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The first law of thermodynamics requires that a balance of energy exist between the loss and gain in heat at the surface of a body of water. Thus, the insolational energy absorbed at a water-surface may be equated to the heat-losses from the surface through the process of radiation, conduction, and convection and to the energy expended in raising the temperature of the water and in the process of evaporation. In 1915 Schmidt [see 11 of “References” at end of paper] applied this principle of conservation of energy to the problem of evaporation and computed the moisture-losses from large bodies of water. Angstrom [1], in 1920, published a paper on the application of this energy-equilibrium to the problem of evaporation from lakes and adequately pointed out its limitations. Schmidt's treatment of various elements in the heat-balance relations was shown to be unsatisfactory. Specifically, Schmidt's general assumptions regarding the ratio between the heat carried away by convection and heat used for evaporation which involved the further assumption that the water-bodies under consideration will be generally warmer than the air were held untenable. |
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