Other Uses
In addition, the principle is used to make small toys often called "water dancers" or "water devils". The principle is the same, but the eyedropper is instead replaced with a decorative object with the same properties: a tube of near-neutral buoyancy. For example, a blown-glass bubble. If the tail of the glass bubble is given a twist, the flow of the water into and out of the glass bubble creates spin. This causes the toy to spin as it sinks and rises. An example of such a toy is the red "devil" shown here. The device also has a practical use for measuring the pressure of a liquid.
Plastic divers were given away in British cereal boxes as free gifts in the 1950s.
Read more about this topic: Cartesian Diver