ABSTRACT
Theconceptofthehydrologicalcycleformsthebasisfortheengineering hydrologist'sunderstandingofthesourcesofwateratorundertheEarth's surfaceanditsconsequentmovementbyvariouspathwaysbacktotheprincipalstorageintheoceans.Twoofthegreatestproblemsforthehydrologist arequantifyingtheamountofwaterinthedifferentphasesinthecycleand evaluatingtherateoftransferofwaterfromonephasetoanotherwithinthe cycle.Thusmeasurementwithinthecomponentsofthecycleisamajorfunction;thishasnotbeensubjecttocoordinatedplanninguntilthemid20th century.
