170 ON THE INTERACTION OF NATURAL FORCES. 



of this heat is totally independent of the time and steps 

 through which the combination has been effected, pro- 

 vided 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 temperature of 

 8,086 pounds of water one degree of the Centigrade ther- 

 mometer ; 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 cor- 

 responds 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 gene- 

 rated by the fuel. 



From a similar investigation of all the other known 

 physical and chemical processes, we arrive at the conclu- 

 sion that Nature as a whole possesses a store of force 

 which cannot in any way be either increased or dimi- 

 nished, 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 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 pur- 

 poses, and the actions of which we can apply as we think 



