He took two hemispheres, or half globes made of copper. He showed that they could be put together to form a hollow ball. Attached to each half globe was a large metal ring. Von Guericke fitted the two halves together and took them apart several times to show how easily they could be joined or separated. Then he brought out his machine, the vacuum pump. It was an odd-looking contraption, with a handle on one side and a tube coming out the other. He once more fitted the two hemispheres together so that they formed a ball, and attached the tube. Then he turned to the people and stated that he would now remove the air from the globe with his pump.
He attached the tube to a valve in the sphere, and began to operate the handle of the pump. Up and down, up and down, he pumped as the machine hissed with each downward thrust. Soon he pumped slower and slower, just barely able to pump the handle. Finally, Von Guericke could move the handle no more, and wiping the perspiration from his brow, he announced, “I have removed the air from the globe! Inside the globe there now is – a vacuum”.
He went on and explained that there was force, or pressure, of air on the outside of the globe and since there was no air inside the ball, the pressure of air on the outside would prevent the two halves from separating. He then lifted the ball off the ground and held it up high by one of the rings so all could see. He shook it again and again. The other half did not fall away. He invited people to try to pull the two halves apart. A powerful man with all his might tried to pull but could not budge them.
Four powerful horses were led in and hitched in pairs, one pair attached to each ring on the ball. A whip cracked. The horses pulled in opposite directions. Still the halves of the sphere remained together. Two more pairs of horses were brought on the scene and hitched to the first two horses. Now there were four horses pulled and pulled. Same result, the halves stayed together. More horses were added were added until there were eight on each side, sixteen in all, pulling and tugging with all their might. Finally a loud crack was heard. The halves separated. It had taken the strength of sixteen horses to overcome the pressure of the air. Von Guericke had proven his vacuum pump. This was the turning point in Von Guericke’s life and an important milestone in the story of electricity.