History of Oceanography: Voyages of Exploration and Science

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H4 was completed during the period 1755 to 1759. In 1753, Harrison had commissioned John Jefferys, a London watchmaker, to make him a watch following Harrison’s own designs. Harrison discovered with his new watch that if certain improvements were made, it had the potential to be an excellent timekeeper. H4 is completely different from the other three timekeepers. It is just 13cm in diameter and weighs 1.45kg; it looks like a very large pocket watch. Harrison’s son William set sail for the West Indies, with H4, aboard the ship Deptford on November 18, 1761. They arrived in Jamaica on January 19, 1762, where the watch was found to be only 5.1 seconds slow!

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