312 L. Page — A Century's Progress in Physics. 



"Die Erhaltung der Kraft' ' was frowned upon by the 

 members of the Physical Society of Berlin before whom 

 he read it, and received the same treatment as Mayer's 

 from the editor of Poggendorff's Annalen. Helmholtz's 

 "Kraft," like the "vis viva" of other writers, is the 

 quantity which Young had already christened energy. 

 Not many years elapsed, however, until the convictions of 

 Mayer, Joule, Kelvin and Helmholtz became the most 

 clearly recognized of all physical principles. As early 

 as 1.850 Jeremiah Day (10, ±74, 1850), late president of 

 Yale College, admitted the improbability of constructing 

 a machine capable of perpetual motion, even though the 

 "imponderable agents" of electricity, galvanism and 

 magnetism be utilized. 



Thermodynamics. — The importance of the principle of 

 conservation of energy lies in the fact that it unites under 

 one rule such diverse phenomena as gravitation, electro- 

 magnetism, heat and chemical action. Another principle 

 as universal in its scope, although depending upon the 

 coarseness of human observations for its validity rather 

 than upon the immutable laws of nature, was fore- 

 shadowed even before the first law of thermodynamics, 

 or principle of conservation of energy, was clearly 

 recognized. This second law was the consequence of 

 efforts to improve the efficiency of heat engines. In 1824 

 Carnot introduced the conception of cyclic operations 

 into the theory of such engines. Assuming the impos- 

 sibility of perpetual motion, he showed that no engine can 

 have an efficiency greater than that of a reversible 

 engine. Finally Clausius expressed concisely the princi- 

 ple toward which Carnot 's work had been leading, when 

 he asserted that "it is impossible for a self-acting 

 machine, unaided by any external agency, to convey heat 

 from one body to another at a higher temperature." 

 Kelvin's formulation of the same law states that "it is 

 impossible, by means of inanimate material agency, to 

 derive mechanical effect from any portion of matter by 

 cooling it below the temperature of the coldest of the 

 surrounding objects." 



The consequences of the second law were rapidly 

 developed by Kelvin, Clausius, Rankine, Barnard (16, 

 218, 1853, et se'q.) and others. Kelvin introduced the 

 thermodynamic scale of temperature, which he showed 

 to be independent of such properties of matter as con- 



