Nocturnal Side and Calibration
The obverse of the circular plate functions as a nocturnal. It features a blank circular edge and several concentric scales, including a zodiacal calendar and the four seasons, marked as 'VER', '?STAS', 'AVTVMNVS', and 'HYEMS'. A central hour ring, which rotates above the base, is connected to the disc by seven curved bands. Each band supports a hand, and these are marked with Latin labels corresponding to their astronomical function, such as 'DIES MENSIVM', 'LONGITVDO DIEI', and 'ORTVS SOLIS'.
An index arm is mounted above the hour ring, although it is currently incomplete. A small inscription on the base plate, '15[?] AVG', provides further calibration data; a straight line drawn from the center through a nearby dot marks 15 August or 0 Scorpio on the calendar scale.
Evidence for this section
- “The first two form a zodiacal calendar”
- “The final scale is divided into the four seasons: 'VER', '?STAS', 'AVTVMNVS', 'HYEMS'.”
- “Above the plate, secured by a central pierced screw and nut, is an hour ring covering the blank outer portion of the base plate, connected to a central disc by 7 curved bands.”
- “There is a small inscription on the blank portion of the base plate, usually obscured by the hour ring: '15[?] AVG'.”
Sundial and Mechanical Details
The reverse of the plate acts as a horizontal sundial. It incorporates a folding gnomon equipped with a spring plate, which allows for adjustment across four specific latitudes: 45, 48, 51, and 54 degrees. The corresponding hour scales are engraved in both Roman and Arabic numerals. The outer edge is finished with an ornamental band featuring snakes and foliage.
A central space indicates where a magnetic needle would have been situated, though it is now missing. The cardinal points are marked in Latin: 'MERIDIES', 'OCCIDENS', 'SEPTENTRIO', and 'ORIENS'. The design includes an offset target line to account for magnetic variation.
Evidence for this section
- “The reverse side has a horizontal sundial.”
- “A folding gnomon, with a spring plate, is adjustable for latitudes 45, 48, 51 and 54”
- “A circle and central point for a magnetic needle (missing) lacks a cover, to secure which there are two holes in the base-plate”
- “cardinal points marked 'MERIDIES', 'OCCIDENS', SEPTENTRIO', 'ORIENS'; target line offset for magnetic variation.”
Physical State and Provenance
The instrument currently exists as a single plate, though physical evidence indicates it was once part of a larger astronomical device. Holes for a hinge fitting and a catch on the reverse confirm that it was designed to connect to other components. The handle, which is integral to the plate, displays artistic relief work featuring animals, grotesque faces, and plants.
The current condition reflects past use and repair. Several of the bands connecting the hour ring to the center have been repaired using solder, and the magnetic needle is lost. The museum inventory number for the object is 36545.
Evidence for this section
- “Evidence for a hinge and catch, and for the former existence of a folding extension to the index arm of the nocturnal , show that this was once part of an astronomical compendium”
- “Several of the arms have been repaired with solder.”
- “The handle is decorated with figures, grotesque faces, plants and animals.”
- “Inventory number 36545”
