The first person to measure atmospheric pressure was the one who discovered it. Atmosphere pressure

This pressure is called atmospheric pressure. How big is it?

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Atmosphere surrounding Earth, exerts pressure on the surface of the earth and on all objects located above the ground. In a resting atmosphere, the pressure at any point is equal to the weight of the overlying column of air, extending to the outer periphery of the atmosphere and having a cross section of 1 cm 2.

Atmosphere pressure was first measured by an Italian scientist Evangelista Torricelli in 1644. The device is a U-shaped tube about 1 m long, sealed at one end and filled with mercury. Since there is no air in the upper part of the tube, the pressure of the mercury in the tube is created only by the weight of the mercury column in the tube. Thus, atmospheric pressure is equal to the pressure of the mercury column in the tube and the height of this column depends on the atmospheric pressure of the surrounding air: the higher the atmospheric pressure, the higher the mercury column in the tube and, therefore, the height of this column can be used to measure atmospheric pressure.

Normal atmospheric pressure (at sea level) is 760 mmHg (mmHg) at 0°C. If the atmospheric pressure is, for example, 780 mm Hg. Art., this means that the air produces the same pressure as that produced by a vertical column of mercury 780 mm high.

Observing the height of the mercury column in the tube day after day, Torricelli discovered that this height was changing, and changes in atmospheric pressure were somehow related to changes in weather. By attaching a vertical scale next to the tube, Torricelli obtained a simple device for measuring atmospheric pressure - a barometer. Later, pressure was measured using an aneroid ("liquidless") barometer, which does not use mercury, and the pressure is measured using a metal spring. In practice, before taking readings, you need to lightly tap your finger on the glass of the device to overcome friction in the lever transmission.

Based on a Torricelli tube station cup barometer, which is the main instrument for measuring atmospheric pressure on weather stations currently. It consists of a barometric tube with a diameter of about 8 mm and a length of about 80 cm, lowered with its free end into a barometric cup. The entire barometric tube is enclosed in a brass frame, in the upper part of which a vertical section is made to observe the meniscus of the mercury column.

At the same atmospheric pressure, the height of the mercury column depends on the temperature and the acceleration of gravity, which varies somewhat depending on the latitude and altitude. To exclude the dependence of the height of the mercury column in the barometer on these parameters, the measured height is reduced to a temperature of 0 ° C and the acceleration of gravity at sea level at a latitude of 45 ° and, by introducing an instrumental correction, the pressure at the station is obtained.

In accordance with international system units (SI system) the basic unit for measuring atmospheric pressure is the hectopascal (hPa), however, in the service of a number of organizations it is allowed to use the old units: millibar (mb) and millimeter of mercury (mm Hg).

1 mb = 1 hPa; 1 mmHg = 1.333224 hPa

The spatial distribution of atmospheric pressure is called pressure field. The pressure field can be visually represented using surfaces at all points of which the pressure is the same. Such surfaces are called isobaric. To obtain a visual representation of the pressure distribution on the earth's surface, isobar maps are constructed at sea level. To do this on geographical map show atmospheric pressure measured at meteorological stations and normalized to sea level. Then points with the same pressure are connected by smooth curved lines. Areas of closed isobars with high pressure in the center are called pressure maxima or anticyclones, and areas of closed isobars with low pressure in the center are called pressure lows or cyclones.

Atmospheric pressure at every point on the earth's surface does not remain constant. Sometimes the pressure changes very quickly over time, sometimes it remains almost unchanged for quite a long time. IN diurnal course pressure there are two maxima and two minima. Maximums are observed around 10 and 22 hours local time, minimums around 4 and 16 hours. The annual variation of pressure strongly depends on physical and geographical conditions. This move is more noticeable over continents than over oceans.

Atmospheric pressure is the force with which the air around us presses on earth's surface. The first person to measure it was Galileo Galilei's student Evangelista Torricelli. In 1643, together with his colleague Vincenzo Viviani, he conducted a simple experiment.

Torricelli experience

How was he able to determine atmospheric pressure? Taking a meter-long tube sealed at one end, Torricelli poured mercury into it, closed the hole with his finger and, turning it over, lowered it into a bowl also filled with mercury. At the same time, some of the mercury poured out of the tube. The mercury stopped at 760 mm. from the surface level of the mercury in the bowl.

It is interesting that the result of the experiment did not depend on the diameter, inclination or even shape of the tube - the mercury always stopped at the same level. However, if the weather suddenly changed (and the atmospheric pressure fell or increased), the mercury column fell or rose a few millimeters.

Since then, atmospheric pressure has been measured in millimeters of mercury, and pressure is 760 mm. rt. Art. is considered equal to 1 atmosphere and is called normal pressure. This is how the first barometer was created - a device for measuring atmospheric pressure.

Other ways to measure atmospheric pressure

Mercury is not the only liquid that can be used to measure atmospheric pressure. Many scientists in different time they built water barometers, but since water is much lighter than mercury, their tubes rose to a height of up to 10 m. In addition, water turned into ice already at 0 ° C, which created certain inconveniences.

Modern mercury barometers use Torricelli's principle, but are somewhat more complicated. For example, a siphon barometer is a long glass tube bent into a siphon and filled with mercury. The long end of the tube is sealed, the short end is open. A small weight floats on the open surface of mercury, balanced by a counterweight. When atmospheric pressure changes, the mercury moves, dragging the float with it, which, in turn, sets in motion the counterweight connected to the arrow.

Mercury barometers are used in stationary laboratories and at meteorological stations. They are very accurate, but rather cumbersome, so at home or in the field, atmospheric pressure is measured using a liquid-free barometer or aneroid barometer.

How does an aneroid barometer work?

In a liquid-free barometer, fluctuations in atmospheric pressure are sensed by a small round metal box with rarefied air inside. The aneroid box has a thin corrugated membrane wall, which is pulled back by a small spring. The membrane bends outward when atmospheric pressure drops and presses inward when it rises. These movements cause deviations of the arrow moving along a special scale. The scale of an aneroid barometer is aligned with a mercury barometer, but it is still considered a less accurate instrument, since over time the spring and membrane lose their elasticity.