The problem was really one for the watchmaker, since a clock is made for keeping time while standing in one position and a watch for keeping time while being moved about. John Harrison, the inventor of the famous _gridiron_ pendulum, finally won the munificent prize. In 1762, after several trials and failures, he succeeded in producing a timepiece which varied, under test, only a minute and four seconds during a voyage of some five months. This was excellent timekeeping—far within half a second a day; it made it possible for a captain at sea to determine his position within eighteen miles. Harrison's mechanism was too complicated for description in these pages. Indeed, it was so difficult of comprehension that, before paying him his reward, the English government asked Harrison to write a book of explanation in order that his inventions might be copied by other makers. He did so and finally received the money. Harrison's ideas have now been greatly simplified, but, in general, his plan is used in the making of marine chronometers to this day; thus, in a sense, it is due to Harrison's brain that our great ships are able to cross the ocean on almost schedule time. Both the first success of the chronometer and the later efforts toward improving it had a great influence upon the next few generations of watchmakers; the final improvements were made in the days of the American Revolution. It was at this latter period that a man named Thomas Mudge worked out the kind of escapement that is still used in our watches. A little later, the Swiss-Parisian, Abraham Louis Breguét, improved the hair-spring by bending its outer coil across the others to their center and fastening it at that point in order that the spiral of the spring should expand equally in all directions from the center. The last development of importance consisted in doing away with the fusee. The faults of this device had been the need of a thick watch to give it room, and the danger that a broken mainspring might destroy other parts of the movement in its recoil. French and Swiss watchmakers reduced the friction until it needed very little power to run the mechanism, and then were able to employ a mainspring which was not stiff enough to require a fusee. American makers adopted this idea, but the British clung to the fusee and the stiff spring; it has cost them much of their prestige as watchmakers and much of their trade. Thus, the mechanism of both clocks and watches was practically in its present state by the year 1800. The "grandfather's clock" of that date may look old-fashioned, but it tells time a modern way, and the mechanical ideas in George Washington's watch were not so very different from those which we find in our own. There have been many small improvements since, but the great inventions had all been made.