Brass Ring Dial
Record status
Individual type · partial
Period
circa 1480 ?
This unsigned brass ring dial, inventory number 34394 in the collection of the Museum of the History of Science, Oxford, measures 96 by 96 by 2 mm. It is a precursor to the equinoctial ring dial, functioning as an astronomical ring dial without an equatorial ring.
The construction features a square brass plate with a central hole that houses a sliding disc. The dial includes an equal scale of latitudes, a ruler with an unequal scale, and a calendar scale displaying months and solar declination via zodiac signs. One side of the round plate incorporates a shadow square, while the reverse features a lunar volvelle with hour scales. Operation requires setting the sliding ring to the user's latitude and the alidade to the solar declination, then directing the sights toward the sun to measure time using the central ruler.
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 1480 ?
- Type
- German ring dial
- Maker
- Unsigned
- Origin
- German
- Dimensions
- 96 x 96 x 2 mm
- Place recorded
- Germany
- Primary function
- Astronomical ring dial
Design
- Visible features
- • Square brass plate measuring 96 x 96 mm • Sliding disc integrated into central circular aperture • Zodiac signs engraved around the square frame • Counterchanged alidade visible on the central disc
- Inscriptions and Provenance
- The plate bears a partially deleted inscription on one side that reads 'MARTIN FREY'. A historical museum accession card indicates that the text previously extended to read 'REGENSPURE 1590'. Due to the state of the metal, this extended portion of the inscription is no longer legible to observers. The instrument is held by the Museum of the History of Science in Oxford, and it is catalogued under the inventory number 34394,
- Structural Design and Components
- The object comprises a 96 by 96 mm square brass plate, which serves as the primary support for the internal moving components. At the center of this plate is a hole that carries a sliding disc, central to the instrument's operation. Surrounding the sliding disc on the square plate is an equal scale of latitudes ranging from 0 to 90 degrees, marked in 2-degree increments and numbered every 10 degrees. A ruler, marked with an unequal scale from 1 to 12 in increments of 1, is secured to the plate by two slots. The reverse side of the plate contains a calendar scale featuring months and the declination of the sun, identified by the corresponding zodiac signs. This combination of fixed and movable elements facilitates the calculation of time through observed solar positioning.
- Operational Mechanisms and Scales
- The dial is designed to determine time through a specific alignment procedure. To use the instrument, the sliding ring is adjusted to the latitude of the observer, while the alidade is set to match the declination of the sun. The entire assembly is suspended, and the disc is rotated until the sights align with the sun. Time is read by measuring the distance between a notch on the sliding ring and a notch in the center of the zodiac scale using the small ruler. Further functional depth is provided by the round plate, which features a shadow square and a counterchanged alidade on one side. The opposite side includes a lunar volvelle, which provides an hour scale marked from 1 to 12 twice, and 1 to 24, expanding the instrument's capacity for celestial observation.
Identification
- Inventory Number
- 34394
- 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 inscription 'MARTIN FREY' is reported to be likely modern
- Research required: The full inscription 'REGENSPURE 1590' is no longer legible
- Research required: The dating 'circa 1480' is marked with a question mark in the source