Grasshopper Escapement - History

History

The grasshopper escapement was invented by John Harrison who used it in his regulator clocks, and also in the first three of his marine timekeepers, H1 - H3. Determining longitudinal position was a major problem in marine navigation; Newton argued that astronomical positioning could be used, but an easier theoretical possibility was to use accurate knowledge of the time at a specific, base, location. The difference in time between local time, which was easy to measure, and the time at base gives the difference in longitude between the base and the ship, since 24 hours of time is equivalent to 360 degrees of longitude. A large prize was offered for a solution to the problem and Harrison devoted his life to devising and building highly-accurate timekeepers. Precision and friction were the main problems. Two advantages of the grasshopper escapement are the repeatability of its operation and its freedom from the need for lubrication. The repeatability of its operation is inherent in its design. One pallet is released only by the engagement of the other; the impulse given to the pendulum is thus completely regular in its timing. The lubricants available to Harrison were poor, messy and short-lived. This meant that conventional clocks had to be stopped frequently for cleaning and oiling. Using his clean and absolutely stable grasshopper escapement Harrison began a series of long-term investigations into the performance of clocks, leading to his invention of the gridiron pendulum which nullified the effects of changing temperatures. The performance of his improved clocks in turn gave him an accurate, convenient standard against which to test his marine timekeepers.