The act offered a series of rewards, rather than a single prize. The rewards increased with the accuracy achieved: £10,000 (worth over £ in ) for anyone who could find a practical way of determining longitude at sea with an error of not greater than one
degree of longitude (equates to at the equator). The reward was to be increased to £15,000 if the error was not greater than 40
minutes, and further enhanced to £20,000 (equivalent to £3.97 million in 2025) if it was not greater than half a degree. Other rewards were on offer for those who presented methods that worked within 80 geographical miles of the coast (being the most treacherous part of voyages) and for those with promising ideas who needed help to bring them to readiness for trial. Many rewards were paid out over the 114 years of the Board of Longitude's existence.
John Harrison received more money than any other individual, with several rewards from the 1730s–1750s, and £10,000 in 1765. Subsequent Longitude Acts offered different rewards. The act of Parliament of 1767 held out £5,000 for improvements to
Tobias Mayer's lunar tables and the '''''' (
14 Geo. 3. c. 66) halved the amount offered for any method or instrument achieving the degrees of precision outlined in the original act (i.e. £5,000 for a degree, £7,500 for of a degree or £10,000 for a degree). The '
(58 Geo. 3. c. 20), which completely revised the composition and remit of the Board of Longitude, again changed the rewards, by now offered for improvements to navigation in general rather than simply for finding longitude. In addition, the act outlined rewards for navigating the North West Passage, again on a sliding scale from £20,000 for reaching the Pacific through a north-west passage to £5,000 for reaching 110 degrees west or 89 degrees north and £1,000 for reaching 83 degrees north. In 1820, £5,000 was paid to the officers and crews of and under the act. The 1818 act was amended by the (1 & 2 Geo. 4. c. 20). Both acts were repealed by section 1 of the ' (
9 Geo. 4. c. 66). == Notes ==