Although it had long been realised that an effective method of finding longitude was of paramount importance, it took a major naval disaster to bring this fact to the attention of the public. In 1707 a squadron of ships returning from Gibraltar under Admiral Sir Clowdisley Shovel miscalculated their position after bad weather and ran aground in the Isles of Scilly. The result of this error was the loss of four ships and some 2000 lives. The public outcry following this tragedy played a significant part in the discussion to set up a body to attempt to find solutions to the pressing problems of navigation.
The second major influence on this decision was a petition to Parliament in 1714 asking him for a reward to be offered for 'discovering the longitude'. The two petitioners were William Whiston, the former Lucasian Professor of Mathematics at Cambridge, and Humphrey Ditton, the mathematical master at Christ's Hospital, London. Although their own schemes were considered totally impractical, the idea of a reward and a commission to administer it was seized upon with great enthusiasm. A Parliamentary Committee, including both Sir Isaac Newton and Edmund Halley, was immediately set up to report on the question of longitude, and its findings fully supported the ideas of Whiston and Ditton for encouraging suggestions. This report enjoyed unanimous acceptance by the House of Commons and in 1713 an Act for the Discovery of Longitude at Sea was passed.
The terms for the payment of the huge reward offered under the new Act were both strict and complex. Payment was to be on a sliding scale according to the accuracy achieved. Further sums of up to £2000 were permitted to be awarded to the inventors of promising schemes to provide encouragement and to enable experiments to be carried out.
The administration of this scheme was to be the direct responsibility of the Board of Longitude. Its members were: the Lord High Admiral of Great Britain; the Speaker of the House of Commons; the First Commissioner of the Navy; the First Commissioner of Trade; the Admirals of the Red White and Blue Squadrons; the Master of Trinity House; the President of the Royal Society; the Astronomer Royal; the Savilian, Lucasian and Plumian Professors of Mathematics at Oxford and Cambridge; and ten named Members of Parliament.
The earliest meeting recorded in the confirmed minutes of the Board of Longitude took place in 1737. One solution to the problem of determinig longitude was the 'chronometer method' which relied on two factors. Firstly, an accurate measurement of apparent local time deduced from the altitude of the Sun, corrected by way of the Equation of Time perfected by the First Astronomer Royal, John Flamsteed was needed. Secondly it was necessary to have an equally accurate measurement of time by way of a clock set at a specified meridian, from which a precise position could be ascertained.
A clock which could keep accurate time at sea was obviously crucial and John Harrison was encouraged by the Board to develop the accuracy of his 'sea clocks' or chronometers, as they came to be known. It was the fourth of these time-keepers, a large watch known as Harrison 4, on which the inventor pinned his hopes. There was a series of controversial trials of this device between 1761 and 1772 and it was not until 1773 that the Board was persuaded.
At the same time as the Board was in dispute with Harrison, it was also in the process of acquiring another promising method of finding longitude. This method, using lunar distances, was based on the accurate tables produced by the German astronomer Tobias Mayer. In their final form the tables proved to be generally accurate to within three nautical miles, which meant that the position of the Moon could be calculated several years in advance. Indeed, the accuracy was such that the Astronomer Royal, Nevil Maskelyne, was able to use the tables to produce the early editions of the Nautical Almanac and Astronomical Ephemeris, the first of which appeared in 1767. This proved to be of vital importance both in navigation and general astronomy, and annual editions are still published today.
As a reult of the greatly increased accuracy in finding longitude and the awarding of the Board's major prize to John Harrison, the Board had lost its primary reason for existing. However, an new Act in 1774 changed the Board's responsibilities away from longitude to navigation in general.
Much attention was now given to improving other techniques of navigation and related topics. Sextants, almost as important to the accurate discovery of longitude as the chronometer, were refined and improved. Significant improvements were still made to chronometers, however, and submitted to the Board for appraisal. Other areas such as the accurate measurement the tonnage of ships were also dealt with, as were subjects such as meteorology, gravity and magnetism and the production of accurate naval charts.
It was partly to achieve the last of these tasks, partly to test chronometers in the environment for which they were designed and partly to make observations of the southern stars to facilitate better navigation that the Board became linked with the voyages of discovery of the late eighteenth and early nineteenth centuries. The most notable were the second and third expeditions of James Cook to Australia, New Zealand and the Pacific in 1772-1775 and 1776-1780. Others of interest include the voyage to Australia in 1801 of HMS Investigator under the command of Matthew Flinders and the exploration of the north-west coast of North America by George Vancover. On all of these expeditions reputable astronomers were employed by the Board. Their task was to carry out astronomical observations, test the reliability of chronometers, measure magnetic variations at different points around the globe, make determinations of latitude and longitude and measure the Earth's gravity. Another great quest in which the Board was involved was the search for a north-west Passage across the top of the American continent between the Atlantic and Pacific Oceans. Rewards, similar to those offered under the 1714 Act were put up for the discovery of this, and lesser amounts offered depending on the most westerly longitude achieved. A similar reward was offered for progress towards the North Pole.
The last major project undertaken by the Board was the foundation of the observatory at the Cape of Good Hope in 1822 with the aim of greatly increasing the knowledge of the southern skies and consequently improving navigation south of the Equator.
By the 1820s, however, the role of the Board was ever becoming less well defined and more closely linked with the pure astronomy undertaken at the Royal Observatory, Greenwich. In later years the Board's existence became overwhelmed by impractical schemes and interminable attempts to find methods of perpetual motion and the quadrature of the circle. Also the initial ardour for the great voyages of discovery had cooled. This all meant that the significance of the Board of Longitude was greatly diminished and consequently it was dissolved in 1828 by Act of Parliament. Its remaining responsibilities, such as chronometer rating and overseas astronomical observation were subsumed into the work of the Royal Observatory.