EFFECT OF FORESTS ON RIVERS. 165 



they spent the night under the shelter of some large and lofty trees. 

 About two A.M. it began to rain, and it rained about three hours, 

 when it poured in torrents, and continued to do so till they left the 

 place. On mentioning the circumstance they were informed that 

 just in that place it frequently rained in the manner they had de- 

 scribed. 



I accept the statement because I have no reason to question the 

 correctness of the observation. I suspend my judgment, and lie open 

 to light, as our fathers were wont to say, in regard to the occasion of 

 the down-pour. My prejudices are in favour of the supposition that 

 it was a passing thunder-shower, unaffected by the trees one way or 

 another to a perceptible extent ; but it is in accordance with views such 

 I have stated, and which I know to be held by others ; and I cite it 

 as a case which, having been communicated to me, I ought not to 

 ignore because it is at variance with more general views which I 

 entertain. 



Sect. III. — Effects of Forests and of the Destruction of these on 

 Rivers, and Streams, and Springs. 



It is a somewhat prevalent opinion that as rain proceeds from the 

 clouds, rivers have their primary source in springs ; and along with 

 this opinion it is held by many that the primary function of rivers is 

 to carry moisture to lands which otherwise would be barren, and 

 there to diflfuse fertility. But, in point of fact, no water springs from 

 the ground which has not previously been deposited from the atmos- 

 phere ; and the primary function of streams, brooklets, and rivers is 

 simply to carry off surplus moisture in excess of what the soil can 

 retain. 



As rain is produced by the gravitation to the earth of surplus 

 moisture in the atmosphere in excess of what the air can contain 

 suspended in a state of invisible vapour at the temperature to which 

 it has been reduced, rivers are produced by the gravitation to a lower 

 level of the surplus water so precipitated in excess of what is absorbed 

 by the earth or evaporated again into the atmosphere. 



The popular phraseology in regard to many things is far from 

 being in exact accordance with scientific conceptions. We speak of 

 catching cold, of the rising sun, and of the new moon. And so we 

 speak of the little spring of water at the greatest distance or the 

 highest elevation from the mouth of a river as its source ; but no 

 one supposes that the whole of the waters of the river come from this. 



