John Harrison was a self-educated English clockmaker

Clockmaker

A clockmaker is an artisan who makes and repairs clocks. Since almost all clocks are now factory-made, most modern clockmakers only repair clocks. Modern clockmakers may be employed by jewellers, antique shops, and places devoted strictly to repairing clocks and watches...

. He invented the marine chronometer

Marine chronometer

A marine chronometer is a clock that is precise and accurate enough to be used as a portable time standard; it can therefore be used to determine longitude by means of celestial navigation...

, a long-sought device in solving the problem of establishing the East-West position or longitude

Longitude

Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

 of a ship at sea, thus revolutionising and extending the possibility of safe long distance sea travel in the Age of Sail

Age of Sail

The Age of Sail was the period in which international trade and naval warfare were dominated by sailing ships, lasting from the 16th to the mid 19th century...

. The problem was considered so intractable that the British Parliament offered a prize

Longitude prize

The Longitude Prize was a reward offered by the British government for a simple and practical method for the precise determination of a ship's longitude...

 of £20,000 (comparable to £ in modern currency) for the solution.

Harrison came 39th in the BBC

BBC

The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...

's 2002 public poll of the 100 Greatest Britons

100 Greatest Britons

100 Greatest Britons was broadcast in 2002 by the BBC. The programme was the result of a vote conducted to determine whom the United Kingdom public considers the greatest British people in history. The series, Great Britons, included individual programmes on the top ten, with viewers having further...

.
John Harrison was born in Foulby

Foulby

Foulby is a village in the county of West Yorkshire, England. It is situated near Nostell, between Crofton and Ackworth Moor Top, on the A638 east-south east of the city of Wakefield.-Persons:...

, near Wakefield

Wakefield

Wakefield is the main settlement and administrative centre of the City of Wakefield, a metropolitan district of West Yorkshire, England. Located by the River Calder on the eastern edge of the Pennines, the urban area is and had a population of 76,886 in 2001....

 in West Yorkshire, the first of five children in his family.