Torricelli, Evangelista (1608–1647)

Italian physicist who established the existence of atmospheric pressure and devised the mercury barometer in 1644.

In 1643 Torricelli filled a long glass tube, closed at one end, with mercury and inverted it in a dish of mercury. Atmospheric pressure supported a column of mercury about 76 cm/30 in long; the space above the mercury was a vacuum. Noticing that the height of the mercury column varied slightly from day to day, he came to the conclusion that this was a reflection of variations in atmospheric pressure.

Torricelli was born in Faenza and studied at the Sapienza College, Rome. When physicist Galileo read Torricelli's De motu gravium naturaliter descendentium et proiectorum 1641, which dealt with movement, he invited him to Florence, where he served as Galileo's secretary for the three months till his death. From 1642 Torricelli was professor of mathematics at Florence.