Guericke's demonstration was performed on 8 May 1654 in front of the
Imperial Diet, and the
Emperor Ferdinand III in
Regensburg. Thirty horses, in two teams of fifteen, could not separate the hemispheres until the valve was opened to equalize the air pressure. In 1656 he repeated the demonstration with sixteen horses (two teams of eight) in his hometown of
Magdeburg, where he was mayor. He also took the two spheres, hung the two hemispheres with a support, and removed the air from within. He then strapped weights to the spheres, but the spheres would not budge.
Gaspar Schott was the first to describe the experiment in print in his
Mechanica Hydraulico-Pneumatica (1657). In 1663 (or, according to some sources, in 1661) the same demonstration was given in
Berlin before
Frederick William, Elector of Brandenburg with twenty-four horses. The experiment became a popular way to illustrate the principles of
air pressure, and many smaller copies of the hemispheres were made, and are used to this day in science classes. Reenactments of von Guericke's experiment of 1654 are performed in locations around the world by the Otto von Guericke Society. On 18 March 2000, a demonstration using sixteen horses was conducted in
Great Torrington by
Barometer World. A small pair of hemispheres is shown in the painting "
An Experiment on a bird in the Airpump" by
Joseph Wright of Derby, currently on display in the
National Gallery in London. The experiment has been commemorated on three German stamps. After learning about Guericke's pump through Schott's book,
Robert Boyle worked with
Robert Hooke to design and build an improved air pump. From this, through various experiments, they formulated what is called
Boyle's law, which states that the volume of a body of an ideal gas is inversely proportional to its pressure. Much later the
ideal gas law was formulated in 1834. ==See also==