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Harrison, John

miles marine prize time

(1693–1776) English navigator and horologist.

A Yorkshireman, Harrison was a carpenter-turned-clockmaker who invented the marine chronometer and so revolutionized marine navigation and exploration.

With the colonial and naval ambitions of the European nations in the late 17th and early 18th-c, marine navigation was an issue of key importance. In 1707, 2000 lives were lost when an English fleet unexpectedly struck rocks off the Scilly Isles, over 100 miles off course. Such was the need for reliable marine navigation that in 1714 the British government put up a prize of £20 000 for a practical way of measuring longitude at sea to within 30 miles after a voyage of 6 weeks, corresponding to keeping time to within 3 seconds a day.

In those days position at sea was found by measuring the angles of certain stars at an accurately known time. Since the rotation of the Earth means that an error of just 1 minute in time leads to an error of 15 nautical miles in longitude, accurate and reliable measurement of time was the limiting factor.

Harrison set about winning the prize and, after making several remarkable wooden clocks that were the most accurate timekeepers of their day, devised in 1737 a ‘sea clock’ which used a pair of dumb-bells linked by springs in place of a swinging pendulum. H1, as it is known, was tested by the Admiralty and proved a great success, correctly predicting landfall when the ship’s master thought he still had 60 miles to run. Something of a perfectionist, Harrison then proceeded to improve his design, making a number of innovations along the way, including the bimetallic strip to compensate for temperature variations, and 24 years later produced his masterpiece, H4.

During sea trials lasting a year, H4 was found to be a mere 39 seconds out on its return to Britain, well within the error limits required for the prize. Unfortunately for Harrison, now almost 70, the government then proceeded to set him a series of further tasks before it would agree to pay him the prize money. After Harrison had spent another 10 years on these tasks, King George III heard of his plight and intervened, spending 10 weeks personally testing H5 at his private observatory together with Harrison and the Astronomer Royal. They found H5 to be accurate to within a third of a second a day and the following year, in 1773, Harrison was eventually awarded his money, less expenses. Shortly before Harrison’s death in 1776, proved the real value of his work by taking his chronometer on his second voyage to the Pacific, where he used it to accurately map Australia and New Zealand.

Hart to Hart [next] [back] Harris, Wesley L.(1941–) - Educator, scientist, Chronology

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