With Magdeburg hemispheres, it is possible to observe the effect of atmospheric pressure. When the air inside of a plastic bottle is drawn out using a vacuum pump, the plastic bottle collapses because it cannot balance the atmospheric pressure. When air is pumped back in, using a compressor, it returns to its original shape. lnstead of a plastic bottle if Magdeburg hemispheres are used, separating the hemispheres become very difficult. Vacuum system consists of a bell inside a glass balloon, vacuum pump and a vacuum indicator. Before vacuuming the glass balloon, as the bell rings, the ring is heard clearly, but as the vacuuming starts, the ring is heard less. The reason for this is that air is needed to move the sound waves.