Mini Foucault de 19,6 cm (n° 22)
Small adjustable eddy current pendulum from 19.6 to 25 centimetres long. The idea was to improve the reliability of my first Mini Foucault (n°4), whose suspension wire never lasted more than a week, and to turn it into a real Foucault pendulum capable of lasting for decades without interruption. Such a short pendulum (176 oscillations per minute, 8160 per hour) is extremely difficult to build because it is so unforgiving of errors. It requires a lot more work than a one-metre pendulum, the frame has to be very rigid and every detail has to be meticulous. For example: it’s four times shorter than the ones I usually make, but weighs four times as much: 20 kilos!
The sum total of potential problems means that it’s easy to lose yourself in years of adjustments before it works properly. To be effective, it absolutely had to have nine functions that could be fully adjusted in all directions without any tools and without ever interrupting its travel. Namely:
- Rotation of the dial.
- Rotation of the Charron ring.
- Rotation of the sight.
- Rotation of the thread guide.
- Thread rotation.
- Height of thread guide.
- Length of thread.
- Height of Charron ring
- Azimuth of the propulsion spool
(And also to devise a system for measuring rotation, a small rotating plumb bob making its measurement just as accurate as that of a large pendulum)
