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41 Torricelli, Evangelista
SUBJECT AREA: Photography, film and optics[br]b. 15 October 1608 Faenza, Italyd. 25 October 1647 Florence, Italy[br]Italian physicist, inventor of the mercury barometer and discoverer of atmospheric pressure.[br]Torricelli was the eldest child of a textile artisan. Between 1625 and 1626 he attended the Jesuit school at Faenza, where he showed such outstanding aptitude in mathematics and philosophy that his uncle was persuaded to send him to Rome to a school run by Benedetto Castelli, a mathematician and engineer and a former pupil of Galileo Galilei. Between 1630 and 1641, Torricelli was possibly Secretary to Giovanni Ciampoli, Galileo's friend and protector. In 1641 Torricelli wrote a treatise, De motugravium, amplifying Galileo's doctrine on the motion of projectiles, and Galileo accepted him as a pupil. On Galileo's death in 1642, he was appointed as mathematician and philosopher to the court of Grand Duke Ferdinando II of Tuscany. He remained in Florence until his early death in 1647, possibly from typhoid fever. He wrote a great number of mathematical papers on conic sections, the cycloid, the logarithmic curve and other subjects, which made him well known.By 1642 Torricelli was producing good lenses for telescopes; he subsequently improved them, and attained near optical perfection. He also constructed a simple microscope with a small glass sphere as a lens. Galileo had looked at problems of raising water with suction pumps, and also with a siphon in 1630. Torricelli brought up the subject again in 1640 and later produced his most important invention, the barometer. He used mercury to fill a glass tube that was sealed at one end and inverted it. He found that the height of mercury in the tube adjusted itself to a well-defined level of about 76 cm (30 in.), higher than the free surface outside. He realized that this must be due to the pressure of the air on the outside surface and predicted that it would fall with increasing altitude. He thus demonstrated the pressure of the atmosphere and the existence of a vacuum on top of the mercury, publishing his findings in 1644. He later noticed that changes in the height of the mercury were related to changes in the weather.[br]Bibliography1641, De motu gravium.Further ReadingT.I.Williams (ed.), 1969, A Biographical Dictionary of Scientists, London: A. \& C.Black.Chambers Concise Dictionary of Scientists, 1989, Cambridge.A Dictionary of Scientific Biography, 1976, Vol. XIII, New York: C.Scribner's Sons.A.Stowers, 1961–2, "Thomas Newcomen's first steam engine 250 years ago and the initial development of steam power", Transactions of the Newcomen Society 34 (provides an account of his mercury barometer).W.E.Knowles Middleton, 1964, The History of the Barometer, Baltimore.RLHBiographical history of technology > Torricelli, Evangelista
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