Atmos II self winding clock with fitted case

Atmos II self winding clock with fitted case, Jaeger-LeCoultre, 1939, original design by Jean-Léon Reutter.

Clock movement has hermetically sealed bellows filled with a mixture of gas and liquid ethyl chloride (chloroethane) expands and contracts with changes of temperature and atmospheric pressure. The movement of the bellows winds a large spring by a ratchet mechanism (so the clock never needs to be wound). As the temperature rises the spiral spring compresses expanding into an expansion chamber. As the temperature falls the gas condenses and the spring slackens. This motion winds the mainspring. It uses a torsion pendulum, executing two torsional oscillations per minute (1/60th the rate of the pendulum in a conventional clock).