Air gets pulled down by gravity and hence air exerts pressure on objects. One such example of measurement is known as a barometer.

Barometers are scientific instruments that are used for the measurement of atmospheric or air pressure. It is an important and essential tool used in the meteorological department for forecasting short term weather and altitude changes.

See the Video of Barometer

The barometers should be kept at the same level and cannot measure air pressure above the altitude of 5,000 feet. Initially, water-based barometers were used, later it was replaced by mercury and aneroid barometers which the two most commonly used barometers.

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Mercury Barometers

The mercury barometers have a simple construction. They consist of a long thin tube, closed at one end and open at the other and a container.

The tube is 100cm or 1 meter long. Both the tube and container are filled with mercury but the tube is completely filled such that no vacuum or air bubbles are present inside the tube.

The working operation is easy. The open end of the tube that is filled with mercury is closed with the thumb and tilted upside down and placed inside the container having mercury, making sure no external air gets into the tube.

Two types of pressure act on it, the pressure inside the tube and the atmospheric pressure outside.

Due to the pressure difference, the mercury inside the tube falls to a certain extent into the container.

The pressure inside the tube is greater than the atmospheric pressure acting outside.

The principle of how a barometer works is as follows:

When the atmospheric pressure increases, the weight of the air increases and pushes the mercury liquid upwards, whereas when the atmospheric pressure decreases, it drains the mercury downwards. This leads to the measurement of weather on basis of air pressure.

Aneroid Barometers

The aneroid barometers are very different from mercury barometers. These are the non-liquid type and are advanced.

It is made up of an evacuated drum having various markings of measurement. Two indicators are present, one representing high pressure and the other represents low pressure.

The indicators are of black-indicates the current pressure and gold-indicates the constant pressure or turned to changes. The aneroid barometers can be easily converted into a barograph.

Therefore barometers play a vital role in determining weather and climate conditions and can be used indoors and outdoors.

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