The story of how a French physicist proved Earth rotates using nothing but a weight on a wire.
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│ 1819 Jean Bernard Léon Foucault born in Paris │
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│ 1845 Foucault begins work on photography and optics │
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│ 1850 December - Experiments with a 2m pendulum │
│ │ in his basement workshop │
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│ 1851 January - Demonstrates 11m pendulum at Paris │
│ │ Observatory │
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│ 1851 February 3 - Invites scientists to observe │
│ │ his experiment. The pendulum rotates! │
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│ 1851 March 26 - Demonstrates 67m pendulum │
│ │ at the Panthéon to the public │
│ │ First VISIBLE proof of Earth's rotation │
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│ 1851 The "Foucault Pendulum" becomes famous worldwide │
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│ 1852 Foucault invents the gyroscope, another │
│ │ demonstration of Earth's rotation │
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│ 1868 Foucault dies in Paris at age 48 │
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│ Today Foucault pendulums in museums worldwide │
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On the morning of March 26, 1851, crowds gathered in the Panthéon in Paris. Suspended from the dome was a 28-kilogram brass-coated lead bob hanging from a 67-meter steel wire.
Foucault had placed a ring of sand on the floor. As the pendulum swung, a stylus on the bob traced lines in the sand. Hour by hour, the lines shifted, showing that the pendulum's swing plane was rotating.
But Foucault knew the truth: the pendulum wasn't rotating - Earth was rotating beneath it.
"You are invited to see the Earth turn"
— Léon Foucault's invitation to his demonstration
Before the pendulum, evidence for Earth's rotation was indirect:
The Foucault pendulum was the first direct physical demonstration that could be performed anywhere on Earth (except the equator) to prove our planet rotates.