A self-taught carpenter cracked the navigation problem that had stumped the British Navy for centuries — then spent decades fighting the scientific establishment to claim his prize.
For centuries, sailors could calculate their latitude (north-south position) by measuring the sun's height. But longitude — east-west position — was impossible to determine at sea, causing ships to run aground and thousands of sailors to die. In 1714, the British Parliament offered £20,000 (millions in today's money) to anyone who could solve it.
John Harrison was a self-taught carpenter from Yorkshire with no formal scientific training. Beginning in the 1720s, he devoted his life to building a clock precise enough to solve the problem: if you knew the exact time at a fixed reference point, you could calculate how far east or west you had sailed.
Harrison's first three timepieces — H1, H2, and H3 — were extraordinary engineering achievements, each improving on the last. But they were large, heavy marine clocks. His fourth attempt, H4, shocked everyone: it was a pocket watch. On a sea trial to Jamaica in 1761, it lost just five seconds over 81 days.
The Board of Longitude, dominated by astronomers who favored a competing method using lunar tables, refused to award Harrison the prize. They dismissed his results, demanded he hand over his instruments, and required him to build two more copies before they'd consider paying him.
Harrison was 79 years old and had been fighting the Board for nearly 40 years when he finally appealed directly to King George III. The King tested Harrison's H5 himself, declared it accurate, and reportedly told his courtiers 'By God, Harrison, I'll see you righted.' Parliament awarded Harrison £8,750 — but never officially declared him the prize winner.
Harrison's marine chronometer transformed navigation. Within decades, every Royal Navy ship carried one. Captain James Cook used a copy of H4 on his second voyage of discovery, calling it 'our faithful guide through all vicissitudes of climates.'
Harrison died in 1776, just three years after finally receiving compensation. His four original timepieces — H1 through H4 — survive and are on display at the Royal Observatory in Greenwich, still in working order.