Water_Clock

In 1979, French scientist Bernard Gitton began creating his Time-Flow Clocks (Water Clock), which are a modern-day approach to the historical version. His unique glass tube designs can be found in over 30 locations throughout the world, including one at The Children's Museum of Indianapolis in Indianapolis, Indiana, and the Shopping Iguatemi in Porto Alegre, Brazil. There are other modern designs of water clocks, including the Royal Gorge water clock in Colorado, the Woodgrove Mall in Nanaimo, British Columbia, and in the Abbotsford Airport in Abbotsford, British Columbia.

Gitton's design relies on gravity powering multiple siphons; for example, after the water level in the minute or hour display tubes is reached, an overflow tube starts to act as a siphon and thus empties the display tube. Actual time keeping is done by a calibrated pendulum powered by a water stream piped from the clock's reservoir. The pendulum has a carefully-constructed container attached to it; this measures the water that is then poured into the display system.

Today, the use of water flow to power a clock is a rarely-practiced art, whose purpose is more for show and novelty than for functional accuracy, an example being the Hornsby Water Clock in Sydney, Australia.

Ref: http://en.wikipedia.org/wiki/Water_clock