Total evaporation as used in this paper, is the sum of all water‐losses to the atmosphere from a stream drainage‐basin, during the annual climatic cycle. It occurs principally as evaporation from water‐surfaces, moist soil, and snow, as transpiration from vegetation, and as interception. It is quantitatively represented by annual precipitation upon the watershed minus runoff, corrected for change in storage within the watershed and for subsurface leakage. Various terms for this quantity are used in literature such as evapo‐transpiration, fly‐off, natural water‐loss, etc. In view of the growing interest in the determination of water‐losses, hydrologists will doubtless before long unite in selecting a single app