Atmosphere pressure. History and essence of scientific discovery

MOST IMPORTANT SCIENTIFIC DISCOVERIES
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Atmosphere pressure. History and essence of scientific discovery

The most important scientific discoveries

Directory / The most important scientific discoveries

The existence of air has been known to man since ancient times. Greek thinker Anaximenes, who lived in the VI century BC. e., considered air to be the basis of all things. At the same time, air is something elusive, as if insubstantial - "spirit".

The ancient atomists Democritus, Epicurus and Lucretius did not doubt the material nature of air, the atoms of which, in their opinion, have mobility and a round shape. Moreover, they believed that the soul itself has an atomistic nature, the atoms of the soul are especially light, small and mobile. Aristotle, classifying air as one of the four material elements, believed that air has weight, and even thought that he was able to confirm this by experiment, weighing an "empty" and inflated bubble with air. Aristotle was already well aware of the suction effect of rarefied space and derived from this fact the principle "nature does not tolerate emptiness."

A large number of pneumatic devices were invented by Reron, who believed that air consists of particles separated by small voids. However, he considered the existence of large voids contrary to nature and this explained the suction, the action of pumps, siphons, as well as other phenomena now explained by atmospheric pressure.

In the era of the early Middle Ages, the Egyptian scientist Al Haytama (Algazena), who lived in the 40th century, expressed the idea of the atmosphere. He not only knew that air has weight, but that the density of air decreases with height, and by this decrease he explained atmospheric refraction. Observing the duration of twilight, Alhazen estimated the height of the atmosphere at about XNUMX kilometers. However, medieval Europe returned to the Aristotelian concept of the four elements and the principle of "fear of the void", leaving for a long time the study of the physical properties of the ocean of air.

The first to practically measure the pressure of the air ocean were Italian wells. Here is how this fact is described in the "Conversations" of Galileo:

“I saw,” says one of Sagredo’s interlocutors, “once a well in which a pump was placed for pumping water by someone who thought in this way to get water with less difficulty or in more quantity than just buckets. This pump had a piston with the top valve, so that the water was raised by suction, and not by pressure, as is done in pumps with a bottom valve.As long as the well was filled with water to a certain height, the pump sucked in and delivered it perfectly, but as soon as the water dropped below this level, the pump stopped working The first time I noticed such a case, I thought that the pump was damaged, and called the master to repair, the latter said, however, that everything was in order, but that the water had sunk to the depth from which it could not be raised by the pump, while he added that neither pumps, nor other machines that raise water by suction, can raise water even by a hair above eighteen cubits; whether the pumps are wide or narrow, the maximum height remains the same.

Galileo believed that the maximum height of the water column of 18 cubits is a measure of "fear of the void." “Since copper is nine times heavier than water, the resistance to rupture of a copper rod, due to the fear of emptiness, is equal to the weight of two cubits of a rod of the same thickness,” Galileo wrote in Conversations.

In other words, the "fear of the void" (i.e., the force of atmospheric pressure) is balanced either by the weight of a water column of 10 meters, or by the weight of a copper column 1,12 meters high, amounting, according to Galileo, to about 1 kilogram per square centimeter. Thus, practitioners estimated the force of atmospheric pressure with sufficient accuracy, and Galileo's calculations are correct, although the interpretation of his observation made by the Italian masters is still scholastic in nature. A further step had to be taken. Made by Torricelli.

Evangelista Torricelli (1608–1647) was born in Faenza, Italy, to a noble family. Having lost his father early, Torricelli was brought up by his uncle, a learned monk who sent him to a Jesuit school.

At eighteen, Torricelli was sent to Rome to continue his mathematical education. In Rome, Evangelista became close to a student and follower of Galileo - Bendetto Castelli (1577-1644). Castelli was a Dominican priest and professor of mathematics. He early joined the teachings of Galileo and became a faithful assistant and friend of the great scientist.

In 1632 Galileo's famous "Dialogue Concerning the Two Systems of the World" was published, and in 1638 his last and most important work, "A Conversation Concerning the Two Sciences", was published. This essay had a strong influence on Torricelli, and under his influence he wrote the essay "On Natural Accelerating Motion", in which he developed the ideas of Galileo.

Torricelli's manuscript, his teacher Castelli, leaving Rome for Venice, took with him and on the way, having visited Galileo, introduced him to her. Galileo liked Torricelli's work so much that he invited the young scientist to his place.

In October 1641, Torricelli arrived in Arcetri and began to work on completing the Conversations, but his collaboration with Galileo did not last long. Galileo died in January 1642.

The Duke of Tuscany invited Torricelli to take the post of Galileo. Torricelli agreed and spent the rest of his short life in this position.

After the death of Galileo, his two students - Torricelli and Viviani - worked in close collaboration. Now their main task was to validate the experimental method. Several other people joined Torricelli and Viviani. From this circle, the famous Florentine Academy of Experience was born, which received its organizational design on June 19, 1657, ten years after the death of Torricelli.

Already in the Roman period of his life, Torricelli stood on the threshold of a fundamental discovery - the discovery of the pressure of the air ocean. For now, however, a new dynamic is drawing his attention. In the work "On Natural Accelerating Motion", which was presented by Castelli to Galilei and published in an expanded form in Florence in 1641 in Italian under the title "Treatise on the Motion of Heavy Bodies" (a Latin translation of the treatise in two books appeared in 1644), Torricelli develops the mechanics of Galileo.

Torricelli became the first scientist to solve the ballistic problem of the trajectory of an thrown body in a uniform gravitational field in the absence of air resistance.

The most remarkable result of Torricelli's work on mechanics is his discovery of the laws of fluid flow from a hole in a vessel. This discovery, adjacent to the research of his teacher Castelli, created him the fame of the founder of hydraulics.

And finally, Torricelli makes the greatest discovery. He comes up with the idea to measure the weight of the atmosphere by the weight of a mercury column. In 1643, at his direction, an experiment was carried out by Torricelli's friend Vincenzo Viviani. The experiment met all expectations, the mercury stopped at a given height, and a "Torricellian void" formed above it.

Later, Torricelli repeated the experiment with two tubes, as reported in a letter to the Italian mathematician Ricci dated June 11, 1644, which is the only publication about the famous experiments. Here are excerpts from that letter.

"... Many argue that emptiness does not exist at all; others say that obtaining it is achievable only by overcoming the resistance of nature and, moreover, with great difficulty. I believe that in all cases where opposition is clearly detected when obtaining emptiness, there is no need I say this because some scientists, seeing the impossibility of denying the fact of the opposition that manifests itself due to the gravity of the air, during the formation of the void, do not attribute this resistance to air pressure, but stubbornly assert that itself nature prevents the formation of emptiness We live at the bottom of an ocean of air, and experiments prove beyond doubt that air has weight...

We made many glass vials with a tube two cubits long; we filled them with mercury, holding the hole with our finger; when the tubes were then tipped into a cup of mercury, they were emptied, but only partially: each tube remained filled with mercury to the height of an elbow and one finger. Wishing to prove that the vial (in the upper part of the tube) was completely empty, the substituted cup was topped up with water, and then, with the gradual raising of the tube, it could be seen that as soon as its hole was in the water, mercury and the entire vial poured out of the tube, up to at the very top, quickly filled with water. So, the vial is empty, but the mercury is kept in the tube. Until now, it has been assumed that the force that keeps mercury from its natural tendency to descend is located inside the upper part of the tube - in the form of emptiness or very rarefied matter. I do not claim that the reason lies outside the vessel: an air column 50x3000 steps high presses on the surface of the liquid in the cup - it is not surprising that the liquid enters the glass tube (to which it has neither attraction nor repulsion) and rises until not balanced by outside air. Water rises in a similar, but much longer tube, as many times higher as how many times mercury is heavier than water ... "

To be completely convincing, Torricelli set up an experiment with two pipes. He wants to show that mercury is not held by any likes or dislikes, and the shape of the space above the mercury does not play any role and it is only a matter of external air pressure.

“This consideration,” he continues in the same letter, “was confirmed by experiment, placed simultaneously with two tubes A and B, in which mercury was always installed on the same horizon AB, this is a completely reliable indication that the force is not inside (vacuum) , since a greater force must be inside the vessel AB, in which there is a more rarefied attracting something, and it must be much stronger due to the more complete rarefaction than in a very small space B.

Torricelli managed to find even more important proof of the external cause of the formation of the mercury column. The scientist noticed that the height of the column fluctuated, that is, the pressure of the atmosphere changed. Thus, the Torricelli tube became the first barometer. It was from this experience that scientific observation of the weather began, the most important characteristics of which are pressure and temperature.

It is worth noting that Torricelli's experiment was not flawless. The height of the mercury column given by him, if we take into account the height of Florence above sea level, corresponds to 74,2 centimeters of mercury. The small value of this value, apparently, can be explained by the fact that some amount of air still remained in the "Torricellian void".

The struggle against the doctrine of the fear of the void did not end with the experience of Torricelli. The hypothesis about the forces holding the mercury column lived on long after Torricelli's death. Famous experiences Pascal (1623–1662), who proved that the change in the height of a barometer is related to height and built a water barometer, confirmed the conclusions of Torricelli. But only the invention of the air pump by Boyle and Guericke, as well as the effective experiments on demonstrating the force of atmospheric pressure, made by the latter, finally smashed the concept of fear of emptiness. The idea of air as some kind of spiritual principle was finally buried. Guericke proved by direct experience the weight of air by weighing the evacuated vessel and the vessel with air. This experience led him to the main conclusion: "Air is undoubtedly a bodily something." Thus, the notion that air is one of the types of matter that can be removed from the place it occupies and form a "void", "vacuum" has been established in science.

Author: Samin D.K.

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