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Foucault pendulum

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I visited the Houston Museum of Natural Science recently. Near the west end of the exhibit halls is a Foucault pendulum. It is an enormous brass ball with a delicate finial at the tip, depending from a tower reaching storeys above the rest of the building. Its stately swings above the polished floor appear to remain in a plane, but due to the angular momentum of the rotating earth, its path precesses in a ring. Traced on the ground, that path would resemble not a single line endlessly retraced, but a flower with countless narrow petals.

A half-dozen or so visitors surrounded the pendulum. We could not perceive the tiny course changes between swings, so to demonstrate the effect, the exhibitors had set up a ring of pegs just inside the limits of the swing. As the pendulum precessed, its finial periodically toppled a peg.

We could see the finial passing just millimeters from the next peg. I pulled out my digital camera and photographed each pass, hoping to catch the moment of the peg's fall. More visitors appeared, and excitement rippled through us each time the pendulum swung past its target. I switched my camera to video mode and tried to record the fall, but the batteries died, and all around people groaned with me. Now each approach drew a breathless gasp: would the peg fall this time? Now the finial seemed sure to touch it; now the peg wobbled; we all held our breath. As the pendulum swung again, its point lightly brushed the peg, and we cheered noisily as it tipped.

Throughout the experience I was sharply aware of its incongruity in the 21st century. Wonders are routine now. No respectable action film lacks CGI effects. Any event we want is at our fingertips on YouTube; any natural phenomenon is a search away on Wikipedia.

Yet we at the museum crowded around the giant pendulum and its literally mundane movement, captivated by the tiny drama of the effects of the rotation of the earth. And when the peg fell, we cheered.

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