FOREST IXFLUEXCES. 23 



ways of so doing, for we know that not only in the arid 

 regions, but in general Avherever irrigation is used, crops 

 are produced in greatest abundance and certainty. This 

 once recognized, then the proper distribution of the availa- 

 ble water supplies becomes a question of immediate inter- 

 est. Human effort can, to a limited extent, direct the laws 

 of nature that influence climate and soil conditions, and it 

 becomes necessary that we have a clear understanding of 

 the forces that are at work in nature in order that we may 

 know where we may or may not expect to be successful in 

 directing them. In order that we may better understand 

 this subject, I quote the following extract on forest influ- 

 ences from the report of the I orestry Division of the U. S. 

 Department of Agriculture for 1880, with a few changes in 

 the nature of abbreviations: 



''The water capital of the earth may be regarded as con- 

 sisting of two parts, the fixed capital and the circulating 

 capital. The first is represented, not only in the waters 

 on the earth, but also by that amount of water which re- 

 mains suspended in the atmosphere, being part of the 

 original atmospheric water-masses which, after the rest 

 had fallen to the cooled earth, remained in suspension and 

 is never precipitated. 



"The circulating water capital is that part which is evap- 

 orated from water surfaces, from the soil, from vegetation, 

 and which, after having temporarily been held by the 

 atmosphere in quantities locally varying according to the 

 variations in temperature, is returned again to the earth by 

 precipitation in the form of rain, snow, and dew. There it 

 is evaporated again, either immediately or after having 

 percolated through the soil and been retained for a shorter 

 or longer time before being returned to the surface, or, with- 

 out such percolation, it runs through open channels to the 

 rivers and seas, continually returning in part into the atmos- 

 phere by evaporation. Practically, then, the total amount 



