Physics demonstrations: Magdeburg hemispheres

The premise is simple: with the hemispheres pressed together, air is pumped out of the interior, creating at least a partial vacuum. This seals together the hemispheres with a remarkable force.

Guericke first demonstrated this force in 1654 for the Emperor Ferdinand III. Thirty horses, in two teams of 15, were unable to pull apart the evacuated hemispheres! He performed a smaller scale performance in 1656 in his hometown of Magdeburg, using two teams of eight horses.