152 ON THE mTERACTION OF NATUBAL FORCES. 



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 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 our- 

 selves 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 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 portions of the store of 

 Nature are what give his 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 in- 

 applicable to human purposes. In this respect the inferences 

 drawn by William Thomson from the law of Carnot are of im- 

 portance. This law, which was discovered by Carnot during his 

 endeavours to ascertain the relations between heat and me- 

 chanical force, which, however, by no means belongs to the 

 necessary consequences of the conservation of force, and which 

 Clausius was the first to modify in such a manner that it no 

 longer contradicted the above general law, expresses a certain 

 relation between the compressibility, the capacity for heat, and 

 the expansion by heat of all bodies. It is not yet completely 

 proved in all directions, but some remarkable deductions having 

 been drawn from it, and afterwards proved to be facts by ex- 

 periment, it has attained thereby the highest degree of pro- 

 bability. Besides the mathematical form in which the law was 



