THE ADDRESSES, LECTURES, ETC., OF 



numerical relation between them, and we observe with surprise 

 how near his experimental results approached to the now-accepted 

 determination of the mechanical equivalent of heat. 



Sir Humphrey Davy caused the fusion of two pieces of ice by 

 friction, and thus virtually proved the identity of heat and motion, 

 though he failed to give expression to that view. 



Carnot, in 1824, sought to determine how heat produced 

 mechanical work ; and although, in one respect, he appears to 

 have receded from the views already advanced by others before 

 him, in speaking of heat as a subtle fluid, he makes the remarkable 

 statement that the greatest possible work an engine can perform 

 is a function of the temperatures between which it works, and not 

 of the nature of the substance employed. He also was the first to 

 draw attention to the important fact that in working a caloric 

 engine some heat must necessarily descend from a higher to a 

 lower point of temperature, whereas another portion disappears in 

 the operation. 



The next and most important step in the advancement of this 

 branch of science we owe to the independent investigation of 

 three discoverers viz., Grove of London, Mayer of Heilbronn, and 

 Joule of Manchester three men whose modes of thought differed 

 very widely from each other, but who each of them pronounced 

 distinctly the complete identity of all physical forces, proving 

 their mutual convertibility coupled with complete indestructi- 

 bility. To Dr. Joule we owe, moreover, the determination of the 

 numerical equivalent in units of heat by which mechanical effect 

 is measured. 



But although the mechanical equivalents of heat, as well as 

 those of electricity and chemical affinity, were thus absolutely 

 established, much remained to be accomplished to assign to the 

 new theory its actual signification. This was done independently 

 and by different methods by Professor Clausius in Germany, and 

 by your own illustrious townsmen, Rankine and Sir William 

 Thomson, in this countiy. The two former, starting from different 

 hypotheses, determined the general equation of thermodynamics 

 which expresses the relation between heat and mechanical energy 

 under all circumstances ; while the latter, in building upon the 

 basis of Carnot and Joule, solved some important new problems 

 in thermodynamics, and extended analogous principles to electricity 



