Back in 1851, a French scientists named Leon Foucault used a very simple device to demonstrate the rotation of the Earth. This device was a plain pendulum, only in large proportions. A 28 kg brass coated lead bob was suspended by a 67 meters long steel wire from the dome of Pantheon in Paris. The pendulum was put into motion. The oscillation of the pendulum was expected to remain in a fixed plane. But due to the rotation of the Earth, the plane of the oscillation rotated as well! The rotation was about 8 degrees per hour, making a full circle in 32.7 hours.
The next video from Sixty Symbols explain why this happens.