Vacuum experiment. Historical engraving depicting an experiment on the strength of a vacuum conducted by Otto von Guericke (1602-1686). At the top of the apparatus is a sphere, formed by two bronze hemispheres placed together with a greased leather seal. After the air inside the hemispheres was evacuated, the sphere was demonstrated to take an enormous load. On releasing a valve on the sphere and admitting air, the sphere would fall apart. This principle was used by Guericke in his famous Magdeburg experiment, where two teams of horses failed to pull apart an evacuated sphere 3.6 metres in diameter. Published in Experimenta nova Magdeburgica de vacuo spacio in 1672.