How Did John Harrison Solve the Greatest Scientific Problem of His Time?

October 25, 2022
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A book review for geography lovers

Most of us take GPS for granted. As geographers, we understand how it works, but I have to explain this to laypeople several times. At its most basic, your GPS is a clock, receiving a time stamp from a satellite.

Distance = velocity * time of travel

Velocity is a constant, the speed of light.

What we may not realize is that this concept was developed centuries ago. In the novel, “Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time,” Dava Sobel tells the intriguing tale of its development.

Latitude is an empirical measurement — the distance you are between the pole and the equator — and has been measured for millennia by the stars. Longitude, on the other hand, is a human construct. For centuries, sailors navigated without a clear means of measuring longitude despite many attempts. Even Galileo and Newton remained convinced there was a stellar solution, but none was found.

Far from the limelight, a clockmaker named John Harrison had another approach: build a sea-worthy clock. Two would be deployed on board: one set to Greenwich Mean Time, the other to local time, calibrated by resetting it to noon each day using an astrolabe. Harrison finally perfected his clock… forty years after the British Parliament offered a reward of £20,000, more than a small fortune in those times.

This book details Harrison’s dogged pursuit of this goal, as he battled time, physics, mechanics, Parliament, the Astronomer Royal and others at the Greenwich Observatory, and ruthless competitors. Using Harrison’s own journals and diagrams, as well as historical documents, Sobel tells an intriguing and engaging story. Despite its meticulous attention to detail, the book is very readable. There is also an illustrated version which offers maps, pictures of Harrison’s diagrams and data sheets, photographs of the actual clocks and more.


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Time and Navigation from the Smithsonian Institution

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