What is a barometer? This technical term is called a device for measuring atmospheric pressure. The most widely used barometers of two types. A mercury barometer is used to measure atmospheric pressure mainly at meteorological stations.
It is more cumbersome, but it also gives greater
measurement accuracy, which is why scientists prefer it. A barometer of this type was invented and built by the Italian scientist Evangelista Torricelli in 1644. The principle of its action is balancing a column of mercury with a column of atmospheric air. Due to the high
density of mercury, the height of the column is very small (when they say that atmospheric pressure is 760 millimeters of mercury, it means that atmospheric air presses with the same force at the measurement point).
Aneroid barometer is a more complex device. Although the idea of the device was expressed almost simultaneously with the invention of the mercury barometer (this was done in the same seventeenth century by the German scientist Gottfried Leibniz), the idea of the great German was put into practice only two hundred years later. In 1847, the talented French engineer Lucien Vidi created the world's first aneroid barometer. What is the principle of its action?
The barometer received the name "aneroid", that is, anhydrous. With this term, the creator wanted to emphasize that the device does not use any liquid, unlike a mercury barometer, where the liquid metal is a sensitive element .
In the aneroid, the sensitive element is a sealed box of corrugated material, which, with an increase or decrease in atmospheric pressure, slightly contracts or expands. The leverage moves the arrow, which on a specially graded scale indicates atmospheric pressure in millimeters of mercury.
It would seem nothing complicated, and the aneroid barometer could be created at the level of technological development both from the time of Torricelli and before it. Why didn’t this happen? Most likely, a combination of several factors played a role here. The first and main is the lack of need for such a device at that time. In fact, meteorology as a science was only in its infancy, and the dependence of small fluctuations in atmospheric pressure and weather was only realized by scientists of that time. In addition, the lack of suitable material for the corrugated box may have played a role (it should have acceptable elasticity and not stretch during long-term operation).
As science developed, both the first and second circumstances ceased to impede the creation of the aneroid.
After the invention of Lucien Vidy, the aneroid barometer began to spread rapidly to private homes and apartments. There was even a peculiar fashion: the presence of this device in the house emphasized the social and intellectual status of the owner. Such a person, in modern language, was considered "advanced."
As the adoption of the international metric system (SI) by most countries, the graduation of the aneroid scale began to be supplemented by a scale where the pressure was indicated not only in millimeters of mercury (this is not a system unit), but also in pascals. There is also a graduation of the aneroid scale in bars. A bar is also an unsystematic unit, approximately equal to one atmosphere. Sometimes measuring pressure in bars is more convenient than in millimeters of mercury or in system units.
However, the habit of measuring atmospheric pressure in millimeters of mercury was very strong. Even now, in weather forecasts, atmospheric pressure is indicated in these non-system units.