# Earliest use of the word 'polytropic' to describe an equation of state or process

When and by whom was the word 'polytropic' first used to describe an equation of state or process of the form $$P \propto V^n$$? Why was this particular word chosen?

The earliest use of the word that I could find by searching on Google Books was in https://doi.org/10.1080/14786445408647467, which seems to be unrelated to the use I am looking for. The other 'contemporaneous' results I could find seemed to be mostly newer books mislabelled as older ones, or works in which the word was used without any explanation, suggesting it was already well-established.