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

On October 22, 1707 four English warships crashed into the rocks of the Scilly Isles southwest of England. They quickly sank killing 2,000 men. The cause of this catastrophe was the inability to determine longitude, a problem that beset mariners everywhere. In 1714 the British Parliament set a £20,000 reward for whoever could solve the problem. The Board of Longitude, which would be primarily comprised of astronomers, was set up to award the money. To win the full prize, the method or device had to be accurate to within one-half degree on a trip from England to the West Indies.

There had been many ideas about how to determine longitude, but none worked reliably. They fell into two basic camps: the astronomical and the clock. The idea behind astronomy was to find a pattern of stars, the track of the moon or even the eclipses of the four known moons of Jupiter that would yield longitude. The clock idea was based on time difference. 15 degrees of longitude equals an hour. So a clock that could keep accurate time set to London time could be compared with a clock set to local time. The local time could be determined by sighting the sun at noon. The time difference would give the degrees of longitude from London. But prior to the eighteenth century clocks didn't work reliably in the rough environment of ships at sea, so the London clock would be off.

In 1727, a self-educated village carpenter and clock maker, John Harrison, heard about the prize. In 1730 he had plans for a chronometer as mariner's clocks of sufficient accuracy would later be called. He showed his plans to Edmund Halley of comet fame, a board member, who sent him to a prominent clockmaker and fellow Royal Society member who encouraged Harrison to build his clock. Five years later Harrison presented the clock to the board. He had been able to take it on a voyage to Lisbon where it proved its worth. Harrison's clock was original, intricate and exquisitely crafted. The board was impressed but Harrison himself was not. He felt he could do better and took another five years to build a second chronometer. The Royal Society tested the second clock and gave it accolades but Harrison again decided he could do even better and took twenty years to build a third.

In the thirty years Harrison was building his three clocks astronomers were busily cataloging stars and navigational instruments were vastly improving. By 1760 the board was considering a complicated but effective method of calculating a ship's longitude from the positions of the moon and stars. And since the board was mostly made up of astronomers, they instinctively preferred an astronomical solution to a simply mechanical one.

Harrison was awarded the prestigious Copley Gold Medal in 1749 at the recommendation of the Royal Society for the many innovations he had made in his clocks that made them so accurate and reliable. But as usual Harrison himself was the hardest to satisfy. Immediately after completing clock three he built a fourth, a pocket watch that ultimately would win the coveted prize. On a West Indies trip the pocket chronometer worked perfectly, but the astronomers on the board dawdled about awarding the prize since they were now enamored with an astronomical solution.

Since presenting his first chronometer, Harrison had been receiving stipends so that his work could continue, but the prize was elusive. Harrison felt his chief nemesis was Astronomer Royal, Nevil Maskelyne, a strong advocate of the astronomical method. Maskelyne took it upon himself to conduct further tests on Harrison's watch. Finally in 1765 the board awarded Harrison £10,000, half the prize, and ordered him to make two more of the watches to show it could be duplicated. The board also commissioned another clockmaker to build an identical twin of Harrison's watch. The twin was selected to accompany Captain Cook on his second voyage around the world. The chronometer won high praise from Cook who used it to make accurate maps. Finally through the intervention of King George III, Harrison received a final £8,750 in 1773.

One of the biggest problems with Harrison's chronometer was the cost, at least £400 to duplicate when a sextant and tables cost £20. But fifteen years later the price would drop to £80 and would keep declining. By 1815 over 5,000 chronometers were in service. The problem of longitude had been solved.

Sobel's short history reads quickly. The book contains nice photographs of Harrison's clocks showing their complex inner workings. The chronometers have been restored and now reside in British museums. Sobel explains some of the principles of clock mechanisms and details some of Harrison's innovations. She also covers failed as well as successful astronomical approaches to finding longitude. But this is also a human interest story of an odd difficult man, a homespun insular genius, who faces the complex scientific society of eighteenth century England. Recommended for the science buff and general reader alike.