NATURAL PHILOSOPHY. 127 



by experiment, particularly by those of Joule ; and during the last year the 

 most eminent physicist of France, Kegnatilt, has adopted the new mode of 

 regarding the question, and by fresh investigations on the specific heat of 

 gases has contributed much to its support. For some important conse- 

 quences the experimental proof is still wanting, but the number of confirma- 

 tions is so predominant, that I have not deemed it too early to bring the sub- 

 ject before even a non-scientific audience. 



How the question has been decided you may already infer from what has 

 been stated. In the series of natural processes there is no circuit to be 

 found, by "which mechanical force can be gained without a corresponding 

 consumption. The perpetual motion remains impossible. Our reflections, 

 however, gain thereby a higher interest. 



We have thus far regarded the development of force by natural pro- 

 cesses, only in its relation to its usefulness to man, as mechanical force. 

 You now see that we have arrived at a general law, which holds good wholly 

 independent of the application which man makes of natural forces ; we must 

 therefore make the expression of our laAv correspond to this more general 

 significance. It is in the first place clear, that the work which, by any 

 natural process whatever, is performed under favorable conditions by a 

 machine, and which may be measured in the way already indicated, may be 

 used as a measure of force common to all. Further, the important ques- 

 tion arises, " If the quantity of force cannot be augmented except by cor- 

 responding consumption, can it be diminished or lost ? For the purposes of 

 our machines it certainly can, if we neglect the opportunity to convert 

 natural processes to use, but as investigation has proved, not for a nature as 

 a whole." 



In the collision and friction of bodies against each other, the mechanics of 

 former years assumed simply that living force was lost. But I have already 

 stated that each collision and each act of friction generates heat ; and, 

 moreover, Joule has established by experiment the important law, that for 

 eveiy foot-pound of force which is lost, a definite quantity of heat is always 

 generated, and that when work is performed by the consumption of heat, 

 for each foot-pound thus gained a definite quantity of heat disappears. The 

 quantity of heat necessary to raise the temperature of a pound of water a 

 degree of the centigrade thermometer, corresponds to a mechanical force by 

 which a pound weight would be raised to the height of 1,350 feet; we name 

 this quantity the mechanical equivalent of heat. I may mention here that 

 these facts conduct of necessity to the conclusion, that heat is not, as was 

 formerly imagined, a fine imponderable substance, but that, like light, it is a 

 peculiar shivering motion of the ultimate particles of bodies. In collision 

 and faction, according to this manner of viewing the subject, the motion of 

 the mass of a body which is apparently lost is converted into a motion of 

 the ultimate particles of the body ; and conversely, when mechanical force 

 is generated by heat, the motion of the ultimate particles is converted into a 

 motion of the mass. 



Chemical combinations generate heat, and the quantity of this heat is 

 totally independent of the time and steps through which the combination 



