Skip to content
The Encyclopedia of Horology

Marine timekeeper (large sea clock) · England

Harrison H3

Verified

Harrison's third sea clock, on which he worked for nearly two decades, introducing the bimetallic strip (a direct ancestor of the bimetallic compensation balance used in later chronometers) and caged roller bearings to reduce friction.

Technical facts

Escapement
Grasshopper-derived escapement of Harrison's own design, further refined from H1
Innovation
Believed to be the first practical use of a bimetallic strip for temperature compensation
Bearings
Caged roller bearings, an early anti-friction device

Historical significance

  • Harrison's third sea clock, on which he worked for nearly two decades, introducing the bimetallic strip (a direct ancestor of the bimetallic compensation balance used in later chronometers) and caged roller bearings to reduce friction.
  • Never itself fully solved the longitude problem at sea in the way H4 later did, but the mechanical innovations developed while building H3 fed directly into H4's design.
  • Illustrates that Harrison's path to H4 was incremental across four increasingly refined machines (H1–H4), not a single isolated invention.

Related photographs

Replica of John Harrison's first marine timekeeper, by Herbert Davies, Emsworth, Hampshire, completed c. 1962 - Clockmakers' Museum - London, UK - DSC05428
Replica of John Harrison's first marine timekeeper, by Herbert Davies, Emsworth, Hampshire, completed c. 1962 - Clockmakers' Museum - London, UK - DSC05428 — Daderot, CC0. Wikimedia Commons file page

No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.

Sources & references

  1. Royal Museums Greenwich, catalogue and gallery notes on Harrison's timekeepers
  2. Sobel, D., Longitude

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