Torricelli, Evangelista
Torricelli, Evangelista (1608-1647), an Italian physicist and mathematician. In 1643 he invented the mercury barometer and used it to show that the atmosphere has weight. The space above the mercury in a barometer is called a Torricellian vacuum in his honor. Torricelli also improved methods for grinding optical lenses and developed a theorem for the speed at which fluids flow from small openings. Torricelli was born in Faenza and studied in Rome. He became Galileo's assistant in 1641, and, upon Galileo's death in 1642, succeeded him as court mathematician in Florence.