How do barometers work to measure atmospheric pressure?

Barometers measure atmospheric pressure by balancing the weight of the atmosphere against a column of liquid.

A barometer is a scientific instrument used to measure atmospheric pressure, also known as barometric pressure. The concept of a barometer was first developed in the 17th century by Evangelista Torricelli, an Italian physicist and mathematician. The traditional barometer, known as a mercury barometer, consists of a long glass tube, closed at one end, filled with mercury and inverted into a dish also containing mercury.

The principle behind a barometer is quite simple. When the tube is placed upside down in the dish of mercury, the mercury in the tube falls a little, creating a vacuum at the top. This happens because the pressure of the air pushing down on the mercury in the dish is balanced by the weight of the mercury in the tube. If the atmospheric pressure changes, the level of mercury in the tube changes accordingly.

When the atmospheric pressure rises, it pushes more strongly on the surface of the mercury in the dish, causing the mercury in the tube to rise. Conversely, when the atmospheric pressure falls, the mercury level in the tube also falls. The height of the mercury column is then measured, usually in millimetres, and this measurement represents the atmospheric pressure.

In modern times, digital barometers have been developed which use sensors to measure atmospheric pressure. These are more convenient and safer than mercury barometers, but the basic principle of operation remains the same: they measure the force exerted by the weight of the atmosphere.

Understanding how a barometer works is not only important for predicting weather changes, but also for various scientific and industrial applications. For instance, in aviation, barometers are used to determine altitude, as atmospheric pressure decreases with increasing height.