Joseph Wright of Derby’s An Experiment on a Bird in the Air Pump shows a family arrayed around a pneumatic demonstration. While the picture has been much written about, previous commentators have been inclined to dismiss the experiment that is its ostensible subject, seeing this as merely a pretext for the elaboration of other apparently more pressing issues. I will show, instead, that by understanding the painting within mid-eighteenth-century ideas about air we can gain a more complex sense of its position within the changing aesthetic and scientific discursive fields of the Enlightenment.