Transactions of the Royal Society of Edinburgh

Research Article

XXXVI.—An Account of Carnot's Theory of the Motive Power of Heat;* with Numerical Results deduced from Regnault's Experiments on Steam.

William Thomsona1

a1 Professor of Natural Philosophy in the University of Glasgow.

1. The presence of heat may be recognised in every natural object; and there is scarcely an operation in nature which is not more or less affected by its all-pervading influence. An evolution and subsequent absorption of heat generally give rise to a variety of effects; among which may be enumerated, chemical combinations or decompositions; the fusion of solid substances; the vaporisation of solids or liquids; alterations in the dimensions of bodies, or in the statical pressure by which their dimensions may be modified; mechanical resistance overcome; electrical currents generated. In many of the actual phenomena of nature, several or all of these effects are produced together; and their complication will, if we attempt to trace the agency of heat in producing any individual effect, give rise to much perplexity. It will, therefore, be desirable, in laying the foundation of a physical theory of any of the effects of heat, to discover or to imagine phenomena free from all such complication, and depending on a definite thermal agency; in which the relation between the cause and effect, traced through the medium of certain simple operations, may be clearly appreciated. Thus it is that Carnot, in accordance with the strictest principles of philosophy, enters upon the investigation of the theory of the motive power of heat.


* Published in 1824, in a work entitled, “Réflexions sur la Puissance Motrice du Feu, et sur les Machines Propres à Déveloper,cette Puissance. Par S. Carnot.” An account of Carnot's Theory is also published in the Journal d'École Polytechnique, vol. xiv., 1834, in a paper by Mons. Clapeyron.

† An account of the first part of a series of researches undertaken by Mons. Regnault, by order of the late French Government, for ascertaining the various physical data of importance in the theory of the steam-engine, has been recently published (under the title, “Relation des Expériences,” &c.) in the Mémoires de l'lnstitut, of which it constitutes the twenty-first volume (1847). The second part of these researches has not yet been published.