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Touching the Spring of the Air

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In the 17th century, many scientists in Europe investigated the properties of air, and their work led the Irish-British scientist Robert Boyle to deduce the mathematical laws that explain the pressure in a gas. This work was associated with a broader discussion of the nature of space between stars and planets. To the "atomists" there was empty space between the celestial bodies; For the Cartesians (following the French philosopher Rene Descartes), the space between particles was filled with an unknown substance called ether, and it was impossible to generate a vacuum.

In Italy, mathematician Gasparo Berti conducted experiments to understand why a suction pump could not lift water above 10 meters. Berti took a long pipe, closed one end and filled it with water. Then he put his mouth in a tub of water and turned it upside down. The water level in the tube dropped until the column rose about 10 meters.

In 1642, her compatriot Evangelista Torricelli, aware of Berti's work, built a similar device, but used mercury instead of water. Mercury is 13 times denser than water; so the liquid column was only 76 centimeters high. Torricelli's explanation for this was as follows: the weight of the air above the mercury in the bowl was pushing the mercury down, balancing the weight of the mercury in the column. He said that the area above the mercury inside the tube is a vacuum. This situation is explained by pressure (force over a certain area) today, but the basic idea is the same. Torricelli had invented the first mercury barometer.

Blaise Pascal's barometer experiments showed how air pressure changes with altitude. Pascal made important contributions to mathematics as well as physics.

French scientist Blaise Pascal became aware of Torricelli's barometer in 1646 and immediately began to conduct his own experiments. One of these experiments, carried out by his brother-in-law, Florin Perier, would show that air pressure varied with altitude. A barometer was placed on the floor of a monastery in Clermont and was observed by a monk during the day. Perier took another barometer to the top of Puy de Dôme, about a thousand meters above the town. The mercury column at the top of the mountain was 8 cm shorter than the one in the monastery garden. Since the amount of air above the mountain was greater than that above the valley below, the weight of the air indeed held the liquid in the water or mercury tubes there. Because of this and other studies, the modern unit of pressure is called Pascal.

– If you take a barometer to the top of a mountain, the height of the mercury in the barometer will decrease.

– This is because the air pushing the mercury down is less at the top.

– When the receiver is evacuated in a barometer, the level of mercury drops.

– That is, the less air in the receiver, the lower the pressure.

– The smaller the mass of the air, the smaller the “spring of air”.

Experimental Results

Boyle conducted many different experiments with the air pump and described them in his 1660 book New Experiments Physico-Mechanicall, Touching the Spring of the Air and its Effects. In the book, he tried to point out that all the results described were the product of experimentation, at a time when even famous experimenters such as Galileo often announced the results of "thought experiments."

Boyle's Law

According to Boyle's law, the pressure of a gas multiplied by its volume was a constant as long as the amount of gas and temperature were kept the same. In other words, if you decrease the volume of a gas, its pressure increases. It is this increased pressure that produces the air spring. On a bicycle pump, you can feel the effect if you cover the end of the pump with one finger and push the pump handle in.

 

Although this law was named Boyle, it was not Boyle's first proposed it, but English scientists Richard Towneley and Henry Power, who conducted a series of experiments with the Torricelli barometer and published their results in 1663. Boyle saw the first draft of the book and discussed the results with Towneley. He verified the results by experiment and published "Mr Towneley's Hypothesis" in 1662 as part of a response to criticism of his early experiments.

 

Boyle's work on gases was particularly important because of his careful experimental technique and because he fully reported his experiments and possible sources of error, whether they yielded the expected results or not. For this reason, many sought to expand his work. Today Boyle's Law is combined with laws uncovered by other scientists to form the "Ideal Gas Law", which approximates the behavior of real gases under changes in temperature, pressure, or volume. His thoughts eventually led to the development of kinetic theory as well.

 Who is Robert Boyle?

Robert Boyle was born in Ireland, the 14th child of the Earls of Cork. He was tutored at home before attending Eton College in England and later traveled around Europe. In 1643, his father died, leaving enough money for him to devote all his time to science. Boyle moved back to Ireland for two years; but from 1654 to 1668 he lived in Oxford in order to carry out his studies more easily, then moved to London.

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