Reflections on the Motive Power of Fire and on Machines Fitted to Develop that Power is a scientific treatise written by the Frenchmilitary engineerSadi Carnot.[1][2][3][4][5] Published in 1824 in French as Réflexions sur la puissance motrice du feu et sur les machines propres à développer cette puissance, the short book (118 pages in the original) sought to advance a rational theory of heat engines. At the time, heat engines had acquired great technological and economic importance, but very little was understood about them from the point of view of physics.