John Harrison solved longitude at sea, the Board of Longitude withheld the £20,000 prize, and his son took the case to the king

In 1714 Britain offered £20,000 for a way to find longitude at sea within 30 nautical miles. John Harrison, a self-taught clockmaker, built four timekeepers. On a voyage to Jamaica in 1761 and 1762 his son William took the watch known as H4. It arrived 5 seconds slow, an error of about two miles. The Board of Longitude called the result a fluke and demanded a second trial. In 1764 William took H4 to Barbados, where it fixed longitude within about ten miles. The Board still refused to certify the prize. A 1765 Act promised £10,000 once Harrison disclosed how H4 worked and the rest once other makers could copy it. On 5 May 1766 the Astronomer Royal, Nevil Maskelyne, took H4 for ten months of tests and published poor results, which Harrison disputed. In 1772 William had a fifth watch lodged at King George III's private observatory at Richmond, and Harrison appealed to the king. On 14 June 1773 Parliament granted a further sum, given as £8,750 by one source and £8,570 by another. The Board said it was a bounty, not the prize. The official prize was never awarded. Harrison died on his 83rd birthday, 24 March 1776. The original H2, H3 and H4 are at the Royal Observatory, Greenwich. H1 is being conserved.