Historic Notice of the Mechanical Theory of Heat. 467 



ciples I have so often asserted in this Magazine, nor from the 

 views of the ultimate qualities of matter, and the nature of phy- 

 sical forces, which Newton has left on record. The readiness 

 with which those principles apply in the solution of the difficult 

 problem of the sun's heat, may be taken as evidence of their 

 being founded in truth. If the tendency of the explanations is 

 to show that all the forces of nature are either active pressures 

 of the sether, or passive resistances of atoms, I do not see that 

 this conclusion should not be accepted because it reduces physical 

 forces to such conceptions as can be perfectly reached by experi- 

 ment and common observation. 

 Cambridge, May 21, 1863. 



LXIII. Historic Notice of the Mechanical Theory of Heat. 

 By M. Verdet* 



THE importance to be attached to this new theory (the dy- 

 namical theory of heat) makes it a duty on my part to 

 finish this exposition by a short historic review, in which I shall 

 attempt to render justice to the principal discoverers. This is 

 all the more necessary as I have hitherto constantly followed 

 the logic of the ideas without any regard to the historic order of 

 the discoveries. 



Two periods may be distinguished in this history. During one 

 of these, which extends to the year 1842, ideas similar to that em- 

 bodied in the mechanical theory of heat have been expressed by 

 various authors, while in some cases the same phenomena that 

 this theory explains have been regarded in accordance with other 

 principles, and useful attempts have been made to refer them to 

 general laws. But the true principle not being found, these 

 efforts remained isolated, sterile, and without sensible influence 

 on the general progress of science. All this labour, however, 

 finished by bearing its fruit, and towards the year 1842 the new 

 idea, as is often the case with great discoveries, clearly revealed 

 itself to several minds almost at the same moment. Soon 

 afterwards began that period of rapid progress which always 

 follows the discovery of a true principle, and a few years sufficed 

 to establish the magnificent assemblage of results which I have 

 attempted to lay before you. 



The first name on the list of those who may be regarded as 

 the precursors of the mechanical theory of heat is that of the 

 illustrious Daniel Bernoulli. The 'Hydrodynamics' of this 

 great geometer and physicist contained — for a century for- 



* Translated from the Expose de la Theorie Mecanique de la Chaleur, 

 p. 109-118. 



