360Harrison's sea clock solves the longitude problem
In 1761 and 1762, John Harrison's fourth sea clock, H4, sailed from England to Jamaica and lost only about five seconds over the voyage. Accurate time at sea let sailors calculate their longitude, their position east or west, for the first time. Harrison, a self-taught carpenter and clockmaker, had worked on the problem for decades.
For centuries, sailors could not reliably measure their longitude. Thousands of lives and many ships were lost. In 1714, the British Parliament offered a large prize for a solution.
Longitude can be found by comparing local time with the time at a home port, but that needs a clock that keeps perfect time on a rolling ship, through heat and cold.
John Harrison, a carpenter from Yorkshire, built a series of sea clocks. His fourth, H4, looked like a large pocket watch. On a voyage to Jamaica in 1761 and 1762, it lost only about five seconds.
The prize committee was slow to pay, and Harrison received his full reward only in 1773, with the help of King George III. Marine chronometers became standard on ships for two centuries. Harrison's clocks can be seen at the Royal Observatory, Greenwich.
- 1714
- The Longitude Act offers a prize
- 1735
- Harrison's first sea clock, H1
- 1761–1762
- H4 sails to Jamaica
- 1773
- Harrison receives his reward
Sources: Royal Museums Greenwich · Britannica.