24 ELEMENTARY FORESTRY. 



"We must therefore enter into our discussions acknowl- 

 edging ignorance of one of the most important factors, at 

 least as to its numerical or quantitive value. 



"The distribution of the circulating water capital is 

 influenced by various agencies. The main factor which sets 

 the capital afloat is the sun, which, by its heat and the air 

 currents caused by it, and by the rotation of the earth, pro- 

 duces the evaporation which fills the atmosphere with vapor. 

 Anything, therefore, that influences the intensity of insolation, 

 the action of the sun. or obstructs the passage of winds, must 

 influence the local distribution of the water capital. The 

 great cosmic influences which produce the variability of all 

 climatic conditions, and therefore also of the circulating 

 water capital, are the position of the earth's axis to the sun, 

 by which the angle and therefore the heat value of the sun's 

 rays vary in different parts of the earth and at different times 

 of the year; the distribution of land and water areas, which 

 produces a difference of insolation because the water has less 

 heat capacity than the land, and which also influences the 

 direction of air and sea currents; the configuration of the 

 earth, by which the density of the atmosphere is made unequal, 

 and in consequence of which differences of insolation and of 

 air temperature are induced. Thus we have not only climatic 

 zones, but also continental climates and mountain climates in 

 opposition to coast climates and plain or valley climates. 



"While this classification of cosmic climates satisfies the 

 climatologist, there are many local climates to be found 

 within the range of the cosmic, and the local climatic condi- 

 tions are those which affect human life and human occupa- 

 tions most sensibly. 



"The same causes, different only in degree, which modify 

 the cosmic climates, making a classification of the same pos- 

 sible, effect further modifications and give rise to local cli- 

 mates; these causes are different in the degree of insolation, 

 obstruction to air currents, presence of water surfaces, or 

 moisture-laden, air-strata. 



"Among the factors which thus modify the cosmic climate 

 and help to produce a local climate differing from other local 

 climates, the soil-cover and especially the presence of forest 



