Consists of a pair of hollow brass hemisphere with a handle on each. There's a gasket around the circumference, so that when they're put together they make a seal. When put together, the air inside may be evacuated with a pipe fitting and a valve.

Demonstrates the power of atmospheric pressure.

• Magdeburg Hemispheres
• Handheld vacuum pump (or the electric vacuum pump, if you're using it anyway)

1. While holding the hemispheres together, use the vacuum pump to evacuate the space between them. Make sure the valve is open. If you're using the handheld vacuum pump, this is easiest if you hold the hemispheres together with one hand and pump the vacuum pump with the other.
2. Close the valve and disconnect the pump. ¹⁾
3. The sphere can now hold up to 5 kg. It can be pulled apart by hand, but only with some effort.
4. To unlock the spheres, open the valve.

Suction cups can be thought of as Magdeburg Hemispheres that create their own vacuum in the action of pressing them onto a surface.