the earth rotates!
Foucault’s pendulum, named after the French physicist Léon Foucault, is a simple device conceived as an experiment to demonstrate the rotation of the Earth. While it had long been known that the Earth rotated, the introduction of the Foucault pendulum in 1851 was the first simple proof of the rotation in an easy-to-see experiment.
The first public exhibition of a Foucault pendulum took place in February 1851 in the Meridian of the Paris Observatory. A few weeks later Foucault made his most famous pendulum when he suspended a 28 kg brass-coated lead bob with a 67 meter long wire from the dome of the Panthéon, Paris. The plane of the pendulum’s swing rotated clockwise 11° per hour, making a full circle in 32.7 hours.(Wikipedia)
We saw this when we visited the Pantheon a few years back. What a sign! I stood and watched and took photos as I watched the pendulum inch itself along the degree marks. Foucault’s pendulum had tucked itself away in my knowledge bank for a long time, a miracle I wanted to see. And seeing it felt like I’d completed some circuit of my own.
janetsunderland.com 
I stayed right by there when I went to Paris, and it was the first place I went while I waited for my hotel room to be ready. Nothing made any sense to me in that building, why it was there, what it was, what that pendulum was doing, and that set the tone for my whole trip. Mostly in a nice way.
Nice comment. Thank you. Not only is Foucault in that building, but the tombs of Voltaire and Rousseau are in the basement down a fabulous spiral staircase. That could have made your visit even stranger!
the smithsonian had one set up at the american history museum for years, it would knock over little pegs to denote time
I remember that! And remember watching as the pegs went over one by one. I’ll bet that’s where I first became fascinated with it. Thanks Willy for feeding my memory!!