As the Age of Exploration got underway in the late 1400s, ships ventured far out to sea: a vast expanse with no landmarks to give sailors their position. Though they could determine their distance north or south of the Equator by observing the sun, moon, and stars, they had no way of knowing how far east or west they were. This was the “longitude problem,” named for the vertical lines of longitude on maps of the Earth. Without knowing a sailing vessel’s position relative to one of those lines, it and its crew effectively were lost. Although methods existed by which captains could estimate their longitude, being even slightly off could prove disastrous as errors compounded over time and distance. A ship might wander for weeks while its crew starved or, as it neared known land, crash onto shores hundreds of miles east or west of its destination. This was what happened in 1707, when four British naval vessels and nearly everyone on board sank after striking rocks miles away from their expected location.

In 1714, the English Parliament passed the Longitude Act, which provided a large cash prize to anyone who could develop a method of determining a ship’s longitude to within half a degree (roughly 34 miles at the Equator), with lesser prizes for methods that neared that level of accuracy: “The fact that the government was willing to award such huge sums for ‘Practicable and Useful’ methods that could miss the mark by many miles eloquently expresses the nation’s desperation over navigation’s sorry state” (54).