FORESTS AND WATER SUPPLY. 31 
“We must therefore enter into our discussions acknowledg- 
ing 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, produces 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 dis- 
tribution 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 configura- 
tion of the earth, by which the density of the atmosphere is 
made unequal, and in consequence of which differences of inso- 
lation 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 cli- 
mates. 
“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 conditions are 
those which affect human life and human occupations most sen- 
sibly. 
“The same causes, different only in degree, which modily 
the cosmic climates, making a classification of the same possi- 
ble, effect further modifications and give rise to local climates; 
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 
areas, is claimed as one that, under certain conditions, is potent: 
