We asked some fellows in Etwinning projects that make us a post with classical references into our blog. Manuel Diaz Escalera, Etwinning Prize 2010, is the first, with his marvellous experiment "The cup of Tantalus".
The cup of Tantalus is never filled. Tantalus, son of Zeus, got a the cruel punishment, according to Greek mythology. His punishment was to be in a lake with water up to his chin, under a tree with low branches full of fruit. Whenever Tantalus, desperating of hunger or thirst, tries to choose a fruit or sip some water, branches and water immediately move away.
The cup of Tantalus is a siphon. When filling the glass is also filled rubber tube (the short arm). When the water reaches the top of the rubber tube begins to fall for the long arm dragging the fluid inside the rubber tube. The level goes down until the orifice tube.
You can see in Spanish here.