how does mercury barometer work

How does mercury barometer work? When you are interested in keeping track of a change in atmospheric pressure for whatever reason, you cannot do it with a barometer.

With various types available, most people experiment with multiple options.

And mercury barometer is among the most commonly found instruments.

But, interestingly, many people want to know, “how do mercury barometers work?” And of course, what does a mercury barometer measure?

A Mercury barometer uses a mercury column and tells you about any change in atmospheric pressure by pushing mercury up or down a tube. 

Learning More about a Barometer

The primary function of a barometer is to measure atmospheric pressure.

Since air pressure changes as one travels above, near, or below sea level, it is most typically utilized for weather forecasting and establishing one’s altitude. 

The Invention of the Barometer

the invention of the barometer

In 1643, Evangelista Torricelli, a colleague of Galileo’s, constructed the first barometer.

Galileo proposed placing a 4-foot-long glass tube upside down on a dish after being filled with mercury.

Torricelli found that a vacuum was formed because some of the mercury did not leave the tube.

By keeping careful tabs on the height of mercury over the course of several days, he discovered that it varied from day to day as a result of variations in atmospheric pressure.

This discovery led to the development of the Torricelli Tube (barometer).

Several common varieties of barometers and their operation are available these days. 

Types of Barometers

Today, you can find many different varieties of barometers that use different mechanisms but do the same thing – they help you notice changes in atmospheric pressure.

Some of the most common ones include the following:

  • Digital Barometer
  • Water Barometer
  • Aneroid Barometer
  • Mercury Barometer 

Digital Barometer

new digital barometer

In this day and age, digital barometers have become the standard.

Micro-electromechanical (MEM) systems, also called detecting cells or chips, are built into these digital instruments.

These little integrated circuits (IC) react to changes in atmospheric pressure. 

Water Barometer

Water is used in place of mercury, and the instrument’s spout is open at the top so the liquid can rise or fall as air pressure changes.

This type of gadget is also known as a weather or storm glass

Aneroid Barometer

In appearance, aneroid barometers are often round, like clocks or compasses.

An aneroid barometer has a metal chamber on the inside that is nearly airless.

aneroid barometer old

The needle on a barometer moves in response to variations in air pressure by expanding or contracting the metal chamber housing the instrument.

The barometer’s ability to tell variations in atmospheric pressure is based on the motion of the needle. 

Mercury Barometer

A mercury barometer is an instrument for gauging atmospheric pressure.

The atmosphere exerts pressure on Earth’s surface, and that pressure can be measured when mercury moves up and down a tube.

You can use the height of the mercury column to gauge the pressure in the atmosphere and hence forecast the weather.

Fact: You can find other unusual types of barometers, including Hooke's Otheometer, Collins Patent Tablet Barometer, and the Shark Oil barometer. 

How Does Mercury Barometer Work?

mercury barometer vintage

Italian physicist and mathematician Evangelista Torricelli introduced the mercury barometer in 1643.

A long glass tube was utilized, which he filled with mercury and then inverted in a dish.

Atmospheric pressure at sea level equals a height of about 760 mm above the mercury level in the dish, where the mercury column rested. 

The Working Mechanism of Mercury Barometers

The traditional mercury barometer is essentially a long glass tube with a sealed end and an open one.

After entirely filling the tube with mercury, the open end is sealed off with a finger.

the working mechanism of mercury barometer

Then, it is important to pour mercury into the dish until it reaches a predetermined height in the tube, at which point the tube is inverted. 

The height of the mercury column in the tube is proportional to atmospheric pressure.

When the pressure rises, so does the mercury column in the tube; conversely, as the pressure falls, so does the mercury column. 

The height of the column, in either millimeters or inches, is used to calculate the air pressure. 

An Important Consideration

The height of the mercury column is measured using a ruler or a calibrated scale to determine the barometric pressure.

Atmospheric pressure, typically given in millibars (mb) or inches of mercury, is calculated from the measured value (inHg).

Fact: At sea level, the average air pressure is 29.92 inches of mercury (1013.25 millibars). 

Learning about the Benefits of Mercury Barometer

Mercury barometers have been used to gauge atmospheric pressure for hundreds of years.

Since precise pressure readings are crucial in a variety of fields, including aviation, meteorology, and more, it has seen extensive use.

benefits of mercury barometer

As electronic and digital pressure sensors have emerged, the mercury barometer still has many uses due to its many advantages.

For instance: 

Excellent Precision

In terms of precision, the mercury barometer provides excellent readings of atmospheric pressure.

It is perfect for weather forecasting and scientific research since it can pick up on subtle shifts in pressure that other sensors cannot. 


stability of mercury barometer

Mercury is a great material for barometers since it is a stable liquid that does not evaporate or freeze at typical atmospheric temperatures.

As a result, pressure readings will remain stable over time because the mercury column will remain unchanged. 

Good Measuring Range

A mercury barometer can measure pressures from near vacuum to several thousand pounds per square inch.

And that is mainly due to the mercury barometer’s vast measuring range. 

Quite Durable

quite durable

Mercury barometers are made to last, with sturdy construction and high-quality materials.

They are resilient against extreme temperatures and pressure changes and need little in the way of upkeep. 


Because of their compact size and lightweight, mercury barometers can be easily taken on the go.

They can be used everywhere, regardless of proximity to an electrical grid, because they do not need batteries or complicated wiring.

Fact: When compared to digital and electronic pressure sensors, mercury barometers have lower production costs 

A Few Important Considerations

Despite their usefulness, mercury barometers have several drawbacks. A major issue is the toxic nature of mercury.

Mercury is a heavy metal that, if not handled correctly, can cause harm to both humans and the environment. 

Factors Affecting the Accuracy of Mercury Barometer

factors affecting the accuracy of mercury barometer

Many things can alter a mercury barometer’s accuracy.

A mercury barometer’s precision may be diminished by the following, among others: 


One factor that can alter a mercury barometer’s accuracy is the surrounding temperature.

Since mercury expands and contracts depending on the temperature, any variation in the mercury column’s height can be attributed to temperature.

An accurate mercury barometer requires a steady temperature, ideally in a climate-controlled setting. 


altitude affects the accuracy of mercury barometer

The accuracy of a mercury barometer may also be impacted by the user’s altitude.

Due to lower atmospheric pressure at higher altitudes, mercury levels may fall.

To compensate for this, the height of the mercury column in the barometer must be changed depending on the user’s altitude. 

Changes in Pressure

As atmospheric pressure fluctuates, it can throw off the reading of a mercury barometer.

Changes in pressure can cause the mercury column’s level to rise and fall, leading to erroneous readings if not properly compensated for.

You need to give it some time to settle to get an accurate reading from a barometer. 


mishandling affects the accuracy of mercury barometer

Mercury barometers are similarly susceptible to vibrational error.

The mercury column can move due to vibrations, causing inaccurate readings.

Keeping a mercury barometer in a secure and steady location can help reduce the impacts of vibration. 

Mercury Leaks

The accuracy of a mercury barometer can potentially be affected by leaks.

There are three potential entry points for air to escape the barometer:

  • The mercury levels
  • The tube’s base
  • The instrument’s top
mercury leaks

A mercury barometer’s accuracy depends on regular maintenance that includes checking for leaks and fixing them.

Fact: A barometer's precision can also be affected by the quality of the mercury it uses, as impurities in mercury can produce incorrect readings. 


How does mercury barometer work? A mercury barometer is a cheap and reliable tool for gauging atmospheric pressure.

The device is based on the time-honored method of utilizing a column of mercury in a glass tube to display shifts in atmospheric pressure.

The mercury barometer is still used today, even though electrical and digital methods of monitoring atmospheric pressure have mostly superseded it.