Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time

A woodworker by trade, John Harrison was born in 1693 and took an early interest in physics and engineering. In 1727 he accepted Parliament’s challenge of inventing a solution to the problem of finding longitude to within half a degree. A self-taught clockmaker, Harrison constructed five precision clocks, known as H-1 through H-5, which were accurate enough to pin down a ship’s longitude to within half a degree. The pride Harrison took in his work is evident not only in the decades he devoted to it, but also in the fact that he declined an early offer of the prize money because he was dissatisfied with his results.

In vying for Parliament’s prize, Harrison faced stiff competition from astronomers, especially the directors of the Greenwich Royal Observatory, whose celestial method of determining longitude threatened to bypass all of Harrison’s efforts. There was an element of class prejudice and intellectual snobbishness to the Board of Longitude’s treatment of Harrison; he came from a family of tradesmen rather than the gentry or professional classes, and his more mechanistic work wasn’t considered scientific in the same sense as more abstract fields like astronomy. Harrison and his son William eventually turned to King George III, who championed the clockmaker’s cause and helped John gain respect and prize money. Harrison’s H-4 and H-5 clocks, each small enough to hold in one hand, became the mechanical standards, soon copied by other watchmakers, by which sailors could efficiently determine their location at sea.

The Reverend Nevil Maskelyne was born in 1732 and educated at Cambridge. He was “a bit of a prig” and a meticulous record-keeper who from a young age was determined to be an astronomer (112). In 1765 he became the fifth Astronomer Royal. Maskelyne and John Harrison became enemies over the longitude problem, with Maskelyne working closely with former Astronomer Royal James Bradley on the lunar method in an effort to win the longitude prize. As a member of the Board of Longitude, Maskelyne requisitioned all of Harrison’s notes and sea clocks, subjected them to abusive tests, and insisted they weren’t accurate. Despite these efforts to quash Harrison’s timepieces, the clockmaker prevailed, and history relegated Maskelyne’s lunar tables and sextants to checking the accuracy of the sea clocks that did the important work.

In 1675, astronomer John Flamsteed convinced England’s King Charles II to build him an observatory where he could make detailed observations of the sun, moon, and stars; his idea was to use that data to develop a means for mariners to reckon their longitude while at sea. As the first director of the Royal Greenwich Observatory, Flamsteed spent 40 years compiling data about the locations and motions of celestial objects. His successors, from Edmund Halley to Nevil Maskelyne, spent the ensuing decades updating and improving Flamsteed’s collection of sky data.

The famous discoverer of Halley’s Comet became the second Astronomer Royal in 1720. He charted 341 stars in the Southern Hemisphere, tracked the moon’s motions and reasoned that it is speeding up over time (in fact, the Earth’s daily rotation is slowing down), recorded magnetic variations around the globe, and labored to improve the celestial method of determining longitude. However, unlike some of his colleagues (most notably Maskelyne), he admired John Harrison’s clockwork solution and championed it as an alternative.

Third Astronomer Royal James Bradley promoted the lunar method of determining longitude. He also was on the Board of Longitude—a conflict of interest, since he was judging the competing sea clocks of John Harrison. At his death, his colleague Nevil Maskelyne took over his office and seat on the Board, continuing the battle to win the longitude prize against Harrison.

Cook’s second voyage to the South Pacific in 1772 included a replica of Harrison’s H-4 timepiece, which worked so well that Cook sang its praises. The captain’s enthusiasm bolstered Harrison’s claim to the longitude prize. Cook brought another, similar chronometer on his third and final trip to the South Seas.

In the early 1600s King Philip III of Spain offered a “fat life pension in ducats to ‘the discoverer of longitude’” (25). The Italian astronomer Galileo discovered the moons of Jupiter through his telescope and realized that the moons disappeared behind the planet and reappeared at regular intervals, which could be catalogued and used to determine longitude. Galileo presented this system, conceptually similar to the lunar method adopted in England a century later, to King Philip’s prize committee. The committee rejected Galileo’s idea on the grounds that Jupiter wasn’t always available in the night sky for observation, and because it required that a telescope be used on a rolling, pitching ship.

George III, a science enthusiast, took up Harrison’s cause. He tested the H-5 clock at his private observatory. When the clock at first behaved oddly, the king remembered that he had left magnetic stones in a cabinet near the watch; after he removed them, the timepiece performed beautifully. George’s efforts caused Parliament to award Harrison most of the remaining prize money promised to the first-place winner.

The officer at the center of the great English naval disaster of 1707, Admiral Sir Clowdisley Shovell misgauged his squadron’s longitude on a foggy night and ran four ships onto the rocks of the Scilly Isles, killing 2,000 men. One of only two men to survive, Shovell washed ashore and promptly was killed for his elegant emerald ring. The disaster awakened shipping interests to the importance of solving the longitude problem: Seven years later, Parliament passed the Longitude Act, and its prize money inspired John Harrison to build his successful sea clocks.