Derby was friends with some members of a scientific group called the Lunar Society (referenced in the painting by the full moon seen through the window) and this scene shows some of the members watching an experiment of a vacuum pump. The pump had been invented roughly one hundred years before this painting, and the experiment was frequently reenacted for paying spectators or even in private homes for those who could afford it as a party trick. Inside the glass chamber above the table lays a bird convulsing from lack of air, while the central figure pumps the air out and looks at us viewers, seemingly inviting us to join in. Most observers to the experiment quietly watch, although the couple on the left seems disinterested, and the two girls are being comforted by their father who implores them to look on the action. The painting seems to be a commentary on the cruelty us humans can inflict on animals, sometimes in the name of science.
