Page:Popular Science Monthly Volume 62.djvu/134

128 invariable in nature, that it is never, properly speaking, either produced or destroyed. In truth, it simply changes form—sometimes producing one kind of motion, sometimes another; but it is never annihilated.

This is a clear and positive statement of the now well-known 'Principle of the Conservation of Energy'; and yet, by reason of the fact that these notes were not published by their author and did not come to light for half a century after his death, the world awaited the enunciation of this universal principle till the day of Mayer, Helmholtz and Joule. Shall all honor be denied Carnot simply because his work remained undiscovered so long? While we ascribe great and merited praise to those philosophers who were fortunate enough first to present the doctrine of energy to the world, we must not forget him who by reason of the much earlier day in which he lived, made a far greater stride in arriving at the same conclusion.

We complete our quotations by giving some of the passages in which Carnot outlines experiments for determining the mechanical equivalent of heat:

Stir vigorously a mass of water in a small barrel or in the cylinder of a double-action pump, the piston of which is pierced with small holes. Experiments of the same kind on the agitation of mercury, of alcohol, of air, and of other gases. Measure the motive power consumed and the heat produced Allow air to enter a vacuum or a space occupied by air more or less rarefied; the same for other gases or vapors; examine the rise in temperature. Estimate the error of the thermometer by noting the time taken for the temperature of the air to vary a given number of degrees. These experiments will serve to measure the changes of temperature produced in a gas by changes in volume; they will furnish, among other things, the means of comparing these changes with the quantities of motive power produced or consumed Allow a quantity of air compressed in a larger reservoir to escape therefrom, and check its velocity by having it escape through a large tube containing a number of solid bodies; measure the temperature when it has become uniform. See if it is the same as that in the reservoir. Same experiments with other gases and with vapor formed under various pressures.

How effectually such experiments did accomplish what Carnot expected is fully attested by the subsequent researches of Joule, Kelvin, Hirn, Regnault and others.

Carnot's work was followed up by the epoch-making papers of Sir William Thomson (now Lord Kelvin) in England, and of Rudolph Clausius in Germany.

The science of thermodynamics, founded on the labors of these three illustrious men, has led to the most important development in all departments of physical science. It has pointed out relations among the properties of bodies which could scarcely have been anticipated in any other way; it has laid the foundation for the science of chemical physics; and, taken in connection with the kinetic theory of gases, as developed by Maxwell and Boltzmann, it has furnished a general view of the operations of the universe which is far in advance of any that could have been reached by purely dynamical reasoning.