Heron's Fountain

Found on Makezine.com
Antique Heron's Fountain on Makezine.com
Wikipedia-Heron's Fountain

Heron's Fountain is a water fountain that squirts water upwards because of the falling of other water. The concept uses hydraulics and pneumatics. It can seem paradoxical and like a perpetual-motion machine, especially since the water shoots up higher than its "original source."

Here's how it works. The water in the basin falls to the bottom beaker. The water coming in pushes the air out of the beaker. This is the important mechanism. The vise versa happens in the top beaker. The air coming in from the bottom beaker pushes the water out of the top beaker. This water gets squirted out into the original basin.

This is not a perpetual motion machine because water will eventually run out or fill up somewhere. The typical justification is that the basin will never run out of water because it is continually being refilled. But consider:

1. the basin is being refilled by the top beaker, but the system will stop if that beaker runs out of water to squirt.
2. the bottom beaker could completely fill with water and there would be no air to push out.
3. I don't know if this would actually work, but there might end up to be too little water in the basin to provide enough pressure to push the air and water out of the beakers. The reason that the water gets squirted out is that there is more water in the basin that provides more weight and pressure than the amount of water being squirted out. But if an equilibrium occurred because the basin water runs down, the system would stop. Maybe the refilling of the basin is just enough to keep it going until something else stops the system.

Something interesting is that the top beaker doesn't need to be above the bottom beaker. It could be positioned anywhere and squirting water anywhere. It is not affected by gravity as the falling basin water is. It would be different if we were squirting with a tube coming directly from the basin: as soon as you point or position it too high, the water would stop squirting.

It is popular to position these fountains in a straight line (to be more mysterious) and make them artistic, like this one. If you want to experiment, there are multiple instructions online that show you how to make one from pop bottles and straws.