AMOUNT OF FORCE IN THE UNIVERSE UNALTERABLE. 227 



cles of a pound of coal and the quantity of oxygen that corre- 

 sponds 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 physi- 

 cal 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, there- 

 fore, 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 Conser- 

 vation of Force." 



"We cannot create mechanical force, but we may help our- 

 selves 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 the living 

 force of the moving wind, as his possession. These por- 

 tions of the store of Nature are what give his property its 

 chief value. 



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

 absolutely lost, it does not follow that a portion may not be 

 inapplicable to human purposes. In this respect the infer- 

 ences drawn by William Thomson from the law of Carnot 

 are of importance. This law, which was discovered by Car- 

 not during his endeavours to ascertain the relations between 

 heat and mechanical force, which, however, by no means 

 belongs to the necessary consequences of the conservation of 



