Vasos de Pascal
Clearly demonstrates that pressure in a static fluid is the same in all directions. Three different shaped glass vessels have bottom openings of equal diameter. A plastic disc with a cord is used as a watertight seal. When lowered into water disc first, water pressure holds the assembly in place. At a given depth, water is poured into the test vessel. At the point of equilibrium when the disc falls off, the depth of water within the test vessel will be the same regardless of shape.