Clausius R. The mechanical theory of heat, with its applications to the steam-engine and to the physical properties of bodies

Translated by T. Archer Hirst. — London: John van Voorst, 1867. — XVI + 376 p.This book collects English translations of nine papers, published in journals by Clausius, between 1850 and 1865. This collection of original papers should not be confused with a later book of the same title, also by Clausius, where he worked his original papers into a textbook.The first paper (1850) stated the two laws of thermodynamics: the principle of the equivalence of heat and work, and the principle of Carnot. Clausius turned the first law into the form known today: the first law connects the internal energy of a body to the work done and heat received. He was clear that the internal energy is a function of state, but the work and heat depend on path. He then applied the first law to ideal gases. To do so he recalled PV = RT, but that was not enough. He then added “a very natural incidental assumption”. This assumption turned out to be that the internal energy is a function of temperature only and is independent of volume. He further assumed that the specific heat is independent of temperature. He analyzed both isothermal and adiabatic processes. Clausius did not, however, applied these results to analyze the Carnot cycle. We know today that this analysis gives the Carnot efficiency, which gives the principle of Carnot a quantitative form. In this paper, Clausius’s analysis of the second law did not reach anything like entropy.“This memoir marks an epoch in the history of physics,” wrote Gibbs in an obituary of Clausius in 1889. “...it might have been said at any time since the publication of that memoir, that the foundation of the science (of thermodynamics) were secure, its definitions clear, and its boundaries distinct.”Did Gibbs really mean that? Thermodynamics without entropy is a play without its leading actor.