On November 12, 1713 the Parliament of Great Britain passed An Act for Providing a Publick Reward for Such Person or Persons as Shall Discover the Longitude at Sea. This was duly published in 1714.
One of the most famous early examples of government incentive for scientific research, this Act of Parliament established a reward of £20,000 for anyone who could invent a reliable and practicable method of finding longitude at sea to within half a degree, with lesser prizes offered for ways of finding it to within one degree and within forty minutes. The Act also established a permanent body of Commissioners, known as the Board of Longitude, to evaluate the merits of all proposed methods, award the prizes and provide research grants of up to £2,000. Despite the incentive provided by the enormous first prize, the problem, which had baffled navigators for centuries, remained unsolved for nearly fifty years, until astronomer Johann Tobias Mayer calculated lunar tables which were accurate enough to calculate longitude at sea to within about half a degree, and John Harrison invented the first accurate marine chronometer about 1760. For his tables in 1763 Mayer's widow received £3000 of the £20,000 prize. Later, after a long struggle, John Harrison received between £8000 and £9000 of the same prize money.
A preliminary version of Mayer’s tables was published in the proceedings of the Göttingen Scientific Society in 1753; meanwhile, Mayer continued to improve the tables until his death in 1762. In 1763 Mayer’s widow sent a copy of the improved tables to the Board of Longitude in application to the prize. The improved tables were first edited for publication by Nevil Maskelyne, the Astronomer Royal, as Tabulae motuum solis et lunae novae et correctae. . . quibus accedit methodus longitudinum promota, eodem auctore, and published in London by John Nourse in 1770. Maskelyne had tested Mayer’s earlier tables with positive results on a voyage to the island of St. Helena in 1761. He also used Mayer’s tables to compute the lunar and solar ephemerides in the early editions of his Nautical Almanac, and since Maskelyne was on the Board of Longitude we may assume that he was influential in having a portion of the prize awarded to Mayer’s widow. Appended to Mayer’s tables are two short tracts, one on determining longitude by lunar distances, together with a description of the reflecting circle (invented by Mayer in 1752), and the other on a formula for atmospheric refraction, which applies a remarkably accurate correction for temperature.
Four years earlier Maskelyne had co-authored with Yorkshire clockmaker John Harrison a technical manual on the design of the chronometer, The Principles of Mr. Harrison's Time-Keeper, with Plates of the Same. This had also been published in London by John Nourse. Harrison perfected a chronometer accurate enough to measure time at a steady rate over long periods, thus permitting the measurement of longitude by comparison of local solar time with an established standard time. Although it was soon supplanted by simpler mechanisms, Harrison's chronometer revolutionized the science of navigation, as it gave navigators their first means of observing true geographical position at any given moment during a voyage. There was no comparable advance in navigational aids until the development of radar in the twentieth century.
Harrison's chronometer was tested on two voyages to the West Indies in 1761 and 1764 and found to be well within the range of accuracy demanded by the 1714 act. In view of this success Harrison felt that he had a legitimate right to the prize money, but the Board of Longitude, on which Nevil Maskelyne sat, raised several objections, one of them being that Harrison had not given them a satisfactory demonstration of how the chronometer worked. Harrison finally agreed to dismantle the instrument before a committee chosen by the Board and to give a full account of its mechanism and manufacture; the results of this demonstration, which took place in 1765, were noted by Nevil Maskelyne and published along with Harrison's own explanation of his invention. The demonstration was ruled satisfactory, but even so Harrison was awarded only half the prize money; it was not until 1773, following the intercession of George iii, that Harrison received the balance.
Baillie, Clocks & Watches: An Historical Bibliography (1951) 140-141, Gould, The Marine Chronometer: Its History and Development (1960) 1-17. Horblit, One Hundred Books Famous in Science (1964) no. 42a. Hook & Norman, The Haskell F. Norman Library of Science and Medicine (1991) Nos. 2, 995, 1468. Wepster, Between Theory and Observations: Tobias Mayer's Explorations of Lunar Motion (2010) 33-40.