To demonstrate the principle of vacuum pressure.
In the town of Magdeburg, Germany, in 1650, a famous experiment was performed with two hollow iron hemispheres. They were placed together and the air removed from insides. This created a very strong vacuum that required eight teams of horses to pull the hemispheres apart. This experiment can be shown on a smaller scale by means of two glasses and a piece of wet blotting paper. Ignite several matches and drop them into one tumbler and then put the wet blotting paper on the brim, then quickly invert the second glass on the paper as shown. The burning matches will consume the oxygen in the glasses thus making a strong vacuum inside. When the upper glass is lifted it will be observed that the wet paper and lower glass cling tightly to it.