whom he lived were entirely ignorant of the fund of knowledge he had accumulated. His brother, who was called upon to read the manuscript of his memoir on the motive power of heat in order to see that it was clear enough to be understood by others than scientists, says that he never did understand why Carnot made this one exception. It seems that his solitary life in small garrisons, in the office and in the laboratory served to increase his natural reserve. Yet he was not in the least reticent in a small company; he took part willingly in the gayest joys and abandoned himself to the liveliest conversation. His language was then full of witticism, biting but not malignant, original but not eccentric, sometimes paradoxical, but never with any other pretension than that of an active mind.
It was in 1824 while still an officer on the general staff that Carnot published his 'Reflections on the Motive Power of Heat.' Struck with the fact that chance alone seemed to direct the construction of steam engines, he undertook to raise to the rank of a science the art that was still so imperfect in spite of its importance. He investigated the phenomena of the production of motion by heat from the most general point of view, independent of any particular mechanism and of any particular agent. It was only some years after his death that the value of his work was revealed to his fellow countrymen by an echo from England. However, it did merit the attention of a few French scientists, notably the celebrated engineer, Clapeyron, who in 1834 published in the Journal École Polytechnique a paper which was a comment upon and an extension of the ideas of Carnot, in which he called attention to Carnot 's reasoning, represented Carnot 's processes in an analytical form and arrived at some new results, usefully applying, and for the first time, the principle of Watt's indicator diagram to the geometrical exhibition of the different quantities involved in the cycle of operations by which work is derived from heat by the temporary changes it produces in the volume and molecular state of bodies. It was through this work of Clapeyron that Carnot 's ideas became known to Lord Kelvin, who presented them to the world in 1848, pointing out that they enabled us to give for the first time an absolute definition of temperature, i. e., a thermodynamic scale of temperature which is independent of the properties of any particular substance. On this scale the absolute values of two temperatures are defined to be in the same ratio as the amounts of heat-energy taken in and rejected by a perfect (i. e., reversible) thermodynamic engine, working with its source and its refrigerator at the higher and lower of these temperatures respectively. Lord Kelvin showed that the ratio between these quantities of heat-energy depends only on these two working temperatures and is independent of the substance used in the engine,
