The painting depicts a natural philosopher, a forerunner of the modern scientist, recreating one of Robert Boyle's air pump experiments, in which a bird is deprived of oxygen, before a varied group of onlookers. The group exhibits a variety of reactions, but for most of the audience scientific curiosity overcomes concern for the bird. The central figure looks out of the picture as if inviting the viewer's participation in the outcome.
In 1659, Robert Boyle commissioned the construction of an air pump, then described as a "pneumatic engine", which is known today as a vacuum pump. The air pump was invented by Otto von Guericke in 1650, though its cost deterred most contemporary scientists from constructing the apparatus. Boyle, the son of the Earl of Cork, had no such concerns—after its construction, he donated the initial 1659 model to the Royal Society and had a further two redesigned machines built for his personal use. Aside from Boyle's three pumps, there were probably no more than four others in existence during the 1660s: Christian Huygens had one in The Hague, Henry Power may have had one at Halifax, and there may have been pumps at Christ's College, Cambridge and the Montmor Academy in Paris. Boyle's pump, which was largely designed to Boyle's specifications and constructed by Robert Hooke, was complicated, temperamental, and problematic to operate. Many demonstrations could only be performed with Hooke on hand, and Boyle frequently left critical public displays solely to Hooke—whose dramatic flair matched his technical skill.
Despite the operational and maintenance obstacles, construction of the pump enabled Boyle to conduct a great many experiments on the properties of air, which he later detailed in his New Experiments Physico-Mechanicall, Touching the Spring of the Air, and its Effects (Made, for the Most Part, in a New Pneumatical Engine). In the book, he described in great detail 43 experiments he conducted, on occasion assisted by Hooke, on the effect of air on various phenomena. Boyle tested the effects of "rarified" air on combustion, magnetism, sound, and barometers, and examined the effects of increased air pressure on various substances. He listed two experiments on living creatures: "Experiment 40," which tested the ability of insects to fly under reduced air pressure, and the dramatic "Experiment 41," which demonstrated the reliance of living creatures on air for their survival. In this attempt to discover something "about the account upon which Respiration is so necessary to the Animals, that Nature hath furnish'd with Lungs", Boyle conducted numerous trials during which he placed a large variety of different creatures, including birds, mice, eels, snails and flies, in the vessel of the pump and studied their reactions as the air was removed. Here, he describes an injured lark:
By the time Wright painted his picture in 1768, air pumps were a relatively commonplace scientific instrument, and itinerant "lecturers in natural philosophy"—usually more showmen than scientists—often performed the "animal in the air pump experiment" as the centrepiece of their public demonstration. James Ferguson, the Scottish astronomer and probable acquaintance of Joseph Wright—both were friends of John Whitehurst—noted that a "lungs-glass" with a small air-filled bladder inside was often used in place of the animal, as using a living creature was "too shocking to every spectator who has the least degree of humanity".
During his apprenticeship and early career Wright concentrated on portraiture. By 1762, he was an accomplished portrait artist, and his 1764 group portrait James Shuttleworth, his Wife and Daughter is acknowledged as his first true masterpiece. Benedict Nicholson suggests that Wright was influenced by the work of Thomas Frye; in particular by the 18 bust-length mezzotints which Frye completed just before his death in 1762. It was perhaps Frye's candlelight images that tempted Wright to experiment with subject pieces. Wright's first attempt, A Girl reading a Letter by candlelight with a Young Man looking over her shoulder from 1762 or 1763, is a trial in the genre, and is fetching though uncomplicated. Wright's An Experiment on a Bird in the Air Pump forms part of a series of candlelit nocturnes that he produced between 1765 and 1768.
The first of his candlelit masterpieces, Three Persons Viewing the Gladiator by Candlelight, was painted in 1765, and showed three men studying a model of the "Borghese Gladiator". The Gladiator was greatly admired; but his next painting, A Philosopher giving that Lecture on the Orrery, in which a Lamp is put in place of the Sun (normally known by the shortened form A Philosopher Giving a Lecture on the Orrery or just The Orrery), caused a greater stir, as it replaced the Classical subject at the centre of the scene with one of a scientific nature. Wright's depiction of the awe produced by scientific "miracles" marked a break with previous traditions in which the artistic depiction of such wonder was reserved for religious events, since to Wright the marvels of the technological age were as awe-inspiring as the subjects of the great religious paintings. An anonymous review from the time called Wright "a very great and uncommon genius in a peculiar way". The Orrery was painted without a commission, probably in the expectation that it would be bought by Washington Shirley, 5th Earl Ferrers, an amateur astronomer who had an orrery of his own, and with whom Wright's friend Peter Perez Burdett was staying while in Derbyshire. Figures thought to be Burdett and Ferrers feature in the painting, Burdett taking notes and Ferrers seated with his son next to the orrery. Ferrers purchased the painting for £210, but the 6th Earl auctioned it off, and it is now held by Derby Museum and Art Gallery.
To one side of the boy at the rear, the cockatoo's empty cage can be seen on the wall, and to further heighten the drama it is unclear whether the boy is lowering the cage on the pulley to allow the bird to be replaced after the experiment or hoisting the cage back up certain of its former occupant's death. It has also been suggested that he may be drawing the curtains to block out the light from the full moon. Jenny Uglow believes that the boy echoes the figure in the last print of William Hogarth's The Four Stages of Cruelty by pointing out the arrogance and potential cruelty of experimentation, while David Fraser also sees the compositional similarities with the audience grouped round a central demonstration. The neutral stance of the central character and the uncertain intentions of the boy with the cage were both later ideas: an early study, discovered on the back of a self-portrait, omits the boy and shows the natural philosopher reassuring the girls. In this sketch it is obvious that the bird will survive, and thus the composition lacks the power of the final version.
The cockatoo would have been rare at the time, as the bird did not become well-known until after it was shown in the illustrations of the voyages of Captain Cook in the 1770s. Prior to Cook's voyage, the birds had been imported in small numbers to decorate the houses of wealthy industrialists. Wright had painted a cockatoo in 1762 at the home of William Chase, featuring it both in his portrait of Chase and his wife (Mr & Mrs William Chase) and as a separate study, The Parrot. In selecting such a rare bird for this scientific sacrifice, Wright not only chose a more dramatic subject than the "lungs-glass", but was perhaps making a statement about the values of society in the Age of Enlightenment.
On the table are various other pieces of equipment that the natural philosopher would have used during his demonstration: a thermometer, candle snuffer and cork, and close to the man seated to the right is a pair of Magdeburg hemispheres, which would have been used with the air pump to demonstrate the difference in pressure exerted by the air and a vacuum: when the air was pumped out from between the two hemispheres they were impossible to pull apart. The air pump itself is rendered in exquisite detail, a faithful record of the designs in use at the time. What appears to be a human skull in the large liquid-filled glass bowl would not have been a normal piece of equipment; William Schupbach suggests that it and the candle, which is presumably lighting the bowl from behind, form a vanitas—the two symbols of mortality reflecting the cockatoo's struggle for life.
The powerful central light source creates a chiaroscuro effect. The light illuminating the scene has been described as "so brilliant it could only be the light of revelation". The single source of light is obscured behind the bowl on the table; some hint of a lamp glass can be seen around the side of the bowl, but David Hockney has suggested that the bowl itself may contain sulphur, giving a powerful single light source that a candle or oil lamp would not. In the earlier study a candle holder is visible, and the flame is reflected in the bowl. Hockney believes that many of the Old Masters used optical equipment to assist in their painting, and suggests that Wright may have used lenses to transfer the image to paper rather than painting directly from the scene, as he believes the pattern of shadows thrown by the lighting could have been too complicated for Wright to have captured so accurately without assistance.
Wright's Air Pump was unusual, in that it depicted archetypes rather than specific people, though various models for the figures have been suggested. The young lovers may have been based on Thomas Coltman and Mary Barlow, friends of Wright's, whom he later painted in Mr and Mrs Thomas Coltman after their marriage in 1769; Erasmus Darwin has been suggested as the man timing the experiment on the left of the table, and John Warltire, whom Darwin had invited to help with some air pump experiments in real life, as the natural philosopher; but Wright never identified any of the subjects or suggested they were based on real people. In The Orrery, all the subjects have been identified apart from the philosopher, who has physical similarities to Isaac Newton but differs enough to make positive identification impossible. Nicholson detects the strong influence of Frye throughout the picture. Particularly striking is the similarity between Frye's mezzotint Portrait of a Young Man of 1760–1761 and the figure of the boy with his head cocked staring intently at the bird. In 1977, Michael Wynne published one of Frye's chalk drawings from around 1760, An old man leaning on a staff, which is so similar to the observer in the right foreground in Wright's picture to make it impossible that Wright had not seen it. There are other hints of Frye's style in the painting: even the figure of the natural philosopher has touches of Frye's Figure with Candle. Though Henry Fuseli would later also develop on the style of Frye's work there is no evidence of him having painted anything similar until the early 1780s. So, although he had already been in England at the time the Air Pump was produced, it is unlikely that he was an influence on Wright.
Wright's scientific paintings adopted elements from the tradition of history painting but lacked the heroic central action typical of that genre. While ground-breaking, they are regarded as peculiar to Wright, whose unique style has been explained in many ways. Wright's provincial status and ties to the Lunar Society have been highlighted, as well as his close association with and sympathy for the advances made in the burgeoning Industrial Revolution. Other critics have emphasized a desire to capture a snapshot of the society of the day, in the tradition of William Hogarth but with a more neutral stance that lacks the biting satire of Hogarth's work.
The scientific subjects of Wright's paintings from this time were meant to appeal to the wealthy scientific circles in which he moved. While never a member himself, he had strong connections with the Lunar Society, a group of prominent industrialists, scientists and intellectuals who met regularly in Birmingham between 1765 and 1813: he was friends with members John Whitehurst and Erasmus Darwin, as well as Josiah Wedgwood, who later commissioned paintings from him. The inclusion of the moon in the painting was a nod to their monthly meetings, which were held when the moon was full. Like The Orrery, Wright apparently painted Air Pump without a commission, and the picture was purchased by Dr Benjamin Bates, who already owned Wright's Gladiator. An Aylesbury physician, patron of the arts and hedonist, Bates was a diehard member of the Hellfire Club who, despite his excesses, lived to be over 90. Wright's account book shows a number of prices for the painting: Pd£200 is shown in one place and £210 in another, but Wright had written to Bates asking for £130, stating that the low price "might much injure me in the future sale of my pictures, and when I send you a receipt for the money I shall acknowledge a greater sum. Whether Bates ever paid the full amount is not recorded; Wright only notes in his account book that he received £30 in part payment. Wright exhibited the painting at the Society of Artists exhibition in 1763 and it was re-exhibited before Christian VII of Denmark in September the same year. Viewers remarked that it was "clever and vigorous", while Gustave Flaubert, who saw it on a visit to England, remarked on its "naiveté et profondeur". It was popular enough that a mezzotint was engraved from it by Valentine Green and published on 24 June 1769. 20th century art historian Ellis Waterhouse called it "one of the wholly original masterpieces of British art".
From Bates, the picture passed to Walter Tyrell; another member of the Tyrell family, Edward, presented it to the National Gallery, London in 1863. The painting was transferred to the Tate Gallery in 1929 (although it was actually on loan to Derby Museum and Art Gallery between 1912 and 1947). It was lent out for exhibitions to the National Gallery of Art in Washington, D.C. in 1976 and to the National Museum of Fine Arts in Stockholm between 1979 and 1980. It was reclaimed by London's National Gallery in 1986.
The striking scene has been used as the cover illustration for many books on topics both artistic and scientific. It has even spawned pastiches: the book cover of The Science of Discworld, by Terry Pratchett, Ian Stewart and Jack Cohen, is a tribute to the painting by artist Paul Kidby, who substitutes the book's protagonists for Wright's figures. Shelagh Stephenson's play An Experiment with an Air Pump, inspired by the painting, was the joint winner of the 1997 Margaret Ramsay Award and had its premiere at the Royal Exchange Theatre, Manchester in 1998.