FORCE. 379 



of carbon and oxygen. The atoms thus in close union 

 resemble our lead weight while resting on the earth ; 

 but we can wind up the weight and prepare it for 

 another fall, and so these atoms can be wound up and 

 thus enabled to repeat the process of combination. In 

 the building of plants carbonic acid is the material 

 from which the carbon of the plant is derived ; and 

 the solar beam is the agent which tears the atoms 

 asunder, setting the oxygen free, and allowing the 

 carbon to aggregate in woody fibre. Let the solar rays 

 fall upon a surface of sand ; the sand is heated, and 

 finally radiates away as much heat as it receives ; let 

 the same beams fall upon a forest, the quantity of heat 

 given back is less than the forest receives ; for the 

 energy of a portion of the sunbeams is invested in 

 building the trees. Without the sun the reduction of 

 the carbonic acid cannot be effected, and an amount of 

 sunlight is consumed exactly equivalent to the mole- 

 cular work done. Thus trees are formed ; thus the 

 cotton on which Mr. Bazley discoursed last Friday is pro- 

 duced. I ignite this cotton, and it flames ; the oxygen 

 again unites with the carbon ; but an amount of heat 

 equal to that produced by its combustion was sacrificed 

 by the sun to form that bit of cotton. 



We cannot, however, stop at vegetable life, for it 

 is the source, mediate or immediate, of all animal 

 life. The sun severs the carbon from its oxygen and 

 builds the vegetable ; the animal consumes the vege- 

 table thus formed, a reunion of the severed elements 

 takes place, producing animal heat. The process of 

 building a vegetable is one of winding up ; the process 

 of building an animal is one of running down. The 

 warmth of our bodies, and every mechanical energy 

 which we exert, trace their lineage directly to the sun. 



