Cox's timepiece

Cox claimed that his design was a true perpetual motion machine, but as the device is powered from changes in atmospheric pressure via a mercury barometer, this is not the case.

The change of pressure in the Earth's atmosphere acts as an external energy source and causes sufficient movement of the winding mechanism.

The clock is designed to enable the timepiece to run indefinitely and overwinding is prevented by a safety mechanism.

The prime mover, encased in a finely detailed clock body, is a Fortin mercury barometer.

[2] A similar design is Cornelis Drebbel's circa 1610 device that told the time, date, and season.