. The lower left hand side of the plate is engraved with a quadrant and the Dominical Letters 'A', 'C' on an inner circle, and the Dominical letters 'C B G F E D B' on an outer circle.The inside of the upper leaf has a universal pin gnomon dial (pin missing), for the winter half-year with a brass arm fixed on the left hand side.
The inside of the thicker lower leaf has a wind rose with 32 directions named in French, Italian and English, the cardinal points with two flower symbols flanking the name. Around the wind rose is a degree scale, in four quadrants divided by ten and by two with alternate shading, numbered from 10 to 90 by ten with 90 at the top. Surrounding the circle are four wind names in Italian, 'MAGISTRAL', 'GRECO', 'SIROCCHO' and 'LEBECCIO', with flower symbols flanking the names. A scale of latitudes is inscribed on the left-hand side, from 10 to 90 divided by two and numbered by ten. Below is a brass plate covering the compass, engraved '[star] AVRIL [star]' referring to the upper plate, and below a series of [star]. In the centre of the round plate (and of the compass) are three rings: the external one with dominical letters 'A G F D C B A F E D C A G F E C B A G F D', then the following circle with '1570 E G 16B44 D 16F44'. The numbers for '1570' are in a slightly different script than the other numbers on this round plate. The third circle is engraved with star symbols, and next to the centre are the inscriptions 'Fre' and 'Eng'. The circular plate is fixed on the left hand side and reveals the compass, engraved with the initials of the cardinal points 'S', 'O', 'M', 'O'.
The outer side of the lower leaf is engraved with a degree scale in two quadrants on the top half, divided by ten, subdivided by two by alternate shading, numbered from 10 to 90 by 10. The bottom half is engraved with a shadow square from [0] to 60, divided by 10, subdivided by 5, numbered from 10 to 60 by 10. The shadow square is inscribed '[star] VMBRE [star] [star] [star] DROIC ? TE [star]' and '[star] VMBRE [star] VERSE [star]' twice. The centre of the leaf is inscribed '[star] [flower] FEIT [flower] A [flower] PAV [flower] P [flower] [star] [star] [flower] HIER [?] E [star] VIZE [flower] [star] MEN[?]ER [flower] [star] [star] 1567 [star]'. A counterchanged and decorated alidade with two folding hole and slit sights is fixed at the centre by means of a screw.
The instrument has a triangular suspension apparatus ending with a swivel ring.
The instrument was purchased in 1893 and was formerly in the Spitzer collection. It is described in F. A. B. Ward, A Catalogue of European Scientific Instruments in the Department of Medieval and Later Antiquities of the British Museum (London, 1981), p. 127, no.366.
Ilaria Meliconi
