104 THE MECHANISM OF LIFE 



there must be a fall of temperature in the machine. If I 

 were greater than I, i.e. if the temperature at the outlet were 

 greater than that at the inlet, the efficiency would be a 

 negative one, and the transformer would have to borrow heat 

 from some external source. 



Entropy. — In every transformation of energy a certain 

 portion of the energy is transformed into heat : a lamp gives 

 out useless heat as well as light, a machine gives out useless 

 heat as well as mechanical work. This loss of useful energy 

 as heat occurs in every transference or transformation of 

 energy; it is only in the case of heat passing from a hotter to 

 a colder body that there is no such transformation. Wlun 

 equality of temperature is established there has been no loss 

 of energy, but the whole of the energy has become unutilizable, 

 i.e. untransformable. In the formula of efficiency the fall of 

 intensity I — I' is now zero, and therefore the efficiency of the 



machine I — - — 1 is also zero. 



Since in all its transformations a certain fraction of the 

 energy is changed into heat, there is a tendency in nature for 

 all differences of temperature to become equalized. Hence 

 the quantity of utilizable energy in the universe tends to 

 diminish. Clausius called this unutilizable energy enmeshed 

 in the substance of a body its entropy, and showed that in 

 every transformation the amount of this unutilizable energy 

 tended to increase. "The entropy of a system always tends 

 towards a maximum value." 



If this gradual incessant increase of entropy is universal in 

 nature, and if there is no compensatory mechanism, the 

 universe must be tending towards a definite end. when the 

 whole of its energy shall have been transformed into unutiliz- 

 able heat with a uniform temperature. There is, however, 

 reason to suppose that some such compensatory mechanism 

 does in fact exist. Behind us stretches an infinite past, and 

 in the future we believe thai the phenomena of nature will be 

 unrolled in a cycle which has no end. But the arguments 

 derived from a study of entropy apply only to the facts and 

 phenomena actually under our notice, the supposed impossi- 



