| Longitude Written by Dava Sobel |
| Imagine being on a ship at sea, during an era when there were no global positioning satellites and no radios. Maps were inaccurate, and the keeping of precise time aboard ship was impossible. This is the setting for Longitude, a delightful historical account of the search for a solution to a problem which vexed the world’s sea-faring nations for centuries. Throughout the fifteenth through seventeenth centuries, and much of the eighteenth, there existed no reliable method by which a ship’s captain could accurately determine the ship’s longitude - its distance east or west of home port. Unlike latitude - the distance north or south of the equator - which yields its measure easily with simple astronomical observations, longitude remained elusive despite perennial attempts to solve the problem. As a result of the frequent mis-estimation of longitude, history records numerous nautical disasters involving tremendous loss of life and destruction of property. This culminated in 1707 when two thousand British sailors drowned as their fleet of warships ran aground not far from home essentially because the ship’s navigators incorrectly estimated the fleet’s longitude. The catastrophe in 1707 was a turning point of sorts. The British Parliament passed the Longitude Act in 1714 and offered a prize of L 20,000 for a solution to the unyielding longitude problem. The Longitude Act, its monetary prize and a determined clockmaker by the name of John Harrison form the framework for Longitude’s account of this fascinating slice of scientific and nautical history. Why a clockmaker? As Sobel explains, one principal method for determining a ship's Longitude is to compare the local time aboard ship with the time back home. The difference in time can then be translated into the difference in longitude at a rate of fifteen degrees per hour of time difference. The ship's local clock can easily be set by observation of local Noon for instance. The time back home must be carried along by the nautical clock however, and therein lies the difficulty. The clocks of the day could not keep accurate time aboard an ocean-going ship. Harrison devoted some forty years to designing, building, testing and refining a series of increasingly accurate time keeping machines (clock seems too simple a word to convey the complexity of these devices), machines with the wherewithal to function accurately at sea. Any such clock had to be particularly robust in order to overcome the extreme changes in temperature and humidity experienced during a voyage on the ocean as well as the constant pitching and rolling motions of the ship. Sobel’s account explains the science that underlies these challenges and their solutions and follows Harrison's life-long pursuit of the perfect nautical clock. The marvelous working prototypes that he constructed along the way are on display to this day at the National Maritime Museum in Greenwich. The techniques and mechanisms that Harrison invented became standard components of time- keeping and other devices everywhere. What makes Longitude such a worthwhile book are the many side trips Sobel takes the reader on along the way. Of course, Harrison’s approach was not the only viable means of solving the longitude problem and with so much at stake - including financial rewards and a place in history - the competition was fierce and often devious. There were numerous other longitude proposals, some patently bizarre, several of which are described in the book. One viable method, however, provided the primary competition to Harrison’s clockwork approach. This relied upon astronomical events and observations - a method devised and refined by such scientific heavyweights as Galileo, Cassini and Isaac Newton. The astronomical method for determining longitude was personally favored by some of the same figures who stood in judgement of Harrison's competing approach as members of the Longitude Board. Naturally, politics and personal ambition became important factors in determining the fate of John Harrison and his sea-worthy clocks. Despite their superior performance, Harrison’s machines were subjected to ever more painstaking tests, not to mention changing rules, in his pursuit of the L20,000 prize. Longitude has something of interest for everyone: history, astronomy, maritime disasters, politics, intrigue and the science and art of time keeping. It is also the story of a man’s life- long pursuit of time-keeping perfection. Did John Harrison achieve his goal? That the reader must decide. Overall Rating: A Longitude (Paperback/175 pages) will make an excellent gift for anyone interested in science, history, astronomy, nautical adventures and clock-making. Retail price $11.95. Available on-line at BarnesandNoble.com for $10.75. Hardcover and Illustrated editions also available. |
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