THE ORGANISM AS A MECHANISM 63 



irreversible changes. In all these processes energy 

 descends the incline, and some (considerable) fraction 

 of the amount involved passes into conditions in which 

 it is incapable of further transformation ; in all, energy- 

 becomes less and less available. Expressed in its most 

 technical form, the second law of thermodynamics 

 states that entropy tends continually to increase. 

 Every such process as we can study in physics " leaves 

 an indelible imprint somewhere or other on the progress 

 of events in the universe considered as a whole." ^ 



We cannot observe a truly isolated system. The 

 earth itself is part of the solar system, and the latter 

 receives energy from., and radiates it to the rest of, the 

 universe. Our only isolated system is the whole 

 universe. We must think of it, in so far as we regard 

 it as physical, as a finite system : if it is infinite, 

 our speculations become meaningless. The universe 

 therefore is a system in which energy tends continually 

 towards degradation. In every process that occurs 

 in it — that is to say every purely physical process — 

 heat is evolved, and this heat is distributed by conduc- 

 tion and radiation, and tends to become universally 

 diffused throughout all its parts. When this ultimate, 

 uniform distribution of energy will have been attained, 

 all physical phenomena will have ceased. It is useless 

 to argue that universal phenomena are cyclical. We 

 vainly invoke the speculations (founded on rather 

 prematurely developed cosmical physics) of stellar 

 collisions, light-radiation pressure, the distribution of 

 cosmic dust, etc. to support our notions of alternate 

 phases of dissipation and concentration of energy ; 

 close analysis will show that all these processes must 

 be irreversible. The picture physics exhibits to us is 

 that of the universe as a clock running down ; of an 



^ Bryan, Thermodynamics, p. 195. 



