All Over the Map
The invention of the chronometer and its effect on navigation.
Longitude: The Story of a Lone Genius Who
Solved the Greatest Scientific Problem of His Time.
By Dava Sobel. 384 pp. New York: Walder & Company.
A review by John Ellsworth
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First appeared in The NY Times, Nov 19, 1995 • All rights reserved • © 2006 John Ellsworth
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JOHN HARRISON (1693-1776) spent his lifetime inventing and perfecting a series of timepieces to measure longitude. As Dava Sobel relates in her engaging narrative, "Longitude," until the 18th century sailors navigated by following parallels of latitude and roughly estimating distance traveled east or west. Ships routinely missed their destinations, often taking excessive time to arrive or succumbing to reefs off fogbound shores. Thousands of sailors and tons of cargo were lost.
In 1714, England's Parliament offered £20,000 (the equivalent of about $12 million today) to anyone who provided a "practicable and useful" means of determining longitude. Countless solutions were suggested, some bizarre, some impractical, some workable only on land and others far too complex.
Most astronomers believed the answer lay in the sky, but Harrison, a clockmaker, imagined a mechanical solution—a clock that would keep precise time at sea. By knowing the exact times at the Greenwich meridian and at a ship's position, one could find longitude by calculating the time difference. However, most scientists, including Isaac Newton, discounted a clock because there were too many variables at sea. Changes in temperature, air pressure, humidity and gravity would surely render a watch inaccurate.
Harrison persisted. As Ms. Sobel writes, he worked on his timepiece for decades, though he suffered skepticism and ridicule. Even after completing his timepiece, an instrument we now call a chronometer, in 1759, he underwent a long series of unfair trials and demonstrations. Ultimately he triumphed.
Ms. Sobel, a science writer who contributes to Audubon, Life, Omni and other magazines, captures John Harrison's extraordinary character: brilliant, persevering and heroic in the face of adversity. He is a man you won't forget.
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