The Problem of Place
For centuries the longitude problem stood unsolved — a navigator at sea could read the sun's noon-height to know his latitude, but his east-west position remained a guess against the swell. Ships ran aground on shores that were not on the chart they thought they were sailing. Empires lost cargo, sailors lost their bearings, and admiralties lost patience.
The remedy, when it arrived, was not astronomy but horology. If you can keep the time of one place exactly, ran the argument, and read the local time from the sun, then the difference between the two will tell you where on the Earth you are. The Earth turns fifteen degrees of longitude in an hour. A clock that loses no more than a few seconds in a month becomes a chart of the world.
John Harrison, a Yorkshire carpenter, gave forty years of his life to the construction of such a clock. The Board of Longitude offered £20,000 to anyone who could solve the problem; Harrison's H4 chronometer of 1761, no larger than a pocket watch, finally claimed it. The story is, by some lights, the founding myth of every civilisation that has wished to know precisely where it stood.
— after Sobel, Dava. Longitude. Walker & Co., 1995.