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The Encyclopedia of Horology

Marine chronometer (large watch form) · England

Harrison H4

Verified

A radical departure from Harrison's earlier sea clocks: a large silver pocket-watch-sized instrument rather than a pendulum-like machine.

Technical facts

Escapement
Verge-derived escapement with diamond pallets, remontoire-assisted
Diameter
Approximately 13 cm — large by pocket-watch standards of the day
Case
Silver pair case
Compensation
Bimetallic compensation curb affecting effective balance-spring length

Historical significance

  • A radical departure from Harrison's earlier sea clocks: a large silver pocket-watch-sized instrument rather than a pendulum-like machine.
  • On its 1761–1762 sea trial to Jamaica it kept time accurate enough to determine longitude well within the Board of Longitude's requirements, though Harrison had to fight for full recognition and payment of the prize.
  • Established that a watch-form timekeeper, not a large clock, was the practical solution to the longitude problem, shaping all subsequent marine chronometer design.

Photographs

Harrison H4 chronometer
Harrison H4 chronometer — Colonel Warden at en.wikipedia, CC BY-SA 3.0. Wikimedia Commons file page
Harrison H4 clockwork 2
Harrison H4 clockwork 2 — Photograph by Mike Peel (www.mikepeel.net)., CC BY-SA 4.0. Wikimedia Commons file page
Harrison H4 clockwork 3
Harrison H4 clockwork 3 — Photograph by Mike Peel (www.mikepeel.net)., CC BY-SA 4.0. 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. Royal Museums Greenwich, catalogue and gallery notes on Harrison's timekeepers
  2. Sobel, D., Longitude
  3. Gould, R. T., The Marine Chronometer: Its History and Development

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