Physicist and mathematician, b. 15 October 1608 (Faenza, Romagna, Italy), d. 25 October 1647 (Florence).
A work on mechanics by Evangelista Torricelli entitled De Motu ("On Movement") came to the knowledge of Galileo Galilei and left a positive impression. In 1641 Galilei invited him to Florence, where he was living under house arrest. Torricelli became his secretary and assistant.
The harmonious relationship had lasted only a few weeks when Galilei died. Torricelli became Galilei's successor as professor of mathematics at the Academy of Florence. He had inherited some of Galilei's ideas, and following one of them he filled a 1.2 m tall tube with mercury and inverted it into a dish. He noticed that when some mercury flowed out this produced a vacuum in the upper part of the tube.
Over a lengthy period Torricelli observed the size of the vacuum (indicated by the level of the mercury) and concluded that it depended on variations in the atmospheric pressure. His inverted mercury tube was the first working barometer. For the next 300 years the mercury level in an inverted tube served as the unit of measure for atmospheric pressure.
Torricelli's main interest was in the area of mathematics. In 1644 he published Opera Geometrica ("Geometric Works"). He never published his experiments in physics, nor did he write anything on the principle of the barometer.
His mathematical writings contain a description of fluid flow from an orifice in a tank now known as Torricelli's Theorem or Torricelli's Law: The velocity v of a fluid flowing from an orifice in a tank under the force of gravity is given by
where g is gravity (9.8 m s-1 on Earth) and h is the height of the fluid's surface above the orifice. The law holds regardless whether the fluid leaves the tank through an orifice that is directed upward, downward or horizontally.