In 1851, when French physicist Léon Foucault performed his pendulum experiment in Paris, he became the first to prove what many scientists of his day already suspected—that the Earth spins on an axis. He conducted his first experiments 170 years ago, in early January 1851, with a relatively small prototype in the cellar of his home. Just a month later, Foucault performed his most famous pendulum demonstration, using a 62-pound spherical weight attached to a 220-foot wire, which was hung from the dome of the Panthéon, a Parisian monument. As the pendulum swung back and forth in a fixed plane, the pointed end of the weight traced lines in a compass-like circle of sand below it. As time passed, the angle of these lines began to change, demonstrating to onlookers that the Earth itself was rotating underneath the pendulum, and by extension, everyone watching was rotating as well, spinning on the surface of the great blue marble around its axis.
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Today in History
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Rainbow Mountain
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Happy St. Patricks Day!
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Spiegelgracht canal in Amsterdam, Netherlands
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International Day for Biosphere Reserves
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Giving Tuesday
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It s Census Day—make it count
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Strolling across the Red Lagoon
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National Love a Tree Day
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St. Gregory Church in Ani Ruins, Kars, Türkiye
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The Guggenheim turns 60
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America s Playground by Derrick Adams
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Autumn in the Prosecco Hills
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International Day of the Worlds Indigenous Peoples
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Valentines Day
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European river otter, Netherlands
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Winter solstice
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Falling for the Canadian Rockies
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Happy Canada Day!
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