The Italian scientist Evangelista Torricelli was born on 15 October 1608 in Faenza. Torricelli studied for two years at the Jesuit college at Faenza, followed by two years of self-study. Because Torricelli showed such great talents for the sciences, his uncle sent him to Rome in 1626, where he became a scholar of the abbot Benedetto Castelli.

Castelli, a student and friend of Galileo Galilei, taught the 18 year old Torricelli the work of the old master on the laws of motion. Torricelli was secretary for Castelli from 1626 to 1632. During the next nine years he became secretary for Monsignor Giovanni Ciampoli, another friend of Galileo and governor of various cities in the Marches and Umbria. Not much is known of this period; Torricelli may have been secretary for several other people.

Inspired by Galileo's work, Torricelli wrote a treatise on mechanics called De Motu ("Concerning Movement"), that dealt with the movement of projectiles. Benedetto Castelli was highly impressed, and sent the document with strong recommendations to Galileo Galilei. Consequently, Galileo invited the young scholar. It was no earlier than 1641, three months before Galileo's death that the two scientists finally met. There is some speculation that Torricelli was reluctant to visit Galileo, because of Galileo's problems with the inquisition, but the death of Torricelli's mother also may have played a role. However, after a sad letter from Galileo describing his poor health and a possible sudden death, Torricelli left for Florence instantly. He remained with Galileo until his death on January 8, 1642.

After Galileo's death, Ferdinando II de Medici requested that Torricelli take over Galileo's position as mathematician to the Grand Duke of Tuscany and reader in mathematics at Pisa University. This was a highly respected and well paid position that Torricelli kept until his death.

Torricelli's scientific contributions include many solutions to mathematical problems, such as the finding of the area and the center of gravity of a cycloid, properties of curves and shapes, and a continuation of Galileo's work on the motion of projectiles. Torricelli has sometimes been called the father of hydrodynamics, due to his discovery of the law of efflux of a liquid through a small aperture in the wall of a vessel (the effluent velocity is equal to that of a droplet in a vacuum falling from the top of the water level to the hole.) He was also a skilled lens grinder, making lenses for telescopes and microscopes. This was a significant source of income in the last period of his life.

Despite all his achievements, Torricelli became most famous for his invention of the barometer. Pump makers of the Grand Duke of Tuscany observed that they could not raise water over great heights with their traditional suction pumps. Earlier, Galileo had already struggled with this observation stating that indeed nature abhors a vacuum, but that the horror only extends to approximately thirty two feet. Torricelli found the correct explanation; he filled a three feet long tube with quicksilver (mercury), closed one end, and placed the tube with the open end vertically in a basin of mercury. The level fell to about twenty-eight inches of mercury, creating an empty space (Torricellian vacuum). Torricelli observed that the height of the mercury level was dependent on the surrounding air pressure, and thus created the first barometer.

Torricelli died due to an unknown illness in Florence on 24 or 25 October, 1647. In honor of his work, a unit of measure (torr) is named after him.

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