a French physicist who developed the theory of heat engines. Carnot’s Réflexions sur la Puissance Motrice du Feu (Reflections on the Motive Power of Fire (1824)) laid out principles that would influence the most fundamental laws of science and engineering: the law of conservation of energy and the first and second laws of thermodynamics. In Réflexions Carnot sought to answer two fundamental questions: firstly, whether there was an upper limit to the power of heat, and secondly, whether there was a better means than steam to produce this power. He proposed that work was generated by the passage of caloric from a warmer to a cooler body, with caloric being conserved in the process. Clausius later showed, however, that heat was in fact not conserved; yet this did not undermine the validity or importance of Carnot’s results. Carnot deduced that the efficiency of the engine depended only on the temperature at the heat source and at the heat sink, and not on the temperature of the working substance. The first deduction amounted to the Carnot cycle; the second was known as Carnot's theorem.