For centuries, the inability to calculate longitude at sea doomed many a sailing vessel and its cargo. Unable to calculate their exact position, ships would run aground or miss their destinations entirely, leaving their crews to suffer and sometimes parish from starvation, scurvy, or infectious disease. By the 18th century, the lives and monies lost as a result of this inability to navigate properly had become such an obstacle to commerce and political ambitions that, in 1714, England's Parliament offered an extraordinary sum of money to anyone who could devise a method of reliably calculating longitude at sea. Dava Sobel's "Longitude" is the story of the approximately 60-year race to solve the longitude problem and its hero, a clockmaker from Yorkshire named John Harrison, who invented what we now call the chronometer. Ms. Sobel has written a short, very readable account of the technologies, personalities, and politics surrounding the quest for a solution to the longitude problem and its accompanying prize. The book owes its economy -only 180 pages- to the fact that the author doesn't attempt to place the longitude problem in a greater historical context or to say more than is necessary about the individuals who play a part in the story. "Longitude" concentrates on one story, which is the book's strength as well as a limitation. If the story intrigues you, there is more to be learned elsewhere about navigation at sea, the technology of the chronometer, John Harrison, and all the other grand personalities that inhabit this tale of discovery and the politics of science. But "Longitude" is a brisk, enjoyable account of the invention that solved a centuries-old problem and propelled Great Britain to global dominance.