ABSTRACT
Heat is indeed a complex notion which has been difficult to define and to put into equations for a long time. Clausius introduces the notion of “mechanical theory of heat” or “thermodynamics” that aims at finding a common ground between Carnot’s principle and the then well-established concept of conservation of energy. At the end of Clausius’ book “The Mechanical Theory of Heat: With Its Applications to the Steam-engine and to the Physical Properties of Bodies”, the authors find the following two fundamental theorems of the mechanical theory of heat: “Die Energie der Welt ist constant” (The energy of the universe is constant) and “Die Entropie der Welt strebt einem Maximum zu” (The entropy of the universe tends to a maximum). The development of statistics provides a new means to understand thermodynamics.
