Experiment #118 · Scientific experiment

Torricelli's Barometer

The vacuum is real; air has weight

Evangelista Torricelli · 1644 · Physics, meteorology

First published: Letter from Torricelli to Michelangelo Ricci (1644); reported in subsequent correspondence.

Invert a sealed tube of mercury in a basin of mercury. The mercury falls until it stands at about 76 cm — supported by the weight of the atmosphere.

Torricelli filled a closed-end glass tube with mercury, inverted it into a basin of mercury, and observed that the mercury fell to a height of about 76 cm above the basin level, leaving a vacuum above. The Aristotelian doctrine "nature abhors a vacuum" was thereby falsified, and the column height was explained by atmospheric pressure supporting it from outside. The experiment established the existence of vacuum, the weight of air, and the first practical barometer. Pascal's Puy de Dôme experiment (1648) confirmed atmospheric pressure decreases with altitude. The result reshaped pneumatics and was the empirical foundation for the gas laws and the engineering of steam engines.

Formulation

Long sealed tube filled with mercury, inverted into mercury basin. Predicted (Aristotelian): no vacuum forms; mercury stays. Observed: mercury falls to ~76 cm, vacuum forms above. Explanation: atmospheric pressure on basin balances mercury column; pressure ≈ ρgh.

Compare this experiment

Dimensions Engaged

◉

Matter

Air has weight; matter (atmosphere) exerts pressure that supports the mercury column.

✦

Space

A genuine vacuum exists above the mercury — empty space is physically realisable.

⚡

Energy

Bears on Energy · Dispersibility through the pressure relationship.

Responses — How Schools Engage

Affirms / takes the bait 4

Naturalism

A model demonstration: a long-standing theoretical doctrine ("horror vacui") is falsified by a clean experiment, and a new quantitative concept (atmospheric pressure) is introduced.

Realism

Vacuum is real; air has weight. The experiment opens the empirical investigation of gases.

Empiricism

A canonical empirical refutation: Aristotelian doctrine cannot survive direct observation. Methodological model.

Logical Positivism

Operationally clean: a quantitative measurement (76 cm column) directly refutes the qualitative Aristotelian doctrine.

Reframes the question 2

Catholic/Thomistic

Forces a theological accommodation: the Aristotelian "horror vacui" was integrated into scholastic natural philosophy. The vacuum's realisation requires re-reading the metaphysics.

Relationalism

The vacuum above the mercury is "empty" of matter but not metaphysically inert; later physics (electromagnetism, QFT) fills it back in. Strict Leibnizian relationalism is in tension with active vacuum.