Otf THE INTERACTION OF NATURAL FOECES. 171 



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 he 

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

 be inapplicable to human purposes. In this respect the 

 inferences drawn by William Thomson from the law of 

 Carnot are of importance. This law, which was discovered 

 by Carnot 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 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 expan- 

 sion 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 

 experiment, it has attained thereby the highest degree of 

 probability. Besides the mathematical form in which 

 the law was first expressed by Carnot, we can give it the 

 following more general expression : ' Only when heat 

 passes from a warmer to a colder body, and even then 

 only partially, can it be converted into mechanical work.' 



The heat of a body which we cannot cool further, 

 cannot be changed into another form of force into 

 electric or chemical force for example. Thus in our 

 steam-engines we convert a portion of the heat of the 

 glowing coal into work, by permitting it to pass to the 

 less warm water of the boiler. If, however, all the bodies 

 in Nature had the same temperature, it would be impos- 

 sible to convert any portion of their heat into mechanical 

 work. According to this we can divide the total force 

 store of the universe into two parts, one of which is heat, 



