The stately Classical background of Paris’ Panthéon has been the perfect location to house the invention of 19th-century physicist Léon Foucault: a massive pendulum made of a 62-lb brass-coated led bob, suspended from the Panthéon’s central dome by a 220-foot wire. Foucault debuted his pendulum in 1851, and although the original was damaged in 1995, an exact replica still swings back and forth to this day.
In fact, Foucault pendulums exist in all sorts of science museums around the planet, and there is a good reason for this. The apparatus was famous straight away because it demonstrated that our spherical planet rotates on its axis. It worked because even though no outside forces moved the pendulum clockwise, the swing of the pendulum drifted that way and made a complete circle in about 24 hours. The pendulum was stationary, but the earth was not.
If a Foucault pendulum were suspended above the north pole, the circle would be super close to taking 24 hours, but at the equator, it wouldn’t seem to make any rotation, and at the south pole, the path of the oscillations would travel counterclockwise.
Foucault’s pendulum came straight outta Enlightenment-and-French Revolution era France. The French Panthéon was built in the late 18th century, using popular Neoclassical elements like the dome. Public science experiments had become super popular by Léon Foucault’s time, and French culture held scientists in high esteem. By 1851 there were probably fewer flat-earthers than there are now, but Foucault’s pendulum could demonstrate to the public in gigantic and obvious ways that the earth was spherical and rotated on an axis.
Sources: YouTube “stick science,” “How Foucault Pendulum works and proves Earth is a round spinning sphere”. This video has a great explanation of the mechanics of the pendulum and what is proves about Earth’s rotation.
