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Law and Longitude: A Trip to Greenwich

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The following is a guest post by Constance A. Johnson, a Legal Research Analyst at the Law Library’s Global Legal Research Center.  Connie has previously blogged about Water Rights at Star IslandHuman Rights Day, and our Guide on Legal Translation

Prime Meridian

On a recent short vacation to London with my husband, I was lucky on the weather and was able to take a lovely boat ride down the Thames to Greenwich.  There we visited the Royal Observatory and, like every other tourist, stood with one foot on either side of the Prime Meridian, the zero point of measurement of longitude, so we could span the two hemispheres of the earth.

At the Observatory there is a museum exhibit on the history of the development of ways to measure longitude accurately, so that ships could pinpoint their locations.  Latitude, the indicator of north/south location, had long been measurable by reference to the height of the sun in the sky, but there was no easy way to determine longitude, the east-west locator.

Longitude Act

Without such a method, ship captains could not be sure where they were and numerous wrecks occurred, with much loss of life.  In 1714, the British Parliament passed the Longitude Act, to set up a Board of Longitude and offer a prize of £20,000, a vast sum at the time, to whoever could invent a practical way to measure longitude at sea with an accuracy of one-half a degree.  Lesser prizes of £15,000 for accuracy within two-thirds of a degree and £10,000 for within one degree were also offered.

In the 18th century there were two schools of thought on how best to do this, with some scientists arguing for measuring by time and others for using references to the positions of the moon and stars.  Other, more fanciful methods were also proposed, as many vied to win the prize, including a plan to station ships with firecrackers at various points to be visual location markers.  That one failed because it was not possible to anchor boats in the deepest parts of the ocean; without an anchor, of course the locations of the floating flares would be constantly moving.

The one who eventually solved the problem was John Harrison, a mechanically gifted Englishman who made several accurate timepieces.  He was never awarded the full prize, but received partial payments.  His fourth attempt, known as the H4 watch, was taken by Captain James Cook (coincidentally there is a map of Captain Cook’s tracks in what is now Tina’s office) on his second voyage to the South Pacific, from 1772-1774, during which the timepiece was successfully used.  That watch is on display at the Greenwich Observatory.  The whole exhibit was fascinating, both as history and science, and I recommend a trip to Greenwich to anyone visiting the London area.  Anyone wanting to read more about the development of a method to measure longitude at sea might enjoy the book Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time, by Dava Sobel.

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