What is a barometer?

The Earth's atmosphere, which extends toseveral hundred kilometers up, presses on the surface of our planet. It is this pressure that is called atmospheric pressure. To measure it, a device called a barometer was invented. The creator of the device was the Italian Evangelista Torricelli, who lived in the XVII century. He explained to people why a barometer is needed.

Atmospheric pressure usually "jumps" because ofchanges in weather conditions: before the storm falls, and in good weather - increases. Meteorologists fix on the map any pressure fluctuations and determine the movement of cyclones and wind direction. Lines of equal pressure are called isobars from the Greek baros (gravity) and isos (equal).

Types of barometers

In total there are two types of barometers - aneroid and mercury. The second is much more accurate and reliable, the first is more compact and more convenient, if necessary it can become a pocket one.

The mercury barometer shows the height pressureThe mercury column next to which is attached a measuring scale. Usually it is a glass tube 80 cm, filled with mercury, which is soldered at one end, and on the other - it is open and immersed in a cup of mercury. There is no air in the tube, so the space in the upper part is called the Torricelli emptiness. There is no liquid in the aneroid. It shows the pressure that acts on the corrugated metal box with thin walls, inside which a vacuum was created. When the atmospheric pressure drops, the box expands slightly, when it rises, it contracts, and the pressure itself acts on a special attached spring. Typically, several aneroid boxes are used, which are connected in series. With the help of the lever transmission system, the needle rotates and moves along a graduated scale according to the mercury barometer. It can be inscribed: "alternating", "rain", "very dry", "clear."

It is the aneroids used on airplanes, sea vessels, and also at meteorological stations. As a rule, a pen is attached to the arrows, and it automatically records the readings.

What pressure is the norm?

The fact is that there is no standard definitionatmospheric pressure. Depending on the geographic location of the region, the norm, which the barometer shows, is different. For example, in St. Petersburg, which is located at an altitude closest to the sea level, it is 760 mm Hg. But in Moscow, located on a hill - 748 mm Hg.

It is only in the local branch of the hydrometeorological service that you can precisely identify what is the norm for a specific city.

Now you know what a barometer is. Successful discoveries to you!