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The Encyclopedia of Horology

Marine chronometer · Two-day marine chronometer

Thomas Mercer Two-Day Marine Chronometer No. 19116

Partially verified

This Thomas Mercer two-day marine chronometer is housed in a two-tier mahogany deck box. The instrument features a four-pillar single chain fusee movement with Harrison’s maintaining power and an Earnshaw-type spring detent escapement. It includes a split bimetallic balance with cylindrical compensating weights and a helical palladium balance spring. The 4-inch circular silvered dial displays Roman numerals, a central subsidiary seconds dial, and a power reserve indicator marked UP/DOWN. Uniquely, the dial contains a side aperture exposing electrical contacts and terminals on the case side, configured to emit a one-second pulse. The chronometer is mounted in gimbals within a lacquered brass bowl with a shuttered winding aperture at the rear. The mahogany box features a glazed viewing panel in the lid and an applied brass plate identifying the maker, location, and serial number.

A front-facing view of the Thomas Mercer marine chronometer in its open mahogany deck box, showing the silvered dial, gimbal mounting, and electrical terminals.
A front-facing view of the Thomas Mercer marine chronometer in its open mahogany deck box, showing the silvered dial, gimbal mounting, and electrical terminals. — Flints Auctions Ltd (via Invaluable). Rights pending — permission not yet requested. Original source

Catalogue identity

Source
www.invaluable.com
Category
Marine chronometer · Two-day marine chronometer
Maker / attribution
Thomas Mercer
Reference
Not recorded
Catalogue / lot identifier
183
Source-reported date
2nd Quarter of 20th Century
Source-reported place
England
Source-reported serial
19116

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

Movement and Escapement Construction

The movement is constructed as a four-pillar single chain fusee mechanism. It incorporates Harrison’s maintaining power to ensure continuous operation during winding. The escapement is of the Earnshaw-type spring detent variety.

The regulation is controlled by a split bimetallic balance fitted with cylindrical compensating weights and a helical palladium balance spring. The backplate of the movement is spotted, and the pillars and backcock are secured with blued-steel screws.

Evidence for this section
  • “four-pillar single chain fusee movement”
  • “Earnshaw-type spring detent escapement”
  • “helical palladium balance spring”

Dial and Electrical Features

The 4-inch silvered dial is engraved with Roman numerals and carries the maker's signature and serial number. It features a power reserve indicator at the top labeled UP/DOWN and a pierced subsidiary seconds dial.

An aperture in the dial reveals electrical contacts which connect to external terminals. These contacts are designed to emit a one-second pulse. The dial also features an engraved caution reading 'HANDS FORWARD ONLY' around the circumference.

Evidence for this section
  • “4-inch circular silvered dial”
  • “incorporating a subsidiary seconds dial at the centre pierced to expose the seconds wheel”
  • “designed to emit a one-second pulse”

Case and Housing

The chronometer is enclosed in a lacquered brass bowl with a screw-down bezel. A shuttered aperture at the rear allows for winding. The instrument is suspended in gimbals.

The entire assembly is housed in a two-tier mahogany deck box. The lid is fitted with a glazed viewing panel. A brass plate applied to the box identifies the manufacturer as Thomas Mercer Ltd of St. Albans, England, and repeats the serial number 19116.

Evidence for this section
  • “lacquered brass bowl, complete with shuttered winding aperture to the rear”
  • “mounted in gimbals within a two-tier mahogany box fitted with a glazed viewing panel to the lid”
  • “applied with brass plate inscribed THOMAS MERCER LTD, ST. ALBANS, ENGLAND No 19116”

Open research questions

  • What specific survey or astronomical projects utilized Thomas Mercer chronometers with electrical contact outputs in the mid-20th century?
  • What are the specific technical specifications of the pulse-generating contacts compared to standard nautical chronometers of the era?

Source evidence

Recorded claims and source quotations for Thomas Mercer Two-Day Marine Chronometer No. 19116
FieldSource-reported valueSource quotation
MakerThomas Mercer“THOMAS MERCER LTD, ST. ALBANS”
Movement TypeFour-pillar single chain fusee“four-pillar single chain fusee movement”
EscapementEarnshaw-type spring detent“Earnshaw-type spring detent escapement”
Balance SpringHelical palladium“helical palladium balance spring”
Dial FeaturesPower reserve and electrical contacts“incorporating a subsidiary seconds dial at the centre pierced to expose the seconds wheel, and an additional side aperture revealing electrical contacts”
Box Dimensions17cm x 19cm“17cm x 19cm”

Visible details

  • The dial is engraved with the caution 'HANDS FORWARD ONLY'.
  • A subsidiary seconds dial at the centre is pierced to expose the seconds wheel.
  • Electrical terminals are visible on the side of the brass bowl.
  • The mahogany box includes a glazed lid section.

Research qualifications

  • The exact survey or astronomical purpose of the electrical pulse mechanism remains unconfirmed beyond the suggested likelihood.
  • The functional status regarding accuracy is not verified by the auction description.

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

Consulted source

Mahogany Cased Two Day Marine Chronometer, Thomas Mercer,

Reviewed 2026-10-26 · Record f44d42cc92

Terms in this record

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

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