Heron's fountain
A hydraulic machine demonstrating air and water pressure.
Heron's fountain is a hydraulic device created by Heron of Alexandria, a first-century inventor, mathematician, and physicist. He investigated air and steam pressure, documented an early steam engine, and constructed water-spurting toys—one of which is this fountain. Modern physics classes still use various versions to illustrate hydraulics and pneumatics.
The fountain has three containers: a basin (top), a water supply (middle), and an air supply (bottom). Three pipes connect them. One pipe runs from the basin’s bottom to the air supply’s bottom. Another goes from the top of the air supply to the top of the water supply. The third pipe extends from the water supply’s bottom, up through the basin’s floor, to a height above its rim—this is where the water jets out. The maximum height of this spout depends on the vertical distance between the middle and bottom containers. The basin can be open or airtight, but the middle and bottom containers must be sealed and able to withstand atmospheric pressure. Plastic bottles can work, but glass is better; balloons fail because they deform under pressure.
The fountain’s energy comes from water descending from the basin into the bottom container. Water falling through the first pipe builds pressure in the bottom container, proportional to the height difference between the basin and bottom container. This pressure travels via air through the second pipe into the water supply, pushing water up the third pipe. The rising water replaces the water falling from the basin, creating a loop. For this to work, the first pipe must reach the bottom of the air supply so water seals it, preventing air escape. Similarly, the third pipe must reach the bottom of the water supply. The second pipe must connect the tops of both middle and bottom containers to avoid water blocking the air pressure.
Heron’s fountain is not perpetual. With a narrow nozzle, it may run for several minutes before stopping. The spout can shoot water higher than any container’s water level, but the net flow is downward. If the air supply and water supply containers are much larger than the basin, and the nozzle flow is steady, the fountain can operate much longer. Its action resembles a siphon with the upper arch removed; air pressure between the lower containers lifts the water over the arch, earning it the name Heron’s siphon. The gravitational energy of water
- field
- Hydraulics, pneumatics
- known_for
- Heron's fountain, first steam engine
- century
- 1st century AD
- location
- Alexandria
Lore & Background
Heron of Alexandria studied the pressure of air and steam, described the first steam engine, and built toys that would spurt water, one of them known as Heron's fountain. The fountain uses three containers: a top basin (A), a middle water supply (B), and a bottom air supply (C), connected by three pipes. Water falling from A to C builds air pressure, which pushes water from B up through a pipe above the basin.
Reader's Guide
Heron's fountain is not a perpetual motion machine; it stops when the water in B is depleted. Its action can be understood as a siphon with pneumatic pressure lifting water. The fountain can spout almost as high as the water falls from the basin to the lower container. Variants include switching container positions, adding valves, or using boiling and condensing to transfer water. The device is featured in popular culture, such as in the television show Numb3rs and How Britain Worked.
Did You Know?
- Heron's fountain is not a perpetual motion machine; it stops when the water supply in the middle container is depleted.
- The fountain can spout almost as high as the water falls from the basin into the lower container.
- Variants include a four-container fountain that can be turned upside down to switch full and empty containers.
- The fountain was featured in the 8th episode of the 4th season of the television show Numb3rs.
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