Barometers - How They Work

Barometers are a commonly used instruments for atmospheric pressure measurement. They are of three types: water-based, mercury and aneroid barometer. The water barometer was built (though unintentionally) by Gasparo Berti and the mercury barometer came into existence around the year 1644, thanks to the Italian physicist and mathematician Evangelista Toricelli. The aneroid one was invented by the French scientist Lucien Vidie in 1843. These weather instruments are primarily used for interpreting and forecasting the weather. This is a brief overview on these different barometers and how they work.

Water Barometers - How They Work?
This water-based barometer has its principle based on what was postulated by French physicist Lucien Vidie. He said, "decreasing atmospheric pressure predicts stormy weather". The barometer is built with a glass container which has a sealed body. This container is half filled wit colored water. Colored water makes it easy to determine the readings. Now, this container has a narrow spout connected to it, below the water level. A spout is an opening that allows the passage of liquids or grain. The spout has its other end open and above the water level of the container.

If you notice the water level in the spout rising above the water level in the main body, that would signify that the atmospheric pressure was lower than what it was when the glass container was sealed. On the another hand, if the atmospheric pressure was higher than what it was when the container was sealed, then the water level in the spout will be lower than the water level in the body.

So from this, it can be inferred that when the water level in the body is lower than that in the spout, the atmospheric pressure is low and it indicates warmer temperature. Reversely, when the body shows a water level higher than that in the spout, then the atmospheric pressure is high and the temperature of the surrounding is colder.

Mercury Barometers - How They Work?
The apparatus used in a mercury barometer consists of an 33 inches (approx.) glass tube. This tube has its one end sealed and its other end (which is open) in a mercury-filled reservoir at the base. Before placing this tube upside down in the reservoir, it is also filled with mercury (Hg). Due to the weight of this liquid metal, the level of mercury falls down, creating a vacuum at its closed end or at the top. Now the barometer working in this case goes like this. If the weight of the mercury in the glass tube is more than the atmospheric pressure exerted on the reservoir, then the Hg level falls. When the weight of the mercury is lesser than the atmospheric pressure exerted on the reservoir, then the level will rise. Thus, when the atmospheric pressure rises, there will be a rise in the mercury. When the atmospheric pressure decreases, so will the mercury level.

The level of mercury will keep on changing, until the atmosphere pressure which is exerted on the reservoir is equal to the weight of the mercury column in the tube. Read more on how does a barometer work.

Aneroid Barometers - How They Work?
The aneroid barometer's working is void of use of any liquid instead, it makes the use of a metal box known as the aneroid cell (capsule) or a series of such capsules. These capsules are partially evacuated and left with very small amount of air. When atmospheric pressure increases, contraction occurs and the sides of the cells come closer together. One side is connected to the base of the barometer and the other is connected to delicate levers and pulleys. These levers and pulleys are again connected to a rotating pointer which show amplified readings on a scale on the face of the aneroid barometer. Check out more on how to build a weather station.

Hope this article about barometers and how they work have helped to answer your queries. Now a days, most weather stations make use of digital barometers which are easier to read and set, enabling them to provide us with more accurate weather forecasts.