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The Encyclopedia of Horology

Tool · English quadrant

Quadrant by Robert Dudley

Partially verified

This brass quadrant, measuring 370 mm in radius, was signed and dated by Robert Dudley in 1597. It is a navigational and astronomical instrument densely engraved with various scales for timekeeping, solar and lunar calculations, and celestial tracking. The front face features a limb with a scale of degrees, tables for the solar cycle, dominical letter, and epact, a zodiacal scale, and a calendar for the date of Easter. The centre displays hour lines, solar latitude scales, and the named tropes of Cancer and Capricorn, alongside planetary hours. The reverse side includes a shadow square, a wind rose with 32 directions, and a calendar scale paired with an additional zodiac scale. A central hole is present, interpreted as a pivot point for a sighting vane or alidade. The instrument originates from the Dudley bequest and is held in the collection of the Istituto e Museo di Storia della Scienza in Florence.

Obverse face of the brass quadrant by Robert Dudley, 1597.
Obverse face of the brass quadrant by Robert Dudley, 1597. — 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 · English quadrant
Maker / attribution
Robert Dudley
Reference
Not recorded
Catalogue / lot identifier
3365
Source-reported date
1597
Source-reported place
England

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

Front Face Configuration

The obverse of the quadrant is dominated by a limb engraved with a degree scale divided to one-quarter degree increments. Near the apex, multiple tables provide astronomical data, including the solar cycle, dominical letter, epact, and the lunar cycle. A zodiac scale is also positioned near the apex, displaying names and symbols, complemented by a signature identifying Robert Dudley as the inventor.

The central field of the quadrant contains hour lines numbered from 1 to 12 and an unequal scale representing the sun's latitude. The major celestial boundaries, specifically the tropics and the equator, are explicitly marked. Furthermore, the instrument displays planetary hours and a double concentric circle containing the date.

Evidence for this section
  • “The limb of the quadrant is engraved with a scale of degrees”
  • “Further to the apex are two tables with the solar cycle 'CICLVS SOLIS' and the dominical letter 'LITERA D<OMI>NICALIS'”
  • “On the centre of the quadrant are hour lines numbered from 1 to 6 to 12”
  • “The tropics and equator are engraved 'TROPIC CANCRI', 'TROPIC CAPRICOR' and 'LINEA AEQVINOCTIALIS'”

Reverse Face Features

The back of the quadrant repeats the degree scale on the limb, but shifts focus to terrestrial and further temporal measurement. It incorporates a shadow square, which is divided to 5 and 1 and numbered from 1 to 60. This component is labeled as 'VMBRAE RECTAE' and 'VMBRAE VERSAE', with an inner side numbered continuously across the edges.

Occupying the interior of the shadow square is a wind rose featuring 32 directions, with the north marked by a fleur-de-lis. Surrounding this are two further concentric scales: a calendar scale with month names in Latin, and a zodiac scale indicating the position of the sun, where the first point of Aries is set to March 10.

Evidence for this section
  • “The back of the quadrant is engraved on the limb with a scale of degrees similar to the front”
  • “The shadow square is inscribed 'VMBRAE RECTAE' and 'VMBRAE VERSAE'”
  • “Inside the shadow square is a wind rose with 32 directions numbered, north indicated by a fleur-de-lis”
  • “The first point of Aries corresponds to March 10”

Provenance and Physical Condition

The instrument is part of the Dudley bequest and is currently managed by the Istituto e Museo di Storia della Scienza in Florence. The brass surface features intricate engraving, including alternate shading on various scales to facilitate reading. A central hole is present, which is noted by the museum records as a feature possibly intended for the mounting of an alidade.

The overall design includes tables for the calculation of the date of Easter, known as the 'Tabula Pascalis', and a multi-decade list of cycles covering years from 1539 to 1868. This extensive information suggests the quadrant was intended to function as a long-term astronomical reference tool.

Evidence for this section
  • “The instrument originates from the Dudley bequest.”
  • “In the centre of the quadrant is a hole, possibly for fixing an alidade.”
  • “The first one is used to find the date of Easter 'Tabula Pascalis' and the other lists years 'An Do' and 'REVOLVTIONES CICLI LVNAE' and 'REVOLVTIONES CICLI SOLIS' for years from 1539 to 1868.”

Open research questions

  • What specific purpose did the numerical values '4, 4, 4, 1' inside the wind rose serve?
  • Is there evidence of the original alidade or sighting vane that would have occupied the central hole?

Source evidence

Recorded claims and source quotations for Quadrant by Robert Dudley
FieldSource-reported valueSource quotation
MakerRobert Dudley“Signed by Robert Dudley”
Date1597“Dated 1597”
MaterialBrass“Brass; 370 mm in radius”
Inventory Number3365“Inventory number: 3365”
InscriptionSir Robert Duddeley was the Inventer of this Instrument Ano 1597“On the right of the scale is the signature 'Sir Robert Duddeley was the Inventer of this Instrument Ano 1597'”
Radius370 mm“370 mm in radius”

Visible details

  • Signature of Sir Robert Dudley dated 1597 visible on the obverse face
  • Engraved hour lines and zodiacal information
  • Central hole present for potential alidade attachment
  • Brass construction with alternating shading on scales

Research qualifications

  • The function of the central hole is described only as a possibility for an alidade
  • Specific purpose of numerical values in the centre of the wind rose remains unexplained

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

Consulted source

Quadrant

Reviewed 2026-10-26 · Record 740b73a3b1

Terms in this record

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

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