John Harrison gets his due. Even now his name is virtually unknown, but he made one of the most important discoveries in the history of exploration—how to find longitude. It’s easy to find one’s latitude. If you can see the North Star, you’re in the northern hemisphere. The higher up in the sky it is, the farther north you are. Ditto for the Southern Cross and other features in the southern hemisphere’s night key.
Longitude is also easy in concept—just compare when noon local time is with noon Greenwich Mean Time (GMT), and you’ll know exactly how far east or west you are. The trouble is that building a clock that kept accurate time while enduring rough shipboard conditions was impossible for all of human history. Everyone from Phoenician sailors on up through Columbus and Magellan had no idea what longitudes their discoveries were located at. They could only guess, and they often did a lousy job of it.
The key to finding accurate longitude was a centuries-long pop culture joke, similar to pre-1969 “they’ll put a man on the moon before that happens” jokes. The longitude joke’s currency ended in the mid-1700s when a watchmaker named John Harrison, spurred on by a £20,000 prize sponsored by the Royal Society, invented a series of clocks that were finally up to the task.
Sobel tells the story masterfully, setting up the history of the problem and why it matters, the origins of the Royal Society and prizes for inventions, the significance of the Scientific Revolution, John Harrison’s life story and his chase of the prize, and fascinating descriptions of the materials and craftsmanship that went into Harrison’s remarkable inventions. He made five clocks, each outdoing the last, though H-4, as it is known, is the most famous.