Board of Longitude

Board of Longitude, the general name by which the commissioners for the discovery of the longitude at sea were known. The board was established by Act of Parliament in 1714 during the reign of Queen Anne. Its early history is closely associated with William Whiston, a dissenting clergyman, and Humphrey Ditton, mathematical master at Christ's Hospital School. On 14 July 1713, in a letter to a newspaper, they attributed the disaster that had overcome Admiral Sir Clowdisley Shovel's fleet on September 1707 to its inability to determine its longitude. They appealed to Parliament to offer a substantial award to overcome this problem and in due course a committee was appointed to examine it. Eminent mathematicians and astronomers, including Sir Isaac Newton, president of the Royal Society, and Edmond Halley, who succeeded Flamsteed as Astronomer Royal, were consulted, and on their recommendation the Board of Longitude was established. This offered a prize of £20,000 for a solution to the problem, stipulating an accuracy to within 30 miles (48 km).

It had long been understood that since time measurement is a function of the earth's rotation on its axis, time and longitude must be interchangeable and, for example, if an event (such as an eclipse) could be seen simultaneously at two places on earth the difference in their local times at that instant would be (translated into angular measure) the difference in their longitudes. Local time was comparatively simple to establish—for instance, by taking equal altitudes of a body either side of the meridian—but before the advent of radio there was no means of transmitting instantaneously the time of the event in question. However, as early as 1522, the Flemish astronomer Gemma Frisius had pointed out that if a voyager carried an accurate enough clock and kept it wound up he would only have to compare its reading with the local time to find the change in longitude.

An alternative solution, probably favoured by most astronomers, lay in the observation of lunar distances using the moon's movements in the sky as a form of clock face. But the prize was ultimately awarded in 1765 to John Harrison, the designer of several remarkable timepieces, the most accurate of which, during its voyage from Britain to Barbados and back, lost only fifteen seconds in 156 days. Only half the prize money was awarded at first, as some commissioners expressed doubts as to the validity of Harrison's achievement, since the Act of Parliament called for a method to be generally applicable and a single chronometer could scarcely be classed as a universal solution. However, in 1773 the balance of the prize money, to some extent due to the king's influence, was paid to Harrison.

The commissioners had also been empowered to grant sums of money up to £2,000 annually to assist bona fide investigators, and award prizes for minor discoveries and improvements in relation to the longitude problem. The first such grant was made in 1737 and the last in 1815. The board continued to operate until 1828, by which time the problem of longitude had ceased to attract attention. During its existence, it had disbursed more than £100,000.

This had been a remarkable period in the development of celestial navigation that saw the invention of the double-reflection sextant, an enormous increase in the knowledge of the theory of the motion of the moon that led to the practice of lunar distance observations, and finally the ultimate solution of the longitude problem by the development of the marine chronometer.

Bibliography

Andrewes, W. (ed.), The Quest for Longitude (1993).
Howse, D. , Greenwich Time and the Discovery of the Longitude (1980).
Sobel, D. , Longitude (1996).

Mike Richey