Barometer: The Birth of Atmospheric Science.
Imagine a world without weather forecasts, without understanding storms, and without knowing why air moves from place to place. Before the 17th century, people had no way to measure air pressure, and the atmosphere itself was poorly understood. This changed thanks to the work of the Italian scientist Evangelista Torricelli, who invented the barometer in 1643. This simple yet revolutionary instrument opened the door to meteorology, physics, and a deeper understanding of our environment.
Who Was Evangelista Torricelli?
Evangelista Torricelli (1608–1647) was an Italian mathematician and physicist born in Faenza, Italy.
Studied under Benedetto Castelli, a student of Galileo Galilei.
Became Galileo’s assistant in the final months of Galileo’s life.
Known not only for inventing the barometer but also for contributions to hydrodynamics, geometry, and optics.
Torricelli lived during the early scientific revolution — a time when thinkers began to rely on experiments and observation rather than purely philosophical reasoning.
The Problem: Why Won’t Water Rise Higher?
In the 17th century, engineers used suction pumps to raise water from wells. But these pumps couldn’t lift water higher than about 10 meters (approximately 33 feet). This puzzled scientists and engineers alike, who believed that nature abhorred a vacuum and should keep pulling the water up endlessly.
Even Galileo suggested this might be a limit of nature, but he did not find a full explanation.
Torricelli’s Experiment: Invention of the Barometer
Torricelli reasoned that it wasn’t nature’s dislike of a vacuum, but rather the weight of air itself pushing down on the water that limited its rise. To test this, he conducted a now-famous experiment in 1643:
He filled a glass tube, about 1 meter long, completely with mercury (which is 13 times denser than water).
He sealed the top and inverted the tube into a dish of mercury.
Instead of the mercury flowing out completely, it fell only partially, leaving an empty space (vacuum) at the top and standing about 76 centimeters (about 30 inches) above the mercury in the dish.
This column of mercury was being pushed up by the pressure of the atmosphere on the mercury in the dish, balancing the weight of the mercury column inside the tube.
Torricelli had invented the first mercury barometer — a device to measure atmospheric pressure.
Why Was This Revolutionary?
Torricelli’s invention did more than create a scientific instrument:
Proved air has weight: The mercury stayed up because the atmosphere exerted pressure.
Created the first sustained vacuum (the space at the top of the tube), which challenged the long-standing belief that a vacuum couldn’t exist.
Laid the foundation for meteorology, as scientists soon noticed that mercury levels changed with weather — rising in fair weather and falling before storms.
The Impact on Science and Weather Forecasting
After Torricelli:
Scientists like Blaise Pascal showed that atmospheric pressure decreases with altitude.
Barometers became essential tools for sailors, farmers, and scientists to predict changes in weather.
The concept of air pressure became central to the study of gases, leading to discoveries like Boyle’s Law and advances in thermodynamics.
Today, modern aneroid barometers, digital pressure sensors, and weather satellites all trace their origins back to Torricelli’s mercury tube.
Torricelli’s Legacy
Beyond the barometer, Torricelli made significant contributions:
Developed Torricelli’s theorem in fluid dynamics.
Worked on problems of motion and geometry.
Inspired generations of scientists to explore the physical properties of air and fluids.
In his honor, the unit of pressure “torr” (1 torr = 1 mmHg) was named after him.
Conclusion
The invention of the barometer by Evangelista Torricelli in 1643 was a turning point in science. It transformed the invisible weight of the atmosphere into something measurable, challenged ancient beliefs about vacuums, and laid the groundwork for modern weather forecasting and the science of gases.
Torricelli’s elegant experiment — a glass tube, some mercury, and curiosity — changed the way humanity understands the air we breathe and its invisible power.