[Make it Lady (OP)]

I caught the end of Cash in the Attic the other day and they were selling someones atmospheric clock. The auctioneer said that it never needs winding and is the first type of mechanical clock that didn't need winding. How does it work? Is it some kind of perpetual motion clock? Mr Hammer, blacksmith, do you know?

[DoctorBeaver]

from http://216.239.59.132/search?q=cache:6oZ7vqGDCNYJ:www.dg-chrono.de/bibliothek/english/hoijmaijers.pdf+%22atmospheric+clock%22&hl=en&ct=clnk&cd=17&gl=uk

...functions similar to an sand-glass, featuring a vertical glass-tube sealed at both ends with semiporous material, allowing a glob of mercury to descend slowly indicating the time on a scale, before the whole tube is flipped upside down every 24 hours.

[LeeE]

Hmm...  I'm surprised that no one has used variations in ordinary atmospheric air-pressure to wind a clockwork clock - if it's able to displace an inch of water from the U-bend in my loo I'm sure it could wind a clock.  All it would need is a ratchet, and something to stop it from being over-wound.

[lyner]

I always thought that was what they were based on, actually.

[Make it Lady (OP)]

The clock looked like a normal clock so I guess this was as LeeE predicts.

[lyner]

A bellows (partially evacuated) like in an anaeroid barometer which expands and contracts as the air pressure changes would provide enough energy. You could work out the energy available by multiplying the atmospheric pressure by the change in volume of the bellows over, say, a week.