Also known as «The Fair Cup» is an invention that is attributed to Pythagoras and that presents an unusual feature in conventional glasses: If you fill the glass more than three quarters (approx.), the entire contents of the glass fall out of the bottom, and the container remains completely empty.
This is not magic, but rather an application of Pascal's Principle quite ingenious, known as the theory of Communicating Ducts.
The operation itself is quite simple.: The tube is filled with air, and although one part of the conductive glass is filled with liquid at the same time as the cup, the other part of the conduit remains full of air. The problem arises when you allow the liquid from one part of the tube to reach the top and fall down the other side, since the air is pushed out by the liquid and creates a small pressure that generates an effect similar to that of absorbing liquid through from a straw, dragging with it the 100% of the liquid that remained in the cup.
The drains and pipes in our home use the same theoretical concept, which has been called Siphon System.
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