Evaporation from Lakes

Evaporation can be determined by the aid of the first law of thermodynamics in such a way that wind velocity need not enter the calculation. Air temperature and humidity enter only as terms in a correction which can have a relatively small average value under typical conditions. The complete equation is $E=\frac{\mathrm{}(H-S-C)\mathrm{}}{L(1+R)\mathrm{}}$ where $E$ is the evaporation, $H$ the difference between the incoming and outgoing radiation, $S$ the heat stored in a column of water having unit cross-section, $C$ a correction for heat carried by flowing water and leakage of heat through the walls of the vessel, $L$ the latent heat of water, and $R$ is Bowen's ratio. A method of finding the difference between the incoming and outgoing radiation, by means of observations on a well insulated pan is described, and also a method of finding the ratio of sensible heat to latent heat transmitted through the air-water surface. Bowen's theoretical conclusions respecting this ratio were found to be consistent with observations.