Inventory no. 39980 - Epact entry
Epact number: 98313
Horizontal Dial
Erasmus Habermel
Late 16th century; German
Gilt copper and brass; 175 x 175 mm
Main text
The upper face of this instrument has a common horizontal dial with the shadow cast by a string stretched from the centre to the top of a folding standard.
The most unusual feature of the dial is that diagonal lines are used to sub-divide each hour into single minutes. This degree of accuracy cannot be achieved in practice for several reasons, for example the imprecision of setting the dial to the meridian using the magnetic compass.
Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 39,980
Detailed text
The upper face has a horizontal string-gnomon dial, the string supported by a sprung folding upright, shaped to accommodate a plumb-line (missing). Approximate latitude 48 degrees. The edge of the square plate is divided to hours, with Roman numerals, sub-divided to half and to quarter hours. Within the square is a series of concentric circles: each hour is divided by a diagonal line to 5 minutes, marked by concentric circles, and sub-divided to single minutes, marked by dots, numbered by 5. A central glazed compass, with a diagonal bar for the lower end of the string, blued steel magnetic needle, silvered plate with cardinal points marked 'ME', 'OC', 'SE', 'OR', target offset to the east for variation. The corners have foliate decoration typical of Habermel.
Oppose the folding upright is a volvelle for converting between 12 and 24-hour systems, with the inscription arranged in a spiral: 'HOAR 24 TRADVCTA AD HORAM ORTVS SOLIS INDICAT HORAS ITALICAS & NORICAS DIVRNAS: AD OCCASVM BOHEMICAS & NORIBERGENSES NOCTVRNAS: AD MERIDIEM VERO ASTRONOMICAS'
The dial itself carries the inscription: 'OMNIA PERVERTIT SÆCLI MVTABILIS ORDO'.
Signed on the rim: 'Erasmus Habermel Fec:'.
Underneath are four ball feet. The plate carries a zodiacal calendar, with engraved zodiac signs, month and zodiac names in Latin, the former divided to single days, the latter to single degrees, the first point of Aries is at 20|1/2| March. Two circular scales give times in hours and minutes of sunrise throughout the year in ordinary and Italian hours. Foliate decoration in the corners and on the silvered base of the compass plate.
Jim Bennett