Magdeburg hemispheres

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.

The Magdeburg hemispheres, around 50 cm (20 inches) in diameter,[3][4][5][6] were designed to demonstrate the vacuum pump that Guericke had invented.

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 20 kilonewtons (4,500 lbf; 2.2 short tons-force),[7][8] equivalent to lifting a car or small elephant; a dramatic demonstration of the pressure of the atmosphere.

[11] Thirty horses, in two teams of fifteen, could not separate the hemispheres until the valve was opened to equalize the air pressure.

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.

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.