ON THE NATURE OF LIFE 217 



In the activities of life as a whole, what we observe, then, is 

 the tendency for the perpetuation of differences of energy 

 intensity. In purely physical happenings energy tends to 

 become unavailable, but organic changes set themselves against 

 this tendency. When sunlight falls upon desert sand, rocks, 

 raw soil, and upon the surface of the sea, its energy of radiation 

 transforms into heat. Sand and stones become warm, and when 

 the sunlight is withdrawn this heat becomes radiated away into 

 outer space, is dissipated, and is, for us at least, for ever irre- 

 coverable. When it falls on the surface of the sea it heats up 

 the water, which then evaporates, rises up into the atmosphere, 

 is distributed in winds, and is precipitated in rain, etc., returning 

 ultimately to the ocean from which it came. In these changes 

 the motions of the winds and water become transformed by 

 friction into waste heat, which, as before, is radiated away and 

 lost. Sunlight, which is energy of high intensity, thus, of itself, 

 becomes degraded or levelled down, entropy increasing in all the 

 transformations that occur. 



Let, however,the sunlight fall upon green vegetation, and some- 

 thing very different occurs. Its energy transforms into chemical 

 changes, as the result of which water and carbonic acid (sub- 

 stances which are fully degraded and have no free or available 

 energy) become combined together, with increase of available 

 energy, to form carbohydrate. Trace the entropy change, and it 

 will be found that this is positive, and has a certain value when 

 solar radiation transforms wholly into waste, low-temperature 

 heat. Trace it again when sunlight is absorbed by the green 

 plant and transforms into the potential chemical energy of 

 carbohydrate, and it will be found that the increase of entropy 

 is now much less than it was. In the first case the solar energy 

 is for ever lost to this world, but in the second it becomes fixed, or 

 stored up, as the chemical energy of wood, vegetation, oil, or coal. 



Vegetable life (that is, the predominant form in which life 

 exists on our world), then, has for its tendency the storing up of 

 available chemical energy. The latter becomes locked up, so 

 to speak, in the form of starches, celluloses, proteids, and oils of 

 fruits, seeds, woody tissues, etc. The vegetative processes of 

 reproduction are the most powerful in the animate world, so that 

 on every available place on the surface of the earth, in swamps 

 and in the shallow water of seas and lakes and ponds, plant life 

 spreads and accumulates to the greatest extent possible. Even 



