54 FRAGMENTS OF SCIENCE 



In the case of vital phenomena, the source of power con- 

 sists in the forcible separation of the atoms of compound 

 substances by the sun. We name the force which draws 

 the water earthward "gravity," and that which draws 

 atoms together "chemical affinity"; but these different 

 names must not mislead us regarding the qualitative 

 identity of the two forces. They are both attractions; 

 and, to the intellect, the falling of carbon atoms against 

 oxygen atoms is not more difficult of conception than the 

 falling of water to the earth. 



The building up of the vegetable, then, is effected by 

 the sun, through the reduction of chemical compounds. 

 The phenomena of animal life are more or less compli- 

 cated reversals of these processes of reduction. We eat 

 the vegetable, and we breathe the oxygen of the air; 

 and in our bodies the oxygen, which had been lifted 

 from the carbon and hydrogen by the action of the sun, 

 again falls toward them, producing animal heat and de- 

 veloping animal forms. Through the most complicated 

 phenomena of vitality this law runs the vegetable is 

 produced while a weight rises, the animal is produced 

 while a weight falls. But the question is not exhausted 

 here. The water employed in our first illustration gen- 

 erates all the motion displayed in its descent, but the 

 form of the motion depends on the character of the ma- 

 chinery interposed in the path of the water. In a simi- 

 lar way, the primary action of the sun's rays is qualified 

 by the atoms and molecules among which their energy is 

 distributed. Molecular forces determine the form which 

 the solar energy will assume. In the separation of the 

 carbon and oxygen this energy may be so conditioned 

 as to result in one case in the formation of a cabbage, 



