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The Encyclopedia of Horology

Marine timekeeper (spring-and-balance sea clock) · England

Harrison H1

Verified

John Harrison's first sea clock, built to compete for the longitude prize established by the Board of Longitude's 1714 act.

Technical facts

Escapement
Grasshopper escapement of Harrison's own design
Regulator
Twin balances linked by connecting wires, largely temperature-compensated by bimetallic strips
Materials
Predominantly wood (lignum vitae and oak) with brass fittings
Weight/size
Large — approximately 34 kg; not a portable pocket instrument

Historical significance

  • John Harrison's first sea clock, built to compete for the longitude prize established by the Board of Longitude's 1714 act.
  • Uses paired balances connected by wires and springs to cancel the effect of a ship's motion, entirely without a pendulum.
  • Trialled at sea to Lisbon in 1736 with encouraging results, leading the Board to fund further work (H2, H3, H4).

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

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

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