228 INTERACTION OF NATURAL FORCES. 



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 considered as actually proved, buf some remarkable 

 deductions having been drawn from it, and afterwards proved 

 to be facts by experiment, it? has attained thereby a great 

 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 frqm 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 store 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, mechanical, electrical, and magneti- 

 cal 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 radition 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, 



