I teach a modern physics laboratory course at a state university. in this course, the students reproduce and analyze some of the defining experiments in the history of modern physics.
One of these experiments is a torsional pendulum to measure the gravitational constant, first conceived by the British scientist, Henry Cavendish in 1798. It is said that this experiment measures the weight of the earth. The pendulum consists of two spheres connected by a rod suspended at the middle from a long wire. A small impulse starts the pendulum oscillating. Cavendish put two stationary spheres close to the pendulum, which made the pendulum show a small deflection towards them. Measuring this deflection, he calculated the gravitational constant which defines the weight of things on earth as well as the motions of the planets and galaxies.
Cavendish pendulum oscillations die down after a while, limiting the time available to make the measurements. I modified the experiment with sets of three spheres and adding a small electrical impulse every cycle so the oscillations continue indefinitely. The stationary spheres gravitational attraction change the pendulum frequency by a small amount. This change in frequency instead of the pendulum deflection, is a basis for calculating the gravitational constant. The experiment can be extended for may hours increasing the measurements precision.
TEMPUS means “time” in Latin.
I designed and built the clock in its entirety. My version of the Cavendish Gravity Experiment was the inspiration for the designing an actual clock. I had to take into consideration the technical and esthetic aspects and also the capabilities of my small workshop, It took may months of computer and shop work, and many corrections to come up with the present model.
The clock’s aesthetic appearance comes from an overall design that is simple, functional and without unnecessary ornaments.
As shown on the photographs below, the pendulum consists of three brass spheres suppported by arms extending from a central column. On top of the column is the gear mechanism that brings the pendulum motion to the clock dial. The clock enclosure is a glass bell that provides protection and total visibility of the mechanism.
The three pads supporting the wood base are adjustable to level the clock as shown by a bubble indicuator.
A soft blue light around the dial rim may be turned on as desired.