KINETIC QUALITY OF WATER WORK 201 



exists and moves; as an agency, it works; as a worker, it modifies both 

 its environment and itself. 



MECHANISM OF WATER WORK 



The work of the running water (even as autonomously modified) varies 

 with external factors, predominantly declivity: Solvency may increase 

 little with the motion, though it is doubtless rendered more effective by 

 prompt removal of the dissolved matter; washing is facilitated both by 

 the vigorous flow attending high declivity and by the added volume and 

 weight and viscosity of the loaded water, while corrasipn is engendered 

 and extended by the mechanical action of the load, especially the part 

 carried in saltation. In transportation the measure of the work increases 

 cumulatively and in a high geometric ratio with declivity and with varia- 

 bility of load, the latter itself consequent on declivity. Failing to dis- 

 criminate between suspended and saltatory matter (which intergrades in 

 nature yet must be viewed separately in analysis), Dupuit ascribed the 

 carrying of sediment to the difi'erential movement of adjacent layers of 

 the flowing water; though a fairer prima facie view may be gained by 

 conceiving the liquid, like the included matter, to consist of particles 

 moving freely among one another under the combined action of gravity, 

 inertia, impact, adhesion, friction, etcetera. In any event, clear water is 

 practically inert mechanically and incapable of corrasion (so that a jet 

 might play on a solid strong enough to resist its weight with no more 

 effect than a jet of air, though like the air it may be converted into a 

 cutting sand-blast by loading it with corrasive material) ; still water, too, 

 is practically inert mechanically, though it may carry finely comminuted 

 matter in suspension for an indefinite period (or drop it on the intro- 

 duction of clear water in such manner as to initiate flocculation), while 

 the transportative power of running water increases cumulatively (cer- 

 tainly within limits) with the sjDeed and differential movement of the 

 water particles attending either (a) high declivity or (6) large volume. 



The competence of running water (using the term employed by Gilbert 

 in his monograph on the geology of Henry mountains to denote the ability 

 of water of varying velocity to move particles of given size) was long 

 ago shown by Hopkins to vary as the sixth power of the rate of flow, 

 though this ratio holds only until the particle begins to move, when it 

 decreases geometrically — that is, remains proportionate to the sixth 

 power of the difference between the velocities of particles and stream (this 

 variability, in which the stationary particle is always subjected to a 

 stronger impiilse than the moving particle, contributing to that saltatory 

 movement characteristic of effective stream-work). 



