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How a Clockmaker Made Sailing the Seas Safer


By Dava Sobel

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Walker & Co.

184 pp., $19

In the days before wireless and global positioning satellites, the most vexing problem in navigation was to determine longitude: how far east or west you had sailed.

Finding latitude, the distance north or south of the equator, was a simple problem by comparison. Instruments to measure the height of the sun, moon, and stars had been known since antiquity. Once out of sight of land, however, the only guide to longitude for the sea voyager was dead reckoning, a rough guess at how far the ship might have come since the last landfall.

A solution to the problem was sought after one foggy night in 1707, when a proud English admiral made a disastrous misjudgment. The improbably named Sir Clowdisley Shovell called together the captains of his five ships of war for a council about the flagship, the Association. The question was: Where were they? The consensus had the ships safely in the English Channel. But a common seaman who had kept his own reckoning during the voyage, argued that the fleet was headed for the rockbound Scilly Isles.

''Such subversive navigation by an inferior was forbidden in the Royal Navy.... Admiral Shovell had the man hanged for mutiny on the spot,'' writes Dava Sobel in, ''Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time.'' The Association and three other ships struck the rocks and sank, with the loss of thousands of lives. In response, England's Parliament voted the then-enormous sum of 20,000 to reward the inventor of a reliable means for determining longitude.

This handsome little volume is the account of those efforts, and the final triumphant solution. The author is a respected science journalist and former science reporter for The New York Times. The ''Longitude Problem,'' as it became known, was a byword in the 18th century for an insuperable difficulty. Many of the solutions offered were bizarre in the extreme.

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Sobel's book engagingly brings together astronomy, mathematics, clockwork, and human passions in this compelling tale of genius and persistence.

Perhaps the strangest attempt to solve the vexing longitude problem was the ''wounded dog'' method. A quack cure called the ''powder of sympathy,'' cooked up in 1687, was supposed to heal at a distance. The idea was simple enough, Sobel writes: ''Send aboard a wounded dog as a ship sets sail. Leave ashore a trusted individual to dip the dog's bandage into the sympathy solution every day at noon.... The dog's cry would mean, 'The sun is upon the Meridian in London.' The captain could then compare that hour to the local time on ship and figure the longitude accordingly.''

In fact it was the fourth dimension, time, that provided the answer to determining a ship's position on the ocean's surface. A mariner could easily determine noon, local time, by observing the moment at which the sun paused in its climb across the sky. With a clock to tell the time back home in England, it was only a matter of arithmetic to calculate how far around the globe the ship had come. One hour's difference, a 24th of the earth's daily round, meant 15 degrees of longitude.

The problem was to make a clock accurate enough to keep time on a pitching ship at sea. One man, John Harrison, labored for 40 years to build his nautical chronometer.

Harrison was a self-taught artificer, born in Yorkshire in 1693. With his brother James and later his sons, he made his reputation as a maker of friction-free clocks that would work without oiling and that were immune to variations in temperature.

The story of Harrison's solution to the longitude problem is a dramatic tale of one man's struggle against the scientific establishment. His final success was hard won against the forces of bureaucracy as well as the inherent stubbornness of mechanical objects.

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