Foucault's Pendulum Snaps, Crashes To Paris Museum Floor

In 1851, French scientist Leon Foucault gave a sensational demonstration in the Paris Pantheon proving that the Earth revolved around its axis - known as diurnal motion - before a group of dignitaries that included Napoleon III. He suspended a heavy brass bob by a wire from the Pantheon's ceiling to create a pendulum and let it swing freely in any direction along its vertical axis (a key feature).

As time passed, the swings rotated in response to the Earth's rotation. Quod erat demonstratum. Einstein's theory of general relativity further buttressed the phenomenon by provided an explanation of "why the oscillation plane of the pendulum does not remain fixed in absolute space, as expected by Foucault, but is slowly dragged by the presence of the rotating Earth."

While scientists already knew that the Earth had a rotation in Foucault's day, they had struggled to come up with a way of definitively proving this was so. The pendulum was such a simple proof of the theory, it became one of Foucault's most famous contributions to science. Many modern science museums have a version of Foucault's pendulum on display, including Griffith Observatory in Los Angeles. And it inspired novelist Umberto Eco's bestselling historical thriller, Foucault's Pendulum, to boot.

Alas, earlier this month, Times Higher Education reported that the original Foucault's pendulum has been irreparably damaged, when its cable snapped unexpectedly, sending the brass bob crashing to the marble floor in the Musee des Arts et Metiers in Paris. (It's not the first time the pendulum has been at risk: in May 2009, during a party, one of the guests grabbed the pendulum and swung it into a security barrier, but fortunately the instrument suffered no permanent damage.) Science historian Amir D. Aczel (Boston University) joined the throngs of history buffs mourning the loss, telling the THE that "It's a bit like hearing that one of the statues at the Vatican has been broken."

While the original will always hold special significance, there's still a gorgeous replica of the pendulum still swinging away in the Paris Pantheon, not to mention countless other places around the globe. Here to tell you more about Foucault's pendulum, and how it works, is Jim LaBelle, professor of physics and astronomy at Dartmouth, which also boasts a version of the instrument: