John Harrison’s “Clock B” Breaks World Record
By Andrew DeKeyser, CW21
Dubbed simply “Clock B,” the timekeeper designed by John Harrison some 250 years ago and made by clockmaker Martin Burgess, ran its way into the Guinness World Records on April 18, 2015, after running only 5/8 of a second slow over 100 days. Guinness described it as the “most accurate mechanical clock with a pendulum swinging in free air.” The trials were overseen by the Worshipful Company of Clockmakers and the National Physical Laboratory beginning on January 6 of this year.
Harrison described this clock in his controversial book that he used to criticize his competitors and make the audacious claim that his clock could keep time within a second over a 100 day period. Burgess’s second attempt to construct that clock to Harrison’s exact specifications achieved this goal.
The Harrison-designed clock features a grasshopper escapement as well as a light pendulum bob and large amplitude. Harrison sought to improve on the design of the verge escapement while utilizing Christiaan Huygens’s application of the pendulum to horology. Harrison, a self-taught clockmaker, often used wood in his early clocks because he was a carpenter. He made his first clock at the age of 20, using metal only where absolutely necessary. He preferred wood as a building material because he was very skilled working with it. He discovered that the wood of the lignum vitae tree was naturally greasy and acts as a self-lubricating building material. A tower clock he completed in 1722 has run continuously (other than a short period in 1884 for reconditioning) for more than 270 years. As his skills as a clockmaker grew, he invented the grasshopper escapement and the gridiron pendulum and befriended several other horologists such as George Graham and Thomas Tompion.
John Harrison is best known for his invention of the marine chronometer. He dedicated his life to win the British government’s £20,000 challenge issued in 1714 to solve the problem of establishing longitude at sea within half a degree or two minutes time. When travelling west, the local time moves back one hour for every 15° of longitude. So, if the local times are known at two different points, the distance between them can be calculated, thus establishing longitude. Local time is established by the position of the sun in the sky at that specific time of year, and Greenwich local time is kept by Harrison’s marine chronometer.
“John Harrison and the Longitude Problem.” Royal Museums Greenwich website: www.rmg.co.uk/explore/astronomy-and-time/time-facts/harrison.
McKie, R. “Clockmaker John Harrison Vindicated 250 Years after ‘Absurd’ Claims.” The Guardian. www.theguardian.com/science/2015/apr/19/clockmaker-john-harrison-vindicated-250-years-absurd-claims.
Singleton, M. “John Harrison’s ‘Clock B’ Sets A World Record over 250 Years after It Was Designed.” The Verge. www.theverge.com/2015/4/20/8456821/john-harrison-clock-b-world-record.
Sobel, Dava and William J. H. Andrewes. The Illustrated Longitude. New York: Walker and Co., 1998.
Andrew DeKeyser is the owner of HCP Watchmaking in Sisters, Oregon. He graduated from the Lititz Watch Technicum with WOSTEP certification.