The Right Chemistry: What a classic painting tells us about vacuums — and science



Why Joseph Wright’s An Experiment on a Bird in the Air Pump continues to resonate.

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Will the bird live or die? That is the question we are left pondering when contemplating Joseph Wright’s marvellous 1768 painting titled An Experiment on a Bird in the Air Pump. The canvas on display in the National Gallery of London depicts a “natural philosopher,” as scientists were called in those days, cranking a vacuum pump to remove the air from a glass bulb in which a cockatiel is struggling to breathe as onlookers express a range of emotions, from curiosity to horror. The demonstrator’s hand hovers above a valve at the top of the glass globe. Is he about to open the valve and allow the bird to survive, having made the point that air is necessary for life? Or is he ready to ensure that the valve is closed so that the experiment can come to its deadly conclusion?

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The subject of the painting has a fascinating history that traces back to Evangelista Torricelli’s classic 1643 experiment in which he filled a metre-long tube sealed at one end with mercury. With his finger over the open end he then inverted the tube and set it vertically into a basin of mercury. The column of mercury in the tube fell until it measured 76 centimetres in height. The space above the mercury now contained nothing, the first recorded case of a permanent vacuum! Torricelli’s explanation was that we live in a “sea of air” that exerts a downward pressure the same way that water exerts pressure on a submerged object. The reason the mercury did not fall all the way down in the tube was because air was exerting a pressure on the pool of mercury in which the tube had been immersed. Torricelli, who was a pupil of Galileo, had invented the barometer, a device that measures air pressure.

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Torricelli’s experiment inspired Otto von Guericke, mayor of the German town Magdenburg, to create a device capable of producing a vacuum whenever desired. He managed to design the world’s first vacuum pump, consisting of a piston in a cylinder equipped with one-way flap valves. A hand crank allowed the piston to move down and suck air out of a container to which the pump was attached. Think of the way a syringe can be used to produce suction.

To demonstrate his pump, von Guericke devised a pair of “Magdeburg hemispheres” that when fitted together formed a sphere about half a metre in diameter. Connecting a valve on one of the hemispheres to the pump allowed the air to be removed from inside the globe. Then came von Guericke’s historic public display. In 1654, in front of a crowd that included Emperor Ferdinand III, two teams of 15 horses each were attached to the sphere and were unable to pull the hemispheres apart until the valve was opened allowing air to rush in.

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Robert Boyle, with his view that matter was composed of elements that cannot be resolved into simpler substances, is regarded as one of the founders of modern chemistry. He was also a champion of arriving at conclusions based not on philosophy but experimentation. Boyle learned about von Guericke’s vacuum pump and with the help of Robert Hooke constructed an improved version that allowed for experiments resulting in the formulation of Boyle’s Law, stating that the volume of a gas is inversely proportional to its pressure, now drilled into the brains of high school students.

Boyle tested the effects of “rarified air” on various phenomena including sound, combustion and magnetism. Then in a famous experiment, described in his 1660 book, Boyle placed mice, snails, flies and birds in a glass globe that he then evacuated and demonstrated that air was necessary for life. He describes placing a lark in the chamber and watching as “the bird threw herself over two or three times, and died with her breast upward, her head downwards and her neck awry. This is precisely the experiment depicted in the Wright painting, replete with an accurate portrayal of Boyle’s pump.

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In the 18th century, science was emerging out of the darkness as the age of “enlightenment” unfolded and itinerant lecturers, more entertainers than scientists, performed experiments in front of paying audiences or in the homes of the wealthy. Wright’s portrayal of the bird experiment affords a glimpse into the public’s attitude toward science at the time and has relevance to today’s controversies. Two girls are being urged, likely by their father, to pay attention to the experiment but appear to be reviled. An inquisitive boy looks on with curious anticipation of the outcome, a man with an obvious inclination toward science is timing the experiment, another is lost in thought, possibly contemplating the ethics involved. A young couple seem to have eyes only for each other, totally disinterested in the plight of the bird.

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If we substitute “climate change,” “endocrine disruptors” or “the COVID situation” for the bird, the painting can be seen to represent current views on scientific controversies. Some “onlookers” are focused on evidence, some prefer to ignore it, some are unsure of what is going on and some live in ignorant bliss.

A boy in the painting holds a rope that seems to be swung over a beam to enable the empty birdcage to be raised or lowered. Is he moving it out of the way because a dead bird will no longer need it? Or is he lowering it to house the bird that will be allowed to live? The “philosopher” appears to be looking out of the picture, straight at us, as if imploring us to think about all the aspects of the situation. A wonderful, timeless painting. And if you look carefully, you will note a clever nod to von Guericke with a pair of Magdenburg hemispheres sitting in the shadows.

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Joe Schwarcz is director of McGill University’s Office for Science & Society ( He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m.

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