Harrison's H4 Marine Chronometer Sea Trial
November 18, 1761 · Early Modern
On November 18, 1761, John Harrison's marine chronometer (H4) began its sea trial aboard HMS Deptford from Portsmouth to Jamaica. The pocket watch-sized timepiece addressed the centuries-old longitude problem by keeping accurate time at sea, losing only 5.1 seconds over the 81-day voyage. This enabled navigators to determine east-west position within approximately one nautical mile. The demonstration represented the culmination of Harrison's decades-long effort to meet the standards of the British Longitude Prize.
Key Figures
John HarrisonWilliam Harrison
Locations
Portsmouth Historic DockyardHMS DeptfordKingston, Jamaica
Topics
inventionnavigationmaritimelongitudechronometer
Connected Events — 2 Connections
Harrison proven longitude solution enabled precision navigation Cook used to chart the Pacific; Cook second voyage carried K1 copy of H4 James Cook's First Voyage
Harrison chronometer solved the longitude problem at sea, enabling precise longitudinal measurement that made the 1884 standardization of a prime meridian both practical and necessary International Meridian Conference
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