FORESTRY 191 
tural operations can be performed with the greatest possible 
success. 
Now let me take the case of a country completely, or almost 
completely, denuded of trees, say a hilly portion of the interior ol 
the Sahara desert — for that region is by no means a flat expanse 
of sand, as we were told not so many years ago. I will suppose 
that a large body of cloud, containing sufficient moisture to 
produce abundant rain in England, approaches this piece of almost 
rainless desert ; the heat radiated from the surface of this hot 
locality, and the heated air rising from it, will carry the cloud 
upwards into attenuated atmosphere and dissipate it into such 
fine vapour that there will be no rainfall; and this is what 
usually happens during the greater part of the year. 
Next let it be supposed that the cloud is driven towards a 
hilly desert region so situated, say near the sea, that rain falls 
on it less rarely than in the former case, for the land is not so 
much heated as the more central desert, and when the clouds 
are very heavily charged they will resist the smaller upward 
pressure of less heated air. The rain falls violently on the hills, 
a little of it soaks in, to be evaporated directly the cloud is gone, 
by the sun’s rays, whilst the greater part runs from the sides 
of the hills as from the roof of a house, fills the hitherto dry 
water courses with raging torrents, and floods the valleys and 
plains in its impetuous rush towards the sea. 
Lastly, I will take the case where the cloud comes to a land 
with the hillsides covered with their natural clothing of trees, 
but where, in the lower parts of the valleys, and in the plains, the 
forest has been cleared away and the greater part is under culti- 
vation : there are plantations here and there where the ground is 
unsuitable for grass or tillage ; and orchards of fruit trees and 
pleasant gardens abound. Such a country has running streams 
and rivers, and though the cultivated ground has been artificially 
drained by man, there is sufficient moisture everywhere for the 
maintenance of life in trees and plants : water is retained in the 
forests, and from them, from the rivers, ponds and streams, as 
well as from every square foot of ground, arises continually 
more or less watery vapour. The approaching cloud meets this 
ascending vapour, it meets the trees on the hills, it encounters 
the cool sides of the hills — there is a downfall of rain. Then the 
water, instead of rushing violently down the hills, is to a large 
extent retained upon them amidst the trees, their roots, and the 
undergrowth, and the trees protecting the earth from the rays of 
the sun, the soil acts as a sponge, and the water remaining in 
the woods on the hills, is given off gradually to the streams and 
rivers. Here is a perfect system, here is Nature modified to suit 
the wants of man. 
I have read many times that trees bring rain, but how they 
do so is but imperfectly understood. However that may be, we 
have here a sufficient explanation for our present purpose. Trees 
seem to be made to take from clouds their moisture. If we watch 
