[1] While working as a companion for Lord Shelburne, Priestley had a great deal of free time to engage in scientific investigations.

[2] These experiments helped repudiate the last vestiges of the theory of four elements; as one early biographer writes: "taken collectively, [Priestley] did more than those of any one of his contemporaries to uproot and destroy the only generalisation by which his immediate predecessors had sought to group and connect the phenomena of chemistry", however "he was wholly unable to perceive this fact.

As historian of science Simon Schaffer points out, it "has been seen as a branch of physics, or chemistry, or natural philosophy, or some highly idiosyncratic version of Priestley's own invention.

"[4] Also, the volumes were both a scientific and a political enterprise for Priestley; he argued in them that science could destroy "undue and usurped authority," writing that the government has "reason to tremble even at an air pump or an electrical machine.

[6] After a small history of the study of airs, he explained his own experiments in an open and sincere style: "whatever he knows or thinks he tells: doubts, perplexities, blunders are set down with the most refreshing candour.

One of these letters was read aloud to the Royal Society, and he published a paper in Philosophical Transactions titled "An Account of further Discoveries in Air."

… For my own part, I will frankly acknowledge that at the commencement of my experiments recited in this section I was so far from having formed any hypothesis that led to the discoveries I made in pursuing them that they would have appeared very improbable to me had I been told of them; and when the decisive facts did at length obtrude themselves upon my notice it was very slowly, and with great hesitation, that I yielded to the evidence of my senses.