32 



INDIRKCT UTILITY OF FORESTS. 



decided fall is shown, ascribed to the presence of dense forests. 

 Similar results have been obtained in India by the late 

 Mr. H. Blanford, by drawing a line across the Gangetic 

 plains into Assam, Sylhet and Cacliar. 



These and other similar data are very interesting and 

 suggestive of certain effects on the temperature exercised by 

 the presence of large forests ; still, they should be received 

 with caution, because it is impossible to ascertain in how far 

 other circumstances may have produced the reductions, such 

 as the amount of rainfall due to other causes, exposure to air 

 currents, presence of lai'ge sheets of water, swamps, etc. 



b. Tcmperataro of the Soil. 



As the temperature of the soil follows the temperature of 

 the air near the surface in its upward and downward move- 

 ments, it is necessary to observe it at various depths. The 

 following is an abstract of the Swiss, Bavarian, and 

 Wlirtembergian observations : — 



The following conclusions may be drawn from these 

 figures : — In the first place, the differences in the mean 

 annual temperature of the soil are nearly the same from 

 1 foot below the surface down to 4 feet. Next, it is evident 

 that the mean annual temperature of forest soil is decidedly 

 lower than that of soil in the open ; in summer by nearly 

 7'^, and very little in winter, while spring and autumn hold 



