A jet of water jumps from one flight case into another. The shape of the water describes very neatly the mathematical function of a parabola.
Since the water jet is very smooth, light can be directed through the jet into the second case.
HOW DOES IT WORK?
When you throw an object into the air, it flies along a parabola (neglecting the effects of air resistance and its rotation). This allows for the very easy calculation of where a water jet will land.
The light spreads out in the water jet, due to its smooth surface causing total reflection - that is, completely reflecting the light and keeping it inside the water.
