Dr. J. R. Mayer on the Mechanical Equivalent of Heat. 501 



"While following in general the direction indicated, it was 

 accordingly needful for me in the end to fix my attention chiefly 

 on the physical connexion subsisting between motion and heat ; 

 and it was thus impossible for the existence of the mechanical 

 equivalent of heat to remain hidden from me. But, although I 

 have to thank an accident for this discovery, it is none the less 

 my own, and I do not hesitate to assert my right of priority. 



In order to ensure what had been thus discovered against 

 casualties, I put together the most important points in a short 

 paper which I sent in the spring of 1842 to Liebig, with a 

 request that he would insert it in the Annalen der Chemie und 

 Pharmacie, in the forty-second volume of which, page 233, it 

 may be found under the title " Bemerkungen iiber die Krafte 

 der unbelebten Natur"*. 



It was a fortunate circumstance for me that the reception 

 given to my unpretending work by this man, gifted with so deep 

 an insight, at once secured for it an entrance into one of the first 

 scientific organs, and I seize this opportunity of publicly testi- 

 fying to the great naturalist my gratitude and my esteem. 



Liebig himself, however, had about the same time already 

 pointed out, in more general but still unmistakeable terms, the 

 connexion subsisting between heat and work. In particular, he 

 asserts that the heat produced mechanically by a steam-engine 

 is to be attributed solely to the effect of combustion, which can 

 never receive any increase through the fact of its producing 

 mechanical effects, and, through these, again developing heat. 



From these, and from similar expressions of other scientific 

 men, we may infer that science has recently entered upon a 

 direction in which the existence of the mechanical equivalent of 

 heat could not in any case have remained longer unperceived. 



In the paper to which reference has been made, the natural 

 law with which we are now concerned is referred back to a few 

 fundamental conceptions of the human mind. The proposition 

 that a magnitude, which does not spring from nothing, cannot be 

 annihilated, is so simple and clear that no valid argument can 

 be urged against its truth, any more than against an axiom of 

 geometry ; and until the contrary is proved by some fact esta- 

 blished beyond a doubt, we may accept it as true. 



Now we are taught by experience, that neither motion nor 

 heat ever takes its rise except at the expense of some measur- 

 able object,and that in innumerable cases motion disappears with- 

 out anything except heat making its appearance. The axiom 



[* A translation of this paper appeared in the Philosophical Magazine for 

 November last (see vol. xxiv. p. 3/1). In this translation are embodied 

 the corrections of several misprints in the original, given by the author 

 in a foot-note inserted at this point of the present paper. — G. C. F.] 



