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first given a solid basis by the experiments of Count Raraford (i>enjamin 

 Thompson), in 1700-7, of which an account "was given in a paper read by 

 Rumford before the Royal Society of Great Britain in 1798, by the ex- 

 periments of Sir Humphry Davy in 1708-1'. and by the later and more 

 precise determination of the value of tlie mechanical equivalent of heat, 

 by Joule, in 1843, and subsequently. 



The science of thermodynamics has for its essential basis the esta- 

 blished fact of the dynamical nature of heat, and the fact of the 

 quantivaltnce of two forms of energy -heat and mechanical motion, mole- 

 cular energy and mass energy. Resting, as it does, on fundamental, 

 experimentally-determined principles, it could have no existence, until 

 during the early part of the present century these ])henomena and these 

 truths were well investigated and firmly established. Immediately upon 

 the settlement of the controversy relating to tlio natui'e of heat, it be- 

 came possible to commence the construction of the science which, assert- 

 ing the mechanical theory of heat as its fundamental fact, and the conser- 

 vation and qnantivalence of tlic two forms of energy as its fundamental 

 principle, led to the determination of the method and extent of the trans- 

 formation of the one into the other during any prescribed series of 

 physical changes. 



It is not within the province of this paper to examine the claims made 

 for rival philosophers in the debate over the matter of priority of dis- 

 covery of the mutual relations of the phenomena and principles of the 

 new science. It is sufficiently evident that the revelation of the facts of 

 the case led many minds to stud}- the subject, and led to its nearly con- 

 temporaneous development in several countries. The first period of the 

 development of the science was occupied almost exclusively by the 

 exposition of the dynamical theory of heat, which lies at the bottom of the 

 whole. This strikingly interesting and obviously important subject so 

 absorbed t^'> "' ention and occupied the thoughts of physicists that tlicv 

 seem hardly .j have attempted to look beyond it, as a rule, and hence 

 failed, at first, to see into what a magnificent department of the theore- 

 tical and experimental investigation they were called. Mohr, in 1837 ; 

 Seguin, in 1830; Mayer, of Hcilbronn, in ISl'i; and Colding, in 1843, 

 each took a step into a field, the limits of which and the importance of 

 which they could at that time hardly have imagined. Mayer certainly 

 had a very clear conception of the bearing of the new theory of heat 

 upon dynamics, and exhibited remarkable insight into the far-reaching 

 principles of the new science. He collated, the facts more exactly deter- 

 mined later by Joule and others with the principle of the conservation of 

 energy, and applied the rudiments of a science thus constructed to the 

 calculation of the quantity of carbon and expenditure of heat which are 

 unavoidably needed by a mountain climber, doing a given quantity of 

 work, in the elevation of his own body to a .specified height. The work 

 of Mayer may be taken as representing the first step in the production of 

 a science of thermodynamics, and in the deduction of the consequences 

 of the fact which had, until his time, so seldom engaged the attention of 

 men of science. It was only about the middle of the century that it 

 began to be plainly seen that there existed such a science, and that the 

 dynamic equivalence of heat, and energy in the mechanical form, was 

 but a single fact, which must be taken in connection with the general 

 principles of the persistence of energy, and applied in all cases of per- 



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