Evangelista Torricelli

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[b Faenza (Italy), October 15, 1608, d. Florence (Italy), October 25, 1647]

To investigate why vacuum pumps fail to raise water higher than about 10 m (30 ft), Torricelli, who suspected the answer, tried a heavier fluid. In 1643 he filled a long glass tube, closed at one end, with mercury, which is much denser than water, and placed the open end in a dish of mercury. When the tube was vertical, the mercury fell to about 76 cm (30 in.), forming a vacuum in the top of the tube. Torricelli correctly concluded that air pressure pushes on the mercury, lifting it. The vacuum prevents an equal push from the opposite direction. Torricelli also noted the small changes in height of the mercury related to changes in weather.

The Italian mathematician and physicist Evangelista Torricelli (1608-1647) invented the mercury barometer and made important contributions to calculus and the theories of hydraulics and dynamics.

Evangelista Torricelli was born in Faenza on Oct. 15, 1608. Left fatherless early in life, he was educated by his uncle, who was in monastic orders. In 1627 his uncle sent him to Rome to study mathematics and natural philosophy under Benedetto Castelli, professor of mathematics at the Collegio di Sapienza, who had been one of Galileo's pupils.

Torricelli spent the next 10 years in study. He corresponded with Galileo and studied his writings. He was especially impressed by the Dialogues concerning Two New Sciences (1638) and at once generalized Galileo's analysis of projectile motion. His conclusions on this and other subjects were set down in his book De motu gravium (1640; published 1644). Galileo invited Torricelli to Florence in 1641, and he became the amanuensis and companion of the great scientist until Galileo died 3 months later. Soon after, Torricelli succeeded him as grand-ducal mathematician and professor of mathematics at the Florentine Academy.

Scientific Work

Torricelli experimented with telescopes and simple microscopes, grinding his own lenses, and by carefully controlling their curvature, he produced telescopes superior to most of those of his contemporaries. His most important practical invention was the mercury barometer, first described in a letter to Michelangelo Ricci dated June 11, 1644. Torricelli had repeated Galileo's experiments with the thermoscope and was led to his discovery when he substituted mercury for water in the tube. He found also that water could be used as the liquid in the barometer if the containing vessel was sufficiently long ("18 cubits, " that is, approximately 33 feet), and he realized that the column of liquid was held up by the pressure of the atmosphere.

In the course of his experiments, Torricelli observed that the quantities of water discharged from a hole in the bottom of a tank in equal increments of time were propor-tional, from the last increment to the first, to successive odd numbers. This observation is said to have reminded him of Galileo's law of the velocity of a falling body, and it suggested to him that he should treat the jet of water as a series of freely falling particles, each with a speed determined by the original height of the water surface in the tank - Torricelli's law of efflux.

Mathematical Work

Torricelli saw the advantages of the method of indivisibles, which is used in mathematics to find lengths, areas, and volumes. He thought that the ancients might have used the method in the discovery of difficult theorems, the proofs of which were put in geometrical forms "to hide the secret of their method or to avoid giving jealous detractors an opportunity to object." In a book on the areas of parabolas, he gave 21 propositions on areas, 10 by the methods of the ancients and 11 by the geometry of indivisibles.

Torricelli used the methods of so many other mathematicians that he was frequently involved in disputes over priority. Especially bitter was his controversy with G. P. Roberval, which flared up after Torricelli had published in 1644 a tract on the properties of the cycloid. Roberval accused him of plagiarizing his earlier solution of the problem of its quadrature. The controversy was still alive when Torricelli died in Florence on Oct. 25, 1647.

Further Reading

Most of the biographical writings on Torricelli are in Italian. On the history of the barometer see William E. Knowles Middleton, The History of the Barometer (1964). For background see Abraham Wolf, A History of Science, Technology and Philosophy in the 16th and 17th Centuries (1935; rev. ed. 1950).

Evangelista Torricelli
Evangelista Torricelli portrayed on the frontpage of Lezioni d'Evangelista Torricelli
Born	October 15, 1608 Faenza, Romagna, Italy
Died	October 25, 1647 (aged 39) Florence
Nationality	Italian
Ethnicity	Italian
Fields	Physicist Mathematician
Known for	Mericural Barometer Torricelli's Law
Influences	Galileo

Evangelista Torricelli ( pronunciation (help·info); October 15, 1608 – October 25, 1647) was an Italian physicist and mathematician, best known for his invention of the barometer.

Contents 1 Biography 2 Contributions to physics 2.1 Barometer 3 Torricelli's Law 3.1 Cause of wind 4 Italian Submarines 5 Selected works 6 See also 7 References

Biography

Torricelli was born in Faenza, then part of the Papal States. He was left fatherless at an early age and educated under the care of his uncle, a Camaldolese monk, who first entered young Torricelli in a Jesuit College in 1624 to study mathematics and philosophy until 1626, when he sent Torricelli to Rome in 1627 to study science under the Benedictine Benedetto Castelli, professor of mathematics at the Collegio della Sapienza in Pisa.

In 1632, shortly after the publication of Galileo's Dialogues of the New Science, Torricelli wrote to Galileo of reading it "with the delight [...] of one who, having already practiced all of geometry most diligently [...] and having studied Ptolemy and seen almost everything of Tycho [Brahe], Kepler and Longomontanus, finally, forced by the many congruences, came to adhere to Copernicus, and was a Galileian in profession and sect". (The Vatican condemned Galileo in June 1633, and this was the only known occasion on which Torricelli openly declared himself to hold the Copernican view.)

Torricelli's statue in the Museo di Storia Naturale di Firenze.

Aside from several letters, little is known of Torricelli's activities in the years between 1632 and 1641, when Castelli sent Torricelli's monograph of the path of projectiles to Galileo, then a prisoner in his villa at Arcetri. Although Galileo promptly invited Torricelli to visit, he did not accept until just three months before Galileo's death. During his stay, however, he wrote out Galileo's Discourse of the Fifth day. After Galileo's death on January 8, 1642, Grand Duke Ferdinando II de' Medici asked him to succeed Galileo as the grand-ducal mathematician and professor of mathematics in the University of Pisa. In this role he solved some of the great mathematical problems of the day, such as finding a cycloid's area and center of gravity. He also designed and built a number of telescopes and simple microscopes; several large lenses, engraved with his name, are still preserved at Florence. In 1644, he famously wrote in a letter: "We live submerged at the bottom of an ocean of air."

Torricelli died in Florence a few days after having contracted typhoid fever, and was buried in San Lorenzo. The asteroid 7437 Torricelli was named in his honor.

Contributions to physics

Barometer

Torricelli's chief invention was the mericual barometer, which arose from solving an important practical problem. Pumpmakers of the Grand Duke of Tuscany attempted to raise water to a height of 12 meters or more, but found that 10 meters was the limit to which it would rise in the suction pump. Torricelli thought to employ mercury, fourteen times as heavy as water. In 1643 he created a tube c. 1 meter long, sealed at the top end, filled it with mercury, and set it vertically into a basin of mercury. The column of mercury fell to about 76cm, leaving a Torricellian vacuum above. As we now know, the column's height fluctuated with changing atmospheric pressure; this was the first barometer. This discovery has perpetuated his fame, and the Torr, a unit of pressure commonly used in vacuum measurements, was named in his honor.

Torricelli's Law

Torricelli also discovered Torricelli's Law, regarding the speed of a fluid flowing out of an opening, which was later shown to be a particular case of Bernoulli's principle.

Cause of wind

Torricelli gave the first scientific description of the cause of wind:

... winds are produced by differences of air temperature, and hence density, between two regions of the earth.[1]

Italian Submarines

Several Italian Navy submarines were named after Evangelista Torricelli

• A Micca class submarine, built in 1918, stricken in 1930
• An Archimede' class submarine (1934), transferred to Spain in 1937 and renamed General Mola, striken in 1959
• A 'Benedetto Brin class submarine (1937), sunk in the Red Sea by the British Navy in 1940
• Evangelista Torricelli , the former USS Lizardfish , transferred to Italy in 1960 and decommisssioned in 1976

Selected works

His manuscripts are preserved at Florence, Italy. The following have appeared in print:

• Trattato del moto (before 1641)
• Opera geometrica (1644)
• Lezioni accademiche (printed 1715)
• Esperienza dell'argento vivo (Berlin, 1897).

See also

• Torricelli's Equation
• Torricelli/Fermat point
• Gabriel's horn

References

• Aubert, André; Bombieri and Goldfeld, eds. (1989). "Prehistory of the Zeta-Function". Number Theory, Trace Formulas and Discrete Groups. Academic Press. 
• de Gandt (1987). L'oeuvre de Torricelli. Les Belles Lettres. 
• Shampo, M A; Kyle R A (March 1986). "Italian physicist-mathematician invents the barometer". Mayo Clin. Proc. 61 (3): 204. PMID 3511332. 
• O'Connor, John J.; Robertson, Edmund F., "Evangelista Torricelli", MacTutor History of Mathematics archive, http://www-history.mcs.st-andrews.ac.uk/Biographies/Torricelli.html .

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