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.