Magdeburg Hemispheres

The Magdeburg hemispheres were a pair of large copper hemispheres with mating rims. When the rims were sealed with grease and the air was pumped out, the sphere contained a vacuum and could not be pulled apart by teams of horses. The Magdeburg hemispheres were designed by German scientist and mayor of Magdeburg, Otto von Guericke in 1650 to demonstrate the air pump which he had invented, and the concept of atmospheric pressure.

The first artificial vacuum had been produced a few years earlier by Evangelista Torricelli, and had inspired von Guericke to design the world's first vacuum pump, which consisted of a piston and cylinder with one-way flap valves.

Von Guericke's demonstration was performed on 8 May 1654 in front of the Reichstag and the Emperor Ferdinand III in Regensburg. Thirty horses, in two teams of 15, could not separate the hemispheres until the valve was opened to release the vacuum. In 1656 he repeated the demonstration with 16 horses (2 teams of 8) in his hometown of Magdeburg, where he was mayor. In 1663 the demonstration was given in Berlin before Frederick William, Elector of Brandenburg with 24 horses.

The hemispheres became popular in physics lectures as an illustration of the power of air pressure, and are still used in education. The original hemispheres are preserved in the Deutsches Museum in Munich.