This small Foucault pendulum clock, located anywhere in the world, is able to tell you by itself the time, the latitude, the hemisphere and is an experimental proof of the earth's rotation.

A Foucault pendulum is very simple: a free oscillating bob. The forces acting on the pendulum, gravity and friction, cannot change its plane of oscillation. But the rotating earth does. This plane of oscillation is 24 hours clockwise at the north pole, increases until an infinite time above the equator, and decreases when going further south, 24 h counterclockwise above the South pole. But a viewer located on another star will always see the same plane of oscillation. The force that causes the plane of oscillation to rotate is called the Coriolis force.

The pendulum's propulsion is given by a coil wich impulses the magnet located under the bob every second. The base of time is given by the pendulum's lenght, as usual.
Shorts Foucault pendulums (less than 1 meter) are very rare because they are not easy to built at all. Reducing the lenght and mass of the pendulum reveals the imperfections of the system. The longer pendulums are always easier.

The first problem comes from the suspension, wich should be perfect. Any lack of symmetry in the bending charasteristics of the supporting wire will perturb the plane of oscillation. So the wire must be perfectely round and without internal tensions.

Once this problem is solved, we fall into the next (the worst) one: the turning due to the ellipticity of the motion. This kind of trouble doesn't affect  the huge Foucault pendulums we are used to see. On the smaller ones (less than 2 m) this force of the ellipticity is bigger than the Coriolis one and the pendulum has an erratic course without any device able to limit it. A good way to limit the growth of the ellipticity is to insert a Charron Ring in the first third of the pendulum's lenght.

The amount of these problems put together makes  a working short Foucault sounds like a miracle. The time for tooling and making is 1/10 of the total time, the rest is spent in settings. And as every time a new setting is performed, it takes 16 hours (one pendulum's rotation) before to see any resultat. If there is one...

The pendulum lenght is set in order to have an oscillation of 1 second, wich moves the seconds, minutes and hours of the left display. A Foucault pendulum employed like a clock imposes the requirement to be able to set the pendulum's lenght, to compensate the effect of the temperature and to stabilise the swing's amplitude. On  pendulum n°1, the wire go through a hole and can be adjusted the same way than we tune a guitar. But pulling the wire provoques another unhappy fact: the magnet moves a little bit higher from the coil, wich changes the power of the impulses. So I had to improve the system. The steel wire of this clock is firmly tightened to a bimetallic piece, but the hole and the Charron ring can be moved up or down together wich changes the period. The bimetallic suspension compensates the temperature's effects.

This clock has two displays: one (left), called "pendule", driven by the pendulum's passages and the other (right), called "référence", is a quartz clock. It allows one to see the difference between the two times and makes it easy to set the pendulum's lenght. One thingshould always be kept in mind while setting the pendulum's lenght: We set the average to a half period of the pendulum's revolution. (16 h 34 minuts 14 seconds under my latitude). So it will compensate any eccentricity due to the Charron ring. Then if the clock is three seconds too fast in one position, it will be three seconds too slow 8 hours 15 later. What we must set is the average, and we can always check the moving differences between the two displays.

Please feel free to write me if you are interrested by buying one. The latitude should be given, as the display is personalized. The delay is three month. Special executions (another socket or design, glasspipe, material or other) are also available if needed.