164 OUTLINES OF FORESTRY. 



XVII. THE BALANCE OF NATURE. 



such a complex organization as the earth to 

 be properly maintained in operation, an exact bal- 

 ance must be preserved between its five great 

 geographical forms or parts, namely, the land, 

 the water, the air, plants, and animals. So inti- 

 mately are these different parts associated with one 

 another, and so exact is the balance that is main- 

 tained between them, that no one can be changed, 

 either in amount or distribution, without markedly 

 affecting all the others. 



The five geographical forms receive practically, 

 entirely from the sun, all the energy by which 

 they are actuated, and which activity constitutes 

 the order of created things. 



A part of the heat of the sun stirs the air or 

 water into vast movements called currents that 

 flow between the equator and the poles. By their 

 means an interchange is effected between the ex- 

 cessive heat of the equatorial regions and the 

 excessive cold of the poles. Another part heats 



