Originally published in 1923, this is a facsimile edition of the definitive reference work on the Marine Chronometer, with seventy additional photographs. This revised edition, now with the author's later revisions and corrections, covers the chronometer's history from the earliest attempts to measure longitude while including detailed discussions and illustrations of the various mechanisms and their inventors. It is difficult to grasp, at first sight, the extraordinary fact that the first machines capable of performing the extraordinary feat of accurately determining a ship's longitude, were designed and made by an obscure Yorkshire carpenter, John Harrison (1693-1776). Harrison was entirely self-educated and never served a day's apprenticeship to any clock maker. The Marine Chronometer is not only the entirely absorbing story of John Harrison's marine timekeepers, which won him the reward of GBP20,000 offered by the British Government for any method of finding a ship's longitude within thirty geographical miles at the end of a six weeks' voyage, but also covers the inventions of such famous scientists and pioneers as Christian Huyghens (1629-95), Jeremy Thacker, Henry Sully and Leibniz. The book also recounts in detail the inventions of other professional clock makers such as Paul Ditisheim, J.G. Ulrich, Thomas Earnshaw, John Arnold, Ferdinand Berthoud, Thomas Mudge and Pierre Le Roy.