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The Encyclopedia of Horology

France / England · Principle c. 1748–1765 (Le Roy); English spring-detent form patented separately by Arnold and Earnshaw in the 1780s

Detent (Chronometer) Escapement

Partially verified

The detent escapement's near-frictionless detached impulse made it the standard for marine chronometers into the twentieth century, though its lack of self-starting made it unsuitable for wristwatches.

Pierre Le Roy is generally credited with the first detached escapement usable in a marine timekeeper, giving the balance a free, unimpeded swing for most of its arc.

John Arnold and Thomas Earnshaw independently developed practical spring-detent escapements in England in the 1780s; both men held English patents for their own detailed constructions, and priority between them was contested in their lifetimes.

How to verify this yourself

Arnold's and Earnshaw's English patents are catalogued in The National Archives, Kew (series C 66 and later patent office series). Exact patent numbers are not stated here pending direct archive lookup; researchers should search the archive's patent index by inventor surname and decade.

Manufacturers known to have used it

  • John Arnold & Son
  • Thomas Earnshaw
  • later British and Swiss chronometer makers

Photographs

Description of the Le Roy detent escapement mechanism 14 August 1748
Description of the Le Roy detent escapement mechanism 14 August 1748 — Academie des Sciences, France 14 August 1748, Public domain. Wikimedia Commons file page
British Museum Marine Chronometer 1
British Museum Marine Chronometer 1 — Photograph by Mike Peel (www.mikepeel.net)., CC BY-SA 4.0. Wikimedia Commons file page
Diagram of the chronometer detent escapement Britten's Clock and Watchmaker's Handbook 9th Edition 1896
Diagram of the chronometer detent escapement Britten's Clock and Watchmaker's Handbook 9th Edition 1896 — F.J. Britten, Public domain. Wikimedia Commons file page

Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.

Sources & references

  1. Betts, J., Arnold & Earnshaw: The Practicable Marine Chronometer (National Maritime Museum)
  2. The National Archives, Kew — patent index, consulted for existence only

Where sources disagree, the disagreement is stated rather than resolved silently.