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Sailing And Longitude: How Chronometers Were Born

Last week we offered an inside look at what it means when a watch is classified as a certified chronometer. That blog post naturally sparked some interest from watch aficionados about the origins of chronometers — a topic so vast that several books have been written on the subject.

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John Arnold Marine Chronometer no. 12, London, 1778-1779; photo: Arnold & Son

Here, we try to put that long historical saga of how chronometers came to be into a compact overview for those who love the water and love precision. The invention of today’s chronometer was no easy feat. In fact, it was one that took nearly a century. As early as the mid-1600s, when European countries were intent on sea-faring expeditions and exploration, they faced a single deadly obstacle: being unable to find longitude at sea, often causing them to run aground and sink.

England, France and other countries tirelessly pursued a way to create a ship’s timepiece that could keep accurate time on the high and frequently savage seas, and enable captains to chart longitude via a standard time and celestial navigation. In 1714, the United Kingdom’s Parliament established the Longitude Act, complete with a Board of Longitude, and offering the Longitude Prize (20,000 pounds, comparable to 2.87 million pounds or $4.5 million today) to anyone who could find a method for determining a ship’s longitude. This quest became the life work of many watchmakers and inventors, including British watchmakers John Arnold and also John Harrison, who worked until the age of almost 80 to introduce and perfect the invention of the chronometer.

Traditional clocks with pendulums did not work on a moving vessel that was continually rolling and pitching with the waves. Harrison, instead, created a vertical escapement clock with larger balance and temperature compensation. The clock could be used as a portable standard because it offered accurate time at a fixed location — Greenwich Mean Time — despite the sea’s wrath. With that knowledge, and with some calculations at local noon, sailors could determine the ship’s longitude.

Of course, while it sounds relatively easy, it was not – especially in the days when every part of the clock was cut and made by hand. Each time a clock was finished, it went on a voyage of length to determine its reliability. It was John Harrison’s fifth clock that was finally deemed to be highly accurate at sea — in the year 1773. That invention resulted in fewer lives lost and a grand proliferation of seafaring dominance by the Brits.