How Does a Barometer Work? The Answer Will Leave You Dazed

Abhijit Naik Jun 18, 2019
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An important tool in the field of weather forecasting, a barometer is used to measure the atmospheric pressure. Here we will review the functioning of this device to understand how it works.
A barometer is an instrument used to measure the atmospheric pressure (weight of the air) by using water, air, or mercury. It helps in determining surface troughs and high pressure systems on the planet. The data collected from it can help in forecasting sudden changes in the weather.

Water-based Barometers

Lucien Vidie's law, which states that "decreasing atmospheric pressure predicts stormy weather" forms the basis of the 'weather glass' or 'Goethe barometer'. It is primarily a sealed glass container, which is half filled with water.
A narrow spout is connected to it, at a point below the water level, which extends all the way above the water level where it is open. Preferably colored water is used, as it is easier to collect the readings.
When the atmospheric pressure rises, then the water level in the spout drops below the level of water present in the container, indicating that the temperature is getting colder.
On the other hand, when the atmospheric pressure falls, then the level of water in the spout exceeds the water level in the container, indicating that the temperature is getting warmer.
When the level of water in the container is higher than the level of water in the spout, it means that the atmospheric pressure is high. In contrast, when the level of water in the container is lower than the level of water in the spout, it means that the atmospheric pressure is low.

Mercury Barometers

A mercury barometer is a 30-inch glass tube, which is sealed at one end and open at the other. The tube is filled with mercury at the base and placed upside down in a container called the 'reservoir'. It works by balancing the weight of mercury within the glass tube with the atmospheric pressure.
When the weight of mercury is less than the atmospheric pressure, there is a significant rise in the mercury level in the glass tube. Similarly, when the weight of mercury exceeds the weight of atmospheric pressure, there is a fall in the mercury level.
The level of mercury continues to change till the weight of the mercury in the glass tube is equal to the weight of the air above the reservoir. In low pressure conditions, the air rises from the surface before it is replaced by air from the surrounding areas, therefore the weight of air above the reservoir is reduced and mercury drops.
In high pressure conditions, air sinks towards the Earth's surface faster than its ability to move out to the surrounding areas, thus more air gets accumulated above the reservoir. As the weight of the air is higher, mercury soars.

Aneroid Barometers

An aneroid barometer consists of a small flexible metal box called the aneroid cell. It is made from an alloy of copper and beryllium. This cell is supported by a strong spring to prevent it from collapsing.
Even minute changes in the external air pressure cause it to expand or contract. This expansion and contraction triggers the mechanical levers, as a result of which tiny movements of the cell are amplified and displayed. A manually set needle is used to mark the recent measurement, so that the change doesn't go unobserved.
Today, technologically advanced digital barometers, which resort to electrical charges to calculate air pressure, are fast replacing their older counterparts. This sophisticated technology helps to record accurate data about the pressure conditions and thus, helps in highly accurate weather forecasting.