The Beverly Clock

The Beverly Clock is a clock situated in the foyer of the Department of Physics at the University of Otago, Dunedin, New Zealand. The clock has been running continuously without the need to be wound up since its construction in 1864 by Arthur Beverly. It is a contender for the title of longest continuously running scientific experiment.
The clock mechanism is driven by variations in atmospheric pressure and by daily temperature variations; of the two, the temperature variations are the more important. Either cause the air in a one cubic-foot air-tight box to expand and contract, pushing on a diaphragm. A six-degree Celsius temperature variation over the course of each day creates enough pressure to raise a one-pound weight by one inch (energy extracted = 11 Joule (my wiki contribution :)), which drives the clock mechanism.

Here is a commercial version...