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The Encyclopedia of Horology

Marine chronometer · Two-day marine chronometer

Two-day Marine Chronometer by Thomas Mercer, no. 12827

Partially verified

The Science Museum Group collection holds this two-day marine chronometer made by Thomas Mercer in St Albans. Preserved under object number 1931-716, the instrument is housed within an ebony timber case fitted with corner stringing, flush brass carrying handles, and an inset mother-of-pearl plaque on the lid. The chronometer bowl rests in a brass gimbal mount alongside a locking mechanism. The dial shows Roman hour numerals, blued hands, an up-and-down state-of-wind indicator below XII, and an expanded subsidiary seconds dial above VI. Museum records list construction materials including brass, mother-of-pearl, glass, elinvar, and ebony.

Two-day marine chronometer by Thomas Mercer, no. 12827, in an ebony case
Two-day marine chronometer by Thomas Mercer, no. 12827, in an ebony case — Science Museum Group. Rights pending — permission not yet requested. Original source

Catalogue identity

Source
collection.sciencemuseumgroup.org.uk
Category
Marine chronometer · Two-day marine chronometer
Maker / attribution
Thomas Mercer
Reference
Not recorded
Catalogue / lot identifier
1931-716
Source-reported date
1860-1930
Country
United Kingdom
Source-reported serial
12827

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

Identity and Documented Provenance

This two-day marine chronometer, catalogued under object number 1931-716 by the Science Museum Group, is attributed to maker Thomas Mercer of St Albans and is identified in the title with number 12827. Museum documentation records a credit line to Thomas Mercer Ltd., though comprehensive acquisition details are not provided in the entry.

The object is recorded as a chronometer type under the category Time Measurement, with its housing described as an ebony case.

Evidence for this section
  • “Two-day Marine chronometer, by Thomas Mercer, St Albans, no.12827, in ebony case, 1860-1930”
  • “Object Number: 1931-716”
  • “credit: Thomas Mercer Ltd.”
  • “Category: Time Measurement”
  • “type: chronometer”

Casing and Physical Construction

The chronometer bowl is suspended in a brass gimbal ring inside an open hinged wooden case. Closed case dimensions are documented as 194 mm in depth, 189 mm in width, and 193 mm in height, alongside another set of recorded measurements: depth 190 mm, height 190 mm, and width 180 mm.

The wooden case is bordered with double line stringing and brass corner reinforcements, with a brass keyhole escutcheon on the front face. Its upper lid features a plain rectangular mother-of-pearl plaque and an interior glazed viewing window reflecting the dial. Listed materials in the museum catalogue include brass (copper, zinc alloy), mother-of-pearl, glass, elinvar (alloy including nickel, steel and chromium), and ebony.

Evidence for this section
  • “Chronometer bowl suspended in a brass gimbal ring inside an open hinged wooden case.”
  • “overall (closed): 194 mm x 189 mm x 193 mm,”
  • “Measurements: depth: 190mm height: 190mm width: 180mm”
  • “Wooden case is bordered with double line stringing and brass corner reinforcements, with a brass keyhole escutcheon on the front face.”
  • “Upper lid features a plain rectangular mother-of-pearl plaque and an interior glazed viewing window reflecting the dial.”
  • “Materials: brass (copper, zinc alloy) , mother-of-pearl , glass , elinvar (alloy including nickel, steel and chromium) and ebony”

Source Discrepancies and Limitations

The museum record presents conflicting chronological data within the same catalogue entry: the 'Made' field states '1850-1880 in St Albans', whereas the title cites '1860-1930'.

The source explicitly notes that records undergo ongoing revision and that the institution cannot guarantee the accuracy of information shown on the website. Internal mechanical components, such as any specific balance parts related to the listed elinvar alloy, are not detailed beyond the general materials list.

Evidence for this section
  • “Made: 1850-1880 in St Albans”
  • “Two-day Marine chronometer, by Thomas Mercer, St Albans, no.12827, in ebony case, 1860-1930”
  • “Our records are constantly being enhanced and improved, but please note that we cannot guarantee the accuracy of any”
  • “Materials: brass (copper, zinc alloy) , mother-of-pearl , glass , elinvar (alloy including nickel, steel and chromium) and ebony”

Open research questions

  • Which internal component of chronometer no. 12827 is composed of the listed elinvar alloy?
  • Can Mercer company ledgers reconcile the conflicting dates of 1850–1880 and 1860–1930 for serial number 12827?
  • What was the specific nature and date of the transaction credited to Thomas Mercer Ltd. under object number 1931-716?

Source evidence

Recorded claims and source quotations for Two-day Marine Chronometer by Thomas Mercer, no. 12827
FieldSource-reported valueSource quotation
Object Number1931-716“Object Number: 1931-716”
MakerThomas Mercer“maker: Thomas Mercer”
Place of ManufactureSt Albans“Made: 1850-1880 in St Albans”
Serial Number12827“no.12827”
Case Dimensions (Closed)194 mm x 189 mm x 193 mm“overall (closed): 194 mm x 189 mm x 193 mm”
Secondary Dimensions190 mm depth x 190 mm height x 180 mm width“Measurements: depth: 190mm height: 190mm width: 180mm”
Credit LineThomas Mercer Ltd.“credit: Thomas Mercer Ltd.”
CategoryTime Measurement“Category: Time Measurement”

Visible details

  • Chronometer bowl suspended in a brass gimbal ring inside an open hinged wooden case.
  • Silvered dial marked with Roman hour numerals, subsidiary seconds dial above VI, and state-of-wind indicator below XII.
  • Upper lid features a plain rectangular mother-of-pearl plaque and an interior glazed viewing window reflecting the dial.
  • Wooden case is bordered with double line stringing and brass corner reinforcements, with a brass keyhole escutcheon on the front face.

Research qualifications

  • Dating is ambiguous in the source, which gives both '1850-1880' and '1860-1930'.
  • Internal movement components, including the elinvar balance reported by the museum, are enclosed within the brass bowl and not visible.

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

Consulted source

Marine Chronometer by Mercer, 1860-1930 | Science Museum Group Collection

Reviewed 2026-10-21 · Record 14e4d555f4

Terms in this record

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

Other two-day marine chronometer records