In 1643, an Italian physicist and mathematician came up with a crucial invention to help measure atmospheric pressure laying foundation for weather forecasts and unraveling many secrets in thermodynamics and modern meteorology

In 1643, an Italian physicist and mathematician came up with a crucial invention to help measure atmospheric pressure laying foundation for weather forecasts and unraveling many secrets in thermodynamics and modern meteorology. The scientist was Evangelista Torricelli, an Italian physicist and mathematician who invented the mercury barometer. The instrument gave scientists a way to measure atmospheric pressure by observing the height of mercury inside a glass tube. Torricelli also created a sustained vacuum during the experiment. His observations helped establish that air has weight and that atmospheric pressure can change. The invention later became linked with weather tracking, altitude measurement, pressure units and the development of modern meteorology.

The invention that changed pressure measurement

The invention was the mercury barometer. It is regarded in the source material as the first instrument used to measure atmospheric pressure. Torricelli developed it in Florence in 1643.


The basic design used a glass tube that was closed at one end. The tube was filled with mercury and then inverted into a vessel containing mercury. When the tube was turned upside down, some mercury moved into the vessel. A column of mercury remained inside the tube.

The mercury did not continue falling completely. It stopped when the weight of the mercury column was balanced by the pressure of the air acting on the mercury in the open vessel.

A space was left above the mercury column. Torricelli understood that this space contained no trapped air. It became known as a Torricellian vacuum. The experiment therefore provided a method for creating a sustained vacuum.

At sea level, the mercury column settled at about 76 centimetres, or 760 millimetres. This became associated with the standard atmospheric pressure of 1 atmosphere, equal to 760 mmHg.

Why Torricelli began the experiment?

Torricelli's work followed earlier experiments and ideas linked to Galileo. The source states that Torricelli built on work involving water pumps and siphons. Earlier experiments had raised questions about how far water could rise in a tube and whether a vacuum could be produced. Water could rise only to about 10 metres in such experiments. Torricelli used mercury instead of water because mercury is about 14 times heavier than water.

Using mercury meant that the same pressure could be demonstrated with a much shorter tube. Torricelli filled a glass tube about one metre long with mercury, closed the open end temporarily, inverted it and placed it into a vessel of mercury. The result was a mercury column of about 76 centimetres. A vacuum remained above it.

How the mercury barometer works?

The operation of the barometer can be explained through four steps:

• The setup: A glass tube longer than 75 centimetres is filled with mercury and closed at one end.
• The inversion: The tube is turned upside down and its open end is placed into a bowl or vessel containing mercury.
• The balance: Some mercury leaves the tube, but a column remains. It stops falling when the weight of the mercury column balances the pressure of air outside the tube.
• The vacuum: The space above the mercury contains no air trapped inside the tube, producing a Torricellian vacuum.

The instrument therefore connects the height of the mercury column with atmospheric pressure. When air pressure changes, the mercury level changes as well.

In 1643, an Italian physicist and mathematician measured atmospheric pressure laying foundation for weather forecasts

Torricelli's key observation came after he watched the mercury level over time. He found that the height of the mercury column changed from one day to another. He concluded that these changes were caused by variations in atmospheric pressure. This was important because it showed that air pressure was not constant. The observation also created a way to monitor changes in the atmosphere. A rise or fall in the mercury column could indicate a change in weather conditions.

This became one of the foundations for weather tracking. Changes in atmospheric pressure could be observed before or during changes in weather, helping people identify conditions associated with clear or stormy weather.

What the invention proved about air?

Before Torricelli's work, an older idea associated with Aristotle held that nature "abhors a vacuum." Torricelli's experiment provided evidence against that explanation. The experiment showed that air has weight and that air can exert pressure.

The air outside the tube pressed down on the mercury in the vessel. That pressure supported the mercury column inside the tube. The height of the column therefore provided a way to measure the pressure produced by the atmosphere. This helped establish atmospheric pressure as a measurable physical quantity.

From weather tracking to altitude measurement

The mercury barometer also became useful for understanding changes in elevation. Atmospheric pressure decreases as altitude increases. A barometer can therefore be used to identify changes in elevation by observing pressure.

This connection later made pressure measurement useful in aviation and altitude tracking. The source material also links the invention to weather forecasting because changes in atmospheric pressure can accompany changes in weather.

The barometer also provided a standard for pressure measurement. The unit torr was named after Torricelli. One torr corresponds to one millimetre of mercury in the traditional pressure measurement system.

Torricelli's background and connection with Galileo

Evangelista Torricelli was born on October 15, 1608, in Rome. He later died in Florence on October 25, 1647, at the age of 39. He studied mathematics and became connected with Benedetto Castelli, who had been a student of Galileo Galilei. Torricelli was exposed to scientific experiments and mathematical work during his years in Rome.

Torricelli also studied the work of Galileo. His writings included work on mechanics and projectiles. Galileo became aware of Torricelli's work, and in 1641 Torricelli was invited to Florence to work with him.

Torricelli served Galileo as secretary and assistant during the last months of Galileo's life. After Galileo's death in January 1642, Torricelli succeeded him as a professor of mathematics in Florence.

His work extended beyond the barometer

Torricelli's scientific work was not limited to atmospheric pressure. He worked on geometry, projectile motion, rectilinear motion and fluid movement. His work included Torricelli's law, which describes the speed of a fluid flowing through an opening.

The source also states that his work in geometry contributed to developments that later supported integral calculus. His mathematical work included the study of the cycloid, a geometric curve formed by a point on the rim of a rotating wheel.

Torricelli's findings on fluid motion and projectile motion appeared in his Opera Geometrica, published in 1644. He did not publish the barometer findings separately, as his mathematical studies occupied much of his attention.

How the discovery helped modern science?

The mercury barometer gave scientists a way to measure atmospheric pressure. This helped connect pressure with weather changes and altitude.

Its role extended into several areas:

• Atmospheric science: It provided a method for observing pressure.
• Weather forecasting: Changes in mercury levels could be tracked as pressure changed.
• Altitude measurement: Lower atmospheric pressure at higher elevations made pressure useful for estimating changes in elevation.
• Physics: The experiment provided evidence that air has weight.
• Vacuum studies: Torricelli produced a sustained vacuum.
• Fluid mechanics: His experiments contributed to the study of fluids.
• Pressure measurement: The millimetre of mercury became a pressure measurement, while the torr was named after Torricelli.
• Meteorology: Pressure observations became part of the study of weather and atmospheric conditions.

The source connects Torricelli's work with the later development of thermodynamics, weather science and modern meteorology.

Why the 1643 invention still matters?

The barometer changed how scientists understood the atmosphere. It turned air pressure into something that could be measured rather than treated as an idea. Torricelli's experiment also connected a simple physical observation with larger questions about air, fluids and the vacuum. The mercury column became a record of changes in atmospheric pressure. The same basic principle remained relevant to pressure measurement long after Torricelli's death.

Torricelli died in Florence in 1647. His name remains attached to the torr, a unit of pressure, and to the Torricellian vacuum. His barometer also remains part of the history of weather instruments and atmospheric science.