It hung from the ceiling of the third floor and stretched 71 feet through the center of the building, where it swung slowly and rhythmically across a fancifully emblazoned circle on the first floor. The building-which opened in 1964 on the National Mall in Washington, D.C.-was designed purposely to accommodate a pendulum. The Smithsonian Institution made a pendulum a focal point of its Museum of History and Technology (which later became the National Museum of American History). Pendulums based on Foucault’s calculations began appearing worldwide-and are still iconic features of many science museums in the U.S. The experiment was a hit, drawing flocks of fascinated Parisians and catapulting Foucault to fame. “It really started the cultural shift to fundamentally understanding our universe differently,” Thompson says. But it was Foucault who dispelled lingering doubts once and for all, establishing the phenomenon firmly in the realm of fact. For centuries, it was a commonly held belief that the Earth rotated on an axis. Thompson, head of public outreach for the APS. Over time, the angle of these lines changed, suggesting to audience members that the direction of the pendulum’s travel was shifting under the influence of an unperceived rotational motion-that of Earth.įoucault was able to demonstrate a scientific concept in a way that the average person could easily grasp, says Rebecca C.

As it swung back and forth, the pointed end of the bob traced lines in sand that had been poured on a wooden platform. According to the American Physical Society, he suspended from the Pantheon’s lofty dome a 61-pound brass bob on a 220-foot cable. As it swept through the air, it traced a pattern that effectively proved the world was spinning about an axis.Ī month later, Foucault shared his experiment with all of Paris at the majestic Pantheon building. He called together a group of scientists, enticing them with a note declaring, “You are invited to see the Earth turn.” Foucault hung a pendulum from the ceiling of the Meridian Room of the Paris Observatory. On February 3, 1851, a 32-year-old Frenchman-who’d dropped out of medical school and dabbled in photography-definitively demonstrated that the Earth indeed rotated, surprising the Parisian scientific establishment.Īcting on a hunch, Léon Foucault had determined that he could use a pendulum to illustrate the effect of the Earth’s movement.

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