266 CLASSICS OF MODERN SCIENCE 

 but that, like light, it is a peculiar shivering motion of the ultimate 

 particles of bodies. In collision and friction, according to this man- 

 ner of viewing the subject, the motion of the mass of a body v^hich 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 com- 

 bination has been effected, provided that other actions are not at the 

 same time brought into play. If, however, mechanical work is at the 

 same time accomplished, as in the case of the steam engine, we obtain 

 as much less heat as is equivalent to this work. The quantity of 

 work produced by chemical force is in general very great. A pound 

 of the purest coal gives when burnt, sufficient heat to raise the temper- 

 ature of 8086 pounds of water one degree of the centigrade thermom- 

 eter; from this we can calculate that the magnitude of the chemical 

 force of attraction between the particles of a pound of coal and the 

 quantity of oxygen that corresponds to it is capable of lifting a weight 

 of one hundred pounds to a height of twenty miles. Unfortunately, 

 in our steam engines, we have hitherto been able to gain only the 

 smallest portion of this work; the greater part is lost in the shape 

 of heat. The best expansive engines give back as mechanical work 

 only eighteen per cent, of the heat generated by the fuel. 



From a similar investigation of all the other known physical and 

 chemical processes, we arrive at the conclusion that Nature as a whole 

 possesses a store of force which cannot in any way be either increased 

 or diminished. And that, therefore, the quantity of force in Nature is 

 just as eternal and unalterable as the quantity of matter. Expressed 

 in this form, I have named the general law "The Principle of the 

 Conservation of Force." 



We cannot create mechanical force, but we may help ourselves 

 from the general store-house of Nature. The brook and the wind, 

 which drive our mills, the forest and the coal-bed, which supply our 

 steam engines and warm our rooms, are to us the bearers of a small 

 portion of the great natural supply which we draw upon for our 

 purposes, and the actions of which we can apply as we think fit. The 

 possessor of a mill claims the gravity of the descending rivulet, or 



