Encyclopædia Britannica, Ninth Edition/Evangelista Torricelli

TORRICELLI, Evangelista (1608-1647), physicist and mathematician, was born at Faenza, October 15, 1608. Left fatherless at an early age, he was carefully educated under the care of his uncle, a Camaldolese monk, who in 1627 sent him to Rome to profit by the scientific teachings of Benedetto Castelli. The perusal of Galileo's Dialoghi delle Nuove Scienze (1638) inspired his fertile mind with many fresh developments of the new mechanical principles there set forth, which he embodied in a treatise De Motu (printed amongst his Opera Geometrica, 1644). Its communication by Castelli to Galileo in 1641 led to the adoption as a disciple by the Florentine sage of one who seemed not unworthy to become his successor. Torricelli accordingly, repairing to Florence, October 10, 1641, resided with Galileo, and acted as his amanuensis during the three remaining months of his life. On its close his contemplated return to Rome was anticipated by his nomination as grand- ducal mathematician and professor of mathematics in the Florentine academy. The discovery which has perpetuated his fame was made in 1643. Galileo had failed to perceive why water refuses to rise above 33 feet in a closed tube. It occurred to Torricelli to try the experiment in a more compendious form. The anticipated result ensued that the suspended column of mercury was shorter than that of water in the proportion of its greater specific gravity. He immediately concluded both to be sustained by atmospheric pressure, and con structed the "siphon-barometer" expressly for the purpose of measuring its fluctuations. By this momentous discovery the obscure notion of a fuga vacui was banished from physical science, and its progress most notably quickened. The mercurial barometer was long known as the "Torricellian tube," and the vacuum it includes is still designated the "Torricellian vacuum."

The publication amongst Torricelli's Opera Geometrica (Florence, 1644) of a tract on the properties of the cycloid involved him in a controversy with Roberval, who accused him of plagiarizing his earlier solution of the problem of its quadrature. There seems, however, no room for doubt that Torricelli's was arrived at independently, The matter was still in debate when he was seized with fever and pleurisy, and died at Florence, after twenty days illness, October 25, 1647, at the age of 39. He was buried in San Lorenzo, and a commemorative statue of him erected at Faenza in 1864. He was of a singularly amiable dis position, and possessed qualities the most felicitous for the investigation of nature. Among the new truths detected by him was the valuable mechanical principle that if any number of bodies be so connected that, by their motion, their centre of gravity can neither ascend nor descend, then those bodies are in equilibrium. He also discovered the remarkable fact that the parabolas described (in a vacuum) by indefinitely numerous projectiles discharged from the same point with equal velocities, but in all directions, are situated within a paraboloid which is a tangent to all of them. His theorem that a fluid issues from a small orifice with the same velocity (friction and atmospheric resistance apart) which it would have acquired in falling through the depth from its surface is of fundamental importance in hydraulics. He greatly improved both the telescope and microscope, and invented the simple microscope composed of a globule of melted glass. Several large object lenses, engraven with his name, are preserved at Florence. He used and developed Cavalieri's method of indivisibles.

A selection from Torricelli's manuscripts was published by Tommaso Bonaventura in 1715, with the title Lezioni Accademiche (Florence). They include an address of acknowledgment on his admission to the Accademia della Crusca. His essay on the inundations of the Val di Chiana was printed in Raccolta d'Autori che trattano del Moto dell' Acque (vol. iv. p. 115, Florence, 1768) and amongst Opuscoli Idraulici (vol. iii. p. 347, Bologna, 1822). For his life, see Fabroni, Vitæ Italorum, vol. i. p. 345; Ghinassi, Lettere fin qui Inedite di Evangelista Torricelli (Faenza, 1864); Tiraboschi, Storia della Lett. It., vol. viii. p. 302 (ed. 1824); Montucla, Hist. des Math., vol. ii.; Marie, Hist. des Sciences, vol. iv. p. 133.