Barometer

How a Barometer Works and What It's Used For

A barometer is an instrument designed to measure atmospheric pressure, that is, the weight of the air on the Earth's surface. This pressure varies with altitude, temperature, and weather conditions, making it a fundamental indicator for predicting weather changes. The barometer is therefore an essential tool in meteorology and navigation.

There are two main types of barometers: mercury and aneroid. The mercury barometer, invented by Evangelista Torricelli in the 17th century, consists of a glass tube filled with mercury inverted over a container of the same liquid. When atmospheric pressure increases, it pushes the mercury upwards inside the tube; when it decreases, the level drops. The reading is taken in millimeters of mercury (mmHg) or hectopascals (hPa). This system is very accurate, but due to the toxicity of mercury, it is used less frequently today.

The aneroid barometer, on the other hand, does not use liquids. It works with a small, airtight metal box, called an aneroid capsule, which deforms according to air pressure. This deformation is transmitted via a mechanism of levers and springs to a needle that indicates its value on a graduated scale. It is lighter, more portable, and safer, which is why it is the most common type found in household appliances and mountaineering equipment.

What is a barometer used for? Atmospheric pressure is directly related to weather phenomena. When the pressure drops, it indicates that a low-pressure area is approaching, associated with clouds, rain, or storms. If the pressure rises, it signifies stability and good weather. Thus, barometers allow us to anticipate changes in the weather hours or even days in advance. They are also useful for calculating altitude, since pressure decreases as we gain altitude, making them indispensable in aviation and mountaineering.

In short, the barometer is a simple but vital instrument for understanding the atmosphere. Whether it's an elegant mercury barometer or a practical aneroid one, its function remains the same: to help us interpret the invisible signals of the air to predict the weather and orient ourselves in our environment.