In July of 1714, the British Parliament passed the Longitude Act which offered a top prize of £20,000 (worth about £1.5 million today) to the person that could come up with a straightforward and accurate method for the precise determination of a ship’s longitude. The Board also offered lower prizes for solutions that provide a lesser degree of accuracy as well as financial support to those whose work on the longitude problem looked promising.
Navigating the seas successfully requires the accurate determination of a ships latitude and longitude. While determining latitude was fairly easy for early ship-farers through the altitude of the sun at noon and a table of the sun’s declination for the day. Longitude provides a measurement east or west of a fixed starting point, which is a north-south line called the Prime Meridian (0°) located at the Royal Observatory, Greenwich, England.
At the time of the Longitude Act, comparing the local time of a ship’s position against the home port time is a critical component of determining longitude when out on the seas and away from land. Determining longitude away from sight of land precluded the use of dead reckoning. The difference between the local time and the home port time could be used to determine a ship’s longitude. It takes the earth 24 hours to spin on its axis 360° meaning that one hour of time difference is translated into a distance of 15° longitude. Determining local time was as easy as looking up at the sky to find the highest point of the sun which marked noon. Unfortunately, maintaining an accurate time for the home port was more challenging. Pendulum clocks onboard ships either ran too quickly, too slow, or not at all. An accurate clock that could withstand varying conditions of humidity, temperature, and pressure aboard a ship was needed.
While no person collected the top prize during the Longitude Board’s tenure from 1714 to 1828, John Harrison, a British clockmaker, invented the marine chronometer. He provided the first reliable watch that could maintain accurate time on long sea voyages. One of his prototype watches, called the H5, was tested by King George III and was determined to be accurate to within one third of one second per day.
The 300-year-old archive of the Board of Longitude has been scanned and made available to the public via the the Cambridge Digital Library at http://cudl.lib.cam.ac.uk/. More than 65,000 images have been scanned with the help of a £1.5m gift from the Polonsky Foundation. The effort is a a partnership between Cambridge University Library, the National Maritime Museum, and the AHRC-funded Board of Longitude Project.
O’Donnell, J.. “John Harrison and the Longitude problem.” Royal Museums Greenwich. N.p., 15 Nov. 2002. Web. 13 Aug. 2013. <www.rmg.co.uk/harrison>.
Sobel, Dava. “”The Longitude Problem” by Dava Sobel.” Eco – Papers. N.p., n.d. Web. 13 Aug. 2013. <www.themodernword.com/eco/eco_longitude.html>
“The longitude problem: 300-year-old archive opened to the world.” Cambridge University Library. N.p., 18 July 2013. Web. 13 Aug. 2013.