StormDebris:
The History of Meteorology
Evangelista Torricelli’s Barometer and the Discovery of Atmospheric Pressure
Date: 1643 (experiment conducted; published posthumously in correspondence)
Location: Florence, Grand Duchy of Tuscany
Type: Experimental physics / natural philosophy
Author: Evangelista Torricelli
Why it matters: First clear demonstration that air has weight and exerts pressure
Timeline placement: The Instrumental Turn
Evangelista Torricelli’s barometer experiment of 1643 marked a quiet but irreversible shift in how the atmosphere was understood. For the first time, air was not treated as an invisible medium of weather alone, but as something that could exert measurable force.
Working in the intellectual wake of Galileo Galilei, Torricelli replaced older qualitative explanations of “heaviness of air” with a physical demonstration: a column of liquid could be held up not by nature’s reluctance to form a vacuum, but by the pressure of the surrounding atmosphere itself.
The apparatus he devised was simple in appearance: a glass tube, mercury, and an inverted basin. Yet it opened a conceptual door that would reshape meteorology, physics, and eventually engineering. Atmospheric pressure became not just an idea, but a measurable quantity.
Historical Context
By the early seventeenth century, European natural philosophy was undergoing a slow structural fracture. Aristotelian explanations of nature, still dominant in universities, were being challenged by a growing experimental tradition centered in Italy, England, and the Low Countries.
Galileo Galilei’s work on motion and mechanics had already shifted attention toward measurable quantities and mathematical description. His influence extended beyond astronomy and mechanics into the broader idea that nature could be interrogated through controlled experiments rather than purely philosophical reasoning.
Evangelista Torricelli, Galileo’s former student and intellectual successor, inherited both this mathematical sensibility and a practical problem: how to explain why suction pumps could lift water only to a limited height. Engineers and well diggers had long observed this limit, but explanations varied. Many still invoked the Aristotelian idea that nature “abhors a vacuum,” a concept that functioned more as philosophical principle than mechanical account.
According to historians of science such as Steven Shapin, this period was not a sudden “break” with Aristotelian thought but a gradual reconfiguration of what counted as explanation. Observation, experiment, and quantification began to gain authority alongside inherited philosophical systems.
It is within this transitional landscape that Torricelli’s barometer experiment emerged: not as a single isolated breakthrough, but as part of a broader rethinking of air, space, and physical causation.
This portrait, painted by Florentine artist Lorenzo Lippi, depicts Evangelista Torricelli, the mathematician and physicist best known for inventing the barometer. Created around 1647, shortly after Torricelli’s landmark experiments with mercury and atmospheric pressure, the painting captures him during a period when his work was reshaping ideas about air, vacuum, and the physical behavior of the atmosphere. It remains one of the most widely reproduced early likenesses of Torricelli and reflects the growing status of experimental science in seventeenth-century Italy.
The core of Torricelli’s insight was deceptively simple. He filled a long glass tube with mercury, sealed at one end, and inverted it into a dish also containing mercury. When the tube was turned upright, the mercury column did not drain completely. Instead, it settled at a stable height, leaving an empty space above it.
This space, later called the “Torricellian vacuum,” became the key point of disagreement. If nature could not support a vacuum, then this empty region should not have formed. Yet it did.
Torricelli proposed a different explanation: the column of mercury was not suspended by avoidance of emptiness, but by the weight of the air pressing down on the surface of the mercury in the dish. The atmosphere, though invisible, had measurable weight and could support a column of liquid against gravity.
This interpretation is preserved in correspondence circulated after his death. According to Torricelli’s writings as later reported by Vincenzo Viviani, the experiment demonstrated that “we live submerged at the bottom of an ocean of air.”
The height of the mercury column, approximately 760 millimeters at sea level, became a physical measure of atmospheric pressure. Variations in this height corresponded to changes in weather conditions, linking atmospheric pressure directly to meteorological behavior.
The device itself evolved into what we now call the barometer: a tool that translates invisible pressure into a visible, measurable column.
Torricelli’s conclusion was not immediately universally accepted. The idea of vacuum had long been philosophically contentious.
René Descartes rejected the possibility of empty space altogether, proposing instead that space must always be filled with subtle matter. In this framework, the space above the mercury column was not truly empty but filled with imperceptible fluid.
Other thinkers attempted hybrid explanations, retaining aspects of Aristotelian “natural place” theory while incorporating mechanical pressure.
What made Torricelli’s interpretation distinctive was its willingness to treat air as a physical substance with weight and variability, rather than a passive medium or philosophical abstraction.
According to historian John Heilbron, the barometer experiment helped shift air from the background of physics into a measurable participant in it. The atmosphere ceased to be merely the stage of weather and became an active agent in physical processes.
What It Proposed
This 19th-century mercury barometer, crafted by the instrument maker Charles Frodsham, represents the mature phase of Torricelli’s invention, when atmospheric pressure measurement had become both a scientific tool and a domestic object. Housed in a mahogany case with glass and metal fittings, the instrument contains a sealed column of mercury that rises and falls in response to changes in air pressure. Barometers of this type were widely used in Britain for both meteorological observation and weather prediction, translating the invisible weight of the atmosphere into a readable scale marked in inches of mercury.
Strengths and Insights
The most significant contribution of Torricelli’s work was conceptual compression: a complex set of phenomena reduced to a single measurable principle.
Atmospheric behavior, previously described through qualitative notions like “thin air” or “vapors rising,” could now be related to pressure differences. Weather variation, altitude effects, and suction limits all found a shared explanatory root.
The experiment also introduced a new epistemic standard: reproducibility through apparatus. Unlike observational accounts of storms or winds, the barometer could be constructed and tested anywhere with similar results, provided conditions were comparable.
As Paolo Galluzzi has noted in studies of Galilean science, this period marks the emergence of instrumentation as a form of argument. The device does not merely illustrate theory; it becomes part of the proof itself.
Finally, the barometer linked meteorology to physics in a durable way. Atmospheric phenomena were no longer isolated events but expressions of a continuous pressure system surrounding the Earth.
Limitations and Errors
Despite its revolutionary implications, Torricelli’s interpretation was not fully developed in modern physical terms.
The concept of atmospheric pressure was correctly identified, but the kinetic theory of gases lay far in the future. Air was understood as a continuous fluid rather than a collection of particles in motion.
Early interpretations also struggled with spatial variation. While Torricelli’s system accounted for altitude differences in pressure, it did not yet describe large-scale atmospheric circulation or thermodynamic gradients.
Additionally, the explanation of the Torricellian vacuum remained philosophically contested. Even among supporters of the experiment, the nature of “empty space” was not clearly resolved. Some accepted vacuum as real; others treated it as rarefied matter below detectability.
Instrumentation itself also introduced constraints. Mercury barometers are sensitive, but not yet capable of capturing rapid atmospheric fluctuations or fine-grained spatial variation. The atmosphere was measurable, but only at specific points and moments.
These limitations reflect not failure, but the early stage of a measurement-driven science still learning how to interpret its own tools.
Historical Impact
The barometer rapidly became one of the defining instruments of early modern science.
By the late seventeenth century, it had been adopted across Europe for both experimental and practical use. Weather prediction, while still rudimentary, began to incorporate pressure readings as indicators of changing conditions.
Blaise Pascal’s later experiments extended Torricelli’s findings by demonstrating that atmospheric pressure decreases with altitude, famously using measurements on the Puy de Dôme in 1648. This helped confirm that the atmosphere is finite and physically structured.
Over time, the barometer became central to meteorology. It allowed weather to be described not only in terms of visible phenomena but also in terms of underlying physical states.
According to John Heilbron, the invention of the barometer is one of the key moments in which invisible physical quantities became scientifically real through measurement.
Its legacy extends beyond meteorology into aviation, engineering, and climate science, where atmospheric pressure remains a foundational variable.
Related Pages
Timeline
This development belongs to the period when instruments reshaped atmospheric study.
Themes
The barometer contributes to the measurement and quantification of atmospheric variables.
Later Developments
Later transformations in meteorology emerged in response to the creation of measurement instruments.
Sources & Notes
Primary Sources
Torricelli, Evangelista. Letter to Michelangelo Ricci (1644). https://web.lemoyne.edu/giunta/torr.html
Secondary Sources
Heilbron, J. L. The Sun in the Church: Cathedrals as Solar Observatories. Harvard University Press, 1999. Accessed via Harvard University Press.
Shapin, Steven. The Scientific Revolution. University of Chicago Press, 1996. Accessed via University of Chicago.
Galluzzi, Paolo. Studies on Galileo and the experimental tradition. Accessed via Galilean scholarship archives.
Uffizi Gallery / Museo Galileo. “Evangelista Torricelli and the Barometer.” Accessed via Museo Galileo.
Notes
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The “Torricellian vacuum” was interpreted differently across seventeenth-century Europe; acceptance of vacuum varied significantly between Cartesian and experimental traditions.
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Mercury was used due to its high density, which allowed manageable column heights compared to water.
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The modern unit “millimeters of mercury (mmHg)” directly descends from Torricelli’s original experimental configuration.
Revision Note
Last reviewed: April 2026