Reflections on the Motive Power of Fire

Sadi Carnot's work, Reflections on the Motive Power of Fire, published in 1824, explored the principles of heat engines. Carnot conceived of an ideal cycle, now known as the Carnot cycle, which serves as a benchmark for the performance of all heat engines operating between two temperatures. This cycle involves four stages: heating and expansion at a constant high temperature, adiabatic expansion, cooling and compression at a constant low temperature, and adiabatic compression. Carnot's principle, also known as Carnot's theorem, states that the efficiency of such an engine depends solely on the temperatures of the heat source and sink, not on the engine's design or working substance. Although Carnot worked within the now-outdated caloric theory of heat, his fundamental insights into thermodynamics remain valid.123