1 882.] Forests— their Influence upon Climate and Rainfall. 21 



capacity for moisture is .thereby increased, and naturally absorb 

 with avidity the earth's moisture and produce a drying effect. It 

 is plain to be seen then, that woods by intercepting cold currents 

 and drying winds, mitigate extremes — rendering summer less sul- 

 try and winter less severe, though they may not materially affect 

 the mean temperature. In like manner they must tend to obviate 

 the injurious consequences of cold spring and autumn winds, and 

 thereby relatively lengthen the warm season or term of vegetable 

 development. This is a highly important office, since some crops 

 are slow in maturing. 



The experiment has been tried extensively in France of plant- 

 ing trees in belts one hundred meters apart, and with marked 

 benefit to the climate, and there are some good reasons for be- 



country, would prove equally advantageous. It has been observed 

 many times that fruit grown in the city surpasses in quality and 

 size that grown in the country, and this is ascribable to the more 

 effectual shelter in the former place. 



The wind as it courses over an open country conveys with it a 

 variable quantity of moisture, which, though usually invisible, is 

 always present in the atmosphere, which is likewise arrested by 

 the forest. Now what becomes of this moisture ? The air is 

 forced up by the side of the woods to the tops of the trees just 

 as in the case of a low mountainous elevation, and owing to the 

 attraction between its particles and the constant vis a tergo caused 

 by fresh currents from behind, the volume does not stop here but 

 rises higher. When the temperature of the air above is lower 

 than that in the forest, as is sometimes the case when storms pre- 

 vail, then there would also be an upward current from the tree 

 tops. It is usually considered that in this manner forests in- 

 crease the aggregate general rainfall, viz., by causing ascending 

 currents to sufficiently high regions for the moisture to be con- 

 densed into clouds and rain, and this has been held by some to 

 be the only way in which they influence precipitation. Meteoro- 

 logical science has, however, established the fact that rain is gen- 

 erally formed from one to two miles above the* surface of the 

 earth, and it would scarce be possible that an obstruction no 

 higher than an ordinary forest could, per se, be capable of raising 

 the vapor-laden .air to this extent and could not actually increase 

 the rainfall. On the other hand, when forests are situated on ele- 



