Magdeburg hemispheres

from Wikipedia, the free encyclopedia
The power of the vacuum impressively demonstrated with the Magdeburg hemispheres (engraving from Otto von Guericke's main work Experimenta nova… Magdeburgica )
The Magdeburg hemispheres in a vertical arrangement

With his Magdeburg hemispheres Otto von Guericke demonstrated spectacularly the power of the vacuum in Magdeburg in 1657 . As early as 1654 he had shown various vacuum experiments at the Reichstag in Regensburg . From 1656 Guericke had the first experiments with the Magdeburg hemispheres carried out in Magdeburg. He then performed his popular science experiments in many places, including in 1663 at the court of Elector Friedrich Wilhelm . In this way he showed the effect of air pressure and thus proved the existence of the earth's atmosphereand refuted the so-called horror vacui in an easily comprehensible way , as Blaise Pascal had already done in 1647 with his less vivid experiment Emptiness in the Void .

The course of the experiment

Guericke placed two hemispherical shells made of copper with a diameter of about 42 cm so that they formed a ball. A leather strip soaked with wax and turpentine served as a seal between the spherical shells . Then he drew the air from the cavity created in this way with the piston pump he had invented via a valve . The air pressure , which now only acted on the ball from the outside, compressed it so strongly that it did not even move with 30 (in Regensburg, two teams of 15 each) or 16 (in Magdeburg, two teams of eight) horses let pull apart more. The hemispheres could only be separated again after ambient air had been let back into the sphere through the valve.

The physical relationships

In fact, the external air pressure presses the Magdeburg hemispheres together
a) hemispheres filled with air
b) airless hemispheres
1. handle
2. airtight seal
3. Magdeburg hemisphere
4. air pressure
5. vacuum

The force that compresses the hemispheres results from the area of ​​the circle enclosed by the sealing ring multiplied by the air pressure difference between the interior of the sphere and the environment. The normal air pressure is 1 bar = 0.1 MPa. The circular area is 0.1385 m² (A = r²π). According to F = P • A, 13854 N (for clarification: approx. 1.4 t ) would have to be applied in order to separate the hemispheres if there is a perfect vacuum inside . How good the vacuum was that Guericke's air pump was able to create is not known exactly.

From a mechanical point of view it should be noted that the horses' effective pulling power is only applied by one of the two teams. In the historical experiment, only the pulling force of 15 or eight horses was effective. The other team only serves to hold the test arrangement in place, which could also have been achieved by tying the ropes to a fixed point. Some suspect that von Guericke deliberately staged the additional effort of two teams for a more impressive experiment. On the other hand, Newton's 3rd law was not published until 1687, so that it is also conceivable that the mechanical relationships were not yet known.

In this respect, the experiment is an interesting example of a whole series of scientific facts ( horror vacui , constant enormous air pressure, actio = reactio ), all of which are in stark contrast to the intuition of "common sense".

Hemisphere sentences

Magdeburg hemispheres with air pump ( Deutsches Museum )

For his demonstrations, Otto von Guericke gradually had several sets of hemispheres made:

  • A set of hemispheres and an air pump from the possession of Otto von Guericke came into the possession of the Technical University of Braunschweig via the University of Helmstedt , where they are exhibited in the library.
  • The Great Elector Friedrich Wilhelm (Brandenburg) invited Otto von Guericke to demonstrate the experiment to him. For this purpose, Guericke had another set of hemispheres made, which were from 1663 to 1889 in the Electoral Library in Cölln on the Spree, where the experiment also took place. On the occasion of the establishment of the Deutsches Museum in Munich in 1903 , the director of the Physics Institute at the University of Berlin, Paul Drude , was asked for a replica of the equipment that arrived there in October 1906 . A month later, Kaiser Wilhelm II paid a visit to Munich and bequeathed the original hemispheres and the air pump to the museum. They have been exhibits there since 1908.

The monument

Memorial at Ratswaageplatz in Magdeburg

On June 15, 2002, the large sculpture for the Magdeburg hemisphere experiment was inaugurated in Magdeburg. On the Ratswaageplatz in the city center, Mayor Lutz Trümper and Otto von Guericke (alias Wolfgang Emmrich) unveiled the large sculpture for the Magdeburg hemisphere experiment. The mayor had previously received the deed of donation for the work of art created by the sculptor Thomas Virnich , who was also present, from Peter Transfeld, CEO of ÖHMI AG . ÖHMI was the initiator and client of the five-meter-high and eight-meter-long cast bronze sculpture, with which, on the occasion of Otto von Guericke's 400th birthday, the academic achievements of the former Magdeburg mayor and scholar were to be honored. 200 sponsors and donors have contributed to making the city of Magdeburg even better known as the site of Guericke's famous hemisphere experiment. The hemisphere experiment is available in the form of various souvenirs.

Simulated experiment in Magdeburg (2015)

Today's demonstrations

The Otto von Guericke Society regularly performs hemisphere experiments in public and in museums.

Others

Postage stamp ( DDR 1969)
  • Luftpumpentaler is the name of the commemorative taler from 1702, the first coinage with the representation of the attempted separation of the Magdeburg hemispheres.
  • The hemispheres are a motif on at least two German postage stamps .
  • On the occasion of Otto von Guericke's 400th birthday in the “Guericke year” of 2002, stylized “Magdeburg hemispheres” were erected as sculptures , which were painted with various motifs relating to social life, spread across the entire city of Magdeburg . More of these works of art were added for the city's 1200th anniversary in 2005.
  • There are also pralines in the shape of the famous hemispheres.
  • On the label of jeans by Levi Strauss & Co. , a modification of Caspar Schott's sketch is used, which shows two horses trying to tear a pair of pants.
  • Magdeburg hemispheres are mounted on the front facade of the German Patent and Trademark Office in Munich as a symbol of the urge to research.

literature

  • H. Dittmar-Ilgen: Why do soap bubbles burst , Hirzel-Verlag; P. 16: The Magdeburg hemispheres
  • Walter Basan : The Secret of the Magdeburg Hemispheres , 1954

Web links

Commons : Magdeburg Hemispheres  - Collection of Images

Individual evidence

  1. ↑ This information is a bit misleading, because 15 or 8 horses and a solid wall on the other side would have been enough. See Jürgen Beetz: E = mc ^ 2: Physics for cavemen . Springer Spectrum, Heidelberg 2015, ISBN 978-3-642-54408-8 , p. 13 and the section The physical relationships .
  2. ↑ Maid. Hemispheres. Retrieved December 29, 2018 .
  3. ^ Report on the hemispheres in Braunschweig
  4. ^ Library magazine : Messages from the State Libraries in Berlin and Munich , 2016, Issue 2, p. 6
  5. ^ Library magazine : Messages from the state libraries in Berlin and Munich , 2016, issue 2, p. 11
  6. ^ Website for the monument
  7. ↑ Demonstrations of the Magdeburg hemispheres by the Otto von Guericke Society ( Memento from September 29, 2013 in the Internet Archive )