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. 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, the setting suggested in both of Wright's demonstration pieces. One of the most notable and respectable of the travelling lecturers was James Ferguson FRS, a Scottish astronomer and probable acquaintance of Joseph Wright (both were friends of John Whitehurst). Ferguson 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".