344 A CENTURY OF SCIENCE 



spite of the conclusive experiments of the American 

 Count Rumford and the English Davy before the year 

 1800. So firmly enthroned was the caloric theory, 

 according to which heat is an indestructible fluid, that 

 evidence against it was given scant consideration. In 

 fact the success of the analytical method introduced by 

 Fourier in 1822 for the solution of problems in conduc- 

 tion of heat only added to the difficulties of the adherents 

 of the kinetic theory. But recognition of heat as a form 

 of energy was on the way, and when it came it made its 

 appearance almost simultaneously in half a dozen differ- 

 ent places. Perhaps Robert Mayer of Heilbronn was 

 the first to state explicitly the new principle. His paper 

 "On the Forces of Inorganic Nature" was refused 

 publication in Poggendorff 's Annalen, but fared better at 

 the hands of another editor. During the next few years 

 Joule determined the mechanical equivalent of heat 

 experimentally by a number of different methods, some 

 of which had already been devised by Carnot. Of those 

 he used, the most familiar consists in churning up a 

 measured mass of water by means of paddles actuated by 

 falling weights and calculating the heat developed from 

 the rise in temperature. However, the work of the 

 young Manchester brewer received little attention from 

 the members of the British Association before whom it 

 was reported until Kelvin showed them its significance 

 and attracted their interest to it. Meanwhile Helmholtz 

 had completed a very thorough disquisition on the con- 

 servation of energy not only in dynamics and heat but in 

 other departments of physics as well. His paper on 

 "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 PoggendorfPs 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 1850 Jeremiah Day (10, 174, 1850), late president^ of 

 Yale College, admitted the improbability of constructing 



