24 PRINCIPLES OF AMERICAI^ FORESTRY. 



of water capital remains constant ; only one part of it — the 

 circulating capital — changes, in varying quantities, its loca- 

 tion, and is of interest to us more with reference to its local 

 distribution and the channels by which it becomes available 

 for human use and vegetation than with reference to its 

 practically unchanged total quantity. 



*'As to the amount of this circulating water capital we 

 have no knowledge ; hardly an approximate estimate of the 

 amount circulating in any given locality is possible with our 

 present means of measurement; for it appears that so 

 unevenly is the precipitation distributed that two rain 

 gauges almost side by side will indicate varying amounts, 

 and much of the moisture which is condensed and precipi- 

 tated in dews escapes our observation, or at least our 

 measurements entirely. Thus it occurs that while the 

 amount of water calculated to be discharged annually by 

 the river Rhone into the sea appears to correspond to a 

 rainfall of 44 inches, the records give only a precipitation 

 over its watershed of 27.6 inches. 



'' 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 influ- 

 enced 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 



