132 THINNING. 



as climate, soil, and situation, to which they have been 

 transplanted, and by progressive but imperceptible 

 degrees they grow up, expand, and gradually shade and 

 completely cover the ground, till not a ray of the sun 

 directly reaches it. The branches and foliage of a 

 plantation constitute a sort of canopy whereby the sur- 

 face of the ground is completely shaded from the rays 

 of the sun, and consequently never, even during the 

 hottest weather, does the ground become greatly heated : 

 that is to say, the ground in a plantation is less heated 

 in hot weather than it is where there are no trees ; and 

 again, in winter, it is warmer in the plantation than 

 outside of it. Every person knows that it is cooler 

 and more enjoyable to sit under the shade of a tree, 

 on a hot summer day, than under the direct rays of 

 the sun ; and the footsore and weary traveller can 

 cheerfully testify to the relief he experiences and the 

 joy afforded him by the shade of a spreading tree 

 across his path. If any one wishes to experience 

 the great difference between the temperature of the 

 soil on a hot summer day under the shade of a tree, 

 and that beyond it, he has only to walk leisurely 

 along, and with his eyes closed, though walking in 

 thick-soled boots, he will at once feel and determine 

 the limits of the shady part of the footpath. This 

 being clearly demonstrated, the whole subject relative 

 thereto may be known, and the results sufficiently 

 ascertained. 



The shading of the rays of the sun from a few acres, 

 or even miles of ground, may produce comparatively 

 little effect upon an extensive country ; but when hun- 

 dreds of square miles are covered from the face of 

 day, so that neither light nor heat reaches the earth 

 for ages in succession, the results cannot but be im- 



