Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. Chapter XVIII. Extends the ordinary definition of entropy to a body or system in which the temperature or pressure, or both, are not the same throughout the body or system, and thus opens up a mode of dealing with intrinsically irreversible transforma tions the same as that followed when the transformations are reversible.