Determining Longitude

As brought out in the book, "Longitude," by David Sobel (1995), in the 18th century the "'longitude problem' was the thorniest scientific dilemma of the day and had been for centuries. Lacking the ability to measure their longitude, sailors throughout the great ages of exploration had been literally lost at sea as soon as they lost sight of land. Thousands of lives, and the increasing fortunes of nations, hung on a resolution." Sailors could determine their latitude (distance north or south of the equator) by making reference to the position of the sun and the north star. But determining longitude was another matter, due to the spinning of the earth. Finally, to try to resolve the problem the English Parliament in 1714 offered the very handsome reward of 20,00 pounds (over 12 million dollars in today's money) to one that could provide the longitude within half-a-degree. All of the great scientists of the time worked on the problem. Sir Isaac Newton doubted that it was possible. The winner of the prize, after devoting 40 years of his life to the project, was a lowly self-educated clockmaker named JOHN HARRISON. He developed a clock, now known as a chronometer, that could keep precise time while located on board ship despite the many physical obstacles of the high seas. This was the way they were able to determine longitude with Harrison's chronometer: The navigator at sea would set his ship's clock to the local time at noon when the sun reached its highest point in the sky, and see how that time compared to the chronometer's time. Every hour's difference in the time between the two translates into another 15 degrees of longitude. This is true because it takes the earth 24 hours to complete one full revolution of 360 degrees, and one hour marks 1/24th of a spin or 15 degrees. "Longitude" is a very fascinating book--recommended to me by Larry Marsh.