Heron's fountain

From Wikipedia, the free encyclopedia

This article needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (February 2008)

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:

(Everything should be sealed against air unless otherwise stated)

Start with a large basin of water, open to the air. Loop a pipe from that basin to an air supply flask filled with air significantly below the basin.
Then place another pipe from the top of that small flask up to the top of the fountain flask, which is filled with water.
In this fountain flask, have a pipe going from the bottom of the container (under the water), through the air sealed top up to the spout of the fountain.

If you suck in air from the fountain flask's air supply to get it started, then this is what happens:

The water from the basin is pulled by gravity and falls down into the air supply flask. It fills the flask, displacing the air.
The air flows into the fountain flask, displacing the water, which shoots out higher than the original basin.

Contrary to initial appearances, this is not a perpetual motion machine. It quickly comes to a stop. The water coming out of the tube may go higher, but it is less volume than the amount of water that goes down. Assuming the fountain flask started out with enough water, when the water from the basin has filled the air supply and the pipes, the machine will stop.

In order to make the fountain run again, the top and bottom bottles are swapped, as well as the "input" and "output" tubes going to the fountain. Swapping the bottles provides enough energy to start the fountain again.