Atmos clock

Is the brand name for a torsion pendulum clock made in Switzerland by Jaeger-LeCoultre.

Its’ claim to fame is that it doesn’t need to be manually wound as it gets the energy it needs from atmospheric changes in temperature and air pressure.

The mainspring is continuously wound by the compression and decompression of a spiral spring caused by the expansion and reduction in size (due to the atmospheric changes) of a mixture of gaseous and liquid ethyl chloride held in a hermetically sealed capsule.

For this to work the clock needs to run with the least friction possible. The timekeeping uses a torsion pendulum which uses less energy than the traditional pendulum, with only two oscillations per minute rather than the more usual one per second of the grandfather clock.