Demonstrations
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 equalize the air pressure. In 1656 he repeated the demonstration with 16 horses (2 teams of 8) 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 demonstration was given in Berlin before Frederick William, Elector of Brandenburg with 24 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. Re-enactments of von Guerike's 1654 experiment are performed in locations around the world by the Otto von Guericke Society. On the 18th of March 2000, a demonstration using 16 horses was conducted in Great Torrington by Barometer World.
The experiment has been commemorated on at least two 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. Soon the ideal gas law was formulated.
Read more about this topic: Magdeburg Hemispheres