Deserts 91 



that trees have been planted again the rain is said to be 

 returning. 



So much, then, is certain: cut down forests and you 

 will have less rain; and though the natives of Namaqua 

 Land, South Africa, attributed the great diminution in 

 their rainfall to the presence of the missionaries, others 

 had no hesitation in ascribing it to their own wasteful way 

 of cutting wood. 



But though loss of forest brings loss of rain, it is diflS- 

 cult to say precisely how the change is brought about, and 

 whether rain is actually caused by transpiration or not. 



Wherever there is vegetation, be it grass or be it forest, 

 there, as has been shown, large quantities of water are 

 constantly passing off into the air in the form of vapor. 

 And the amount is large, not merely considering the 

 means by which it is pumped up, but it is large actually; 

 very large, when we compare it with the amount of rain 

 which falls. 



For instance, from the record kept at Greenwich it 

 appears that during July, our wettest month, the average 

 fall of rain is something under three hundred tons to the 

 acre, or under three inches — three hundred tons during 

 the whole month, or less than ten tons each day. But an 

 acre of pasture-grass actually gives up more than ten times 

 this quantity in the course of twenty-four hours — one hun- 

 dred and six tons — that is to say, in a single day and 

 a night. So that an acre of pasture which has received 

 three hundred tons of rain in a month, gives up more than 

 three thousand tons in the same time. 



The question as to where this immense quantity comes 

 from will have to be considered later. At present we are 

 concerned only with the fact that so much water is returned 



