John Arnold (1736-99), a Bodmin man, perfected the ships chronometer. For a ship to navigate accurately it had to know both latitude and longitude. Latitude was calculated by using the sun and a sextant, but longitude had to be worked from an accurate knowledge of the time. Ships timepieces had been inaccurate because of changes in temperature and motion effecting their working.
His watch, No 1/36, made in 1778, operated so accurately on trial at Greenwich that he decided to give it a new name, a 'chronometer', and was the person who invented the word.
John Arnold was born in Bodmin in 1736 and was apprenticed as a watchmaker to his father. He lived and worked in a narrow street off Fore Street in Bodmin, and eventually moved to London. He is still remembered with a plaque over the entrance to the narrow passage where he once lived - Arnolds Passage.
John Arnold quarreled with his father and movered away. First to the Hague, then to London in 1756.
He produced many fine timepieces, including the smallest repeating and striking watch, which was set into a ring and presented to King George III. He was said to have been paid 500 guineas for making it.
He made an extremely accurate clock that Captain James Cook used it on his South Sea Voyages 1772 1775. This used for the first time a temperature compensation device using a bi-metallic strip. He also solved the problem of friction in the balance spring.
In 1788 he produced the first Pocket Chronometer which was so accurate that he coined the term "chronnometer" to describe it.
His son John Roger Arnold was born in 1769 and was apprenticed to his father. He went on to improve on his fathers work. They ran J. Arnold & Son together between 1787 and 1799.
John Arnold died in 1799 at the age of 63 and is buried in Chislehurst, Kent.
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