Why did the Royal Society award Henry Cavendish the Copley Medal?

The Royal Society awarded the Copley Medal to Henry Cavendish in recognition of his 1766 publication, which consisted of three papers detailing his research on "factitious airs," or gases produced in a laboratory setting.1

In this work, Cavendish successfully produced and studied "inflammable air" (hydrogen) and "fixed air" (carbon dioxide). He collected these gases using bottles inverted over water or mercury and performed rigorous quantitative measurements of their specific gravity, solubility in water, and combustibility. This research was significant as gas chemistry became increasingly vital to the scientific advancements of the 18th century.1