Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of his Time

by Dava Sobel

By a grand confluence, Harrison produced his sea clocks at precisely the same period when scientists finally amassed the theories, instruments, and information needed to make use of the clock of heaven.

Most British sailors called the instrument Hadley’s (not Godfrey’s) quadrant, quite understandably.

The quadrant quickly evolved into an even more accurate device, called a sextant, which incorporated a telescope and a wider measuring arc.