Reflections on the Motive Power of Fire," along with other papers in this volume, laid the foundation of modern thermodynamics. Highly readable, "Reflections" contains no arguments that depend on calculus, consisting mostly of statements couched in exact language. It represents a tribute to Carnot's capacity to generalize, and to see fundamental processes at work in complex mechanisms. "Reflections on the Motive Power of Fire" examines the relation between heat and the work done by heat in high- and low-pressure steam engines, air-engines, and an internal combustion machine. Carnot established conditions for the economical working of these engines and invented the closed cycle of operations. He realized that in any engine, the amount of work done by heat is determined solely by the range of temperature through which it fell in the operation. He extended the ideas of his father, Lazare Carnot, on mechanics to thermal processes, deriving statements on the impossibility of perpetual motion and the need to avoid irreversible changes. Little notice was paid to this book upon its 1824 publication; ten years later, Emile Clapeyron's more analytical paper on the same subject received wider attention. This English translation includes selections from Carnot's posthumous manuscripts and a paper by Rudolf Clausius that rewrote Carnot's results in a terminology that distinguished between change of entropy and quantity of heat.