Harrison was raised in Foulby in Yorkshire, the son of a carpenter. He was expected to follow the family trade but became fascinated with mechanical clockwork when he was bedridden with smallpox, aged six, and spent his convalescent hours toying with a pocket watch he had been given as a gift.
The family relocated to Barrow upon Humber in Lincolnshire in 1700, where the young Harrison rose to become choirmaster of the parish church.
At 20, Harrison combined his interests to build his first grandfather clock, making both the oak cabinet and pendulum mechanism himself. This and two others survive to this day, one of which is on display in London's Science Museum.
Harrison continued to make clocks, often with the aid of his brother James, a gifted joiner. Together they developed the grid-iron pendulum for longcase clocks, making use of alternating brass and iron rods to cancel out the effect of thermal expansion.
Another of Harrison's innovations was the grasshopper escapement, a control device for releasing a clock's driving power that generated minimal friction and did not require lubrication.
The development for which he remains best known is of course his timepiece for determining longitude on long sea voyages.
The Royal Navy had lost too many ships to wrecks over the decades as a result of being unable to determine their positions globally with any accuracy, especially after many weeks on the waves. While latitude could be easily determined by the height of the sun, locating a vessel's position east or west of the prime meridian was a tougher nut to crack.
The British government formed the Board of Longitude in 1714 and tasked it with solving the problem, integral for all maritime operations from defence to trade. The board offered a cash prize of £20,000 to the scientist who could resolve the question.
Isaac Newton doubted it could ever be done: “A good watch may serve to keep a reckoning at sea for some days and to know the time of a celestial observation; and for this end a good Jewel may suffice till a better sort of watch can be found out. But when longitude at sea is lost, it cannot be found again by any watch.”
Harrison, determined to win the prize, worked on his chronometer from 1728 to 1735, presenting an early version of his "Sea clock" to Astronomer Royal Edmond Halley, who referred him in turn to the leading watchmaker of the day, George Graham.
Harrison had constructed a device that could keep time over a 50-day period without suffering from the effects of wavering temperatures, pressure, humidity or corrosion from salt water.
His effort meant that navigators could find longitude by comparing the length of time they had been at sea with local time, ascertainable from the position of the sun in the sky. Local time was one hour ahead for every 15 degrees of longitude eastwards and one hour behind for every 15 degrees of longitude west.
Graham and the Royal Society were sufficiently impressed to test Harrison's device on a sea trial to Lisbon in 1736.
While the clock faltered on its outward journey aboard the HMS Centurion, it performed handsomely on its return aboard the HMS Orford and the Board of Longitude handed Harrison an additional £500 to develop it further for transatlantic voyages.
Harrison's second generation sea clock was smaller and hardier but it was the third - kept back to prevent it falling into Spanish hands during the War of Austrian Succession in 1741 - that really nailed the problem. Harrison realised that he he had not previously reckoned with the effect of a ship's yawing motion when tacking, which had the potential to throw his clocks out of balance.
Although he never quite perfected the sea clock to his satisfaction - having failed to factor in the delicate physics of the springs controlling the clock's balance wheels - his work marked a giant leap forward and revolutionised maritime travel.
Harrison subsequently turned his attention to watchmaking, realising that measuring longitude could be achieved with greater convenience from a pocketwatch.
He continued to receive grants from the board and from parliament to further advance his work on chronometers over the course of his career until his death in Hampstead at the age of 83 in 1776.
Harrison's clocks were used by such famous seaman of the period as Captain James Cook and Captain William Bligh and his innovations continue to be lauded today.
Composer Harrison Birtwhistle wrote a piano piece in tribute in 1998 and Michael Gambon played him in Channel 4's admired costume drama Longitude in 1999. Perhaps more surprisingly, he was central to the 1996 Only Fools and Horses Christmas special, in which the Trotters finally made their fortune by auctioning off one of his lesser prototypes.
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