Ebony Quadrant of Cosimo I de' Medici
Record status
Individual type · partial
Period
1556
This 167 mm radius ebony quadrant is dated 1556 and dedicated to Cosimo de' Medici. The instrument features two distinct faces. One side functions as an horary quadrant calibrated for the latitude of 43 degrees 45 minutes, corresponding to Florence.
It includes an Italian hours dial (9 to 24) marked with silver lines for morning hours and gold lines for the afternoon, alongside a zodiacal calendar and a shadow square of twelve. A bas-relief head of a man within sun rays serves as the apex attachment for a thread cursor. The reverse side contains a complex circular diagram with nine concentric rings detailing solar cycle information, dominical letters, leap years, the golden number, and epact.
Two sighting blocks are mounted on the side. The instrument is associated with the collection of Cosimo I, second Duke of Florence, and remains in the possession of the Istituto e Museo di Storia della Scienza in Florence.
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
- 1556
- Type
- Italian quadrant
- Radius
- 167 mm
- Provenance
- Cosimo I, second Duke of Florence
- Inscription
- QVADRANS HORARVM AD LAT. GRA. XLIII. MIN. XLV
- Place recorded
- Italy
- Maker / attribution
- Attributed to Giovanni Battista Giusti or the Medicean workshop
- Latitude Calibration
- 43 degrees 45 minutes
Design
- Visible features
- • Sighting blocks with scrolled backs on the longer side • Bas-relief male head at the apex within sun rays • Gold-painted symmetrical scrolled foliate decoration in lower corners • Circular calendar diagram on the reverse with nine concentric rings
- Attribution and Provenance
- The instrument is attributed either to Giovanni Battista Giusti or to the Medicean workshop responsible for Grand Ducal measuring instruments. For instance, the use of a specific shadow square division and unique spelling choices suggest a different hand. Ownership is confirmed by an inventory record of 1574 regarding the goods of Cosimo and Francesca Medici, which explicitly mentions the ebony quadrant. The instrument bears an inscription identifying the owner as the second Duke of Florence, Cosimo I, confirming its presence within the ducal collection during the 16th century.
- Face and Dial Configuration
- The front face of the quadrant is structured around a limb divided into a 90-degree scale, incrementing by single degrees within groups of five. The main field incorporates an Italian hours dial (9 to 24), specifically calibrated for the latitude of Florence at 43 degrees 45 minutes. The temporal differentiation is achieved through the use of inlaid lines: morning hours are rendered in silver, while afternoon hours are depicted in gold. Above this dial sits a shadow square of twelve, numbered in three groups of four. The area is inscribed with guidance for reading the morning and afternoon hours. The instrument's vertex serves as the pivot for a thread cursor, featuring a silver attachment ring centered on a male head in bas-relief, set against a circular arrangement of sun rays.
- Reverse and Astronomical Details
- These rings contain calendrical and astronomical data, including the solar cycle for twenty-eight years, dominical letters, leap year cycles starting from 1556, the golden number, and the epact. Additionally, a zodiacal calendar is included, spanning three rings to denote the sun's entry into each sign. The center of this diagram displays the date 1556 in Roman numerals. The lower corners of the instrument are embellished with symmetrical scrolled foliate designs in gold paint. Functionally, the side of the quadrant features two sighting blocks with pinnules and level lines to facilitate its use as a measuring instrument.
Identification
- Inventory Number
- 2521
- 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: Authorship remains debated; while tentatively ascribed to Giovanni Battista Giusti in 1954, differences in material and lettering compared to signed works suggest it may be from a Medicean workshop
- Research required: The inscription 'COSIMO M.R.P. FLO. DVC. II' may perhaps be interpreted as referring to Cosimo Medici, second Duke of the State of Florence