The history
From a pump that would not lift water past ten metres to a steel ball on the floor of the deepest sea: 400 years of learning that air and water push.
For two thousand years people said that nature hates empty space, and that this is what makes pumps suck. In the 1640s Torricelli and Pascal showed the real answer: we live at the bottom of a sea of air that presses on everything. Scientists then learned to pump air out, squeeze it, trap steam and measure all of it with dials and cuffs. Today one idea, force divided by area, explains weather maps, pressure cookers, blood pressure, aircraft cabins and the crushing deep ocean, and its unit carries Pascal's name.
1586
Liquid pressure depends only on depth
Simon Stevin, Leiden
1643
Mercury barometer and a made vacuum
Evangelista Torricelli, Florence
1648
Air pressure shown to fall with height
Florin Périer for Blaise Pascal, Puy de Dôme
c. 1650
Air pump
Otto von Guericke, Magdeburg
1662
Law linking gas pressure and volume
Robert Boyle, Oxford
1679
Safety valve on a pressure vessel
Denis Papin, London
1896
Easy-to-use blood pressure cuff
Scipione Riva-Rocci, Turin
1960
Crewed dive to the Challenger Deep
Jacques Piccard and Don Walsh, Trieste
1580 – 1640
Stevin works out how water presses on a vessel, and Galileo puzzles over why pumps stop at about ten metres.
1586
In his book on the weight of water, De Beghinselen des Waterwichts, Stevin showed that the push of water on the bottom of a vessel depends only on how deep the water is. The shape of the vessel and the amount of water do not matter. A thin tall tube can press on its base as hard as a wide tank of the same height.
Why it mattered. It was the first clear statement that liquid pressure depends on depth.
1638
In Two New Sciences, Galileo tells of a workman who said no suction pump could lift water more than eighteen cubits, about ten metres. Galileo believed the old idea from Aristotle that nature abhors a vacuum, and guessed that the water column simply broke under its own weight. His explanation was wrong, but the puzzle was real.
Why it mattered. The ten-metre limit set Galileo's pupils hunting for the true cause.
1640 – 1690
Torricelli's mercury tube, Pascal's mountain, Guericke's horses, Boyle's pump and law, and Papin's steam digester.
1643
1643 (some say 1644)
Torricelli filled a glass tube with mercury and turned it upside down in a dish. The mercury dropped until the column was about 76 cm tall, leaving empty space above it. His young colleague Viviani most likely did the actual experiment, under Torricelli's guidance. Torricelli wrote that we live at the bottom of an ocean of air, whose weight holds up the mercury.
Why it mattered. It was the first barometer, and the first vacuum made on purpose.
1648
19 September 1648
Pascal was too ill to climb, so his brother-in-law Florin Périer carried a mercury tube up the Puy de Dôme volcano. At the foot the column stood at 26 inches 3½ lines; at the top it was 23 inches 2 lines, about 3 inches lower. Less air above means less weight pressing down.
Why it mattered. It proved that the air has weight and that air pressure falls as you go up.
1654
8 May 1654 · Magdeburg c. 1656
Around 1650 Guericke, mayor of Magdeburg, built the first air pump. At Regensburg in 1654 he pumped the air out of two copper half-spheres about 50 cm across, and two teams of horses could not pull them apart. He repeated the show with sixteen horses in Magdeburg around 1656, and in Berlin in 1663. The air outside was pressing the halves together with a force of roughly 20,000 newtons.
Why it mattered. It showed, loudly and in public, how strong ordinary air pressure is.
1659
1659 (published 1660)
Boyle's assistant Robert Hooke built a better air pump with a glass globe, so people could watch what happened inside. With it Boyle found that sound fades in a vacuum, flames go out and a mercury barometer sinks as the air is removed. He wrote it up in New Experiments Physico-Mechanicall, Touching the Spring of the Air in 1660.
Why it mattered. It turned the vacuum into a place for careful, repeatable experiments.
1662
Boyle trapped air in the short end of a J-shaped tube and poured mercury into the long end. Doubling the pressure halved the volume of the air, so pressure times volume stayed the same. Richard Towneley and Henry Power had noticed it too, and Edme Mariotte found it again in France in 1679.
Why it mattered. It was the first law linking the pressure of a gas to its volume.
1679
Papin showed the Royal Society a sealed iron pot that trapped steam, raising the pressure and the boiling point of the water inside. It could soften bones in a few hours. To stop it bursting he added a safety valve: a weighted lever that lets steam out when the pressure gets too high.
Why it mattered. It was the ancestor of every pressure cooker and every safety valve.
1840 – 1940
Pressure gets measured everywhere: aneroid barometers, Bourdon gauges, weather networks, tyres and blood pressure cuffs.
1844
Vidi sealed a thin, springy metal box with most of the air removed. As air pressure rises and falls the box squeezes and swells a tiny amount, and levers turn that into a needle on a dial. It was small, safe and easy to carry, unlike a long glass tube of mercury.
Why it mattered. It put barometers in homes and ships, and later became the aircraft altimeter.
1849
Bourdon patented a gauge built around a curled, flattened metal tube. When the pressure inside rises, the tube tries to straighten, and that small movement swings a pointer. Edward Ashcroft bought the American rights in 1852. The same design still sits on boilers, gas cylinders and tyre pumps.
Why it mattered. It made high pressures easy to read at a glance, which made steam power safer.
1875
15 January 1875
After a cyclone struck Calcutta in 1864 and monsoon failures caused famines in 1866 and 1873, the government set up one weather service for the whole country. Barometer readings from stations across India could now be collected and compared. Falling pressure in one place helps forecasters spot storms and follow the monsoon.
Why it mattered. Pressure readings became a tool for warning millions of people about cyclones.
1888
1887 · patent 7 December 1888
Dunlop, a vet, wrapped an inflated rubber tube around the wheels of his son's tricycle for a smoother ride. His patent later turned out to be invalid, because Robert William Thomson had patented a pneumatic tyre in 1847. Dunlop's tyre still took over bicycles and then cars.
Why it mattered. Air pressure became the thing that holds up bicycles, cars and aircraft on the ground.
1896
Riva-Rocci wrapped an inflatable cuff around the upper arm, pumped it up and read the pressure on a mercury column. When the cuff pressed harder than the heart's push, the pulse at the wrist vanished. He built it from simple parts, including bicycle inner tube, and refused to patent it.
Why it mattered. Measuring blood pressure became quick, cheap and routine for every doctor.
1905
8 November 1905
Korotkoff, a young army surgeon, put a stethoscope below the cuff and let the pressure out slowly. Tapping sounds start when blood first squeezes through and stop when the artery is fully open. His report was less than a page long.
Why it mattered. It gave us the two numbers, like 120 over 80, that doctors still write down.
1909
c. 1909 (attributed)
Weather scientists needed a handy unit for air pressure, and Bjerknes is credited with the bar: 100,000 newtons per square metre, close to the air pressure at sea level. Weather maps were drawn in millibars for most of the twentieth century. Today forecasters use hectopascals, which are exactly the same size.
Why it mattered. It gave air pressure a round number, and it is why tyres are still pumped in bar.
1938 – today
Pressurised airliners, Indian pressure cookers, dives to the Challenger Deep and a unit named after Pascal.
1938
first flight 31 December 1938 · service 1940
High up, the air is too thin to breathe comfortably. The Stratoliner pumped extra air into a sealed cabin, so at 16,000 feet the passengers felt as if they were at 8,000 feet. It entered airline service in 1940, flying above much of the bad weather.
Why it mattered. Pressurised cabins made high, smooth, long-distance flying normal.
1959
H. D. Vasudeva started the company at 54, with Rs 20,000, in technical partnership with L. G. Hawkins of England. Its cookers trap steam so water boils at about 120 °C, and dal and rice cook much faster. The firm was renamed Hawkins Cookers Ltd in 1986 and says it has sold more than 140 million cookers and pans.
Why it mattered. Papin's digester became the whistle heard in kitchens across India.
1960
23 January 1960
The bathyscaphe Trieste sank for nearly five hours to the deepest point in the ocean, measured then at about 10,900 m. Down there the water presses with roughly 1,086 bar, over a thousand times the air pressure at the surface. A window pane cracked on the way down, but the two men spent twenty minutes on the bottom.
Why it mattered. Humans reached the place of greatest pressure in any ocean on Earth.
1971
The world's measurement conference gave the unit of pressure, one newton per square metre, a name of its own: the pascal. One pascal is tiny, about the pressure of a sheet of paper lying flat on a table. Air at sea level presses with about 101,325 pascals.
Why it mattered. P = F ÷ A got one worldwide unit, honouring the man who sent a barometer up a mountain.
2012
26 March 2012
Film-maker James Cameron piloted Deepsea Challenger alone to about 10,908 m. Its steel pilot sphere had been tested to 114 megapascals before the dive. He spent about three hours on the sea floor, the first crewed visit since Trieste 52 years earlier.
Why it mattered. It showed that careful engineering can make the deepest pressure survivable again.
Did you know?
The famous story of Pascal's barrel, where a tall thin tube of water bursts a wooden barrel, is almost certainly made up. The physics is right, though: only the height of the water matters.
Air presses on every square metre of you with about 101,000 newtons, roughly the weight of ten tonnes. You are not crushed because the fluids inside your body push back just as hard.
Mercury is about 13.6 times denser than water, which is why a mercury barometer is about 76 cm tall while a water barometer would need about 10 m.
A pressure cooker at about 1 bar above the air outside boils water at roughly 120 °C instead of 100 °C, so food cooks much faster. High in the hills, where air pressure is lower, water boils below 100 °C.
At the bottom of the Challenger Deep the water presses with over a thousand times the pressure of the air at sea level: about the weight of a tonne on every square centimetre.
Blood pressure is still written in millimetres of mercury, like 120/80 mmHg, a leftover from Torricelli's tube and Riva-Rocci's mercury column.
The torr, named after Torricelli, is the pressure that holds up about 1 mm of mercury. Standard air pressure is 760 torr.
Weather maps join places of equal air pressure with lines called isobars. Tightly packed isobars mean strong winds.
The people
1548 – 1620 · Engineer and mathematician · Flanders (now Belgium), worked in the Netherlands
Showed that water's push on a base depends only on its depth.
1608 – 1647 · Physicist and mathematician · Italy
Made the first mercury barometer; the torr is named after him.
1623 – 1662 · Mathematician, physicist and writer · France
Planned the Puy de Dôme test and studied how liquids pass on pressure; the SI unit bears his name.
1602 – 1686 · Scientist and mayor of Magdeburg · Germany
Built the first air pump and pitted horses against air pressure.
1627 – 1691 · Natural philosopher and chemist · Ireland, worked in England
Found that squeezing a gas raises its pressure in step.
1647 – c. 1713 · Physicist and inventor · France, worked in England and Germany
Invented the steam digester and its safety valve.
1863 – 1937 · Physician · Italy
Made the arm-cuff blood pressure meter and gave it away unpatented.
1874 – 1920 · Surgeon · Russia
Found the sounds that let doctors read both blood pressure numbers.
c. 1905 – 1993 · Entrepreneur · India
Founded the company behind Hawkins pressure cookers in 1959.
Where it happened
Sources
Dates marked “c.” are approximate, and historians sometimes disagree about who was first. If you spot a mistake, tell us.
↑↓ move↵ open/ or ⌘K search anywhere