ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Sunday, January 14, 1996 TAG: 9601120089
SECTION: BOOK PAGE: F4 EDITION: METRO
TYPE: BOOK REVIEW
SOURCE: REVIEWED BY SIDNEY BARRITT
LONGITUDE. By Dava Sobel. Walker and Company. $19.
Latitude is easy. Sailors from time immemorial have known that the height of the sun or certain guide stars above the horizon tell how far north or south of the equator their vessels sail.
Longitude is a different matter. How far east or west of port a ship lies is no simple calculation. Indeed, Christopher Columbus knew the latitude of India and planned to sail a parallel across the oceans until he reached it, something he would have accomplished had not America thwarted his course.
Longitude he did not know, and neither did any mariners of the age. Reliable clocks that would work at sea just weren't available. The pitching and rolling of the ocean threw pendulum clocks off, and temperature changes warped metal springs and balances.
Basic longitude calculation is simple only if one has a reliable clock. Mariners must know both local time and time in home port where the longitude is known. The difference between the two times translates into distance between port and the ship's actual position.
In 1707 four British warships piled into some rocks off the English coast. Two thousand sailors drowned because their navigators made an error of several hundred miles in guessing longitude ("dead reckoning" they called it). Following this calamity, Parliament offered a prize to anyone who could discover a simple method of determining longitude for navigators. The prize was an amount equivalent today to $12,000,000.
Needless to say, the offer attracted its share of absurd and fantastic solutions, but, ultimately, John Harrison, an untutored clockmaker, solved the problem and collected most of the prize. It wasn't easy. His designs were revolutionary to the point of causing extreme skepticism in the political and scientific establishments. Science eventually won out over professional jealousy, vanity, and political intrigue, and Harrison's clocks became standard equipment on British vessels and probably played a significant role in making Britain master of the seas.
Dava Sobel, a reporter with a string of credits for science reporting, spins out this tale well. The elements of scientific discovery fit together neatly with a bit of naval history and a touch of intrigue. All of this is a pleasant and fascinating evening's reading.
Sidney Barritt is a Roanoke physician.
LENGTH: Medium: 51 linesby CNB