Magdeburg hemispheres

Exhibit on display in Stanislaw Lem Garden of Experiences, a branch of the Museum of Municipal Engineering in Krakow.

Description written by Paulina Kijak

Mounted symmetrically on a steel frame and facing each other are two hemispheres with a diameter of about 30 cm. Attached to each hemisphere is a metal rod with a rope at the end. The hemispheres, the rods and the extended ropes are aligned on one axis. The hemispheres may be moved toward or away from each other. Attached to one of them is a rubber hose that leads to a small pump, located a few steps from the device, near the bench. At the point where the hose is attached to the hemisphere, there is a small valve.

At the beginning of the experiment, one person should close the valve and press the hemispheres together. At this time, a second person should move the pump’s piston a few times. If the hemispheres don’t freely separate, you can stop pressing them together. After a few more strokes of the pump, two people performing the experiment take hold of the ropes on opposite ends of the device and, pulling on the ropes try to separate the hemispheres. The task is not easy, even impossible, as after removing some of the air from the inside of the hemispheres, the pressure exerted by air molecules on the outside is now greater, pushing the hemispheres together.

At the end of the experiment, open the valve on the rubber hose. You’ll hear a quiet hiss of air re-entering the inside of the hemispheres. Now, when the air pressure inside and outside the hemispheres is equal, they can be easily separated.

Listen to the audio description

półkule magdeburskie