Hi there. Long time ago i saw a video of a physical phenom. The procedure was : At the bottom we have something like a puck (a circle with thickness), which is rotating. And above with have a jar of water. And when we throw some dye. We can see that phenom : there is like an invisible cylindre that follow the circle at the bottom but in water. So we have the dye who spread everywear but not in this cylindre. I can't remember what was the name of the phenom, and i coudln't fint it with key-words on internet. Thanks for helping me.