It has been suggested that the loss by evaporation from well-watered crops, E, can usefully be estimated from measurements of the temperature, T, and the global-radiation intensity, QS, using some empirical relationship between T and the ratio LE/QS, in which L = the latent heat of evaporation of water. Relationships that have been proposed are roughly corroborated by data from outside America, but there is considerable scatter. This is partly due to the effects of humidity and cloudiness variations, which are allowed for in a new equation for the ratio.