Grotta Gigante horizontal pendulums

The horizontal pendulums, installed by the geodesist Antonio Marussi in 1959, are sensitive to deviations of the vertical, to rotations and shearing of the cave.

The pendulum beam rotates in the horizontal plane around a virtual near-to-vertical axis that passes through the upper and lower mounting points.

The Earth's crust is the outer brittle layer of our planet, on average 35 kilometres (22 mi) thick in continental areas.

This moves up and down by ten centimeters during the time of 12 and 24 hours due to the attraction of Moon and Sun, and is accompanied by a local tilting of some parts in a billion of radians.

The movements of the pendulums has contributed to identify the free oscillations of the Earth, and to show that the secular term tilting of the cave is towards the northwest.