Latitude—the distance you are north or south of the equator—is fairly easy to measure. Christopher Columbus sailed straight across the ocean in 1492, following a steady latitude. Longitude—your distance east or west—is another story. To measure longitude, you need to measure time.

The inability of sailors to reliably measure longitude created problems. Dava Sobel writes, “untold numbers of sailors died when their destinations suddenly loomed out of the sea and took them by surprise” (6). In 1714, England’s Parliament offered a reward to anyone who could reliably measure longitude. Longitude is the story of that pursuit.

Most interesting here is the human story. The science was necessary, but human prejudice takes centre stage as the astronomers looked down on a mere watch maker named John Harrison. In the end, it was the watchmaker who worked marvels of engineering and definitively answered the challenge.

Sobel, Dava. Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time. Penguin, 1995.