72
It is well known that heat may be used as a cause of motion, and that the motive power which may be obtained from it is very great. The steam-engine, now in such general use, is a manifest proof of this fact.
To the agency of heat may be ascribed those vast disturbances which we see occurring everywhere on the earth; the movements of the atmosphere, the rising of mists, the fall of rain and other meteors, the streams of water which channel the surface of the earth, of which man has succeeded in utilizing only a small part. To heat are due also volcanic eruptions and earthquakes.
From this great source we draw the moving force necessary for our use. Nature, by supplying combustible material everywhere, has afforded us the means of generating heat and the motive power which is given by it, at all times and in all places, and the steam-engine has made it possible to develop and use this power.
The study of the steam-engine is of the highest interest, owing to its importance, its constantly increasing use, and the great changes it is destined to make in the civilized world. It has already developed mines, propelled ships, and dredged rivers and harbors. It forges iron, saws wood, grinds grain, spins and weaves stuffs, and transports the heaviest loads. In the future it will most probably be the universal motor, and will furnish the power now obtained from animals, from waterfalls, and from air-currents.
Over the first of these motors it has the advantage of economy, and over the other two the in calculable advantage that it can be used everywhere and always, and that its work need never be interrupted.
If in the future the steam-engine is so perfected as to render it less costly to construct it and to supply it with fuel, it will unite all desirable qualities and will promote the development of the industrial arts to an extent which it is difficult to foresee. It is, indeed, not only a powerful and convenient motor, which can be set up or transported anywhere, and substituted for other motors already in use, but it leads to the rapid extension of those arts in which it is used, and it can even create arts hitherto unknown.
The most signal service which has been rendered to England by the steam-engine is that of having revived the working of her coal-mines, which had languished and was threatened with extinction on account of the increasing difficulty of excavation and extraction of the coal. We may place in the second rank the services rendered in the manufacture of iron, as much by furnishing an abundant supply of coal, which took the place of wood as the wood began to be exhausted, as by the powerful machines of all kinds the use of which it either facilitated or made possible.
Iron and fire, as everyone knows, are the mainstays of the mechanical arts. Perhaps there is not in all England a single industry whose existence is not dependent on these agents, and which does not use them extensively. If England were to-day to lose its steam-engines it would lose also its coal and iron, and this loss would dry up all its sources of wealth and destroy its prosperity; it would annihilate this colossal power. The destruction of its navy, which it considers its strongest support, would be, perhaps, less fatal.
The safe and rapid navigation by means of steamships is an entirely new art due to the steam-engine. This art has already made possible the establishment of prompt and regular communication on the arms of the sea, and on the great rivers of the old and new continents. By means of the steam-engine regions still savage have been traversed which but a short time ago could hardly have been penetrated. The products of civilization have been taken to all parts of the earth, which they would otherwise not have reached for many years. The navigation due to the steam-engine has in a measure drawn together the most distant nations. It tends to unite the peoples of the earth as if they all lived in the same country. In fact, to diminish the duration, the fatigue, the uncertainty and danger of voyages is to lessen their length.
The discovery of the steam-engine, like most human inventions, owes its birth to crude attempts which have been attributed to various persons and of which the real author is not known. The principal discovery consists indeed less in these first trials than in the successive improvements which have brought it to its present perfection. There is almost as great a difference between the first structures where expansive force was developed and the actual steam-engine as there is between the first raft ever constructed and a man-of-war.
If the honor of a discovery belongs to the nation where it acquired all its development and improvement, this honor cannot in this case be withheld from England: Savery, Newcomen, Smeaton, the celebrated Watt, Woolf, Trevithick, and other English engineers, are the real inventors of the steam-engine. At their hands it received each successive improvement. It is natural that an invention should be made, improved, and perfected where the need of it is most strongly felt.
In spite of labor of all sorts expended on the steam-engine, and in spite of the perfection to which it has been brought, its theory is very little advanced, and the attempts to better this state of affairs have thus far been directed almost at random.
The question has often been raised whether the motive power of heat is limited or not; whether there is a limit to the possible improvements of the steam-engine which, in the nature of the case, cannot be passed by any means; or if, on the other hand, these improvements are capable of indefinite extension. Inventors have tried for a long time, and are still trying, to find whether there is not a more efficient agent than water by which to develop the motive power of heat; whether, for example, atmospheric air does not offer great advantages in this respect. We propose to submit these questions to a critical examination.
The phenomenon of the production of motion by heat has not been considered in a sufficiently general way. It has been treated only in connection with machines whose nature and mode of action do not admit of a full investigation of it. In such machines the phenomenon is, in a measure, imperfect and incomplete; it thus becomes difficult to recognize its principles and study its laws.
To examine the principle of the production of motion by heat in all its generality, it must be conceived in dependently of any mechanism or of any particular agent; it is necessary to establish proofs applicable not only to steam-engines but to all other heat-engines, irrespective of the working substance and the manner in which it acts.
The machines which are not worked by heat for instance, those worked by men or animals, by water-falls, or by air currents can be studied to their last details by the principles of mechanics. All possible cases may be anticipated, all imaginable actions are subject to general principles already well established and applicable in all circumstances. The theory of such machines is complete. Such a theory is evidently lacking for heat-engines. We shall never possess it until the laws of physics are so extended and generalized as to make known in advance all the effects of heat acting in a definite way on any body whatsoever.
We shall take for granted in what follows a knowledge, at least a superficial one, of the various parts which compose an ordinary steam-engine. We think it unnecessary to describe the fire-box, the boiler, the steam-chest, the piston, the condenser, etc.
The production of motion in the steam-engine is always accompanied by a circumstance which we should particularly notice. This circumstance is the re-establishment of equilibrium in the caloric—that is, its passage from one body where the temperature is more or less elevated to another where it is lower. What happens, in fact, in a steam-engine at work? The caloric developed in the fire-box as an effect of combustion passes through the wall of the boiler and produces steam, incorporating itself with the steam in some way. This steam, carrying the caloric with it, transports it first into the cylinder, where it fulfils some function, and thence into the condenser, where the steam is precipitated by coming in contact with cold water. As a last result the cold water in the condenser receives the caloric developed by combustion. It is warmed by means of the steam, as if it had been placed directly on the fire-box. The steam is here only a means of transporting caloric; it thus fulfils the same office as in the heating of baths by steam, with the exception that in the case in hand its motion is rendered useful.
We can easily perceive, in the operation which we have just described, the re-establishment of equilibrium in the caloric and its passage from a hotter to a colder body. The first of these bodies is the heated air of the fire-box; the second, the water of condensation. The re-establishment of equilibrium of the caloric is accomplished between them if not completely, at least in part; for, on the one hand, the heated air after having done its work escapes through the smoke-stack at a much lower temperature than that which it had acquired by the combustion; and, on the other hand, the water of the condenser, after having precipitated the steam, leaves the engine with a higher temperature than that which it had when it entered.
The production of motive power in the steam-engine is therefore not due to a real consumption of the caloric, but to its transfer from a hotter to a colder body that is to say, to the re-establishment of its equilibrium, which is assumed to have been destroyed by a chemical action such as combustion, or by some other cause. We shall soon see that this principle is applicable to all engines operated by heat.
Translated by William Francis Magie
Reading and Discussion Questions
1.What political situation inspires Carnot’s theoretical reflections on steam power?
2.How does the use of Lavoisier’s caloric theory of heat as a fluid influence Carnot’s description of the work produced by heat?
3.Carnot is usually included among several scientists who are given credit for articulating a version of what would later be called the second law of thermodynamics. Why?