“Higgins’ theory [1776] accounted for the phenomenon of the heating (or cooling) of a gas when it is suddenly compressed (or expanded): ‘adiabatic’ heating or cooling as it was later called. This had first been noticed in connection with experiments on the air pump. Cullen mentioned it but had no insight into its significance. Higgins also referred to it, and Johann Lambert pointed out that when air enters an evacuated vessel the temperature rises. His explanation was that even ‘empty’ space contains the ‘matter of heat’, so that the entry of air carrying more heat must cause a rise in temperature; and he went on to suggest that suddenly reducing the volume of a void should have a heating effect.”

— Donald Cardwell (1971), From Watt to Clausius (pg. 58) [1]