This watch helped navigators work out how far east or west a ship had sailed. John Harrison’s H4, completed in 1759, kept reference time that could be compared with local solar time. His son William took it on a 1761 trial toward Jamaica, with a notable prediction on the way to Madeira.
Original animated reconstruction with simplified navigation diagrams. The people, deck, handling and watch exterior are illustrative. This is not a replica of H4’s internal mechanism. Later trials, disputes and wider adoption took further work.
Sources: Royal Museums Greenwich
H4 collection record:
Harrison’s timekeepers:
Longitude and time comparison:
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