1761 For centuries, mariners had been plagued with the inability to determine longitude while at sea. Measuring longitude required the use of a clock, which compared the exact time on the ship with its starting point. The difference in time would tell how far west or east the ship was, making precise navigation possible.
Yit inventing an accurate shipboard clock proved difficult: Fluctuating temperatures and the ship's movement affected performance. British clockmaker John Harrison (1693-1776) first tried building clocks that replaced the pendulum with a circular balance. It took four attempts before his design for a chronometer was successful.
Created in 1771, the successful chronometer was a sea watch with a stable, high frequency balance, housed in a silver case. Among the first to use Harrison's chronometer, British explorer Captain James Cook (1728-1779) took it on his seco voyage of exploration in 1772.