Можете мне текст перевести measuring atmospheric pressure the air surrounding the earth is really a mixture of well-known gases: about 77% nitrogen, 21% oxygen, and 1% argon. the remaining 1% includes small quantities of such gases as carbon dioxide, hydrogen, neon, krypton, helium, ozone, and xenon. the atmosphere is the most dense at sea level. for measuring the atmospheric pressure a device, called a barometer, is used. there are in common use today two kinds of barometers — the mercury barometer and the aneroid barometer. the mercury barometer was invented by the italian physicist, evangelista torricelli, some 300 years ago. torricelli’s experiment is illustrated in fig. 4. a long glass tube is filled with mercury and the finger placed over one end as shown in the diagram. this tube is then inverted with the open end in a dish of mercury and the finger is removed as in the diagram. at the instant the finger is removed, the mercury level drops in the tube to a height h as shown. the mercury drops until the pressure due to its own weight inside the tube is equal to the atmospheric pressure outside. at sea level the height at which the mercury column stands is about 30 in. this height will be the same regardless of the diameter of the tube or the length of the vacuum space at the top. it was the french philosopher and mathematician, blaise pascal, who first showed that when a mercury barometer is taken to the top of a mountain, the height of the mercury column drops considerably. it drops because there is less air above that point and hence a lesser downward pressure on the free mercury surface. standard atmospheric pressure is defined as the pressure equivalent to a column of mereury 76 cm high when the temperature is о °с. (this is equivalent to 29.92 in. of mercury at 32 f.) standard atmospheric pressure is equivalent to 14.7 lb/in2. some barometers work on a different principle from the mercury “weather glass.” they are known as aneroid barometers. an aneroid barometer consists of a thin metal box from which the air has been removed. the atmospheric pressure pushes in (presses) the sides of the box. as the pressure decreases they will spring outwards. this movement is magnified and communicated to a pointer by a system of levers. some aneroid barometers are self-registering (they are called barographs). instead of a pointer a lever is moved. this carries an inked stylo, which moves over a roll of paper fixed to a drum which is slowly turned by clock-work. in this way continuous records of the atmospheric pressure can be taken for periods of a week or longer. atmospheric pressure not only varies with altitude but also with time. although the time variations are small and do not follow any regular law, they can be and are used by the weather bureau for predicting weather conditions. when the barometric pressure begins to fall, it is a sign of changing weather. if the pressure goes on falling rain usually follows. as the storm passes, the barometer rises again. so, watching the changes of barometric pressure the weather for that place can be forecast. if you look at the dial of a household barometer you can see the following readings: “very dry, fair, rain, much rain, change, stormy.”

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