TODAY -- you can see this FOUCAULT PENDULUM demonstration yourself at the

WIRE CLAMPED in tapered support which permits bending in a slightly different direction on each swing What keeps it moving?
Air resistance would normally stop the pendulum after a few hours -- so an IRON COLLAR is installed on the wire surrounded by an electromagnet that attracts the collar as the bob swings out, then shuts off automatically as it swings back, thus, keeping pendulum going.
The magnet is turned on and off by a switch which is activated when the support wire interrupts a beam of light shining across its path.

WIRE is flexible steel aircraft control cable
30 feet long
The longer the wire, the slower the bob swings and the LESS it is retarded by friction with the air.

There are many other demonstrations of the Foucault Pendulum in the U.S. --

UNITED NATIONS -- in lobby of General Assembly building (gift of Queen Juliana of the Netherlands). Has a 200 lb. bob, a 75 foot wire, and rotates about 235º in 24 hours.

WASHINGTON, DC Smithsonian Museum of American History has a 71.5 foot wire, and rotates 226º in 24 hours.


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