John Harrison wasn’t just any 18th-century British watchmaker. He was the genius who won the Longitude Prize, a prize given to the person who could successfully build an accurate watch, an instrument necessary for navigation. But when he wasn’t building clocks, he was envisioning much spiffier clocks. And it turns out that one of his thought experiments was even more thoughtful than anyone except Harrison had realized: Guinness World Records has certified Harrison’s pendulum clock as the world’s most accurate.
Harrison (1693-1776) had claimed that this pendulum clock would not gain or lose a second in one hundred days. It was a radical statement, considering that clocks at that time lost a second a week—or more. He never built this particular clock, but horologists at the Greenwich Royal Observatory in London did. And they found it to be as accurate as Harrison had claimed. Guinness World Records concurs.
According to the Royal Museum of Greenwich, “[I]f we know the local times at two points on Earth, we can use the difference between them to calculate how far apart those places are in longitude, east or west...[Sailors] could measure the local time, wherever they were by observing the Sun, but navigation required that they also know the time, at that same moment, at some reference point, e.g. Greenwich, in order to calculate their longitude.” And the reference point they needed was an accurate clock that would not be affected by stormy seas, salty air, and humidity.
Wtihout knowing the longitude of a ship’s position, ships frequently needed to take an indirect route across the waters; the longer the journey, the higher the likelihood of scurvy and starvation.
Want to know more about Harrison’s remarkable feats? You can read about his inventions -- as well as his multiyear struggle for acceptance -- in Dava Sobel’s book Longitude. You can also see the movie starring Jeremy Irons and Michael Gambon.