128 POPULAR SCIENCE MONTHLY. 



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, Helm- 

 holtz 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. Ex- 

 periments of the same kind on the agitation of mercury, of alcohol, of air, and 

 of other gases. Measure the motive power consumed and the hent 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 ex- 

 pected is fully attested by the subsequent researches of Joule, Kelvin, 

 Hirn, Eegnault and others. 



Carnot 's work was followed up by the epoch-making papers of 

 Sir William Thomson (now Lord Kelvin) in England, and of Kudolph 

 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. 



