134 OUTLINES OF FORESTRY. 



dom. Tyndall, in his " Heat as a Mode of Mo- 

 tion," * page 529, says : 



" In the building of plants, carbonic acid is the material 

 from which the carbon of the plant is derived, while water is 

 the substance from which it obtains its hydrogen. The solar 

 rays wind up the weight. They sever the united atoms, set- 

 ting the oxygen free, and allowing the carbon and the hydro- 

 gen to aggregate in woody fibre. If the sun's rays fall upon 

 a surface of sand, the sand is heated, and finally radiates 

 away as much heat as it receives. Let the same rays fall upon 

 a forest ; then the quantity of heat given back is less than 

 that received, for a portion of the sunlight is invested in the 

 building of the trees. We have already seen how heat is con- 

 sumed in forcing asunder the atoms of bodies, and how it 

 reappears when the attraction of the separated atoms comes 

 again into play. The precise considerations which we then 

 applied to heat, we have now to apply to light, for it is at the 

 expense of the solar light that the chemical decomposition 

 takes place. Without the sun, the reduction of the carbonic 

 acid and water cannot be effected ; and, in this act, an amount 

 of solar energy is consumed, exactly equivalent to the molecu- 

 lar work done." 



Concerning the influence of the forests on cli- 

 mate, Hough, in his report to the United States 



* Eeprinted, by permission, from " Heat as a Mode of 

 Motion," by John Tyndall, F.K.S., LL.D. New York: 

 D. Appleton & Company, 5 Bond Street, 1883. Pp. 591. 



