JOHN

See also:

• HARRISON
• HARRISON, BENJAMIN
• HARRISON, FREDERIC (1831— )
• JOHN HARRISON (1693—1776)
• HARRISON, THOMAS (16o6-166o)
• HARRISON, THOMAS ALEXANDER (1853– )
• HARRISON, WILLIAM (1534–1593)
• HARRISON, WILLIAM HENRY (1773–1841)

HARRISON (1693—1776)  , English horologist, was the son of a carpenter, and was born at Faulby, near Pontefract in Yorkshire, in the year 1693 . Thence his father and family removed in 170o to Barrow in Lincolnshire . Young Harrison at first learned his father's trade, and worked at it for several years, at the same time occasionally making a little money by land-measuring and surveying . The bent of his mind, however, was towards mechanical pursuits . In 1715 he made a clock with wooden wheels, which is in the patent museum at South Kensington, and in 1726 he devised his ingenious " gridiron pendulum," which maintains its length unaltered in spite of variations of temperature (see CLOCK) . Another invention of his was a recoil clock escapement in which friction was reduced to a minimum, and he was the first to employ the commonly used and effective form of " going ratchet," which is a spring arrangement for keeping the timepiece going at its usual rate during the interval of being wound up . In Harrison's time the British government had become fully alive to the necessity of determining more accurately the longitude at sea . For this purpose they passed an act in 1713 offering rewards of £1o,000, £15,000 and £20,000 to any who should construct chronometers that would determine the longitude within 6o, 40 and 30 M. respectively . Harrison applied himself vigorously to the task, and in 1735 went to the Board of Longitude with a watch which he also showed to Edmund Halley, George Graham and others . Through their influence he was allowed to proceed in a king's ship to Lisbon to test it; and the result was so satisfactory that he was paid £500 to carry out further improvements . Harrison worked at the subject with the utmost perseverance, and, after making several watches, went up to London in 1761 with one which he considered almost perfect . His son William was sent on a voyage to Jamaica to test it; and, on his return to Portsmouth in 1762, it was found to have lost only i minute 54z seconds .

This was surprisingly accurate, as it determined the longitude within 18 m., and Harrison claimed the full

reward of £20,000; but though from time to time he received sums on account, it was not till 1773 that he was paid in full . In these watches compensation for changes of temperature was applied for the first time by means of a " compensation-curb," designed to alter the effective length of the balance-spring in proportion to the expansion or contraction caused by variations of temperature . Harrison died in London on the 24th of March 1776 . His want of early education was felt by him greatly throughout life . He was unfortunately never able to express his ideas clearly in writing, although in conversation he could give a very precise and exact account of his many intricate mechanical contrivances . Among his writings were a Description concerning such Mechanism as will afford a Nice or True Mensuration of Time (1775), and The Principles of Mr Harrison's Timekeeper, published by order of the Commissioners of Longitude (1767) .