Evangelista Torricelli (born October 15, 1608, Rome—died October 25, 1647, Florence) was an Italian physicist and mathematician who invented themercury barometer, which is the oldest type ofbarometer. His work ingeometry also aided in the eventual development ofintegral calculus.

Inspired byGalileo’s writings, Torricelli wrote atreatise onmechanics,De Motu (“Concerning Movement”), which impressed Galileo himself. In 1641 Torricelli was invited toFlorence, where he served the elderly astronomer as secretary and assistant during the last three months of Galileo’s life. Torricelli was then appointed to succeed him as professor ofmathematics at the Florentine Academy.

Two years later, pursuing a suggestion by Galileo, Torricelli filled a glass tube 4 feet (1.2 m) long withmercury and inverted the tube into a dish. He observed that some of the mercury did not flow out and that thespace above the mercury in the tube was a vacuum. Torricelli thus became the first man to create asustainedvacuum. After much observation, he concluded that the variation of the height of the mercury from day to day was caused by changes inatmospheric pressure.

Britannica Quiz

Physics and Natural Law

Torricelli never published his findings, however, because he was too deeply involved in the study of pure mathematics—including calculations of thecycloid, a geometric curve described by a point on the rim of a turning wheel. In hisOpera Geometrica (1644; “Geometric Works”), he included his findings onfluid motion and projectile motion.