2B30.30 Magdeburg Hemispheres
When two hemispheres are sealed by vacuum grease and evacuated, it is practically impossible to pull them apart by hand. Atmospheric pressure keeps them sealed and pushed together.
-  Magdeburg hemispheres
-  Vacuum pump with hose
-  Power bar
- Plug in the power bar and turn it off.
- Plug in the pump.
- Open the valve on the hemispheres.
- Make sure people using the demo are in a clear space so if they lose grip on the hemispheres or they trip, they don't hurt themselves or anyone else.
- Show how easy it is to pull apart the hemispheres when the apparatus is full of air.
- Seal the hemispheres together, rotating the seals so that the grease on them spreads evenly.
- Connect the hemispheres to the pump and turn on the power bar.
- When the pressure reaches about −25 inches of mercury (could go a bit lower), close the valve on the hemispheres and turn off the power bar.
- Get volunteers to try (and fail) to pull the hemispheres apart.
- Open the valve on the hemispheres and ask the volunteers to try again.
- PIRA 2B30.30
- Otto von Guericke, inventor of the Magdeburg hemispheres demo, was a German scientist and engineer in addition to mayor of Magdeburg. The Magdeburg hemispheres demo was part of a series of experiments he did for Emperor Ferdinand III of the Holy Roman Empire.
Otto von Guericke, Encyclopaedia Britannica, last updated 7 May 2019
- The demo for the emperor was done with hemispheres 36 cm in diameter, pulled at by 16 horses.
N. Marquardt, in CERN Accelerator School: Vacuum Technology, edited by S. Turner, (CERN, Geneva, 1999), p. 1
- Don't attempt this at home!
- May require periodic re-greasing to ensure a good seal. Use vacuum grease.
If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.