106 OUTLINES OF FORESTRY. 



Huxley, in his " Physiography," * speaks as 

 follows, concerning the formation of rain, on page 

 47: 



" In examining the distribution of rain, it will be found to 

 be regulated partly by the physical features of the country, 

 and partly by the character of the prevailing winds. In the 

 neighborhood of mountains, the rainfall is increased, since, as 

 has already been pointed out, a mass of moist air, when forced 

 up the side of a mountain, is chilled in the ascent, and its 

 moisture consequently discharged. Among our western coun- 

 ties, in the neighborhood of hills, the rainfall rises to eighty, 

 or even to a hundred, inches, and upwards ; while away from 

 hills, though still in the west, it is only from thirty to forty- 

 five inches. A table-land, or high plain surrounded by moun- 

 tains, will generally receive but little rain, since the winds 

 which reach it have been more or less drained of moisture in 

 sweeping over the surrounding hills. For a like reason, but 

 little rain is likely to fall on the lee side of a high hill, and 

 many mountains, consequently, have a wet and a dry side ; 

 the wet side being, of course, that towards which the predomi- 

 nant winds blow. As regards the influence of winds on rain, 

 it is evident that, when air has blown over a large expanse of 

 warm water, it must have become laden with moisture, which 

 will be readily precipitated on exposure to refrigerating influ- 

 ences. Hence, as in Britain, so in the greater part of Europe, 

 the southerly and westerly winds bring rain ; and most rain 



* Eeprinted, by permission, from " Physiography," by T. H. 

 Huxley, F.R.S. London : Macmillan & Co., 1883. Pp. 384. 



