Foucault pendulum sharing the rotation of the earth about its own axis, the suspension point of the pendulum traces out a circular path during one sidereal day. At the latitude of Paris, 48 degrees 51 minutes north, a full precession cycle takes just under 32 hours, so after one sidereal day, when the Earth is back in the same orientation as one sidereal day before, the oscillation plane has turned by just over 270 degrees. If the plane of swing was north-south at the outset, it is east-west one sidereal day later. This also implies that there has been exchange of momentum;
Panthéon cross of the dome, which was retained in compromise, is again visible during the current major restoration project. In 1851, physicist Léon Foucault demonstrated the rotation of the Earth by constructing a Foucault pendulum beneath the central dome. The original sphere from the pendulum was temporarily displayed at the Panthéon in the 1990s (starting in 1995) during renovations at the Musée des Arts et Métiers. The original pendulum was later returned to the Musée des Arts et Métiers, and a copy is now displayed at the Panthéon. It has been listed since 1920 as a "monument historique" by the French