Made On Earth — Pendulum Perfector

Craft & Design


If you’ve visited enough science museums, you’ve seen a Foucault pendulum. Named after its inventor, French physicist Léon Foucault, the pendulum demonstrates the Earth’s rotation by knocking down pins arrayed around the pit over which it swings. Although the pendulum appears to swing around the pit, it’s the pit, and Earth it stands on, that rotate beneath the pendulum. And there’s a good chance the pendulum you know is one of more than 100 made so far by Cary Ponchione.

For 34 years, Ponchione worked in the basement shop of the California Academy of Sciences museum in San Francisco. Shortly before moving from its home of 87 years in Golden Gate Park, the Academy downsized its in-house exhibit-building shop and offered early retirement to Ponchione.

But calls for the pendulums that the Academy could no longer make kept coming in. “They asked me to take [them],” Ponchione says of the pendulum orders, and a small business, Academy Pendulum Sales, was born.

A friendly, outgoing machinist and fabricator, Ponchione keeps a spare, tidy shop by the tracks in Richmond, Calif., where he assembles pendulum kits for customers to install. “As you can imagine,” the semi-retired maker deadpans, “it’s not a full-time job.”

Though he has others join, turn, finish, and polish the cast brass hemispheres that make the 235-pound, 16-inch bob, Ponchione makes and assembles most of the small parts, and still hand-winds the ring electromagnet, which adds the perfectly timed kick that keeps each pendulum swinging.

Foucault Pendulums:

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