Foucault realized that he might be able to demonstrate Earth's rotation using a very long pendulum with a heavy bob to minimize the effect of air resistance that would otherwise bring the pendulum's oscillations to a halt before the precession became apparent. Foucault's first successful demonstration was carried out in the Paris Observatory's Meridian Room using an 11-meter long pendulum in 1851. Just a few weeks later he followed up with a public demonstration using a 67-meter long pendulum with a 28-kilogram bob suspended from the inner dome of the Pantheon in Paris (below). Patient attendees could see that the plane of oscillation precessed clockwise, and those who stuck around long enough (or came back) could see that the plane precessed a full 360 degrees in about 32 hours.
The Foucault pendulum made the Earth's rotation easily visible even to casual observers. Soon Foucault pendulums were installed in academic buildings and museums around the world. Foucault's original Pantheon pendulum was relocated and eventually broke, but a replica of the original pendulum was installed in the Pantheon in 1995 (below).
