The barometer and the atmospheric pressure
The video describes how the barometer works. Initially, it was invented in order to explain the empty gap created in a tube filled with water. Invented by Torriccelli, the mercury barometer remained one of the most common ways to measure atmospheric pressure until 2007, when its use was forbidden due to its toxicity. The video is in English and contains Greek subtitles.
Concerning the gap that is created when filling a tube with water, based on Galileo’ s theory of the atmospheric’s pressure disability to replace the empty vacuum due to its limited force and on the experiment of Gasparo Berti, (which demonstrated that there is a stable vacuum in a tube), Torriccelli conducted an experiment which proved that there is a balance between the atmospheric pressure in and out the tube, because the water level in the tube decreased until the two pressures were equal, that happened when the water was at 10,3 meters. Repeated the same experiment with mercury instead of water using a tube with a bigger vacuum, he showed that the water level was just the same. Pascal confirmed this theory when he proved that in the top of a mountain the mercury level dropped as the atmosphere pressure decreased with altitude.