Introduction
Harrison’s early regulators were largely constructed in wood, yet contained several significant innovations, such as the grasshopper escapement which eliminated sliding friction, and the principle of an oil-free clock. There is a growing appreciation that Harrison’s inventions form an integrated system, with each component influencing and affecting the other. His early background as a skilled woodworker also provided him with means to construct his segmented wheel construction. These were some of the ideas I wished to explore further. So my clock was to incorporate the wheel construction and escapement from the Brocklesby Park clock, with the remontoire from his later clocks. I gave myself a timeframe of six months to design and complete the project. This would necessitate making concessions by simplifying the design while trying to maintain timekeeping accuracy.
Numerous fine copies of Harrison’s clocks have been made, but I wanted to adopt some of his principles and incorporate them into my own design. I started researching this project over the 2009 Christmas break, and was fortunate to be loaned a copy of ‘The Science of John “Longitude” Harrison’ by William Laycock. It is a brilliant read, and he delves into the underlying scientific and mathematical principles of Harrison’s inventions. The other publications I used are listed in the bibliography. Finally, I was fortunate to be assisted by Peter Hastings, who calculated to geometry of the Grasshopper escapement, as well as putting up with my steady stream of questions.
Above: Harrison’s Brocklesby Park tower clock, 1722. The wheels are made from oak, the pinions from brass and the grasshopper escapement pallets from lignum vitae. (Photo from ‘John Harrison Clockmaker’ by Andrew King; page 497 and 505, Antiquarian Horology, Volume 29, June 2006).
