Reflections on the Motive Power of Heat

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Sadi Carnot Boilly 1813.jpg

At the Age of 17.
(From a Portrait by Bailly, 1813.)



Graduate of the Polytechnic School.


R. H. THURSTON, M.A., LL.D., Dr.Eng’g;

Director of Sibley College, Cornell University;
Officier de l'Instruction Publique de France,
etc., etc., etc.

Reflections on the Motive Power of Heat title logo.jpg

London: CHAPMAN & HALL, Limited.


Copyright, 1890,
Robert H. Thurston.


robert drummond, electrotyper and printer, new york.


Sadi Carnot,
President of the French Republic,

That distinguished member of the Profession of Engineering
whose whole Life has been an Honor to his
Profession and to his Country ;
and who, elevated to the highest office within the gift of the

French Nation,

has proven by the quiet dignity and the efficiency with which
he has performed his august duties that he is
a worthy member of a noble family,
already rendered famous by an earlier Sadi Carnot,
now immortal in the annals of science,

and is himself deserving of enrolment in a list of great men
which includes that other distinguished engineer,

our own first president,




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Account of Carnot's Theory. By Sir William Thomson (Lord Kelvin)
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The raison d'être of the following translation of the famous work of Carnot is not the usual one, either with the Publishers or the Editor—expectation of gain in either purse or fame. Neither could reasonably be anticipated from the reproduction of the work of an author of more than a half-century ago, in a field then unrecognized, and to-day familiar to but few; and especially when, as is in this case the fact, the work itself has been long out of date as a scientific authority, even had it ever held such a position. It could not be presumed that a very large proportion of even the men of science of the English-speaking world would be sufficiently familiar with the subject, or interested in its origin, to purchase such a relic of a primitive period as is this little book. Nor could the translation of the work, or the gathering together by the Editor of related matter, be supposed likely to be productive of any form of compensation. The book is published as matter of limited but most intense scientific interest, and on that score only. It has seemed to the Editor and to the Publishers that the product of the wonderful genius of Carnot,—the great foundation-stone of one of the most marvellous and important of modern sciences, the first statement of the grand though simple laws of Thermodynamics,—as illustrated in this one little treatise, should be made accessible to all who desire to study the work in English, and preserved, so far as its publication in this form could accomplish it, as a permanent memorial, in a foreign tongue, of such grand truths, and of such a great genius as was their discoverer. It is with this purpose that Publishers and Editor have co-operated in this project.

The book consists, as will be seen on inspection, of the translation of Carnot's Réflexions sur la Puissance Motrice du Feu, preceded by a notice written by the Editor calling attention to its remarkable features, and its extraordinary character as the product of a most remarkable genius; and by a biographical sketch of the great author, written by his brother, Mons. Hyppolyte Carnot, which sketch we find in the French copy of the work as published by Gauthier-Villars, the latest reproduction of the book in the original tongue. To the main portion of the book, Carnot's Réflexions, is appended the celebrated paper of Sir William Thomson, his "Account of Carnot's Theory," in which that great physicist first points out to the world the treasure so long concealed, unnoticed, among the scientific literature, already mainly antiquated, of the first quarter of the nineteenth century. The distinguished writer of this paper has kindly interested himself in the scheme of the Editor, and has consented to its insertion as a natural and desirable commentary upon the older work, and especially as exhibiting the relations of the fundamental principles discovered and enunciated by Carnot to the modern view of the nature of thermodynamic phenomena—relations evidently understood by that writer, but not by the leaders of scientific thought of his time, and therefore ignored by him in the construction of his new science.

The Appendix contains a number of Carnot's own notes, too long to be inserted in the body of the paper in its present form, and which have therefore been removed to their present location simply as a matter of convenience in book-making.

The dedication of the work to the grand-nephew of the author, who by a singular coincidence happens to-day to occupy the highest position that any citizen can aspire to reach in that now prosperous Republic, will be recognized as in all respects appropriate by every reader of the work of the earlier Sadi Carnot who is familiar with the character, the history, the attainments, the achievements, of the later Sadi Carnot in so many and widely diverse fields. The Carnot talent and the Carnot character are equally observable in both men, widely as they are separated in time and in the nature of their professional labors. Both are great representatives of a noble family, whose honor and fame they have both splendidly upheld.

The Publishers offer this little book to its readers as a small, yet in one sense not unimportant, contribution to the great cause of modern science, as a relic, a memorial, a corner-stone.




“Je me suis proposé de grands desseins dans ce petit ouvrage,” as Bernardin de Saint-Pierre says in the preface to his pathetic story of Paul et Virginie. I have sought to present to the great English-speaking world the work of a genius hitherto only known to a few men of science, and not well known, even among the people of France, for whose credit he has done so much. In placing before the readers of this translation his book—small of size but great in matter as it is—I feel that I have accomplished an easy task, but one of real importance. I have been asked, as Corresponding Member for the United States of the Société des Ingénieurs Civils de France, to communicate to my colleagues scientific and professional memoirs and whatever may be of interest to them—“en un mot, que nous resserrions les liens qui font des ingénieurs en géneral une seule famille.” That were a pleasant task; but a grander and a more agreeable one still is that of bringing “nearer in heart and thought” the members of that still larger community, the men of science of the world, and of weaving still more firmly and closely those bonds of kindly thought and feeling which are growing continually more numerous and stronger as the nations are brought to see that humanity is larger and more important than political divisions, and that the labors of educated men and of the guiding minds in the great industries are constantly doing more to promote a true brotherhood of mankind than ever have, or ever can, the greatest statesmen.

When the wonderful intellectual accomplishments of men like the elder Sadi Carnot become known and appreciated by the world, much more will have been accomplished in this direction. It is perhaps from this point of view that the importance of such work will be most fully recognized. When the little treatise which is here for the first time published in English becomes familiar to those for whom it is intended, it will be, to many at least, a matter of surprise no less than pleasure to discover that France has produced a writer on this now familiar subject whose inspiration anticipated many of the principles that those founders of the modern science, Rankine and Clausius, worked out through the tedious and difficult methods of the higher mathematics, and which were hailed by their contemporaries as marvellous discoveries.



The present edition of this little work is improved by the removal of a few errata observed in the first issue, and by the addition of a recent and excellent portrait of Lord Kelvin, as a frontispiece to his era-making paper, at page 127. This picture, taken within the last year, is thought by the friends of its distinguished subject to be one of the best yet produced. That it is satisfactory to him and his friends is indicated by the fact that the original of this reproduction was presented to the writer by Lady Kelvin, in 1895, immediately after it was taken, and the autograph supplied by her distinguished husband. The Editor takes this occasion to acknowledge cordially the letters of appreciation and commendation received from those who have agreed with M. Haton de la Goupillière that the translation of Carnot and its publication in this manner, with the famous paper of Lord Kelvin, will be considered as worthy of approval by English-speaking readers as well as "appreciated by the whole French nation."

This work was published before January 1, 1923, and is in the public domain worldwide because the author died at least 100 years ago.