210 W J MCGEE OUTLINES OF HYDROLOGY 



assume irregular polyhedral forms in masses, collectively tending also to 

 spread into single layers under gravitative and other stresses and through 

 the consequent interactional movements introducing indefinitely contina- 

 ous internal motion of undulatory character in all masses of more than a 

 single layer, each unit being individually susceptible of moderate defor- 

 mation but otherwise incompressible and inelastic (without molecular 

 rearrangement) and in the collective aspect mutually frictionless and 

 neither attractive nor repulsive ; the constituent molecules being capable of 

 incorporating alien atoms, but the units being capable of incorporating 

 extraneous particles only through frictional contact with the foreign sur- 

 faces and thereby becoming collectively viscid, with the counter-capability 

 of facilitating gravitative separation and clarification and thereby restor- 

 ing complete liquidity by their own internal movements, the aggregations 

 of units thus tending to maintain their own integrity by continuous 

 mechanical adjustment between their own and tlie alien particles; the 

 dimensions of the units being determined (measurably as in air-formed 

 drops) by the balance of internal stresses against external stresses. Since 

 the unit so conceived is the ultimate quantity of HoO capable of function- 

 ing in the characteristic ways and is at the same time the prime deter- 

 minant of the rhythmic movement of HgO in masses, it is the natural 

 measure and modulator of moving water and can hardly be denoted 

 otherwise than as the module of HjO. 



While the analogies and inferences indicating the nature of the water 

 module are less definite than is desirable, they nevertheless combine to 

 yield a concept which is not only worth considering in itself, but would 

 seem infinitely more accordant with the sum of terrestrial phenomena 

 than the concepts of water moving in films or filaments or in separate 

 molecules, hitherto frequently held merely for lack of better. Some con- 

 cept is necessary as a basis for practical applications, and this seems to be 

 in accord with all of the more firmly established hydrologic facts. In 

 turn it indicates a useful direction of approach in dealing with the more 

 pressing problems of hydrolog}'', including soil-erosion, bank-caving, 

 bar-building, silting, flocculation, clarification, etcetera, with their appli- 

 cations ; at the same time it helps to explain in a simple and rational way 

 the nature of that habitual interadjustment of internal and external rela- 

 tions which imparts to moving waters their seemingly autonomous char- 

 acter, and aids in harmonizing terrestrial and celestial mechanics in such 

 wise as to suggest new homologies and open new lines of research. 



CUMULATIVE CHARACTER OP WATER WORK 



Conformably with the undulatory and saltatory properties, the virtually 

 autonomous work (or functioning) of running water is aceelerative in 



