1849.] 



exercised by Trees on Climate. 



421 



Although the complete proof of the subject now under discus- 

 sion is of great importance to India and other tropical countries 

 it must be allowed that further and more exact investigation will 

 be required before the correctness of the foregoing statements be 

 fuUy established. But as it is of consequence for the success of 

 future inquirers to collect the existing information " from the 

 numerous works through which we find it scattered, I have pur= 

 posely selected all that I remember to have met with in the course 

 of my readings for insertion here. 



Humboldt and St. Pierre must be regarded as valuable authori= 

 ties, but there is also very concise information on this interesting 

 subject to be found in a memoir by M. Boussingault, concerning 

 " the effects which the clearing of land has in diminishing the quan- 

 tity of water in the streams of the district."* Whether the labours 

 of the agriculturist are effecting any modification in the climates 

 of the countries subjected to their agency is an interesting ques- 

 tion which is now very generally canvassed. It is moreover in- 

 quired, whether tho immense clearing away of woods in some dis- 

 tricts, together with the draining of morasses which exert so much 

 sway over the distribution of heat during the various seasons of 

 the year exert likewise an influence upon the streams and rivers 

 w^hich water the district, either by diminishing the quantity of 

 water which falls, or by inducing a more rapid evaporation from 

 the surface, when the wide spreading forests has been laid low, and 

 its place been supplied by well cultivated fields. 



A. variety of observations would indicate that such a change 

 has been, and is being, effected. Iii many localities it has been 

 thought manifest, that, for a certain number of years, the streams 

 which were employed in propelling w^ater wheels have very sen- 

 sibly diminished. In other places, many have been led to con- 

 clude that the rivers have become more shallow ; and the increas- 

 ing extent of their beds, covered with pebbles on either side 

 appear to attest the disappearance of a portion of their waters. 

 Einally many abundant springs are now almost dry. These obser- 

 vations have principally been made in valleys which are surrounded 

 by mountains ; and it has been thought apparent, that this dimi- 

 nution in the quantity of the waters, has been nciirly coincident 



* Jameson's Edin. Phil. Joui'nal; p. 85, vol. xiiv,, 1838. 



