Inventor of the marine chronometer  

Born on the 23rd March 1693 and brought up in the village of Foulby, near Wakefield, before his family moved to Lincolnshire, Harrison became a carpenter by trade.   He and his brother, James seemed to have had a natural aptitude for making and repairing clocks. They were so skilled that by 1726 they had made two clocks, so accurate, they only lost a second each month.

Their success decided them to take on the challenge to develop a chronometer, a sea-clock, capable of maintaining its accuracy whilst on board  ships in varying climates and conditions thereby allowing sailors to determine their exact longitude. 

This 'holy grail' of time-keeping had been sought for several centuries and was currently taxing the minds of some of the most distinguished scientists of the age. A prize of  £20,000 had been offered by the Board of Longitude for the person who could come up with a suitable invention.  

Between 1735 and 1772 there were five Harrison chronometers built, each one a gradual improvement on its predecessor. The brothers worked on the first two together but had a disagreement that led to John working on the other three alone. The clocks - now known as H1 through to H5 - were almost friction-free, they required little or no lubrication and no cleaning, were made from materials impervious to rust and which expanded or contracted with changes in temperature but did so in a way that kept the clock's rate constant.  

The final two designs, H4 and H5, were very similar and proved to be the best. The H4 was trailed in 1761 on a two month voyage to Jamaica and found to be only five seconds out on its return.  

The accuracy of Harrison's H4 design (which looked like a giant pocket watch) was sufficient to qualify for the prize. However, he was not liked by many of the country's leading scientists who seemed unable to believe that this uneducated provincial carpenter was worthy of the money despite the evidence of the clocks he'd made. It took the personal intervention of George III before the prize money was given to an elderly and exhausted Harrison in 1773.  

After World War I, Harrison's timepieces were found in a storeroom at the Royal Greenwich Observatory, in very poor condition by retired Naval officer Rupert Gould, who then spent the next 12 years repairing and restoring them. It was Gould, not Harrison, who named the various designs H1 to H5.

Harrison's clocks are still in full working order at the Old Royal Observatory today.    

Useful Websites 

• For further information visit the websites listed under 'Features'.

Further Reading 

Sobel, Dava: Longitude - The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time. (Fourth Estate 1995)

Whittle, Eric A.: The Inventor of the Marine Chronometer - John Harrison of Foulby Wakefield, England. (Wakefield Historical Publications, 1984)  

Quill, H.: John Harrison, Copley Medallist & £20,000 Longitude Prize (Antiquarian Horological Society 1976)