Editing Magdeburg hemispheres (section)

== Demonstrations ==
[[File:Vacuum Pump Hemispheres Stamps Guericke Magdeburg.jpg|thumb|Stamps celebrating the display and test of the vacuum hemispheres of Otto von Guericke in Magdeburg, Germany]] Guericke's demonstration was performed on 8 May 1654<ref>{{cite book |title=The Horizon: A History of Our Infinite Longing |first1=Didier |last1=Maleuvre |publisher=University of California Press |year=2011 |isbn=978-0-520-94711-5 |page=181 |url=https://books.google.com/books?id=pUldN1FCGmwC}} [https://books.google.com/books?id=pUldN1FCGmwC&pg=PA181 Extract of page 181]</ref><ref>{{cite book |title=Twenty-Two Turbulent Years 1639 - 1661 |first1=David C. |last1=Wallace |publisher=Fast-Print Publishing |year=2013 |isbn=978-1-78035-660-0 |page=156 |url=https://books.google.com/books?id=Mkpl2cBZn3gC}} [https://books.google.com/books?id=Mkpl2cBZn3gC&pg=PA156 Extract of page 156]</ref> in front of the [[Imperial Diet (Holy Roman Empire)|Imperial Diet]], and the [[Holy Roman Emperor|Emperor]] [[Ferdinand III, Holy Roman Emperor|Ferdinand III]] in [[Regensburg]].<ref>{{cite encyclopedia|title=Guericke, Otto von|encyclopedia=Encyclopædia Britannica, 11th Edition|volume=9|page=670|publisher=The Encyclopædia Britannica Co.|year=1910|url=https://books.google.com/books?id=GFAEAAAAYAAJ&pg=PA670}}</ref>  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]].

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.