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I seem to remember something about extremely long …

Comment posted on Grandfather Clock by mijj

i seem to remember something about extremely long pendulums (pendula?) hung in some cathedral or something similar in rome or somewhere .. if the pendulum is extremely long, then it’s trajectory is affected by the rotation of the earth. And so it can trace an interesting pattern in the floor below it (in sand, for instance) .. i shall check to see if i can find refs or pics or something.

mijj also commented

wow! .. i thought this pendulum thing was my own personal private topic that noone else was interested in.

(sobs)

welcome!
ahem … … waaaaaaay over the top.
damn .. the first pic location doesn’t take …
… try another ..

[pic: 67 meter 28 kg Foucault's Pendulum in the Panthéon, Paris]
[Wikipedia: The Foucault pendulum, named after the French physicist Léon Foucault, was conceived as an experiment to demonstrate the rotation of the Earth.]
[pic: 67 meter 28 kg Foucault's Pendulum in the Panthéon, Paris]

[Foucault pendulum animated gif]
Animation of a Foucault pendulum showing the direction of rotation on the southern hemisphere. The rate of rotation is greatly exaggerated. A real Foucault pendulum, released from rest, does not pass directly over its equilibrium position as the one in the animation does.
[Foucault's Pendulum at the Kirchhoff - Institute of Physics]
The pendulum happily swinging in the first floor of the Kirchhoff Institute of Physics proves the Earth’s rotation about its own axis. In fact, the vertical plane through which the pendulum swings to and fro is fixed in space, and our planet merely rotates beneath it – the terrestrial observer believes that it is the pendulum that moves!