Clarus est ob [[Torricellii cornu]]s inventionem, et [[barometrum]].<ref>de Gandt, ''l'oeuvre de Torricelli'', Les Belles Lettres, 1987</ref>
''Evangelista Torricelli''' ([[October 15]], [] – [[October 25]], []) was an [[Italy|Italian]] [[physics|physicist]] and [[mathematics|mathematician]], best known for his invention of the [[barometer]].
Torricelli was born in [[Faenza]], then part of the [[Papal States]]. He was left fatherless at an early age and educated under the care of his uncle, a [[Camaldolese]] monk, who first entered young Torricelli in a Jesuit College in 1624 to study mathematics and philosophy until 1626, whereupon he was sent him to [[Rome]] in 1627 to study science under the [[Benedictine]] [[Benedetto Castelli]], professor of [[mathematics]] at the [[Collegio della Sapienza]] in [[Pisa]].
In 1632, shortly after the publication of [[Galileo]]'s ''Dialogue concering the Two Chief World Systems'', Torricelli wrote to Galileo of reading it "with the delight [...] of one who, having already practised all of geometry most diligently [...] and having studied [[Ptolemy]] and seen almost everything of [[Tycho Brahe|Tycho [Brahe]]], [[Johannes Kepler|Kepler]] and [[Christian Sørensen Longomontanus|Longomontanus]], finally, forced by the many congruences, came to adhere to [[Nicolaus Copernicus|Copernicus]], and was a Galileian in profession and sect". (The Vatican condemned Galileo in June 1633, and this was the only known occasion on which Torricelli openly declared himself to hold the Copernican view.)
[[Image:Evangelista Torricelli - Museo di Storia Naturale di Firenze.JPG|thumb|200px|right| Torricelli's statue in the Museo di Storia Naturale di Firenze.|left]]
Aside from several letters, little is known of Torricelli's activities in the years between 1632 and 1641, when Castelli sent Torricelli's monograph of the path of projectiles to Galileo, then a prisoner in his villa at [[Arcetri]]. Although Galileo promptly invited Torricelli to visit, he did not accept until just three months before Galileo's death. During his stay, however, he wrote out Galileo's Discourse of the Fifth day. After Galileo's death on January 8, 1642, Grand Duke [[Ferdinando II de' Medici]] asked him to succeed Galileo as the grand-ducal mathematician and professor of mathematics in the [[University of Pisa]]. In this role he solved some of the great mathematical problems of the day, such as the finding a [[cycloid]]'s area and center of gravity. He also designed and built a number of telescopes and simple microscopes; several large lenses, engraved with his name, are still preserved at Florence.
Torricelli died in Florence a few days after having contracted [[typhoid fever]], and was buried in San Lorenzo. The [[asteroid]] (7437) Torricelli was named in his honor.
== Contributions to physics ==
Torricelli's chief invention was the barometer, which arose from solving an important practical problem. Pumpmakers of the Grand Duke of Tuscany attempted to raise water to a height of 12 meters of more, but found that 10 meters was the limit to which it would rise in the suction pump. Torricelli thought to employ [[mercury (element)|mercury]], fourteen times as heavy as water. In 1643 he created a tube c. 1 meters long, sealed at the top end, filled it with mercury, and set it vertically into a basin of mercury. The column of mercury fell to about 70cm, leaving a Torricellian vacuum above. As we now know, the column's height fluctuated with changing atmospheric pressure; this was the first barometer. This discovery has perpetuated his fame, and the [[torr]], a unit of [[pressure]], was named in his honor.
Torricelli also discovered [[Torricelli's Law]], regarding to the speed of a fluid flowing out of an opening, which was later shown to be a particular case of [[Bernoulli's principle]].