Finding the latitude in the 17th century was straightforward, but finding the longitude was extremely difficult. This compromised the safety of all seafarers, and in one particular incident around 200 lives were lost of the Isles of Scilly.
The admiralty of the day decided to set up a Longitude board and offer a prize to the inventor of a method to reliably calculate the longitude of a vessel. Various methods were tried, including one that took lunar sightings developed by Nevil Maskelyne.
Enter John Harrison. He taught himself to read and write, and was a proficient musician, his real talent was clocks. His first wooden pendulum clock is still in existence, held at The Worshipful Company of Clockmakers. And it was this talent that he put to good use to start to develop the devices that would enable the navy to know their exact longitude.
His first attempt at a device was called H-1 and has lots of new technologies including frictionless bearings, the gridiron pendulum and the grasshopper escapment. This clock lost a second a month compared to the best clocks of the day that would loose 1 minute a day. The clock is still working.
He presented the drawings to the Longitude board, and they gave permission to make one. The clock passed the tests, but as it improved the board decided to amend the original tests make them tougher. Harrison went on to develop 4 versions to meet these changing requirements, culminating in a 5 inch diameter watch that did the same as the H-1.
By this time Nevil Maskelyne was head of the Longitude board. He made it extremely difficult for Harrison as he wanted his preferred lunar method to win. Harrison complied with the demanding requirements, and surrendered his clocks to the board. It was only with the kings intervention that the reward was finally given to Harrison.
Sobel has written quite a dry account of this tale of engineering excellence and political manipulation. Whilst it get all the facts across, it doesn't convey the emotions of the men involved.