M. BECQUEREL, ON THE CLIMATIC EFFECTS OF FOEESTS. 331 



In discussing the important question of the influence of clearing upon 

 watercourses, we come to the following conclusions: 



1. Great clearings diminish the quantity of living waters that flow 

 in a country. 



2. It cannot be said that this diminution is caused by a less annual 

 rainfall or to a greater evaporation of rain-water, or to these causes 

 combined, or to a new distribution of tbe rain-water. 



3. Cultivation established in an open arid country dissipates a part 

 of the currents of water. 



4. In countries where no change in cultivation has occurred, the 

 amount of living waters appears to be constantly the same. 



5. Forests tend to maintain the living waters and to regulate their 

 flow. 



G. The humidity that prevails in the woods, and the intervention of 

 the roots in rendering the soil more permeable, must be taken into con- 

 sideration. 



- 7. Tbe clearing of a mountainous country exercises an influence upon 

 water courses and springs in the plains and especially upon the latter. 



8. The action which the forests exert upon the climate is very com- 

 plex. 



With the means of drainage we now possess, there is no longer any 

 fear of marshes as a consequence of clearing. We need not fear that 

 the clearing of a country will always bring with it sterility, and will 

 cite as examples England and Spain, of which the former has only 2 

 and the latter but 3.17 per cent, of wooded surface. The former has a 

 marine climate, where tbe southwest winds, charged with vapor to tbe 

 point of saturation, often prevail, causing fogs at the least reduction of 

 the temperature; wbile Spain has a different climate, but the more 

 fertile parts are watered by great rivers, and the great plateaux are 

 veritable deserts. 



From all this it results, that if we come to clear a great forest in the 

 vicinity of a fertile plateau with some springs, ought we not to fear 

 that the latter will partly or wholly disappear, and impoverish the 

 country! The clearing of a sandy country may bring drifting sands 

 upon the neighboring plains, as it is easy to conceive from the expla- 

 nation which M. Chevreul has given to the formation of dunes in the 

 Laudes of Gascony. The wind drives the sand along uiitil it meets 

 with some obstacle, where it forms a mound, or the dunes obstruct the 

 waters, which infiltrate into the sands and dampen their base. The 

 waters by capillary attraction cause the grains of sand to adhere, and 

 fix them in the soil. The winds take only the dry parts above, which 

 go to form new dunes beyond the former; and so the process goes for- 

 ward until it ends by finally ensanding the whole plain. 



A forest placed so as to oppose the passage of a current of damp air 

 charged with pestilential miasms, will sometimes protect all that is 

 behind it, while the exposed part is liable to diseases, as we see in the 

 Pontine marshes, where the trees have the effect of taming the infected 

 air and purifying it of its miasms. 



Tbe forests have another efl'ect upon climates. High trees serve as 

 conductors of electricity, withdrawing this element from the clouds, 

 and checking the disastrous effects of storms. 



The reboisement of mountains is a first necessity for their preserva- 

 tion, and results in the following manner: 



1. From the facility with which rain-waters penetrate the soil, and 

 even the subsoil, which the roots open to infiltration. 



2. From the effects produced when the forests oppose an obstacle to 



