Pythagoras Justice Cup – Story

If your cup (literally) runneth over, it may be by design — and that design may be over 2,500 years old. <>

Variously called a Greedy Cup, Tantalus Cup or Pythagoras Cup, this drinking vessel can only be filled with so much wine before a siphoning effect drains it all back out.<>

Pythagoras of Samos was a philosopher and mathematician of the 6th Century BCE. <>

Among other accomplishments, he is widely credited with proving the Pythagorean theorem (though it may well have been the work of his students). <>

He is also given credit for the creation of this ancient practical joke device that likewise bears his name.<>

The cup itself looks ordinary except for its central column. <>

A hidden pipe runs from a void in the bottom of the stem up into the vessel, coiling back on itself in the process. <>

This twist is the key.<>

When the cup is filled too high, liquid tips into the central pipe and, per Pascal’s principle of communicating vessels, the entire contents of the cup begin to drain.<>

Gravity and pressure take over and the rest, as they say, is history — the vessel then empties itself entirely. <>

If filled to just below that point, however, a user can drink from the vessel normally.<>

Cross section of a Pythagorean cup being filled: at B, the cup may be safely drunk from, but at C, the siphon effect causes the cup to drain.<>

Diagram by Nevit Dilmen (CC BY-SA 3.0)<>

As the (possibly apocryphal) story goes: <>

Pythagoras designed the cup so that his students would share equally and balance their consumption. <>

If they poured too much, these self-draining chalices would prevent the students from ending up in their cups, so to speak.<>

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