A Pythagorean cup is a form of drinking cup which forces its user to imbibe only in moderation. Credited to Pythagoras of Samos, it allows the user to fill the cup with wine

Wine

Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...

 up to a certain level. If the user fills the cup only up to that level he may enjoy his drink in peace. If he exhibits gluttony

Gluttony

Gluttony, derived from the Latin gluttire meaning to gulp down or swallow, means over-indulgence and over-consumption of food, drink, intoxicants or wealth items to the point of extravagance or waste...

 however, the cup spills its contents out the bottom (the intention being: onto the lap of the immodest drinker).

Form and function

A Pythagorean cup looks like a normal drinking cup, except that the bowl has a central column in it – giving it a shape like a Bundt pan

Bundt cake

A bundt cake is a dessert cake that is baked in a bundt pan, shaping it into a distinctive ridged ring. The d in "bundt" is assimilated into the t. The term is used chiefly in North America....

 in the center of the cup. The central column of the bowl is positioned directly over the stem of the cup and over the hole at the bottom of the stem. A small, open pipe runs from this hole almost to the top of the central column, where there is an open chamber. The chamber is connected by a second pipe to the bottom of the central column, where a hole in the column exposes the pipe to (the contents of) the bowl of the cup.

When the cup is filled, liquid rises through the second pipe up to the chamber at the top of the central column, following Pascal's principle of communicating vessels. As long as the level of the liquid does not rise beyond the level of the chamber, the cup functions as normal. If the level rises further however, the liquid spills through the chamber into the first pipe and out the bottom. Hydrostatic pressure then creates a siphon

Siphon

The word siphon is sometimes used to refer to a wide variety of devices that involve the flow of liquids through tubes. But in the English language today, the word siphon usually refers to a tube in an inverted U shape which causes a liquid to flow uphill, above the surface of the reservoir,...

 through the central column causing the entire contents of the cup to be emptied through the hole at the bottom of the stem.

Common occurrences

The Pythagorean cup is credited as an invention to Pythagoras. For this reason, it is sold often on the Greek

Greece

Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

 island of Samos

Samos Island

Samos is a Greek island in the eastern Aegean Sea, south of Chios, north of Patmos and the Dodecanese, and off the coast of Asia Minor, from which it is separated by the -wide Mycale Strait. It is also a separate regional unit of the North Aegean region, and the only municipality of the regional...

 as a tourist

Tourism

Tourism is travel for recreational, leisure or business purposes. The World Tourism Organization defines tourists as people "traveling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes".Tourism has become a...

 souvenir

Souvenir

A souvenir , memento, keepsake or token of remembrance is an object a person acquires for the memories the owner associates with it. The term souvenir brings to mind the mass-produced kitsch that is the main commodity of souvenir and gift shops in many tourist traps around the world...

, sometimes with accompanying information, such as: "Tradition says Pythagoras, during water supply works in Samos around 530 BC moderated the workers' wine drinking by inventing the 'fair cup'. When the wine surpasses the line, the cup totally empties, so the greedy one is punished." Whether there is any basis to this historical assertion is unknown. However, water supply was evidently a problem in Pythagoras' time in Samos

Samos Island

Samos is a Greek island in the eastern Aegean Sea, south of Chios, north of Patmos and the Dodecanese, and off the coast of Asia Minor, from which it is separated by the -wide Mycale Strait. It is also a separate regional unit of the North Aegean region, and the only municipality of the regional...

, as demonstrated by the 1036 m (3,399 ft) Tunnel of Eupalinos that the tyrant Polycrates

Polycrates

Polycrates , son of Aeaces, was the tyrant of Samos from c. 538 BC to 522 BC.He took power during a festival of Hera with his brothers Pantagnotus and Syloson, but soon had Pantagnotus killed and exiled Syloson to take full control for himself. He then allied with Amasis II, pharaoh of Egypt, as...

 had dug through rock to serve as an aqueduct

Aqueduct

An aqueduct is a water supply or navigable channel constructed to convey water. In modern engineering, the term is used for any system of pipes, ditches, canals, tunnels, and other structures used for this purpose....

 bringing water to the city.

Hero of Alexandria (c. 10–70 AD) used Pythagorean cups as hydraulic components in his robotic systems.

It is also sold in some toy store

Toy store

A toy store or toy shop is a retail business specializing in selling toys. No longer held to the limitations of a physical outlet, many toy shops now do business over the Internet. Many department stores have toy sections.-External links:...

s as a practical joke gift.