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In Depth: Breguet’s Pendule à Trois Roues
The pendule à trois roues — three-wheel pendulum [clock] — was Abraham-Louis Breguet’s radical answer to a fundamental horological question: how much could a clock be reduced without sacrificing precision? On the February 3, 1788, A-L Breguet walked into the Académie Royale des Sciences on the rue Saint-Jacques and deposited a sealed envelope. A clerk assigned it the number 267. He told no one what was inside. The practice of the pli cacheté was well established in French scientific culture. An inventor who deposited a sealed description with the Académie secured a dated record of priority without surrendering the technical details to competitors. Breguet used it rarely, and this was the only time he used it for a clock. The envelope sat in the Académie’s archives through the Revolution, the Empire, the Restoration, the July Monarchy, and two more republics. It was still there nearly a century later, on December 5, 1881, when Louis Breguet, the founder’s grandson, asked for it to be opened. Inside was a description of a clock movement built around three wheels. By that point, the pendule à trois roues had been made in fewer than a dozen examples over roughly 23 years and had passed largely out of active horological discussion. The unsealing was a formality. The clocks themselves had already made their own argument, revealing another side A-L Breguet’s genius as an inventor. The idea and its ancestry The intellectual territory Breguet was entering in 1787 ...
