Italian mathematician and physicist, born at Faenza, 15 October, 1608; died at Florence, 25 October, 1647. Modigliana, in Tuscan Romagna, and Piancaldoli, in the Diocese of Imola, are named as the birthplace by different biographers.

Torricelli was educated at the Jesuit college of Faenza, where he showed such great aptitude for the sciences that his uncle, a religious of the order of the Camaldolesi, sent him to Rome in 1626 for the purpose of study. There he fell in with Castelli, the favorite pupil of Galileo, who instructed him in the work of the master on the laws of motion. Torricelli showed his thorough understanding by writing a thesis on the path of projectiles. Castelli sent this essay in manuscript to Galileo with strong recommendations of his young friend. Galileo invited Torricelli to his house but for personal reasons he was unable to accept until three months before the death of the blind scientist (1641). The grand duke prevailed upon him to remain at Florence and to succeed Galileo at the Academy. He solved some of the great mathematical problems of the day, such as the finding of the area and the centre of gravity of the cycloid. This problem gave rise to disagreeable discussion on the part of Roberval as to priority and originality. Torricelli's honesty, manliness, and modesty are distinctly shown in his reply.

His chief invention was the barometer. Pumpmakers of the Grand Duke of Tuscany attempted to raise water to a height of forty feet or more, but found that thirty-two feet was the limit to which it would rise in the suction pump. Strange enough, Galileo, who knew all about the weight of the air, had recourse to the old theory that "nature abhors a vacuum", modifying the law by stating that the "horror" extended only to about thirty-two feet. Torricelli at once conceived the correct explanation. He tried the experiment with quicksilver, a a liquid fourteen times as heavy as water, expecting the column which would counterbalance the air to be proportionally smaller. He filled a tube three feet long, and hermetically closed at one end, with mercury and set it vertically with the open end in a basin of mercury, taking care that no air-bubbles should get into the tube. The column of mercury invariably fell to about twenty-eight inches, leaving an empty space (Torricellian vacuum) above its level (1643). He expressed his sorrow at the fact that Galileo had not made this discovery in connection with the pressure of air. The barometer is today one of the most important scientific instruments, while the Torricellian method of getting a very high vacuum is still often employed. Another discovery was the law of efflux of a liquid through a small aperture in the wall of a vessel. He also constructed a number of large objectives and small, short focus, simple microscopes.

His literary contributions are noted for their conciseness, clearness, and elegance. His manuscripts have not all been published and are carefully preserved at Florence. The following have appeared in print:

"Trattato del moto" (Florence, before 1641),

"Opera geometrica" (Florence, 1644);

"Lezioni accademichi" (Florence, 1715);

"Esperienza dell argento vivo" (reprint, Berlin, 1897).

WILLIAM FOX