412 FRAGMENTS OF SCIENCE. 



In what sense, then, is the sun to be regarded as the 

 origin of the energy derivable from plants and animals ? 

 Let us try to give an intelligible answer to this question. 

 Water may be raised from the sea-level to a high elevation, 

 and then permitted to descend. In descending it may be 

 made to assume various forms to fall in cascades, to spurt 

 in fountains, to boil in eddies, or to flow tranquilly along a 

 uniform bed. It may, moreover, be caused to set complex 

 machinery in motion, to turn mill-stones, throw shuttles, 

 work saws and hammers, and drive piles. But every form 

 of power here indicated would be derived from the original 

 power expended in raising the water to the height from 

 which it fell. There is no energy generated by the ma- 

 chinery ; the work performed by the water in descending 

 is merely the parcelling out and distribution of the work 

 expended in raising it. In precisely this sense is all the 

 energy of plants and animals the parcelling out and distri- 

 bution of a power originally exerted by the sun. In the 

 case of the water, the source of the power consists in the 

 forcible separation of a quantity of the liquid from a low 

 level of the earth's surface and its elevation to a higher 

 position, the power thus expended being returned by the 

 water in its descent. In the case of vital phenomena, the 

 source of power consists 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 qualita- 

 tive 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 complicated 



