Longitude ~ 2

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     In 1714 the English Parliament offered a 20,000 prize for a time keeper that was accurate to half a degree. The story of the development of the marine chronometer by John Harrison is told by Dava Sobel in Longitude (Walker and Co., 1995). Over a period of twenty-six years Harrison built four clocks.
     Harrison's Number 1 is pictured on the stamp from Ascension.

SCN 143

     In 1765 the sea trials of Number 4 produced an error of less than one tenth of a second per day. The British stamps show various views of the works of Harrison's Number 4.

SCN 1489     SCN 1490

SCN 1491     SCN 1492

     Now the longitude could be determined with an error of less than a tenth of a mile at the equator.

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