The face is designed to simulate traditional clock faces with Roman numerals. However, our clock, from timekeeping to lights to chimes, is entirely digitally-controlled.

Rather than using hands to show the time like a more traditional clock, the ceiling clock uses a series of lit panels. The most brightly-lit numeral marks the current hour, and the lights in-between the numerals mark the minutes past the hour. As with traditional clock faces, every fifth minute is marked by the numerals themselves and the minutes are counted from the “XII”.

Running around the clock face below the numerals is a series of 60 horses. Look closely—the horses light up in succession giving the impression of movement. These horses are based on photographs taken in 1872 by Eadweard Muybridge. According to popular myth, he took the sequential pictures to prove that a horse has all four hooves off the ground at the peak of a gallop. His series of photographs are considered to be the origin of motion pictures.

Foucault Pendulum

The Foucault pendulum was the first demonstration of the Earth’s rotation that did not rely on astronomical observation. This was first demonstrated in 1851 by French physicist Jean Bernard Léon Foucault. Foucault noticed that if a pendulum is turned, it tries to keep swinging in its original direction. From this, he theorized that a pendulum could be used to observe the rotation of the Earth. Foucault went on to demonstrate the Earth’s rotation publicly at the Paris Observatory and then at the Pantheon in Paris.

As you watch the pendulum for just a short time, it will appear to be moving clockwise across the mosaic map on the floor. But, since there is no outside force making the pendulum rotate as it swings, and no other outside force interrupting the swing, it must be the floor itself that is rotating, while the path of the pendulum’s swing remains constant. The apparent rotation of a Foucault pendulum is affected by two kinds of motion: twisting and travelling. Twisting is circular motion directly on an axis. Travelling is circular motion around an axis.

To help understand this, consider two Foucault pendulums, one placed directly on the north pole and the other placed directly on the equator. At the north pole, the pendulum’s swing rotates in a complete circle every 24 hours – it twists but does not travel any distance. At the equator, the pendulum travels a wide path around the Earth’s axis but does not even begin to make a circle – it travels but it does not twist at all.

A Foucault pendulum placed in between the pole and the equator is affected by both twisting and travelling. The closer it is to the pole, the faster it circles. The library’s pendulum, located at 38 degrees, six minutes, does a complete circle about every 38 hours. Because air resistance would stop the pendulum’s motion, magnets at the top gently pull the pendulum to keep it moving, and the pendulum is suspended in a way that allows it to swing freely, regardless of the building’s movement.

The apparent rotation of the library pendulum is tracked by sensors in the mosaic on the floor, which light up as the plumb bob passes over them. The slow progress of the lights and the pendulum create a truly mesmerizing show.

Horse & Racing Frieze