50 THE TREES OF AMERICA. 



Heat, without motion of the air, would never carry away the least particle 

 of moisture from a given locality. The only waste of moisture, so to speak, 

 in such a case, would be that which would be required by plants and animals, 

 and also in the chemical processes of nature. A single rain, then, might last 

 a country a century. In such a country, however, supplied at first with water, 

 no rain, we should think, would be possible. As in the " Ward Cases," the 

 air would be in a constant state of saturation, and, of course, only certain 

 kinds of plants and animals could exist. The atmosphere, at a temperature of 

 32°, is saturated with y^ of its weight of moisture ; at 59°, with ^o l at 86°, 

 with ^0 — that is, it doubles the quantity at every 27° of increase of tempera- 

 ture. Of course, in a country where there was no lateral motion of the air, 

 moisture would rise in the form of vapor, and fall as dew ; and this process 

 would go on forever, in accordance with the rise and fall of temperature. 



There is a good illustration of the effects of the destruction and reproduction of 

 forests in drying up and restoring streams and ponds, in my immediate neighbor- 

 hood. Within about one half of a mile of my residence there is a pond upon which 

 mills have been standing for a long time, dating back, I believe, to the first set- 

 tlement of the town. These have been kept in constant operation until within 

 some twenty or thirty years, when the supply of water began to fail. The pond 

 owes its existence to a stream which has its source in the hills which stretch 

 some miles to the south. Within the time mentioned, these hills, which were" 

 clothed with a dense forest, have been almost entirely stripped of trees ; and, to 

 the " wonder " and loss of the mill owners, the water in the pond has failed, 

 except in the season of freshets ; and, what " was never heard of before," the 

 stream itself has been entirely dry. Within the last ten years a new growth of 

 wood has sprung up on most of the land formerly occupied by the old forest ; 

 and now the water runs through the year, notwithstanding the great droughts 

 of the last few years, going back from 1856. 



Instances of the same kind, and on a much more extended scale, might be 

 multiplied from all parts of the world. William C. Bryant, in his letters from 

 Spain, adds to the testimony of other travellers, that many of the rivers of the 

 country are dried up or lessened in volume from the destruction of the forests. 



