24 PHOTOSYNTHESIS 



stance, are oxidised to their most stable oxides and converted into other 

 compounds which under existing conditions are extremely stable. Our 

 ores are those stable oxides or salts. Although this condition has not been 

 uniformly attained in the earth, while there are still, for example, natural 

 deposits of metallic copper and silver, yet, unquestionably that is the direc- 

 tion in which the chemical changes are proceeding. 



Now most of these substances before they can be made use of require 

 certain chemical changes which are a reversal of the naturally occurring 

 ones. The ores, oxides or salts of the metals, must be reduced to the ele- 

 mental metals. This, of course, is the reversal of the processes occurring 

 in nature, and to accomplish such a reversal, work must be done, energy 

 must be supplied. 



If then, the tendency is to attain the dead level, this state of equilibrium 

 on our earth, what are the agencies or sources of energy which counteract 

 this tendency and make possible the reverse reaction, the pumping of water 

 up-hill, as it were? 



In searching for such possible sources of energy which might serve 

 this purpose, we find that a little heat is probably given to the surface of 

 the earth from the interior, another very small amount is the result of 

 certain radio-active chemical changes, the action of the tides contributes 

 some, and a further amount is received from radiation from the stars and 

 moon. But these amounts are quite inadequate and insignificant when 

 compared with the primal source of our energy, the sun. The radiations 

 from the sun constitute our main source of energy. This is our main and 

 most consequential import, the only potent factor which counteracts the 

 tendency of complete running down. It is important not only in such 

 reactions as the smelting of ores, but equally to the life on the planet. 



All living things on the earth demand for their maintenance and propa- 

 gation a continuous supply of energy. In final analysis, plants are the 

 fundamental source of energy of all animals as well as man. Just as the 

 herbivorous land animals are the source of food of the carnivor?e, the 

 diatoms are the fundamental source of food of the sea. 



It thus becomes evident that all life on the planet depends upon the 

 energy derived from the sun through the intermediary of the plant, i.e., 

 through the process of photosynthesis. Mankind lives entirely on the 

 energy derived from the sun through the pursuits of agriculture. 



Ikit in addition to this we are squandering the principal of an enormous 

 legacy of solar energy accumulated during the past ages. The plants, 

 which alone are capable of utilizing the enormous floods of solar energy 

 pouring upon the earth, have been at work for many ages prior to man's 

 appearance upon the earth, and have, during time which would make the 

 total s})an of human history appear as but a moment, built the foundations 

 upon which all his present eminence rests. This fossil vegetation, pre- 

 served as coal and oil. represents a very small fraction of the energy which 

 has been falling upon the earth and which has been conserved for man. 

 It is kindled, its energy liberated and used in a thousand ways, and the 



