48 FRAGMENTS OF SCIENCE. 



brought about. If, then, solar light and heat can bo 

 produced by the impact of dead matter, and if from 

 the light and heat thus produced we can derive the en- 

 ergies which we have been accustomed to call vital, it 

 indubitably follows that vital energy may have a proxi- 

 mately mechanical origin. 



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

 the origin of the energy derivable from plants and 

 animals? Let us try and 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 millstones, throw shuttles, work saws 

 and hammers, and drive piles. But every form of 

 power here indicated would be derived from the origi- 

 nal power expended in raising the water to the height 

 from which it fell. There is no energy generated by 

 the machinery: the work performed by the water In de- 

 scending 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 par- 

 celling out and distribution of a power originally ex- 

 erted 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 



