4-72 Historic Notice of the Mechanical Theory of Heat. 



various memoirs of this physicist, written in a language the 

 knowledge of which is but little extended, and first printed 

 several years after their presentation to the Academy of Copen- 

 hagen, have exerted scarcely any influence on the subsequent 

 developments of the science. 



The third discoverer of whom it rests with me to speak, Mr. 

 Joule, is the one who perhaps has done most for the demonstra- 

 tion of the new principle, and for its final adoption. His first in- 

 vestigation, published only in 1843, is incontestibly posterior by 

 some months to the first publications of Mayer and Colding. It 

 contains experiments on the heat developed by induced currents, 

 and does not appear to have excited much attention. It is to 

 his experiments in 1845 on the calorific effects of the dilatation 

 and compression of gases that belongs the privilege of giving the 

 right of citizenship in science to the new ideas*. It is his expe- 

 riments on friction that have given the first determination of 

 the mechanical equivalent of heat which is worthy of confidence. 

 It is his views on the constitution of gases which first gave the 

 only example, up to the present time, of a complete explanation 

 of a phenomenon of which the theory might predict the laws, 

 but could not indicate the mechanism. 



Immediately after these three names, that of M. Helmholtz 

 ought to appear, for having in 1847, in his memoir on the 

 Conservation of Force, united in a body the doctrine of the new 

 ideas, and for having made fruitful and important applications 

 of them to the phenomena of induction, to electro-chemistry, 

 and to thermo-electric currents. 



Lastly, the final constitution of the science, the clear and 

 methodical establishment of the proper processes of investi- 

 gation and of reasoning, as also its application in detail to the 

 theory of machines, are principally due to the efforts of three 

 authors, which are the last that I will cite — MM. Clausius, 

 Macquorn Rankine, and William Thomson. Their most im- 

 portant researches have been published between 1849 and 1851. 



Since the epoch last referred to, there have been many other 

 researches conducted under the inspiration of the same ideas. 

 I have had occasion to refer to several of them during the course 

 of these two lectures. Others are mentioned in the table of 

 mechanical equivalents which I have placed before you. I will 

 not attempt to complete these indications. I will content myself 

 with having shown you how the foundations of that edifice have 

 been laid in the construction of which during the last ten years 

 everybody has taken a part. 



* This is a difficult passage. The original rims thus : — " C'est a ses 

 experiences de 1845, sur les effets calorifiques de la dilatation et de la com- 

 pression des gaz, qu'il appartenait de donner droit de cite dans la science 

 aux idees nouvelles." 



