A METAPHYSICAL DISCUSSION 231 



thorium, polonium, etc. — disintegrate, giving off large quantities 

 of radiant energy. We know that this energy is not created in 

 the atom, but is a store that diminishes by reason of its emission. 

 Therefore, the radio-activity of a disintegrating atom comes to 

 an end sooner or later. Uranium passes into radium, and 

 radium, after a long series of intermediate steps, passes into lead. 

 The atomic energy of lead is hound, since this substance shows 

 no sign of radio-activity. 



Now, the great majority of the chemical atoms are in the same 

 condition as lead, and we know that the few that are still capable 

 of emitting radiant energy will pass into the condition of lead, 

 when their energy will exist entirely in the bound state. Extra- 

 polating the process far into the future, we predict the time when 

 all chemical atoms in the earth, sun, and the luminous stars, will 

 have ceased to emit energy — ^that is, the substance of the cosmic 

 bodies will have passed into the inert material stage. So, also, 

 extrapolating the process far back into the past, we may be sure 

 that we pass through stages in which the rate of emission of 

 energy from radio-active elements was progressively greater and 

 greater, and was at a maximum at some remote stage in the 

 evolution of our universe. In that stage the substance of the 

 latter existed in the pre-material state. With regard, then, to 

 this generation of available energy by radio-activity, the passage 

 of nature is one from a pre-material to an inert material stage ; 

 from the condition of free energy to that of bound energy. 



This, doubtless, accounts for the greater fraction, or perhaps 

 all, of the energy that takes part in universal transformations, or 

 physical phenomena. But consider further the free or available 

 energy emitted by radio-active bodies, or free energy in general, 

 apart from any question as to its origin. This energy degrades. 

 Whatever its nature, and whatever the nature of the trans- 

 formations which it undergoes, it ultimately becomes heat at low 

 temperature. Further, this heat tends always to become equally 

 distributed everywhere throughout the universe, so that the time 

 will come when there will no longer be any difference of 

 intensity, or potential, in the unique form (heat) in which energy 

 wiU then exist. 



That will be the condition of universal physical death (" Warm- 

 Todt," in Clausius' term). 



The universe, therefore, tends from a condition of physical 

 activity to one of physical death. It runs down. Free energy 

 becomes completely dissipated, and unbound energy becomes 

 bound. From a condition of minimum entropy the universe 



