Evangelista Torricelli (15.10.1608-25.10.1647) was an Italian physicist and mathematician. He was born in Faenza. He studied in Rome under B. Castelli, a friend and pupil of G. Galileo. In 1641 he moved to Arcetri, where he assisted Galileo. In 1642 he became court mathematician to the Grand Duke of Tuscany and professor of mathematics and physics at the University of Florence.
His main physical work was in pneumatics and mechanics. In 1643 he discovered atmospheric pressure, striking a blow at the established opinion that “nature abhors a vacuum” (the Torricelli experiment). He invented the mercury barometer (1644). The very fact of “producing” a vacuum was also important, since after Torricelli the “void” became an object of research, which in the end led to its practical use, in particular in the air pump. He improved Galileo's air thermoscope, converting it into the alcohol thermometer. He was the first to explain wind as due to variations in atmospheric pressure.
In the treatise “On the Motion of Freely Falling and Projected Heavy Bodies” (1641) he proved the postulate that heavy bodies falling along inclined planes of equal height reach equal speeds (not knowing that Galileo had already done this), established the parabolic character of the trajectory of bodies projected at an arbitrary angle to the horizontal, and other theorems of ballistics that are well known today. He formulated (1641) the law of the outflow of a liquid from openings in a vessel and derived the formula for the speed of outflow (the Torricelli formula). He reached perfection in constructing microscopes and grinding telescope lenses.