Prof. Helmholtz on the Interaction of Natural Forces. 501 



is not, as was formerly imagiued, a fine imponderable substance, 

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

 mate particles of bodies. In collision and friction, 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 has been effected, provided that other actions 

 are not at the same time brought into play. If, however, mecha- 

 nical 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 temperature of 8086 

 pounds of water one degree of the Centigrade thermometer; 

 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 100 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 18 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 quan- 

 tity 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." 



Wc cannot create mechanical force, but we may help ourselves 

 from the general storehouse 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 wc think fit. The possessor of a mill claims the 

 gravity of the descending rivulet, or the living force of the 

 moving wind, as his possession. These portions of the store of 

 Natui-e are what give liis property its chief value. 



Further, from the fact that no portion of force can be abso- 

 lutely lost, it does not follow that a portion may not be inap- 



