The Magdeburg hemispheres are a pair of large copper hemispheres with mating rims that were used in a famous 1654 experiment to demonstrate the power of
atmospheric pressure
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1,013. ...
. When the rims were sealed with grease and the air was pumped out, the sphere contained a
vacuum
A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...
and could not be pulled apart by teams of horses. Once the valve was opened, air rushed in and the hemispheres were easily separated. The Magdeburg hemispheres were invented by German scientist and mayor of
Magdeburg
Magdeburg (; ) is the Capital city, capital of the Germany, German States of Germany, state Saxony-Anhalt. The city is on the Elbe river.
Otto I, Holy Roman Emperor, Otto I, the first Holy Roman Emperor and founder of the Archbishopric of Mag ...
,
Otto von Guericke
Otto von Guericke ( , , ; spelled Gericke until 1666; – ) was a German scientist, inventor, mathematician and physicist. His pioneering scientific work, the development of experimental methods and repeatable demonstrations on the physics of ...
, to demonstrate the air pump that he had invented and the concept of atmospheric pressure.
Speculation varied about the contents of the sphere. Many thought it was simply empty, while others argued the vacuum contained air or some finer aerial substance. Sound did not transmit through the sphere, indicating that sound needed a medium in order to be heard, while light did not.
The first artificial vacuum had been produced a few years earlier by
Evangelista Torricelli
Evangelista Torricelli ( ; ; 15 October 160825 October 1647) was an Italian people, Italian physicist and mathematician, and a student of Benedetto Castelli. He is best known for his invention of the barometer, but is also known for his advances i ...
and inspired Guericke to design the world's first
vacuum pump, which consisted of a piston and cylinder with one-way flap valves. The hemispheres became popular in physics lectures as an illustration of the strength of air pressure, and are still used in education. The original hemispheres are on display in the
Deutsches Museum
The Deutsches Museum (''German Museum'', officially (English: ''German Museum of Masterpieces of Science and Technology'')) in Munich, Germany, is the world's largest museum of science museum, science and technology museum, technology, with a ...
in
Munich
Munich is the capital and most populous city of Bavaria, Germany. As of 30 November 2024, its population was 1,604,384, making it the third-largest city in Germany after Berlin and Hamburg. Munich is the largest city in Germany that is no ...
.
Aside from its scientific importance, the experiment served to prove the recovery of the city of Magdeburg, which only two decades earlier had undergone the
Sack of Magdeburg - considered the worst atrocity of the
Thirty Years' War
The Thirty Years' War, fought primarily in Central Europe between 1618 and 1648, was one of the most destructive conflicts in History of Europe, European history. An estimated 4.5 to 8 million soldiers and civilians died from battle, famine ...
- when 20,000 of its inhabitants were massacred, and only 4,000 remained at the end of the war in 1648. Von Guericke was concerned with both aspects of the experiment, in his double capacity as a leading scientist and as the mayor who worked tirelessly to restore the city's wealth.
Overview
The Magdeburg hemispheres, around 50 cm (20 inches) in diameter, were designed to demonstrate the
vacuum pump that Guericke had invented. One of them had a tube connection to attach the pump, with a valve to close it off. When the air was sucked out from inside the hemispheres, and the valve was closed, the hose from the pump could be detached, and they were held firmly together by the
air pressure
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The Standard atmosphere (unit), standard atmosphere (symbol: atm) is a unit of pressure defined as , whi ...
of the surrounding
atmosphere
An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
.
The force holding the hemispheres together was equal to the area bounded by the joint between the hemispheres, a
circle
A circle is a shape consisting of all point (geometry), points in a plane (mathematics), plane that are at a given distance from a given point, the Centre (geometry), centre. The distance between any point of the circle and the centre is cal ...
with a diameter of 50 cm, multiplied by the difference in air pressure between the inside and the outside. It is unclear how strong a vacuum Guericke's pump was able to achieve, but if it was able to evacuate all of the air from the inside, the hemispheres would have been held together with a force of around ,
equivalent to lifting a car or small
elephant
Elephants are the largest living land animals. Three living species are currently recognised: the African bush elephant ('' Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian elephant ('' Elephas maximus ...
; a dramatic demonstration of the
pressure of the atmosphere.
Demonstrations

Guericke's demonstration was performed on 8 May 1654 in front of the
Imperial Diet, and the
Emperor
The word ''emperor'' (from , via ) can mean the male ruler of an empire. ''Empress'', the female equivalent, may indicate an emperor's wife (empress consort), mother/grandmother (empress dowager/grand empress dowager), or a woman who rules ...
Ferdinand III in
Regensburg
Regensburg (historically known in English as Ratisbon) is a city in eastern Bavaria, at the confluence of the rivers Danube, Naab and Regen (river), Regen, Danube's northernmost point. It is the capital of the Upper Palatinate subregion of the ...
.
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
Magdeburg (; ) is the Capital city, capital of the Germany, German States of Germany, state Saxony-Anhalt. The city is on the Elbe river.
Otto I, Holy Roman Emperor, Otto I, the first Holy Roman Emperor and founder of the Archbishopric of Mag ...
, 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
Berlin ( ; ) is the Capital of Germany, capital and largest city of Germany, by both area and List of cities in Germany by population, population. With 3.7 million inhabitants, it has the List of cities in the European Union by population withi ...
before
Frederick William, Elector of Brandenburg with twenty-four horses.
The experiment became a popular way to illustrate the principles of
air pressure
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The Standard atmosphere (unit), standard atmosphere (symbol: atm) is a unit of pressure defined as , whi ...
, 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
Robert Hooke (; 18 July 16353 March 1703) was an English polymath who was active as a physicist ("natural philosopher"), astronomer, geologist, meteorologist, and architect. He is credited as one of the first scientists to investigate living ...
to design and build an improved air pump. From this, through various experiments, they formulated what is called
Boyle's law
Boyle's law, also referred to as the Boyle–Mariotte law or Mariotte's law (especially in France), is an empirical gas laws, gas law that describes the relationship between pressure and volume of a confined gas. Boyle's law has been stated as:
...
, which states that the volume of a body of an ideal gas is inversely proportional to its pressure. Much later the
ideal gas law
The ideal gas law, also called the general gas equation, is the equation of state of a hypothetical ideal gas. It is a good approximation of the behavior of many gases under many conditions, although it has several limitations. It was first stat ...
was formulated in 1834.
See also
*
Horror vacui (physics)
References
*
* published in print Summer 2004.
External links
Magdeburg Hemispheres(emergency banknote) depicting two teams of horses attempting to separate the halves of a Magdeburg Hemisphere. http://webgerman.com/Notgeld/Directory/M/Magdeburg3.htm
{{DEFAULTSORT:Magdeburg Hemispheres
Physics experiments
Historical scientific instruments
History of Magdeburg
Atmospheric pressure
1654 in science
1654 in the Holy Roman Empire