It has also been suggested that he may be drawing the curtains to block out the light from the full moon. Jenny Uglow believes that the boy echoes the figure in the last print of William Hogarth's "The Four Stages of Cruelty" by pointing out the arrogance and potential cruelty of experimentation, while David Fraser also sees the compositional similarities with the audience grouped round a central demonstration. 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. Wright, who took many of his subjects from English poetry, probably knew the following passage from "The Wanderer" (1729) by Richard Savage:  The cockatiel would have been a rare bird at the time, "and one whose life would never in reality have been risked in an experiment such as this". It did not become well known until after it was shown in illustrations to the accounts of the voyages of Captain Cook in the 1770s. Prior to Cook's voyage, cockatiels had been imported only in small numbers as exotic cage-birds. Wright had painted one in 1762 at the home of William Chase, featuring it both in his portrait of Chase and his wife ("Mr & Mrs William Chase") and a separate study, "The Parrot". In selecting such a rarity for this scientific sacrifice, Wright not only chose a more dramatic subject than the "lungs-glass", but was perhaps making a statement about the values of society in the Age of Enlightenment. The grey plumage of the cockatiel also shows much more effectively in the darkened room than the small dull-coloured bird in Wright's early oil sketch. A resemblance has been pointed out between the group of the bird and the two nearest figures and a type of depiction of the Trinity found in Early Netherlandish painting, where the Holy Spirit is represented by a dove, to which God the Father (the philosopher) points, while Christ (the father) gestures in blessing to the viewer. 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.