ENERGETICS 107 



vegetable world, or indirectly from vegetables which have 

 passed through the flesh of animals. Vegetables in their turn 

 obtain their substance from the mineral world and their 

 energy from the sun. The salts, the water, and the carbonic 

 acid absorbed by plants possess no store of potential energy. 

 Whence then can they obtain the potential energy which they 

 transmit to animals and man. if not from the sun? The 

 energy of the solar radiations is absorbed by the chlorophyll of 

 the leaves, and stored up in the organic carbohydrates formed 

 by the synthesis of water and carbon. Chlorophyll has the 

 peculiar property of reducing carbonic acid, and uniting the 

 carbon with water in different proportions to form sugar and 

 starch, whilst fats and vegetable albumens are also formed 

 by an analogous reaction. All these complex bodies are 

 stores of energy; the vital processes of oxydation do but 

 liberate in the human body the energy which the chlorophyll 

 of plants has absorbed from the solar rays. 



We must look, then, to the sun as the direct source of all 

 the energy which animates the surface of the earth. The sun 

 looses the winds, and raises the waters of the sea to the 

 mountain-tops, to form the rivers and torrents which return 

 again to the sea ; the sun warms our hearths, drives our ships, 

 and works our steam engines. There is no sign of life or 

 movement on our planet which does not come directly or 

 indirectly from the solar rays. 



It may be asked by what path does the chemical energy 

 of the living organism pass into the mechanical energy of 

 motion. It would appear that the intermediary step cannot 

 be heat, as in the steam engine, since the necessary temperature 

 would be quite incompatible with life. 



The formula for the efficiency of a thermic transformer is 



i i_, the ratio of the difference of the absolute temperatures 



T 

 at the source and at the sink, to the absolute temperature at 

 the source. Calorimetric measurements have shown that the 

 efficiency of the human machine is about one-fifth, i.e. it can 

 transform 20 per cent, of the energy absorbed. The ordinary 

 temperature of muscle is 38° C, or 311" absolute. We have 



