Magdeburg hemispheres
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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 Otto von Guericke in 1650 to demonstrate the air pump he had invented and the concept of air 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. To power the machine, several people would turn a crank arm connected to the vacuum pump.
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[edit] Overview
The Magdeburg hemispheres, a little over a foot (30 cm) in diameter, were designed to demonstrate the vacuum pump that von Guericke had invented. When the air was sucked out from inside them, they were held firmly together by the air pressure of the surrounding atmosphere.
[edit] Demonstrations
Guericke's demonstration was presented on 8 May 1654 to the Reichstag and the Emperor Ferdinand III in 1654 in Regensburg, where 30 horses, in two teams of 15, could not separate the hemispheres until the vacuum was released. In 1656 he repeated the demonstration with 16 horses (2 teams of 8) in his hometown of Magdeburg, where he was mayor. In 1657, Gaspar Schott was the first to describe the experiment in print in his Mechanica Hydraulico-Pneumatica. 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 original hemispheres are maintained by the Deutsches Museum in Munich. Many copies of them (usually smaller) have been made to illustrate the principle of air pressure to students. Re-enactments of von Guerike's 1654 experiment are performed in locations around the world by the Otto von Guericke Society. The experiment has been commemorated on at least two German stamps.
[edit] Related
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.
Based on these concepts, in 1679, an associate of Boyle's named Denis Papin built a bone digester, which is a closed vessel with a tightly fitting lid that confines steam until a high pressure is generated. Later designs implemented a steam release valve to keep the machine from exploding. By watching the valve rhythmically move up and down, Papin conceived of the idea of a piston and cylinder engine. He did not, however, follow through with his design. Nevertheless, in 1697, based on Papin's designs, engineer Thomas Savery built the first commercial steam engine.
[edit] Trivia
A variation of Schott's sketch featuring a single pair of horses trying to separate a pair of jeans appears on the tag of Levi Strauss & Co. jeans.
[edit] References
"GUERICKE, OTTO VON". Encyclopædia Britannica (11). (1911).
The Magdeburg hemispheres. Masterpieces from the Deutsches Museum. Retrieved on June 18, 2005.
The Magdeburg hemispheres. The Draft Horse Journal. Retrieved on October 31, 2006. published in print Summer 2004.
[edit] External links
