"We have made many glass vessels... with tubes two cubits long. These were filled with mercury, the open end was closed with the finger, and the tubes were then inverted in a vessel where there was mercury"

Evangelista Torricelli's quote is referring to an experiment he carried out in 1643. He was trying to gauge the atmospheric pressure of the air. To do this, he produced glass vessels with tubes 2 cubits long, which were loaded with mercury. He after that shut the open end of the tubes with his finger and inverted them in a vessel consisting of mercury. By doing this, he was able to gauge the air pressure of the air. This experiment was the first of its kind as well as it resulted in the innovation of the barometer. Torricelli's experiment was a significant breakthrough in the area of physics as well as it helped to better our understanding of atmospheric pressure. His work laid the foundation for a lot of the discoveries that followed.