The painting by Joseph Wright of Derby on which the present work is based was one of a number of candlelit scenes that Wright painted during the 1760s. It departed from the convention of the time by depicting a scientific subject in the reverential manner formerly reserved for scenes of historical or religious significance.
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 (a white cockatoo) is deprived of air, before a varied group of onlookers. The witnesses display various emotions: one of the girls worriedly watches the fate of the bird, while the other is too upset to observe and is comforted by her father; two gentlemen (one of them dispassionately timing the experiment) and a boy look on with interest, while the young lovers to the left of the painting are absorbed only in each other. The scientist himself looks directly out of the picture, as if challenging the viewer to judge whether the pumping should continue, killing the bird, or whether the air should be replaced and the cockatoo saved.
Aside from that of the children, little sympathy is directed toward the bird. 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.
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 air pump (then described as a "pneumatic engine", but known today as a vacuum pump) was invented by Otto von Guericke in 1650, though its cost deterred most contemporary scientists from constructing the apparatus. In 1659, however, Robert Boyle, Anglo-Irish natural philosopher, chemist, physicist and inventor commissioned an example. For Boyle, the son of the Earl of Cork, the substantial cost did not pose an obstacle. 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. Boyle's pump, which was largely designed to his own 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.
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 centerpiece of their public demonstration. These were performed in town halls and other large buildings for a ticket-buying audience, or were booked by societies or for private showings in the homes of the well-off.
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 may be a human skull in the large liquid-filled glass bowl would not have been a normal piece of equipment.
The powerful central light source creates a chiaroscuro effect. 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. It may be observed, however, that the stand on which the pump is situated casts no shadow on the body of the philosopher, as it could be expected to do.
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: 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. Wright apparently painted the work without a commission, and the picture was purchased by Dr Benjamin Bates. A 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.
The present work was engraved a year after the oil was completed. It is the work of Valentine Green, one of the most talented mezzotint engravers of the 18th century and amongst the first to demonstrate how well the technique could be applied to translate pictorial compositions.