HARRISON, JOHN (1693-1776), English horologist, was the son of a carpenter, and was born at Foulby, near Pontefract. 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 un altered in spite of variations of temperature. 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 arrange ment for keeping the timepiece going at its usual rate during the interval of being wound up.
In 1713 the British government offered rewards of £Io,000, £ 15,00o and f 20,00o to any who should construct chronometers that would determine the longitude within 6o, 4o and 3o m. re spectively. Harrison, 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 1 minute 544 seconds. This was surprisingly accurate, as it determined the longitude within 18 m., and Harrison claimed the full reward of L20,000; 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 ap plied for the first time by means of a "compensation-curb," de signed to alter the effective length of the balance-spring in pro portion to the expansion or contraction caused by variations of temperature. Harrison died in London on March 24, 1776.
See his The Principles of Mr Harrison's Timekeeper, published by order of the Commissioners of Longitude (1767) .