Thanks for the follow-up! The clocks depicted on that website are truly amazing, and lots of fun -- interested people should definitely take a look at them.
The explanation and the advertising seem to point rather to temperature variations as the source of energy needed to run the clocks. I neglected these in my previous answer -- sorry -- they are probably more important than external pressure variations. As temperature increases, gas pressure goes up, or expands if it can, or does a little of both, according to PV=nRT, the ideal gas law, where P=pressure, V=volume, n=number of moles of gas, R=gas constant, and T is the absolute temperature (in degrees Kelvin). A change in the ambient temperature will make the gas inside the can and outside expand, but the gas outside has someplace to go (external winds equalize pressure over large areas), while the pressure in the can changes a lot. Itís the change in the pressure in the can relative to its surroundings which allows work to be done (however tiny an amount). Quite clever!
You could experiment with one to see if pressure variations alone are sufficient to power it. Put an Atmos clock in a temperature-controlled room and see if it runs out of energy. Of course they donít need much of a temperature change -- one advertisement says a 2-degree change in temperature is enough to power it for 48 hours. There might be enough energy in the pressure changes alone to do it.
Iíve seen advertisements of watches that wind themselves up with everyday wrist movements. Typing answers to Physics Van questions would be more than enough for one of these.
Clocks and calculators take very little power to run, and so they are great playgrounds for engineers to come up with all sorts of clever energy sources. The advertising line that they are "more ecological" than other clocks is not right, however. All the clocks on the page are bulky, have big pieces of metal and glass, and are very costly. Just transporting one from the factory to your house takes lots of fuel, not to mention whatís needed to smelt the metal ores. If you want to be ecological, get a wind-up clock or a cheap, tiny LCD battery-powered clock.
(published on 09/12/06)