TREES AS SHELTER TO GROUND TO THE LEEWARD. 163 
the mechanical force of the wind, but its uses are by no means 
limited to this effect. If the current of air which it resists 
moyes horizontally, it would prevent the access of cold or parch- 
ing blasts to the ground for a great distance; and did the wind 
even descend at a large angle with the surface, still a consider- 
able extent of ground would be protected by a forest to the 
windward of it. 
In the report of a committee appointed in 1836 to examine 
an article of the forest code of France, Arago observes: “If a 
curtain of forest on the coasts of Normandy and of Brittany 
were destroyed, these two provinces would become accessible to 
the winds from the west, tothe mild breezes of the sea. Hence 
a decrease of the cold of winter. If a similar forest were to 
be cleared on the eastern border of France, the glacial east 
wind would prevail with greater strength, and the winters’ 
would become more severe. Thus the removal of a belt of 
wood would produce opposite effects in the two regions.” * 
This opinion receives confirmation from an observation of 
Dr. Dwight, who remarks, in reference to the woods of New 
England: “ Another effect of removing the forest will be the 
free passage of the winds, and among them of the southern 
winds, over the surface. This, I think, has been an increasing 
fact within my own remembrance. As the cultivation of the 
country has extended farther to the north, the winds from the 
south have reached distances more remote from the ocean, and 
imparted their warmth frequently, and in such degrees as, 
forty years since, were in the same places very little known. 
This fact, also, contributes to lengthen the summer and to 
shorten the winter half of the year.” + 
It is thought in Italy that the clearing of the Apennines 
has very materially affected the climate of the valley of the 
Po. It is asserted in Le Alpz che cingono 0 Italia that: “In 
consequence of the felling of the woods on the Apennines, the 
sirocco prevails greatly on the right bank of the Po, in the 
* BECQUEREL, Des Climats, etc., Discours Prélim., vi. 
t Travels, i., p. 61. 
