Since ancient times, people have noticed that air, being an “incorporeal” substance, still affects the state of various bodies. The flight of an arrow or dart, the soaring of a bird, the movement of objects during strong winds and hurricanes caused undisguised interest. But also from time immemorial, probably not understanding the very nature of the phenomenon, people have learned how to take advantage of the atmospheric pressure.
Initially, scientists who were interested in this issue formulated it in such a way that air has weight, under the influence of which all atmospheric phenomena occur.
It turned out to be very difficult to prove the weight of air, it took a long time until scientists were able to experimentally establish this physical fact. Moreover, this proof was favored by the case. In the mid-17th century, fountain fashion was common in European cities. They were a kind of symbol of the wealth and respectability of a city, castle or estate. Guided by just such considerations, the Duke of Tuscany, a city in Italy, made the decision to equip a fountain in his palace. The design of the fountain provided for the intake of water from the reservoir, which was located near the fountain itself, but at start-up the water could not rise above 10 meters. Such a phenomenon could not immediately explain even the great Galileo. And only his pupil - Torricelli - was able not only to prove the presence of "weight" in the air, but also was able to measure what is the value of normal atmospheric pressure. He invented a special device for such measurements - a barometer. And then with the help of this device he measured that the optimal atmospheric pressure is such that it can be balanced by a certain volume of water of 32 feet. Then it was found that for 1 square centimeter of the Earth, air pressures weighing 1.033 kg.
This applies to all objects that are on the earth's surface, including the human body itself. If you measure its area, we get a value equal to about 15,000 cm², which means that the body is subjected to air pressure weighing about 15500 kg. Since this pressure spreads evenly over the entire surface, a person does not feel any discomfort from such a “burden”.
Atmospheric pressure is measured in quantities such as millimeters of mercury. The millibar unit (mb) is also used, but recently the most common is the use of Pascal (or hectopascal, hPa), which is equal to one millibar. If we compare all three units, then the ratio between them is as follows: 760 mm Hg. = 1013 hPa = 1013.25 mbar. All these values are taken as the norm of atmospheric pressure for a person. The human body is able to reconfigure, adapting to changes in atmospheric pressure. In addition, a person can form the ability to feel normal at other pressure values through training.
However, it should be understood that such a norm of atmospheric pressure for a person does not mean at all that it will be a climatic norm, because at various points on the Earth there are many factors that significantly affect this indicator. So, for example, in Vladivostok the climatic pressure in the average annual measurement is 761 mm Hg, and this is practically the norm of atmospheric pressure for humans. At the same time, in some places in Tibet, where the height of settlements exceeds 5,000 meters, the pressure is only 413 mm Hg. This value, as it is easy to calculate, is 1.8 times less than the norm of atmospheric pressure for a person.
But the fact is that the magnitude of atmospheric pressure is very dependent on altitude. That is why, in order to coordinate instrument readings and statistical data, it is customary when indicating pressure to indicate its value at a certain level - sea level.