Dava Sobel

Longitude is the fascinating and true story of a lone genius who solved the greatest scientific problem of his time: the immemorial longitude problem, which forced seamen to navigate solely by the stars, causing many to be lost at sea – as chronicled by a deft writer, Dava Sobel and published in 1999. It affords the reader an education in life at sea until 1750, when England’s John Harrison solved the problem.

Until England’s John Harrisono created a timepiece in 1750 that would keep time at sea (despite the ship’s movements and the damage of water, rust, etc.), sailors worldwide were forced to navigate largely “by the stars”, which could often not be seen, or by simply “following the parallel”, as did Columbus in his journey in 1492 to America. If the sailors could know the exact time in TWO different places at once – a longitude prerequisite so easily ascertained from any pair of inexpensive wristwatches today – they could determine their exact location from meridian-to-meridian. Pendulum clocks were largely useless in a rolling sea, and, for 400+ years, mankind struggled to find a solution, as many ships were literally “lost at sea” and others took much longer to reach their destinations. So important was this quest that many “prizes” were offered for solving it, notably by George III and Louis XIV, offering veritable “King’s Ransoms” to anyone who could measure longitude accurately. John Harrison, a simple clockmaker and not a mathematician or astrologer, devoted his life to this quest, and he conquered it, and won the great prize of George III. Harrison’s clock was friction-free, required no lubrication and no cleaning, and was made from materials that were impervious to rust and that kept their moving parts perfectly balanced. He created four versions of this over three decades, the last of which was able to be mass-produced as pocket watches.

Some key terms of interest: “Latitude” (referring to one’s freedom from normal restraints) is cartographically defined as the angular distance north or south of the Equator, and latitude lines on a map are also called “parallels”, as all parallels run east and west and are parallel to the Equator. “Longitude” refers to the meridians (great circles) of longitude which run to the North and South Poles, respectively, from a fixed beginning point, which mankind has arbitrarily chosen to be the Prime Meridian at Greenwich, England. Worldwide time, by treaty, is measured from Greenwich Mean Time (GMT). “Meridian” (meaning highest point or zenith of something) is cartographically defined as a great circle on the earth’s surface passing through both geophysical poles (North and South Poles). “Equator”, which marks the zero-degree parallel of latitude in Ptolemy’s world atlas, is where the sun, moon and planets pass almost directly overhead.

                  Sobel’s entertaining account was nominated for the Pulitzer Prize for Biography.