The history
From Archimedes' floating bodies to the brakes in every car, how people learned that a push on a trapped fluid goes everywhere.
Archimedes and Stevin showed how water presses on what it touches, and Torricelli showed that air presses too. In the 1650s the young Blaise Pascal put it in one rule: pressure on a trapped fluid spreads equally everywhere, so a small piston can move a big one. It took a London locksmith, a Newcastle lawyer and a California brake maker to turn that rule into the machines that lift, press and stop the modern world.
1586
Hydrostatic paradox explained
Simon Stevin, Leiden
1648
Air pressure shown to fall with height
Florin Périer for Blaise Pascal, Puy de Dôme
c. 1654
Principle of equal transmission stated
Blaise Pascal (printed 1663)
1733
Blood pressure measured
Stephen Hales, England
1795
Hydraulic press patented
Joseph Bramah, London
1921
Production car with four-wheel hydraulic brakes
Duesenberg Model A, USA
1971
Pascal adopted as the SI unit of pressure
14th CGPM
250 BCE – 1586
Archimedes explains floating, and Stevin finds that water's push on a vessel's floor depends only on its depth.
250 BCE
c. 250 BC
In his book On Floating Bodies, Archimedes worked out that a body in water is pushed up by a force equal to the weight of the water it pushes aside. He treated water as something that presses on whatever is in it.
Why it mattered. It was the first mathematical treatment of fluids at rest, the starting point for everything Pascal later did.
1586
In De Beghinselen des Waterwichts (The Elements of Hydrostatics), Stevin showed that the force of water on the bottom of a vessel depends only on its depth and the area of the bottom, not on the vessel's shape or how much water it holds. He explained it by imagining parts of the water frozen solid without changing anything.
Why it mattered. It is the surprise behind Pascal's barrel and the first clear statement that pressure depends on depth alone.
1643 – 1663
Torricelli's mercury tube, Pascal's experiments in Rouen, a barometer carried up a volcano, and the treatise that states the principle.
1643
1643 (reported 1644)
Torricelli filled a glass tube with mercury and turned it upside down in a bowl. The mercury fell to about 76 cm and stopped. He argued that the weight of the air outside, pressing on the bowl, was holding the column up.
Why it mattered. It turned air into a fluid with weight and pressure, and sent Pascal off on his own experiments.
1647
1647 (licence to print, 8 October)
Having heard of Torricelli's tube, the young Pascal repeated and extended it in Rouen with tubes, syringes, bellows and siphons of many shapes, filled with mercury, water, wine and oil. He published the results as Expériences nouvelles touchant le vide.
Why it mattered. Pascal learned to treat every liquid, and air, by the same rules, the groundwork for his principle.
1648
19 September 1648
At Pascal's request his brother-in-law measured the mercury column at the foot and the top of the Puy de Dôme, about 1 km higher. At the summit it stood about 3 French inches (roughly 8.5 cm) lower, and he repeated it several times before witnesses.
Why it mattered. It proved that the air's pressure comes from the weight of the air above, the same rule as depth in water.
1654
c. 1651–1654 (printed 1663)
In his Traité de l'équilibre des liqueurs, Pascal stated that pressure applied to a liquid in a closed vessel is passed on equally in all directions. He described a vessel with two openings, one a hundred times bigger than the other: one man pushing the small piston could hold back a hundred pushing the big one. The treatise was printed in 1663, a year after his death.
Why it mattered. This is Pascal's principle, and his idea is exactly the hydraulic press, brake and jack.
1733 – 1896
Blood is measured as a column of liquid, Bramah builds the hydraulic press, and piped water pressure lifts cranes, lifts and Tower Bridge.
1733
1733 (published)
Hales, a clergyman and scientist, connected a long glass tube to an artery in a horse's neck. The blood rose about 8 to 9 feet and rose and fell with each heartbeat. He had measured blood pressure as a height of liquid, ρ g h.
Why it mattered. It was the first measurement of blood pressure, and it showed the pulse as a pressure wave.
1795
Bramah, a locksmith and inventor of an improved flush toilet, patented a press with a small pump piston and a large ram joined by water. It put Pascal's idea to work, pressing cloth, paper and metal with enormous force.
Why it mattered. It turned Pascal's principle from a thought experiment into a factory machine.
1797
c. 1797 (attributed)
Bramah's press leaked where the ram slid through its cylinder. His young workman Maudslay is credited with a cupped leather collar that the water pressure itself pressed tighter against the ram.
Why it mattered. Without good seals no hydraulic machine can hold high pressure; the same idea is in every brake calliper.
1846
1845–1846
Armstrong, then a lawyer, persuaded Newcastle to let him drive a quayside crane with the pressure of the new water mains. It worked so well that more followed, and he gave up law to build hydraulic cranes, sold around the world.
Why it mattered. It showed that pressure piped from far away could do heavy work, a network of force.
1883
September 1883
A company began pumping water at about 800 psi (55 bar) through cast-iron mains under London's streets. Customers used it to run lifts, cranes, dock gates and even theatre stages.
Why it mattered. Pascal's principle carried the pressure, and so the power, through miles of pipe.
1894
30 June 1894
Tower Bridge opened with its two bascules, each weighing over 1,000 tonnes, raised by hydraulic engines. Steam pumps charged six accumulators with water at about 750 psi, and the stored pressure drove the machinery. The water system worked until 1974, when oil and electric motors replaced it.
Why it mattered. A landmark still moved by the principle that moves a car's brakes.
1896
Riva-Rocci wrapped an inflatable band round the upper arm and read its pressure on a mercury column. The cuff's pressure passes through the arm to the artery; when the pulse at the wrist vanished, the cuff matched the peak pressure.
Why it mattered. It made measuring blood pressure safe and simple, without cutting into an artery.
1905 – 1979
Hydraulic brakes reach cars and motorcycles, oil rams build the modern digger, and pressure gets its own unit: the pascal.
1905
Korotkov, a military surgeon, listened with a stethoscope below the cuff while letting it down. Taps start at the systolic pressure and stop at the diastolic. His report was only 281 words long.
Why it mattered. It is still how doctors take blood pressure by hand.
1917
Loughead patented car brakes worked by fluid in pipes, so that the force reached each wheel equally. Duesenberg's Model A of 1921 became the first production car with hydraulic brakes on all four wheels.
Why it mattered. Today almost every car's brakes are hydraulic, and every one relies on Pascal's principle.
1948
The Bruneri brothers built an excavator whose arm and bucket were moved by oil-filled rams. In 1954 they sold the rights to the French firm SICAM, whose Yumbo diggers spread the idea.
Why it mattered. Hydraulic rams replaced cables and made the modern excavator, loader and backhoe.
1965
Fisher patented a ballpoint refill sealed with nitrogen at about 35 psi behind the ink. The gas pushes on the ink from behind, so the pen writes upside down, underwater or in space; NASA astronauts used it from 1968.
Why it mattered. Gas pressure pressing evenly on a liquid, Pascal's idea in a pocket.
1969
The Honda CB750 was the first mass-produced motorcycle with a hydraulic front disc brake as standard, a single-piston calliper squeezing a solid disc.
Why it mattered. Hydraulic discs soon became normal on motorcycles, and later on bicycles.
1979
The British firm JCB formed a joint venture with Escorts to make hydraulic backhoe loaders in India. The machines became so common that many Indians call any digger a “JCB”, whatever its maker.
Why it mattered. Hydraulic machines built India's roads and buildings, and gave the language a new word.
Did you know?
Pascal's barrel, a thin tube bursting a barrel, is told about Pascal in many textbooks, but it isn't in his own writings and may never have been done by him.
Pascal was only 23 when he began his experiments on fluids in Rouen, and he also built one of the first mechanical calculators.
Every 10 metres of water adds about one atmosphere of pressure, so a diver at 30 m feels about four atmospheres in all.
London's hydraulic power network ran from 1883 until 1977, and its pipes were later reused to carry cables.
In India, many people call any backhoe digger a “JCB”, after the British maker.
The people
1623 – 1662 · Mathematician, physicist and writer · France
Stated that pressure on a confined fluid spreads equally everywhere, and imagined the hydraulic press.
1548 – 1620 · Engineer and mathematician · Flanders (Dutch Republic)
Showed that a liquid's push on a floor depends only on depth, the hydrostatic paradox.
1608 – 1647 · Physicist and mathematician · Italy
Made the mercury barometer and showed that air has weight.
1605 – 1672 · Magistrate, Pascal's brother-in-law · France
Carried the barometer up the Puy de Dôme in 1648.
1748 – 1814 · Locksmith and inventor · England
Patented the hydraulic press in 1795.
1810 – 1900 · Lawyer turned engineer · England
Built hydraulic cranes run on water-main pressure, and later Tower Bridge's machinery.
1887 – 1958 · Engineer · United States
Patented hydraulic car brakes in 1917.
Where it happened
Sources
Dates marked “c.” are approximate, and historians sometimes disagree about who was first. If you spot a mistake, tell us.
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