Heron's fountain

Heron's fountain is a hydraulic device that demonstrates the principles of hydraulics and air pressure through a self powered water spouting mechanism. It was built in the first century AD by Heron, or Hero, of Alexandria, an inventor, mathematician and physicist who also studied air pressure and designed an early steam engine, the aeolipile. The device uses three connected containers and a system of pipes, in which water falling from a top basin flows down into a lower, sealed air supply container and builds up pressure there, and that pressure then pushes water up through a third pipe so that it sprays out of a fountain higher than gravity alone would allow. The fountain is not perpetual and eventually stops once the water levels in its containers equalize, but for as long as it runs it shows how air pressure can be made to work against gravity over a short distance.