SLOWLY, ever slowly, back and forth and back again almost hypnotically, Leon Foucault rocked our world.
And the French physicist’s rhythmically rocking big pendulum has been keeping us transfixed — often in museums and universities around the world — ever since.
Foucault himself knew how subtly earth-shaking his pioneering demonstration was, saying in 1851: “Science gains from [the pendulum] more than one can expect.”
And Google itself knows how hypnotic Foucault’s pendulum can be, presenting the bob as a home-page interactive Doodle today (with latitude and clock controls) to mark time — specifically, the 194th anniversary of the birth of Paris inventor Jean Bernard Leon Foucault.
To show the Earth’s rotation, Foucault knew more than 160 years ago that he needed to think big. “With its huge dimensions, the apparatus presents qualities that one would try in vain to communicate by constructing it on a small” scale. So although Foucault first conducted a small-scale experiment — a short pendulum suspended over sand, the eventual “bow-tie” shape etched in the damp sand illustrating the oscillations on a perpendicular plane — French officials were so smitten with the graceful demonstration that they had a large-scale version built in the Paris Observatory’s Meridian Room, a brass-coated bob suspended by a wire of roughly 200 feet from the dome of the Pantheon.
“The observations, so numerous and so important, of the pendulum as object are especially relevant to the length of its oscillations. ... ,” Foucault said. “The direction of the plane of its oscillation, which, moving gradually from east to west, provides evidence to the senses of the diurnal movement of the terrestrial globe.”
Today, these “Foucault pendulums” gently rock in spots around the globe, from the United Nations in New York to San Francisco’s California Academy of the Sciences (whose website has a great animated lesson about the pendulum).
Each of these Foucault pendulums around the globe, naturally, has a different rate of rotation, depending on its latitude, slowing as it nears the equator. (At the North Pole, the pendulum, rotating at 15 degrees as the plane of swing remains fixed in space, would take a day to finish a full round; the Paris pendulum needs more than 32 hours to do so.)
Foucault — whose extensive scientific work included the measurement of the speed of light — died Feb. 11,1868. He was just 48.
To honor his lofty achievement, he is one of 72 scientific minds whose names are engraved on the Eiffel Tower.
Slowly, back and forth and back again: Many happy returns, Monsieur Foucault.