Shown is a small demonstration replica of the original Magdeburg hemispheres. Its diameter is 14 cm (area = 154 sq cm) so that the force of the atmosphere on its cross-sectional area is 1560 Newtons. If a small vacuum pump can remove half of the air, then the force required to pull the hemispheres apart would be about 780 Newtons or 175 pounds.

Some 300 years ago, Otto von Guericke arranged a demonstration in Magdeburg, Germany to demonstrate the air pump which he had invented. He fashioned two hemispherical iron vessels which could be put together to form an airtight enclosure 22 inches in diameter. After pumping air out with his pump, he put 16 horses, eight to a side in a tug-of-war. They failed to separate the hemispheres.

The force of sea-level atmospheric pressure on a circle of diameter 22 inches is 24,840 Newtons or 5,585 pounds.