Longitude Prize

The Longitude rewards refer to the system of inducement prizes offered by the British government as a simple and practical method for the precise determination of a ship's longitude at sea. The rewards, established through an Act of Parliament (the Longitude Act) in 1714, were administered by the Board of Longitude.

This was by no means the first reward to be offered to solve this problem. Philip II of Spain offered one in 1567, Philip III in 1598 offered 6,000 ducats and a pension, whilst the States General of the Netherlands offered 10,000 florins shortly after. In 1675 Robert Hooke wanted to apply for a £1,000 reward in England for his invention of a spring-regulated watch. However, these large sums were never won, though several people were awarded smaller amounts for significant achievements.

The measurement of longitude was a problem that came into sharp focus as people began making transoceanic voyages. Determining latitude was relatively easy in that it could be found from the altitude of the sun at noon with the aid of a table giving the sun's declination for the day. For longitude, early ocean navigators had to rely on dead reckoning, based on calculations of the vessel's heading and speed for a given time (much of which was based on intuition on the part of the master and/or navigator). This was inaccurate on long voyages out of sight of land, and these voyages sometimes ended in tragedy. An accurate determination of longitude was also necessary to determine the proper "magnetic declination", that is, the difference between indicated magnetic north and true north, which can differ by up to 10 degrees in the important trade latitudes of the Atlantic and Indian Oceans. Finding an adequate solution to determining longitude at sea was therefore of paramount importance.

The Longitude Act only addressed the determination of longitude at sea. Determining longitude reasonably accurately on land was, by the 16th century, possible by a well established method using the Galilean moons of Jupiter as an astronomical 'clock'. The moons were easily observable on land, but numerous attempts to reliably observe them from the deck of a ship resulted in failure. For details on other efforts towards determining the longitude, see History of longitude.

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