Editing Clock (section)

===Marine chronometer===

{{main|Marine chronometer}}

A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation. The position of a ship at sea could be determined with reasonable accuracy if a navigator could refer to a clock that lost or gained less than about 10 seconds per day. This clock could not contain a pendulum, which would be virtually useless on a rocking ship. In 1714, the British government offered large [[longitude prize|financial rewards]] to the value of 20,000 pounds<ref name="Rigden2003">{{cite book|author=John S. Rigden|title=Hydrogen: The Essential Element|url=https://books.google.com/books?id=FhFxn_lUvz0C|year=2003|publisher=Harvard University Press|isbn=978-0-674-01252-3|page=185}}</ref> for anyone who could determine longitude accurately. [[John Harrison]], who dedicated his life to improving the accuracy of his clocks, later received considerable sums under the Longitude Act.

In 1735, Harrison built his first chronometer, which he steadily improved on over the next thirty years before submitting it for examination. The clock had many innovations, including the use of bearings to reduce friction, weighted balances to compensate for the ship's pitch and roll in the sea and the use of two different metals to reduce the problem of expansion from heat. The chronometer was tested in 1761 by Harrison's son and by the end of 10 weeks the clock was in error by less than 5 seconds.<ref name=gould>{{cite book|author=Gould, Rupert T.|author-link=Rupert Gould|title=The Marine Chronometer. Its History and Development|location=London|publisher=J.D. Potter|page=66|year=1923|isbn=978-0-907462-05-7}}</ref>