502 Prof. Helmholtz on the Interaction of Natural Forces. 



plicable 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 hia 

 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 con- 

 tradicted the above genei-al law, expresses a certain relation 

 between the compi'essibility, the capacity for heat, and the ex- 

 pansion by heat of all bodies. It is not yet considered as 

 actually proved, but some remarkable deductions having been 

 drawn from it, and afterwards proved to be facts by experiment, 

 it has attained thereby a great degree of probabiUty. 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 the 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 

 impossible to convert any portion of their heat into mechanical 

 work. According to this we can divide the total force stoi'C 

 of the universe into two parts, one of which is heat, and must 

 continue to be such ; the other, to which a portion of the heat 

 of the warmer bodies, and the total supply of chemical, me- 

 chanical, electrical, and maguetical forces belong, is capable of 

 the most varied changes of form, and constitutes the whole wealth 

 of change which takes place in nature. 



But the heat of the warmer bodies strives perpetually to pass 

 to bodies less warm by radiation and conduction, and thus to 

 establish an equilibrium of temperature. At each motion of 

 a terrestrial body a portion of mechanical force passes by friction 

 or collision into heat, of which only a part can be converted 

 back again into mechanical force. This is also generally the 

 case in every electrical and chemical process. From this it 

 follows that the first portion of the store of force, the unchange- 

 able heat, is augmented by every natural process, while the 

 second portion, mechanical, electrical, and chemical force, must 

 be diminished ; so that if the universe be delivered over to the 

 undisturbed action of its physical processes, all force will finally 

 pass into the form of heat, and all heat come into a state of 

 equilibrium. Then all possibility of a further change would be 



