Beschreibung:

An extremely rare late 16th-Century lacquered-copper Polyhedral Dial, circa 1590, signed Pragæ fecit Erasmõs habermel -- 7¼in. (18.5cm.) high; 14in. (35.5cm.) wide; 6 7/8in. (17.5cm.) deep This strikingly large polyhedral dial is most unusual in being finished in bright copper sheet (thickness between 1mm and 1.5mm), lacquered for protection. The engraving is bold in the typical style of Habermel; the restrained decoration incorporates strapwork and small rosettes in various forms. All engraving is filled with niello. The instrument has seven sides, and they record, variously, the time in mean hours, planetary hours, and Bohemian (or Italian) hours, with conversions between them. The top is occupied by a square 17.5 x 17.2cm. horizontal dial. The Southern edge is inscribed: Pro Eleuatione Poli 50 grad . This is the latitude of Prague, the modern value being 50°6'. Below is a small right-angled gnomon with its foot at the centre of a sunburst, whose slanted side is for registering mean hours, while the tip registers the Bohemian hours. The gnomon is followed by a curved ribbon marked with mean hours 6am to 6pm from which straight lines (in quarter-hour intervals) run to corresponding hours engraved on the outer edges of the dial. The top edge has space for two additional hours before and after the 6 o'clock lines. There follow seven curves marking the divisions of the year into the Zodiac. At the top is engraved: Tropicus Cancri , and at the bottom: Tropicus Capricorni ; the Zodiac sigils are at either side, marking the season. The middle, straight, double line is labelled: Æquator . Across the face of the dial is a set of 13 straight, dotted lines for reading the Bohemian hours; these lines are numbered from 10 to 22, the latter being two hours short of sunset at the 24th hour in this system. The tip of the gnomon gives the Bohemian hour from the place where the Zodiac curve crosses the hour line. At the bottom of the face of this dial is a 4.6cm. diameter magnetic compass, and a hinged brass support for a plumb line ( missing ). The compass has a replacement base, magnetic needle and cover glass (which is deliquescent). The base is inscribed with two crossing lines, and the four cardinal points are marked in German cursive: N, O, S, W . A further line shows the magnetic declination at 14°West, which is the value for c. 1710 and c. 1860. It is likely that the replacement compass, along with some other repairs, were effected in the mid-nineteenth century. The original compass would have had a declination of 10°East. Following on from the South side of the horizontal dial is a vertical dial, the top of which is engraved: Horæ Vulgares Planetariæ . Planetary hours result from the division of daylight into twelve parts, which vary in length according to the season of the year, short in winter and long in summer. A small hinged brass gnomon is attached at the top within a ribbon on which are engraved mean hours, in quarter-hour intervals, from 6am to 6pm, from which lines are cut to the corresponding hours marked on the outer edge of the dial in the usual manner for a vertical dial. These hours are read from a shadow cast by the sloping side of the gnomon. Another set of lines, dotted to distinguish them, show the planetary hours numbered 1 to 12, and these are recorded by the tip of the gnomon. Across the face of the dial is a set of curves identified by the sigils of the Zodiac, and hence the season of the year. Below these curves is the signature. From the base of the vertical dial is another plane set at 40° (the co-latitude) to the vertical, with a hinged pin gnomon at the centre. At an angle across the face is engraved: Quãntitas diei , indicating the purpose of this dial, which is to give the hours of daylight through the year. These are read from a set of curves labelled both sides in mean hours from 8 to 16. These are the maximum hours of daylight from mid-winter to mid-summer at the latitude of 50°. Additionally, ther