ABSTRACT
In 1824, the French physicist Nicolas Léonard Sadi Carnot, better known as Sadi Carnot, in Refl ections on the Motive Power of Fire settled the principles of the modern theory of thermodynamics by pointing out that motive power (concept later identi- ed as work) is due to the fall of caloric (concept later identi ed as heat) from a hot to cold body (working substance). ese ideas that provided the scienti c support for the technological jump based on the steam engine were not well understood at that time. ey were actually discovered and further elaborated 30 years later by the German Rudolf Clausius and the British William omson (Lord Kelvin). e fundamental principles ruling the operation of the thermal engines were then summarized in the two basic laws of thermodynamics. While the rst law simply stresses the conservation of the energy, the second one deals with the subtle distinction between a kind of energy that can be used and another one that is dissipated in a physical process, as well as on the balance between both of them.
