Equinoctial Dial by Johann Christoph Keller
Record status
Individual type · partial
Period
circa 1580
This equinoctial dial, held by the Museum of the History of Science in Oxford, is a silver portable instrument attributed to Johann Christoph Keller of Linz, dated circa 1580.
Measuring 85 x 62 x 53 mm, the device features a rectangular base plate raised on four bun feet. The base is intricately engraved with floral and foliate motifs, alongside depictions of two angels positioned on either side of an inset compass. The compass includes magnetic deviation markings and cardinal points denoted as N, O, S, and W. Functionally, the dial utilizes an adjustable hour ring supported by two upright pillars, which can be calibrated to various latitudes.
The mechanism includes a latitude scale marked from 0 to 90 degrees with a hanging plumb line for leveling. The instrument is signed by the maker on the hour ring, which displays common hours numbered from 1 to 12 twice.
Evidence at a glance
- Linked sources
- 1
- Photograph views
- 1
- Catalogue references
- 0
Counts describe this entry’s documentation, not authenticity, rarity or completeness. Photographs may show one specimen; check each caption and licence.
Technical characteristics
- Date
- circa 1580
- Type
- Central European equinoctial dial
- Maker
- Johann Christoph Keller
- Material
- Silver
- Signature
- IO CHRISTOF KELLER MATHE LINCI HOROLOGIVM VNIVERSALE
- Dimensions
- 85 x 62 x 53 mm
- Latitude Scale
- 0-90 degrees
- Place recorded
- Linz
- Maker / attribution
- Johann Christoph Keller
Design
- Visible features
- • Rectangular silver base plate with four spherical bun feet • Inset compass on the base plate with cardinal point indicators • Engraved floral and foliate ornamentation across the base • Adjustable hour ring supported by two vertical metal pillars
- Construction and Design
- The equinoctial dial is constructed from silver and measures 85 x 62 x 53 mm. It rests on four small bun feet, providing a stable foundation for the instrument. The base plate serves as the primary mounting point for the vertical components and is decorated with detailed engravings of flowers, leaves, and two angels placed adjacent to the central compass. The dial’s primary timekeeping component is an adjustable hour ring. This ring is held in position by two pillars rising from the base plate and can be modified to facilitate use at different latitudes. The hours are engraved as common hours, numbered 1 to 12 twice on the ring.
- Signature and Identification
- The instrument bears an inscription identifying the maker as Johann Christoph Keller of Linz. The signature is engraved directly onto the adjustable hour ring alongside the Latin term for a universal dial. The lettering is accompanied by decorative foliage. The record indicates that the object is held by the Museum of the History of Science, Oxford, under the inventory number 51108. The specific attribution and dating to circa 1580 are provided by the museum's catalogue data.
- Compass and Latitude Calibration
- Integrated into the base plate is a compass, which is marked with cardinal points 'N', 'O', 'S', and 'W'. This component also contains markings intended to indicate magnetic deviation. The design of the instrument allows for precise leveling, which is achieved through a hanging plummet suspended from a central latitude scale. The latitude scale itself is graduated from 0 to 90 degrees, with intervals of 1 degree and numbering at every 10 degrees. This calibration allows the user to adjust the tilt of the hour ring according to their geographical position, confirming the object's function as a universal instrument.
Identification
- Source note
- Facts transcribed from the linked source listing or collection record. Attribution and specifications are source-reported and have not been independently authenticated.
Catalogue references
No catalogue numbers recorded. Numbers are only published once transcribed from a verified edition of a standard catalogue — they are never inferred.
Research required
- Research required: The exact extent of restoration or surface wear is not explicitly detailed in the source
- Research required: The precise nature of the 'magnetic deviation' mechanism within the compass is not described