Heron's fountain

Heron's fountain is a hydraulic machine invented by the first century inventor, mathematician, and physicist Heron, also known as Hero of Alexandria.

Heron studied the pressure of air and steam, and built the first steam engine as well as toys that would spurt water, one of them known as Heron's fountain. Various versions of Heron's Fountain are used today in physics classes as a demonstration of principles of hydraulics and pneumatics. Heron's fountain is built as follows:

* Start with a basin, open to the air. Run a pipe from a hole in the bottom of that basin to an airtight air supply container. (Glass flasks are shown here, and serve the purpose well. Cans with airtight lids may also be used.) The air supply container stands significantly below the basin.
* Run another pipe from the top of that container up to the top of the airtight fountain supply container, which is filled with water.
* From the fountain supply container, have a pipe that reaches nearly to its the bottom of the container, through the top up to the spout of the fountain. A refinement is to have the spout coming up through the centre of the basin, and the containers may be concealed in a column supporting the basin, as long as the air supply container is lower than the fountain supply container.

* Fill the basin with water.

* The water from the basin flows by gravity into the air supply container. It fills the container, displacing the air.
* The air flows into the fountain supply container, displacing the water, which shoots out "higher than the original basin".

Contrary to first impressions, this is not a perpetual motion machine. If the nozzle of the spout is narrow, it may play for several minutes, but it eventually comes to a stop. The water coming out of the tube may go higher than the level in any container, but the net flow of water is downward. Its action may seem less paradoxical if it considered as a siphon, but with the upper arch of the tube removed, and the air pressure between the two lower containers providing the positive pressure to lift the water over the arch. The device is also known as Heron's siphon.

In order to make the fountain play again, the air supply container is emptied of water, and the fountain supply container and the basin are refilled. Lifting the water provides the energy required.

ee also

* hydraulic ram
* water hammer

External links

* R.Ya.Kezerashvili, A.Sapozhnikov. [http://arxiv.org/abs/physics/0310039 "Magic Fountain"] , at arxiv.org