Mercury Barometer| Meaning, Inventor, Principle, How it works, Advantages and Uses


In this write-up, we intend to discuss everything about the mercury barometer.

To impart detailed information, we have included the meaning, principle, and working of a mercury barometer. Also, know the inventor of the mercury barometer.

For a better understanding of the topic, know the uses and advantages of a mercury barometer.

Also, explore the difference between a mercury barometer and an aneroid barometer. Some additional information has also been provided to know the topic better.

What is a mercury barometer?

A mercury barometer is a device that is used to measure the atmospheric pressure at a given location.

The barometer consists of a vertical glass tube which is closed at one end.

The closed-end is at the top and it sits in the mercury-filled basin placed at the bottom. It is an absolute pressure gauge.

The air is evacuated from the long, hollow, and vertical glass tube which sits in mercury. A mercury barometer is also known as a Torricellian Barometer.

It measures the atmospheric pressure with the adjustment of mercury in the tube until the weight of the mercury column balances the atmospheric force that is exerted on the reservoir.

In other words, the device depicts the atmospheric pressure by the height of a column of mercury.

According to the design of the mercury barometer, the measurement of atmospheric pressure is in inches or millimetres of mercury.

1 atmospheric pressure is equivalent to 760 mm or 76 cm of mercury head. This is because 1 atmospheric pressure causes mercury to rise to 760 mm up in the tube.

Who invented the mercury barometer?

The mercury barometer was invented by Evangelista Torricelli. He was a physicist and mathematician. Torricelli was born in Faenza, Italy on October 15, 1608.

He died on October 22, 1647, in Florence, Italy. Evangelista moved to Florence, Italy to assist Galileo.

In the vacuum experiments of Evangelista, Galileo suggested him to use mercury. He filled a four-feet long glass tube with mercury.

He then inverted it into an empty dish. A part of the mercury from the tube escaped but some of it remained. He observed the creation of a vacuum in the tube.

Torricelli was the first scientist to create a sustained vacuum and discover the principle of a barometer.

He studied and realized that the day to day height variation of mercury was caused due to the changes in the atmospheric pressure.

He built the first mercury barometer around the year 1644.

What is the principle of a mercury barometer?

The atmospheric pressure at any level in the atmosphere depends on the weight of the air present overhead.

A mercury barometer can be referred to as a device or a scale that measures the weight of the atmosphere above at the location.

The principle of a mercury barometer can be understood with the reference to a seesaw.

With the understanding of the principle of a See-Saw, figuring out the functioning and principle of a mercury barometer is simple.

A mercury barometer serves as a balance. The weight of mercury present in the device balances the weight of the atmosphere at a given place.

The atmospheric pressure cannot be measured on a balancing scale due to the presence of air on both the scales.

Thus, in a barometer, one end is sealed to prevent air from disturbing the scale and measures.

Therefore, a Mercury Barometer works on the principle of balancing the atmospheric pressure with the volume of mercury present in the device.

How does a mercury barometer work?

The modern barometers are electronic and display the pressure reading on an LCD.

However, there are traditional kinds of mercury barometer as well. We have discussed the working of a traditional mercury barometer below.

Also known as a Torricellian barometer, it consists of a container filled with mercury and a glass tube which has one end sealed.

The open end of the long and hollow vertical glass tube is positioned at the bottom inside the mercury container.

At sea level, with the increase in the air temperature, the mercury in the glass tube rises because the increase in a temperature pushes down on the mercury inside the container.

With the decrease in the air temperature, the mercury in the tube drops down due to the decrease in the pressure.

The working of the mercury barometer is affected by the increase in the altitude. At a higher altitude, the pressure falls with the increase in altitude.

The atmosphere at higher altitudes does not push down on the mercury in the container which does not result in the rising of mercury so far in the tube.

The positioned glass tube has measurements or markings on its side. The atmospheric pressure is recorded by reading it through the measurements on the tube.

Why is mercury used in barometers?

Whether it is a barometer or a thermometer, mercury is used. This is because the use of mercury is more convenient than using water.

In effect, water is less dense and less heavy than mercury. Due to this, the air pressure lifts a certain volume of water much higher up the tube than the same volume of mercury.

You might need a tall tube to use water in your barometer which will make it so enormous to be impractical.

With the use of mercury, the same results can be achieved by smaller pieces of equipment.

What are the uses of mercury barometer?

A mercury barometer is primarily designed to be used for measuring the atmospheric temperature. However, there are various other uses of a mercury barometer.

The uses of mercury barometers have been given below which are as follows:-

  • It is used to measure the atmospheric pressure of a place
  • It is used to determine the altitude of a place as the atmospheric pressure differs with the change in altitude
  • A mercury barometer is also helpful in the process of weather forecasting
  • They help in the calibration and checking of the aneroid barometers
  • Mercury barometers are used for surface weather analysis and the preparation of barographs through the readings
  • They have various applications in fluid mechanics, physics, astronomy, and chemistry
  • They help in measuring the pressure in aircraft and also in the preparation of the aircraft altimeters

How do you read a mercury barometer?

Reading a mercury barometer is not an easy task but not too complex. It requires the correct height to be measured after the content is balanced in the glass tube.

Know the complete parts and structure of the barometer before you proceed. We have mentioned the method of reading a mercury barometer below as follows:-

  • Ensure that the height of the meniscus is neither too large nor too small by lightly tapping the barometer
  • Adjust the level of mercury below the zeroing peg using the Zero Adjusting Knob
  • Adjust the height of the movable scale. Ensure that the bottom of both sides are even with the top of the meniscus
  • Read and note the height of mercury using the vernier on the moving scale
  • Now, read and note the temperature with the use of the thermometer that is mounted on the barometer

What are the advantages of a mercury barometer?

There are plenty of advantages of using a mercury barometer to measure atmospheric pressure which is as follows:-

  • A mercury barometer is precise and offers a simple method of measuring the atmospheric pressure
  • It has low vapour pressure and does not evaporate easily
  • It is inexpensive as it does not require any expensive equipment to be made
  • A mercury barometer offers flexible construction and requires low power for its operation

What are the disadvantages of a mercury barometer?

There are a few disadvantages of mercury barometer which we have discussed below:-

  • It can be overwhelming to handle and carry due to its bulky and large size and liquid mercury content
  • The glass tube can break easily if not properly handled
  • With a mercury barometer, taking the readings can be hard under certain hard conditions

What is the difference between a mercury barometer and an aneroid barometer?

Beside mercury barometer, the aneroid barometer is also a device that is used to measure the atmospheric pressure. However, both the devices differ in various aspects.

Below, we have discussed the differences between the aneroid barometer and mercury barometer which are as follows:-

Basis of DifferenceMercury BarometerAneroid Barometer
MeaningA simple barometer that is used to measure the atmospheric pressure with mercuryA compact barometer used to measure the atmospheric pressure with a small flexible metal box
Prime ElementIt primarily uses mercury to measure the air pressureA metal box is primarily used to measure the air pressure
MeasurementMeasurement is done through reading the rise in height of mercury inside the glass tubeMeasures the pressure through the expansion and contraction of the metal box which makes the needle move on a pressure scale
Size and Ease of HandlingLarge. The vertical glass tube is about 3 feet high. It is fragile and bulky due to liquid mercury content. This makes it hard to handle and carry.Compact and Solid. Can be easily handled and transported due to its small size and not liquid content.
Ease of measuringMeasurement can be hard as it requires accurate reading after the mercury content is balancedDirectly gives a value which is easy to note down and measure
ConstructionRequires machinery for constructionCan be manually constructed and does not require machinery
ApplicationsWeather forecasting, laboratories etcAircrafts, homes, recreational boats etc.

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