" One [method] is by a Watch to keep time exactly. But, by reason of the motion of the Ship, the Variation of Heat and Cold, Wet and Dry, and the Difference of Gravity in different Latitudes, such a watch hath not yet been made.” And not likely to be, either, he implied. "

― Dava Sobel , Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time