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The Encyclopedia of Horology

Tool · Italian quadrant

Stefano Buonsignori horary quadrant

Partially verified

This 16th-century horary quadrant is constructed from lignum vitae and features a radius of 145 mm. It was crafted by the Olivetan friar and cosmographer Stefano Buonsignori. The instrument serves multiple functions, including timekeeping, surveying, and astronomical calculation. Its face is calibrated for a latitude of 43° 30', corresponding to the city of Pisa, and displays an Italian hours dial marked with gold and white lines. The reverse side integrates a complex arrangement of a brass degree scale, a zodiacal calendar, and a lunar volvelle that tracks the phase, age, and zodiacal position of the moon. Two block sights with pinnules are attached to the edge for altitude measurements. The instrument also contains an inset compass and is decorated with foliate patterns. It is currently held in the collection of the Istituto e Museo di Storia della Scienza in Florence.

The reverse side of the Stefano Buonsignori quadrant, showing the lunar volvelle, zodiacal calendar, and inset compass.
The reverse side of the Stefano Buonsignori quadrant, showing the lunar volvelle, zodiacal calendar, and inset compass. — Istituto e Museo di Storia della Scienza, Firenze. Rights pending — permission not yet requested. Original source

Catalogue identity

Source
www.mhs.ox.ac.uk
Category
Tool · Italian quadrant
Maker / attribution
Stefano Buonsignori
Reference
Not recorded
Catalogue / lot identifier
2499
Source-reported date
16th century
Source-reported place
Florence

Source-reported attribution and specifications are not independent authentication. A listing does not establish present ownership, current display, availability or permission to reproduce.

Object description

Instrumental Face and Timekeeping

The face of the quadrant is structured around a central Italian hours dial, calibrated specifically for a latitude of 43° 30'. The hours, ranging from 9 to 23, are indicated by distinct color-coded lines: gold lines for the morning hours and white lines for the afternoon. A zodiacal calendar is arranged on either side of this central diagram, positioned to align with specific calendar dates.

Additionally, the face incorporates a shadow square divided into twelve units to assist in calculating heights and distances. The limb is graduated in a 90-degree scale, marked in groups of ten. Inscriptions on the face provide guidance for the user, clearly distinguishing between the morning and afternoon hour lines and specifying the latitude for which the quadrant is intended.

Evidence for this section
  • “the left and centre of the instrument are filled with the diagram for an Italian hours dial (9 to 23 without subdivisions) for 43? 30'”
  • “the morning hours being indicated by gold lines, the afternoon hours by white lines”
  • “Above the hour diagram is a shadow square of twelve divided to single units”

Reverse and Astronomical Functions

The reverse of the lignum vitae quadrant features an inset brass disc that functions as both a calendar and an astronomical calculator. It contains a degree scale covering four quadrants, surrounding a zodiacal calendar that is further subdivided by degree and date. A central lunar volvelle is mounted within this assembly.

The volvelle provides information regarding the moon's age, its zodiacal sign, and its current phase, which is viewed through a circular aperture on the disc. The upper portion of the disc is engraved with an aspectarium, providing further astronomical data. This side of the instrument is also equipped with a magnetic compass and two block sights, which allow the user to perform traditional surveying tasks and solar altitude observations.

Evidence for this section
  • “The reverse of the instrument is filled by a centrally placed inset brass disc stamped with a degree scale in four quadrants”
  • “Mounted at the centre within the calendar is a lunar volvelle showing the age of the moon, its place in the zodiac, and its phase”
  • “Two block sights, both with pinnules, scrolled backs and recessed gold decoration are mounted on the shorter edge”

Physical Construction and Provenance

The quadrant measures 145 mm in radius and is fashioned from lignum vitae. Its maker, Stefano Buonsignori, was a known cosmographer to the court of Francesco I de' Medici and an Olivetan friar. The instrument exhibits decorative details, including symmetrically painted flowing foliate patterns on the reverse side, and recessed gold decoration on the sights.

The object is part of the collection at the Istituto e Museo di Storia della Scienza in Florence, catalogued under inventory number 2499.

Evidence for this section
  • “made by Stefano Buonsignori , an Olivetan friar, and cosmographer to the court of Francesco I de' Medici”
  • “The remaining spaces on this side of the quadrant are filled with symmetrically painted flowing foliate decoration.”
  • “Inventory number: 2499”

Open research questions

  • What specific historical use case dictated the requirement for a Pisa-specific latitude calibration on this instrument?
  • How do the specific lunar and aspectarium calculations performed by the volvelle relate to 16th-century court astrology?

Source evidence

Recorded claims and source quotations for Stefano Buonsignori horary quadrant
FieldSource-reported valueSource quotation
MakerStefano Buonsignori“made by Stefano Buonsignori”
Inventory number2499“Inventory number: 2499”
Date16th century“16th century; Florence”
MaterialLignum vitae“Lignum vitae; 145 mm in radius”
Latitude43° 30'“horary quadrant for latitude 43? 30'”
ProvenanceIstituto e Museo di Storia della Scienza, Firenze“Istituto e Museo di Storia della Scienza, Firenze”

Visible details

  • Inset magnetic compass on the reverse side
  • Two block sights with pinnules and scrolled backs
  • Surface decorated with flowing foliate patterns
  • Lunar volvelle with circular aperture

Research qualifications

  • Latitude calibration is stated as 43° 30' for Pisa
  • Primary material identified as lignum vitae

Photograph identity and source facts were screened before import; rights clearance remains pending.

Consulted source

Quadrant

Reviewed 2026-10-26 · Record 8b628f3c22

Terms in this record

Glossary explanations for terms named in this object’s record.

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