Engraving from The Atmosphere (1873) by Camille Flammarion. Evangelista Torricelli (October 15, 1608 - October 25, 1647) was an Italian physicist and mathematician. In 1642 he became grand-ducal mathematician and professor of mathematics at 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. His chief invention was the mercury barometer, scientific instrument used in meteorology to measure atmospheric pressure. The torr, a unit of pressure used in vacuum measurements, is named after him. He also discovered Torricelli's Law, regarding the speed of a fluid flowing out of an opening. He is also famous for the discovery of the Torricelli's trumpet or horn whose surface area is infinite, but whose volume is finite. He was also a pioneer in the area of infinite series. He died in 1687, after having contracted typhoid fever, at the age of 39.