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Foucault's pendulum

Did you know that it is possible to revise your physics courses at the Panthéon? Then discover the history of the pendulum of Foucault with us !

A physicist of genius

Inventor and experimenter !

The astronomer and physicist at the origin of this revolutionary experiment is French and is called Léon Foucault.

Inventor of the gyroscope He is best known for the pendulum that bears his name. It was in the cellar of his house in Paris that he launched his experiment for the first time alongside his fellow scientists!

From then on, everything followed very quickly, and his numerous advances in experimental physics allowed him to be named physicist of theObservatoire de Paris, and to receive many prestigious international titles throughout his career. His name appears on the famous... Eiffel Tower!

Vue du pendule de Foucault
Pendule de Foucault

© Benjamin Gavaudo

"You are invited to come and see the Earth turn".

This is the sentence written on the invitations sent in 1851, for the presentation of the experiment.

Louis Napoleon Bonaparte, fond of science and history, authorized the physicist Léon Foucault and the engineer Gustave Froment, to use the dome of the Panthéon to conduct their experiment.

They suspended from the dome a steel wire 67 meters long and a sphere of brass and lead weighing 28 kilograms. A device of wood and sand is installed under the pendulum, allowing to visualize the explanations of Foucault in live at each passage: the stylus fixed at the bottom of the pendulum causes a bleeding in the sand which increases hour after hour...

The experiment was a great success and brought together a crowd of Parisians. It is thus sure, the ground is in movement!

Vue d'une illustration de Léon Foucault qui lance son pendule
Illustration de Léon Foucault qui lance son pendule

© Auroramù / Artips

A pendulum in movement

In spite of the craze which it arouses, the experiment in the Panthéon is stopped by the coup d'état of December 1851.

Fifty years later, Camille Flammarion, founder of the Astronomical Society of France, repeated the experiment at the Pantheon. The inaugural session was a popular event and gathered more than 2000 people.

In 1995, the pendulum is reinstalled permanently.

Since the end of the great construction site of the upper parts of the monument in 2015, the pendulum is a major element of the visit.

Installation du pendule de Foucault
Installation du pendule de Foucault

@Megane Thellier / Centre des monuments Nationaux

How does it work?

Using a Galilean reference frame Foucault explains this curious phenomenon: if one throws, in the same axis, a pendulum attached to a fixed point and that one realizes over the hours, that its oscillation deviates from its initial trajectory, one can conclude that it is not the pendulum itself that moves, but its point of attachment. The Pantheon being immobile, its initial point of attachment is indeed the Earth!

You have to see it to believe it! Let's go to the Panthéon, to discover the experiment live.

Vue de sous le pendule de Foucault en mouvement
Pendule en mouvement vue intérieur dôme

© Benjamin Gavaudo

In life, nothing is to be feared, everything is to be understood.

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