Magdeburg hemispheres
Encyclopedia
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
and could not be pulled apart by teams of horses. The Magdeburg hemispheres were designed by German scientist and mayor of Magdeburg
Magdeburg
Magdeburg , is the largest city and the capital city of the Bundesland of Saxony-Anhalt, Germany. Magdeburg is situated on the Elbe River and was one of the most important medieval cities of Europe....
, Otto von Guericke
Otto von Guericke
Otto von Guericke was a German scientist, inventor, and politician...
in 1656 to demonstrate the air pump which he had invented, and the concept of atmospheric pressure. The first artificial vacuum had been produced a few years earlier by Evangelista Torricelli
Evangelista Torricelli
Evangelista Torricelli was an Italian physicist and mathematician, best known for his invention of the barometer.-Biography:Evangelista Torricelli was born in Faenza, part of the Papal States...
, and had inspired von Guericke to design the world's first vacuum pump
Vacuum pump
A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke.- Types :Pumps can be broadly categorized according to three techniques:...
, which consisted of a piston and cylinder with one-way flap valves. The hemispheres became popular in physics lectures as an illustration of the power of air pressure, and are still used in education. The original hemispheres are preserved in the Deutsches Museum
Deutsches Museum
The Deutsches Museum in Munich, Germany, is the world's largest museum of technology and science, with approximately 1.5 million visitors per year and about 28,000 exhibited objects from 50 fields of science and technology. The museum was founded on June 28, 1903, at a meeting of the Association...
in Munich
Munich
Munich The city's motto is "" . Before 2006, it was "Weltstadt mit Herz" . Its native name, , is derived from the Old High German Munichen, meaning "by the monks' place". The city's name derives from the monks of the Benedictine order who founded the city; hence the monk depicted on the city's coat...
.
Overview
The Magdeburg hemispheres, around 50 cm (20 inches) in diameter, were designed to demonstrate the vacuum pumpVacuum pump
A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke.- Types :Pumps can be broadly categorized according to three techniques:...
that von 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 of the surrounding atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
.
The force holding the hemispheres together was equal to the area bounded by the joint between the hemispheres, a circle
Circle
A circle is a simple shape of Euclidean geometry consisting of those points in a plane that are a given distance from a given point, the centre. The distance between any of the points and the centre is called the radius....
with a diameter of 50 cm, multiplied by the difference in air pressure between the inside and the outside. It is unclear how good a vacuum von 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 40 000 N (9 000 lbf), equivalent to lifting a car or small elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
; a dramatic demonstration of the pressure of the atmosphere
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...
.
Demonstrations
Reichstag (Holy Roman Empire)
The Imperial Diet was the Diet, or general assembly, of the Imperial Estates of the Holy Roman Empire.During the period of the Empire, which lasted formally until 1806, the Diet was not a parliament in today's sense; instead, it was an assembly of the various estates of the realm...
and the Emperor
Holy Roman Emperor
The Holy Roman Emperor is a term used by historians to denote a medieval ruler who, as German King, had also received the title of "Emperor of the Romans" from the Pope...
Ferdinand III
Ferdinand III, Holy Roman Emperor
Ferdinand III was Holy Roman Emperor from 15 February 1637 until his death, as well as King of Hungary and Croatia, King of Bohemia and Archduke of Austria.-Life:...
in Regensburg
Regensburg
Regensburg is a city in Bavaria, Germany, located at the confluence of the Danube and Regen rivers, at the northernmost bend in the Danube. To the east lies the Bavarian Forest. Regensburg is the capital of the Bavarian administrative region Upper Palatinate...
. Thirty horses, in two teams of 15, could not separate the hemispheres until the valve was opened to release the vacuum. In 1656 he repeated the demonstration with 16 horses (2 teams of 8) in his hometown of Magdeburg
Magdeburg
Magdeburg , is the largest city and the capital city of the Bundesland of Saxony-Anhalt, Germany. Magdeburg is situated on the Elbe River and was one of the most important medieval cities of Europe....
, 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
Gaspar Schott
Gaspar Schott was a German Jesuit and scientist, specializing in the fields of physics, mathematics and natural philosophy, and known for his piety.-Biography:...
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
Berlin
Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...
before Frederick William, Elector of Brandenburg
Frederick William, Elector of Brandenburg
|align=right|Frederick William was Elector of Brandenburg and Duke of Prussia – and thus ruler of Brandenburg-Prussia – from 1640 until his death. A member of the House of Hohenzollern, he is popularly known as the "Great Elector" because of his military and political prowess...
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
Great Torrington
Great Torrington is a small market town in the north of Devon, England. Parts of it are sited on high ground with steep drops down to the River Torridge below...
by Barometer World
Barometer World
Barometer World was established in 1979 by Philip Collins, is located in the village of Merton, near Great Torrington, Devon, UK and is the world's largest barometer museum . Barometer World makes, sells and restores barometers of a variety of types.-History:...
.
The experiment has been commemorated on at least two German stamps.
After learning about Guericke's pump through Schott's book, Robert Boyle
Robert Boyle
Robert Boyle FRS was a 17th century natural philosopher, chemist, physicist, and inventor, also noted for his writings in theology. He has been variously described as English, Irish, or Anglo-Irish, his father having come to Ireland from England during the time of the English plantations of...
worked with Robert Hooke
Robert Hooke
Robert Hooke FRS was an English natural philosopher, architect and polymath.His adult life comprised three distinct periods: as a scientific inquirer lacking money; achieving great wealth and standing through his reputation for hard work and scrupulous honesty following the great fire of 1666, but...
to design and build an improved air pump. From this, through various experiments, they formulated what is called Boyle's law
Boyle's law
Boyle's law is one of many gas laws and a special case of the ideal gas law. Boyle's law describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system...
, which states that the volume of a body of an ideal gas is inversely proportional to its pressure. Soon the ideal gas law
Ideal gas law
The ideal gas law is the equation of state of a hypothetical ideal gas. It is a good approximation to the behavior of many gases under many conditions, although it has several limitations. It was first stated by Émile Clapeyron in 1834 as a combination of Boyle's law and Charles's law...
was formulated.