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. 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. 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.