Barometer – Concept, types, invention, function and units

We explain what a barometer is, its invention, function and in what units it measures. In addition, the characteristics of each type of barometer.

The barometers made it possible to show that atmospheric pressure decreases with altitude.

What is a barometer?

A barometer is an instrument used to measure atmospheric pressure, that is, the weight that the atmosphere exerts in a certain place on the earth’s surface. Let us remember that the atmosphere is a heterogeneous mass of gases that covers the planet, and therefore has perceptible physical properties, such as weight, and that have a decisive influence on the climate.

It is a very common artifact in meteorology, whose first versions date from the seventeenth century, built by the Italian physicist and mathematician Evangelista Torricelli (1608-1647), a student of Galileo Galilei. The invention of the barometer came about as a means of demonstrating the weight of air, at a time when it was thought that it did not exert any pressure on the earth’s surface.

The first barometer consisted of a glass tube closed at the top and open at the bottom, which is filled with mercury and inverted over a container filled with the same liquid, allowing the mercury to join with the one already in the container. . This happened at the beginning, increasing the level of the mercury in the container, but up to a certain point.

Thus the question arose as to what force was preventing all of the mercury from exiting the tube and spilling out of the container. Precisely, the pressure that the air exerts in the opposite direction. This is what we know as atmospheric pressure.

This interpretation of the barometer was confirmed by Blaise Pascal himself (1623-1662), who carried one of these devices to the top of a mountain and found that, as there was less air above it, the readings of the instrument varied, and the mercury it descended much more in the tube than at lower altitudes.

Thereafter the mercury barometer was used throughout the world and allowed a greater understanding of the behavior of the atmosphere and its link with the climate and the meteorological state. However, since 2007 these instruments have been replaced by more modern versions, given the proven toxicity of mercury to living beings in general.

What is a barometer for?

barometer what is it for
A barometer is used to measure the pressure of air or any other gas.

As we said before, the barometer is used punctually to measure atmospheric pressure, that is, to measure the weight of the air mass above our heads, which can vary according to the altitude and according to the energy levels in the atmosphere.

This, in turn, allowed a better understanding of the atmospheric climate, by checking the link between the variation of atmospheric pressure (especially its decrease) and unstable weather. So thanks to the barometer we can have short-term predictions of atmospheric weather, and know that when the pressure increases there will be stable conditions, while when it decreases there will be bad weather.

Of course, other factors and elements also play a part in this type of prediction, which is why barometer readings are usually combined with an anemometer, a hygrometer and other similar instruments.

Barometers They are also used to measure the pressure of all types of gases, that is why they can also be found in packed gases, such as oxygen tubes

Barometer Units

The current units with which barometers measure atmospheric pressure are Hectopascals (hPa), which are a multiple (x100) of Pascals, the minimum unit of pressure accepted in the International System of Weights and Measures. One Pascal is equivalent to a force of 1 Newton on a surface of 1 square meter, normal to it.

However, mercury barometers were traditionally used, the measurement of which was given in torr, a unit that pays tribute to Evangelista Torricelli, and is equivalent to 1 millimeter of mercury (mmHg).

Types of barometers

aneroid barometer
The aneroid barometer was invented in 1843.

There are several types of barometers, each with its own particularities, as we will see below:

  • Mercury barometer. This is the traditional model created by Torricelli, which consists of an 850 mm high glass tube, filled with mercury and placed on a container filled with the same substance. Its use is discouraged due to the possibility of mercury poisoning.
  • Aneroid barometer. Devoid of mercury, the aneroid is a barometer invented in 1843 by the French physicist Lucien Vidie (1805-1866), which measures atmospheric pressure through the deformations it exerts on a metal box with highly elastic walls, inside which there is a absolute vacuum. Larger than the mercury barometer, it was quite inaccurate, due to the elasticity discrepancies of the materials.
  • Fortin Barometer. A variation of the mercury barometer, which incorporates the elements for a fixed level (a screw that rests on the tip of a small ivory cone), keeping the torricellian tube suspended and then covering it all in a brass box, with a slot to be able to observe the measurements.
  • Digital barometer. The modern variant that takes advantage of new computerization technologies, and that uses special sensors to accurately capture the pressure of the atmosphere.