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Instrument type

Horizontal Dial
Later 16th century; Italian
Gilt and silvered brass; 47 x 46 x 15 mm

This square-section instrument has a single cover leaf hinged over the main box, whose sides are decorated with simple rectangular line engraving. There is a clasp to fix the lid closed.

The outer face of the lid carries a lunar volvelle and aspectarium. The outer fixed scale of hours runs 1 to 12, 1 to 12, divided to 1/2 and 1/4. The edge of the volvelle is cut away to reveal the scale of the age of the moon to 29[1/2] and the remainder of its circumference is occupied by a scale of hours 4 to 12 to 8. A circular aperture gives a graphical indication of the age of the moon with figured representations of the quarters as well as full and new moon. The lightly engraved aspectarium gives polygons and symbols for conjunction, opposition, trine, quadrature and sextile. The corners of the face are decorated with line engraving.

The inner face of the lid carries a wind rose with the eight classical winds named in Italian and a further eight directions represented by the initial letters of the two adjacent winds. A central circular scale of direction begins at the east point and is numbered 1 to 16, divided to 1 and 1/2. These features are surrounded by scrollwork engraving.

The main box carries the horizontal dial whose decorated gnomon folds over the compass. The silvered dial plate has hatched engraving in its corners and the hour scale runs 4 to 12 to 8, with each hour divided to 1/2 and 1/4. The compass bowl is 22 mm in diameter and the cardinal directions are labelled 'N', 'OR', 'S' and 'OC'; the compass plate is marked for a westward variation.

The underside of the instrument has an inset volvelle for converting between equal and Italian hours, surrounded by the same engraved decoration as the outer face of the lid. The outer scale of equal hours runs 1 to 12, 1 to 12 divided to 1/2 and 1/4, while the scale of Italian hours on the disc is marked 'Horae Ab Occasu Solis' and runs 10 to 24. The circumference of the disc is cut away in the form of a pointer to reveal a short scale for the length of the day, from 8 to 16.

Provenance: Billmeir Collection (57-84/197).

Stephen Johnston

Museum of the History of Science, Oxford
Inventory number 51587

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