American Literature of the Sea and Great Lakes
LONGITUDE: THE TRUE STORY OF A LONE GENIUS WHO SOLVED THE GREATEST SCIENTIFIC PROBLEM OF HIS TIME (1995). Written by journalist and science writer Dava Sobel (1947-?), Longitude is a work of scientific and historical nonfiction that became an international best-seller. A fully illustrated edition by Sobel and William J. H. Andrewes was published in 1998. Andrewes also compiled The Quest for Longitude (1996), an illustrated collection of essays by twenty experts. Sobel’s interest in history and science continued with Galileo’s Daughter: A Historical Memoir of Science, Faith, and Love (1999).
Latitude is the distance, either north or south, from the equator. Since before the days of Christopher Columbus,* captains found their ships’ latitude by measuring the angular distance from the horizon to either the North Star or the sun at its highest point during the day. Longitude is the distance, either east or west, from the prime meridian (e.g. Greenwich), a great circle. Longitude is more difficult to determine than latitude: the navigator must know the local time aboard his or her ship and simultaneously know the local time at a point on the prime meridian, because time equals east-west distance as a measure of the earth’s rotation.
By the turn of the eighteenth century, when pendulum clocks kept time onshore, and “dead reckoning” was the only way to calculate longitude on board, a captain could sail across the Atlantic following a parallel of latitude but would be unsure of the longitude. He could not know for certain the ship’s distance from land. The inability to determine longitude accurately resulted in protracted voyages and in shipwreck.* The quest for a means to find longitude at sea involved the greatest scientists of the period, including Galileo, Sir Isaac Newton, Edmund Halley, and Robert Hooke.
Sobel tells the story of 22 October 1707, when weather and navigational error wrecked four British warships and killed 2,000 men. Spurred by this disaster, Parliament enacted the Longitude Act of 1714, which offered up to £20,000 for a solution. Sobel’s hero, John Harrison (1693-1776), craftsman and perfectionist, devoted his life to creating a marine timepiece, later named a chronometer, that could function accurately regardless of shipboard motion and temperature variation. Harrison completed the first of five successful marine timepieces in 1735. His third, H-3, took nineteen years to finish. As a result of his work, by 1815 about 5,000 chronometers were keeping time aboard ship. Captain James Cook, Captain William Bligh, and Captain Robert Fitzroy (master of the Beagle, on which Charles Darwin sailed) used early chronometers. Though Harrison received grants and financial awards, the Board of Longitude maltreated him and his inventions. He received the balance of his prize money only through the intervention of King George III.
In a lucid, logical style, Sobel weaves history and science into an exciting narrative, enabling readers of all levels of maritime experience to understand and enjoy the eighteenth-century race to discover a means to calculate longitude at sea, an essential chapter in maritime history.
Richard J. King