"[T]he function T... hitherto... undetermined; ...by means of a very probable hypothesis it will be possible ...to do. I refer to... my former memoir... that a permanent gas, when it expands at a constant temperature, absorbs only so much heat as is consumed by the exterior work thereby performed. This assumption has been verified by... experiments of Regnault, and in... probability is accurate for all gases to the same degree as Mariotte and Gay-Lussac's law, so that for an ', for which the latter law is perfectly accurate, the above assumption will also be perfectly accurate."