A carpenter solved the problem that had killed thousands of sailors
For two centuries, ships couldn't determine their east-west position at sea. Astronomers had a theory. A self-taught clockmaker from Lincolnshire had a watch.
Longitude — how far east or west you are — defeated navigators for generations. Latitude you could calculate by the sun's height at noon. Longitude required knowing what time it was back at home port while simultaneously noting local time at sea. The mismatch tells you how far you've traveled. The problem was that no clock in 1714 kept accurate time on a rolling ship in changing temperatures.
Britain's Parliament that year offered £20,000 — roughly equivalent to several million pounds today — to whoever could solve it. The scientific establishment focused on lunar-distance calculations. John Harrison, a carpenter and self-taught clockmaker from Lincolnshire, built a series of timepieces that got progressively smaller and more accurate.
His fourth design, completed in 1759, looked like a large pocket watch. Tested on a voyage to Jamaica, it lost only five seconds over ten weeks at sea. It was, by every measure, the answer to the problem.
Harrison then spent years fighting the prize committee, who preferred the astronomical method and kept moving the goalposts. He was 79 and had to appeal directly to King George III before he received full recognition. Dava Sobel's account of his story is a reminder that solving the right problem is often only half the battle.