These three physicists set up a Foucault pendulum at the South Pole to look for the daily rotation of the plane of swing due to the Coriolis force. With the pendulum suspended so it could freely turn in all directions, Earth rotates beneath it once per day, so in the Earth's frame of reference the pendulum is observed to swing through 360° in 24 hours. For more on this kind of pendulum, see the University of New South Wales' Foucault pendulum
