# Barometer

A barometer is an instrument that measures atmospheric pressure. That is, the barometers is a measuring instrument that is used to determine the pressure exerted by the air in the atmosphere on the Earth’s surface.

The barometer was invented in 1643 and its inventor was the Italian physicist Evangelista Torricelli, who was able to measure atmospheric pressure using the first mercury barometers.

In general, the unit of measurement for barometers is usually the hectopascal (hPa), which is equivalent to 100 pascals (Pa). Although many mercury barometers also express atmospheric pressure values ​​using millimeters of mercury (mmHg).

## How a barometer works

Once we have seen the definition of a barometer, in this section we will see how this type of measuring instrument works.

Before using a barometer, it must be calibrated so that the measurements made are correct. To calibrate the barometer you must know the atmospheric pressure (you can ask the nearest meteorological center) and adjust the value marked by the needle to coincide with the real value of atmospheric pressure.

If a reference pressure from another area is used when calibrating the barometer, it is important to take into account the height of the reference pressure, since atmospheric pressure varies depending on altitude. Specifically, the pressure decreases by approximately 1 hectopascal every 8 meters.

Once calibrated, the barometer needle indicates the atmospheric pressure. If the pressure is less than 1013 hPa it indicates a depression, on the other hand, a pressure greater than 1013 hPa is a anticyclone. This value is used to separate the different types of pressures because it is the average atmospheric pressure at sea level.

Finally, if the needle remains still, the pressure may remain stable. However, you can check that the barometer has not been damaged by putting the device inside a plastic bag and then compressing it, if the pressure has not increased it means that the barometer must be readjusted.

## Types of barometers

• Mercury barometer: it was the first type of barometer that was created, specifically, it was invented by Evangelista Torricelli in 1643. It consists of a tube filled with mercury that is closed by a end and open on the other. The tube is inverted and the open end is placed in an open container with the same liquid, then the height of mercury in the tube will decrease until reaching equilibrium, whose value will be the atmospheric pressure. This type of barometers is increasingly less used due to the toxicity of mercury and the fragility of glass.
• Aneroid barometers: invented by Lucien Vidie in 1843, this type of barometers measures atmospheric pressure by the deformations that occur when vacuuming a metal box with very thin walls. elastic.
• Altimeter barometer: this type of barometer indicates the atmospheric pressure in meters or feet of altitude with respect to sea level. They are used especially in aviation to know the height at which the ship is.
• Fortin Barometers: it is made up of a tube with mercury inside a glass tube. The precision of this type of barometers is very high, in fact, they are often used in scientific laboratories.
• Barograph: it is a variant of the barometers, its peculiarity is that it measures atmospheric pressure and, in addition, prints the pressure variations on paper.

### Barometer Applications

The main application of the barometer is meteorology, as the barometer is used to make short-term weather predictions. In general, high pressures mean that there will be good environmental conditions, on the other hand, low pressures indicate possible rain or strong wind.

However, to make a more accurate weather prediction, meteorologists not only use the information provided by the barometer but also use other instruments such as the hygrometer or anemometer.

The barometer is also used in mining as it can help identify hazards in a mine. Because when there is a drop in air pressure, the probability that gases trapped deep inside can escape increases.

Likewise, another use of the barometer is in diving. Specifically, aneroid barometers are used to track pressure.

### Difference between barometer and manometer

Two types of pressure measuring instruments that are often confused are the barometers and the manometer, so in this section we will see what the difference is in their meaning.

The difference between a barometers and a manometer is that the barometers measures atmospheric pressure, that is, it measures the pressure of open containers or of the environment. On the other hand, a manometer measures the pressure of closed containers.