Harrison's third marine chronometer, 1757.
© Science Museum / Science & Society Picture Library
Harrison's third marine chronometer, 1757. John Harrison (1693-1776), English inventor and horologist, discovered the means by which longitude could be determined accurately. He developed a marine chronometer which, in a voyage to Jamaica (1761-1762) determined the longitude within 18 geographical miles. He also invented the gridiron pendulum (1726), the going fusee and the remontoir escapement.