Reasoning in this way, Torricelli proceeded to prove that his theory was correct.

Filling a long tube, closed at one end, with mercury, he inverted the tube with its open orifice in a vessel of mercury.

The column of mercury fell at once, but at a height of about thirty inches it stopped and remained stationary, the pressure of the air on the mercury in the vessel maintaining it at that height.

This discovery was a shattering blow to the old theory that had dominated that field of physics for so many centuries.

It was completely revolutionary to prove that, instead of a mysterious something within the tube being responsible for the suspension of liquids at certain heights, it was simply the ordinary atmospheric pressure mysterious enough, it is true--pushing upon them from without.