Dava Sobel. Anyone alive in the 18th century would have known that '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. The scientific establishment throughout Europe - from Galileo to Sir Isaac Newton - had mapped the heavens in both hemispheres in its certain pursuit of a celestial answer. In stark contrast one man, John Harrison, dared to imagine a mechanical solution. Full of heroism and chicanery, billiance and the absurd, LONGITUDE is also a fascinating brief history of astronomy, navigation and clockmaking.