Evangelista Torricelli was first educated in Jesuit schools in his native Faenza, near Ravenna. His abilities as a physicist and mathematician were so great that he was sent to Rome for further education under the direction of Benedetto Castelli (1578-1643), a student of. Through Castelli, Torricelli was introduced to the aging Galileo, and he became Galileo's secretary and assistant for the last few months of Galileo's life. After Galileo's death in January1642, the Grand Duke of Tuscany offered Torricelli Galileo's old position ascourt mathematician and philosopher. Torricelli held this position until hisdeath from a sudden fever shortly before reaching his 40th birthday.
As a scientist Torricelli became well known for his study of the motion of fluids and was declared the father of hydrodynamics by Ernst Mach. Torricelli also conducted experiments on what we now call gases, though the term was notthen in use. This led to his most important invention, the mercury barometer.The barometer was developed directly from his experimental work on air pressure and his effort to settle a dispute about the nature of the vacuum. The debate was a very old one. The Greek philosopher-scientist Aristotle believed that a vacuum could not exist, stating that "nature abhors a vacuum" Though Galileo felt that a vacuum could exist, he contended that the action of suction(in a water pump, for example) was produced by a vacuum itself and not by the pressure of the air pushing on the liquid being pumped.In fact, Galileo felt that air was weightless. Participants in the debate noted that, for reasonsnot understood, suction pumps in mines could not raise water more than eighteen bracci(about 30 feet or 9 m) regardless of their size or power. Ifnature "abhorred a vacuum" why didn't water flow all the way to the top of these pumps? Torricelli made sense of this phenomenon and, in the process, invented the mercury barometer, an instrument that launched a flurry of study into the physics of the atmosphere and the behavior of gases. Torricelli also made a contribution to meteorology with his suggestion that wind was not caused by the "exhalations" of vapors from a damp earth, but by differences in thedensity of air which in turn were caused by differences in the air temperature.
To replicate the action of a suction pump in a small tube, Torricelli began to substitute heavier liquids such as sea water, honey, and finally mercury for pure water. Using mercury, Torricelli could observe the effect of a vacuumusing relatively short tubes sealed at one end. Torricelli filled such a tubeof about a meter in length with mercury, sealed the open end with his finger, and then, inverting the tube, immersed the open end into a dish of mercury.The column of mercury dropped part way down the tube leaving an empty spaceat the top and a column of mercury in the tube about one and one-third bracci (about 30 inches or.75 m) in height. Torricelli settled the debate about the nature of the vacuum by interpreting his experiment in the followingway: a vacuum was not pulling mercury up the tube, but rather the weight of air pushing down on the dish of mercury prevented the mercury in the tube fromfalling out completely. This weight was enough to retain some thirty inchesof mercury in the tube. Applying his interpretation to the action of suctionpumps in mines, Torricelli observed that such pumps, by evacuating the air pressure above a column of water, could cause the water to move upwards, but that the water would move up only as far as the air pressure below pushed it up. Once the weight of the water exceeded the power of the air pressure below,the water came to a stop, no matter how hard the pump was working. Torricellialso noticed that the height of mercury in his tubes varied slightly from day to day. He concluded that this was due to changes in the air pressure overtime, a principle which has come to have great importance in meteorology andgeophysics. In 1644 the French scientist Marin Mersenne (1588-1648) visited Torricelli and took back to his friend Blaise Pascal (1623-1662) the idea of the mercury barometer. If, Pascal thought, air was indeed pressing downward upon us as Torricelli contended, the total weight of the air, and hence its pressure, should decrease as altitude increases. With the help of his brother-in-law, Pascal showed that barometric pressure did indeed decrease as one ascended a mountain. Pascal's observational evidence showed beyond any doubt thatTorricelli's theory was correct.
Writing some years later, Vincenzo Antinori stated that just as the telescopehad transformed astronomy, Torricelli's invention of the barometer had changed physics. Torricelli was also active in the improvement of the telescope, an instrument that had first been used in astronomy by Galileo. Torricelli wasable to grind lenses with such accuracy that he was able to produce some ofthe finest telescopes of his day.
Torricelli's investigations in mathematics played an important role in scientific history as well. Based on Francesco Cavalieri's " of indivisibles," Torricelli worked out equations upon curves, solids, and their rotations, helpingto bridge the gap between Greek geometry and calculus. Along with the work of René Descartes, Pierre de Fermat, Gilles Personne de Roberval, and others, these works enabled Isaac Newton and Gottfried Wilhelm Leibniz to givecalculus its first complete formulation. Though not as great a scientist ashis older contemporary, Galileo, Torricelli continued the tradition of Italian scientific pioneering. This tradition was not to last long after his own death in the middle of the seventeenth century, however; by the beginning of the next century the center of scientific progress had shifted to northern Europe.
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