Madberg hemisphere

This instrument is used to explain atmospheric pressure in middle school science classes.
This product consists of two cast iron hemispheres with pull rings. The two hemispheres are placed against each other to form a sealed container. One of the hemispheres has an air valve. The air in the sealed hemisphere can be extracted through the air valve using a vacuum device. The pressure difference between the sealed ball and the outside atmospheric pressure presses the two hemispheres tightly so that the two hemispheres cannot be separated within a certain pulling force.