Evangelista Torricelli

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

Inspired by Galileo’s writings, Torricelli wrote a treatise on mechanics, De Motu (“Concerning Movement”), which impressed Galileo himself. In 1641 Torricelli was invited to Florence, 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 of mathematics at the Florentine Academy.

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

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