How it began
In 1644 the Italian physicist and mathematician Evangelista Torricelli described the first mercury barometer in a letter that contained the phrase that people live submerged at the bottom of an ocean of air. Torricelli was born in Rome in 1608 and studied under Benedetto Castelli, a student of Galileo. His experiment built on earlier ideas from Galileo and from Gasparo Berti.
Before it existed
The work grew out of a practical puzzle about suction pumps, which could raise water only to a limited height. Galileo and Gasparo Berti had considered the problem before Torricelli. Torricelli's insight was that the air itself has weight and presses down on everything beneath it.
How it works
Torricelli's setup used a glass tube filled with mercury. The mercury stood at a certain height in the tube, and he explained that it was held up by the weight of the air pressing from above. A change in the height of the column therefore shows a change in the pressure of the atmosphere.
What lasted
Later experiments by Blaise Pascal and Otto von Guericke extended the understanding of atmospheric pressure and its effects. The discovery shaped early ideas in environmental physiology and the study of high altitude. Torricelli died in 1647 at the age of 39. The torr, a unit of pressure, is named after him.
