"[T]he second fundamental theorem in the mechanical theory of heat... appropriately... called the theorem of the equivalence of transformations..: If two transformations which, without necessitating any other permanent change, can mutually replace one another, be called equivalent, then the generation of the quantity of heat Q of the temperature t from work, has the equivalence-value'and the passage of the quantity of heat Q from the temperature t1 to the temperature t2, has the equivalence-value'wherein T is a function of the temperature, independent of the nature of the process by which the transformation is effected."