Why did the Royal Society award Joseph Priestley the Copley Medal in 1773?

The Royal Society awarded Joseph Priestley the Copley Medal in 1773 in recognition of his extensive and innovative work on gases, or "airs," as they were then known.1

Priestley’s scientific success was largely driven by his skill in designing and manipulating ingenious experimental apparatuses. He gained particular renown for developing an improved pneumatic trough that allowed him to isolate and examine gases that were soluble in water by collecting them over mercury rather than water. His research during this period, which included the discovery of numerous new gases, was documented in his multi-volume work, Experiments and Observations on Different Kinds of Air, and through various articles published in the Royal Society’s Philosophical Transactions.1