48 FRAGMENTS OF SCIENCE. 



If, then, solar light and heat can be produced by tl 

 impact of dead matter, and if from the light and h< 

 thus produced we can derive the energies which 

 have been accustomed to call vital, it indubital 

 follows that vital energy may have a proximate! 

 mechanical origin. 



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

 the origin of the energy derivable from plants ai 

 animals ? Let us try to give an intelligible answer 

 this question. Water may be raised from the sea-lev( 

 to a high elevation, and then permitted to descenc 

 In descending it may be made to assume varioi 

 forms to fall in cascades, to spurt in fountains, 

 boil in eddies, or to flow tranquilly along a uniform 

 It may, moreover, be caused to set complex machinei 

 in motion, to turn millstones, throw shuttles, work s 

 and hammers, and drive piles. But every form 

 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 th< 

 machinery : the work performed by the water in d( 

 sceoding is merely the parcelling out and distribute 

 of the work expended in raising it. In precisely thi 

 sense is all the energy of plants and animals the 

 celling out and distribution of a power originally exei 

 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 com- 

 pound substances by the sun. We name the force 

 which draws the water earthward ' gravity,' and that 

 which draws atoms together 'chemical affinity'; but 



