• Physicist and Mathematician Evangelista Torricelli, 1608
  

Evangelista Torricelli was born in Faenza, 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 into a Jesuit College in 1624 to study mathematics and philosophy until 1626, when he sent Torricelli 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 Dialogues of the New Science, Torricelli wrote to Galileo of reading it "with the delight [...] of one who, having already practiced all of geometry most diligently [...] and having studied Ptolemy and seen almost everything of Tycho Brahe, Kepler and Longomontanus, finally, forced by the many congruences, came to adhere to 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.)

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 8 January 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 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. In 1644, he famously wrote in a letter: "We live submerged at the bottom of an ocean of air."

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. He left all his belongings to his adopted son Alexander.

Torricelli's chief invention was the mercury barometer, which arose from solving a practical problem. Pump makers of the Grand Duke of Tuscany attempted to raise water to a height of 12 meters or more, but found that 10 meters was the limit with a suction pump. Torricelli employed mercury, fourteen times more dense than water. In 1643 he created a tube approximately one meter long, sealed at the top, filled it with mercury, and set it vertically into a basin of mercury. The column of mercury fell to about 76 cm, 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 perpetuated his fame, and the Torr, a unit used in vacuum measurements, has been named for him.

Torricelli also discovered Torricelli's Law, regarding the speed of a fluid flowing out of an opening, which was later shown to be a particular case of Bernoulli's principle.

Torricelli gave the first scientific description of the cause of wind:

... winds are produced by differences of air temperature, and hence density, between two regions of the earth.

Several Italian Navy submarines were named after Evangelista Torricelli

• A Micca class submarine, built in 1918, stricken in 1930
• An Archimede class submarine (1934), transferred to Spain in 1937 and renamed General Mola, stricken in 1959
• A Benedetto Brin class submarine (1937), sank in the Red Sea due to the British Navy in 1940
• Evangelista Torricelli, the former USS Lizardfish, transferred to Italy in 1960 and decommissioned in 1976

His manuscripts are preserved at Florence, Italy. The following have appeared in print:

• Trattato del moto (before 1641)
• Opera geometrica (1644)
• Lezioni accademiche (printed 1715)
• Esperienza dell'argento vivo (Berlin, 1897).