Magdeburg hemispheres experiment. Historical artwork of Otto von Guericke's Magdeburg hemispheres experiment, which demonstrated atmospheric pressure. The experiment used two brass hemispheres, seen at top. These were around 50 centimetres in diameter and designed to fit together snugly. When von Guericke pumped the air from between them, they were forced together by the external pressure of the atmosphere. This force was so strong that two teams of eight horses could not pull the hemispheres apart. When the vacuum was released they came apart easily. The experiment was conducted in the 1650s in Magdeburg, Germany.