This pair of rubber suction cups provides for an economical and effective demonstration of atmospheric pressure.
In 1656 Otto von Guericke first showed the force of atmospheric pressure. He put two metal hemispheres together using grease as a sealant. Once he had pumped out the air within the sphere, teams of eight horses were hooked to each side. They pulled, but the hemispheres did not part. They were held together by atmospheric pressure.
A short biography about Otto von Guericke appears on The Robinson Library web site.
Easy to use. Pick up the hemispheres by the handles. Push together the smooth sides to force out the air between the hemispheres - I use a slight twist as I push them together. Ask someone else to take them apart. (If you could remove all the air from between the hemispheres, the force pushing them together would be about 122 pounds - at the Earth's surface.)
Dimensions: 3 1/4" diameter.