PROGRESSIVE HUMAN CONQUEST OVER WATER 217 



smaller and later of larger streams ; still later turbines -n-ere installed and 

 entire rivers -^rere brought under control ; -ndiile in some cases tidal ebb and 

 flow were turned to work, and wave-motors were invented. The chief basis 

 of the stage is the 6,000 cubic miles of stream water annuallj'' descending 

 from an average altitude of 2,300 feet over the 55,000,000 square miles 

 of tlie lands of the globe (equivalent to 6,500,000,000 theoretical horse- 

 power, or perhaps 20 times the aggregate steam-power, animal-power, 

 wind-power, and man-power used throughout the world) ; a secondar)' 

 basis is the tide-power and wave-power of oceans and sounds, seldom 

 available imder existing economic conditions albeit a vast prospective 

 resource ; while an indirect basis is sun-power, of which the availabilitv is 

 absolutely conditioned (as indeed is human and all other terrestrial life) 

 on the aqueous vapor in the atmosphere. 



The direct utilization of water-power entered on a new era within a 

 decade with improvements in electrical transmission. "While no jDcople 

 has thus far undertaken the S3'stematic utilization of this interest or 

 established the proprietary rights arising therein, the leading nations are 

 awakening to its importance, and in America a national policy of com- 

 plete water utilization (including power) has been foreshadowed as an 

 essential of national perpetuity. 



niYERSION 



The fourth stage in utilization is that of diversion of the natural move- 

 ment of water by artificial means for hxunan ends : Even in prehistoric 

 times the natives of India, Peru, and other lands diverted streams either 

 for direct water-supply or for increasing the fruitfulness of lands chiefly 

 by irrigation ; and reclamation b}' irrigation or drainage or both combined 

 (for the processes are correlative) is more or less extensively employed in 

 several countries, while in arid regions generally and in some humid re- 

 gions the natural waters are at least partially diverted and redirected 

 toward agricultural ends. Of late the purposes of diversion are multi- 

 plying apace ; municipal storage and purification ; the development cf 

 power, both directly and through steam; the direct application of power 

 as in hj^draulic mining and excavation; the transfer of material in sus- 

 pension and saltation in connection with dredging and jettying and in 

 warping and filling ; the transfer of material in solution as in salt extrac- 

 tion ; the transmission of power as in hydraulic presses and elevators ; the 

 transmission of thermal energy for heating or cooling buildings; and 

 even the utilization of proper terrestrial heat and qiiiescent ^"xalcanicity 

 by means of circulation through deep borings — these are among the 

 multifarious purposes. 



XXI — Bull. Geol. Soc. Am., Vol. 19, 1907 



