It has been established experimentally by Pasquill that the theory of atmospheric turbulence put forward by O. G. Sutton in 1934 leads to satisfactory theoretical rates of evaporation from plane, saturated, liquid surfaces. The theory, however, overestimates the vapour concentration at any point and underestimates the rate of decay of concentration with height above such evaporating surfaces of finite lateral dimensions. In the present paper it is suggested that one of the reasons for this discrepancy lies in the neglect of the lateral component of turbulence. The aim of the present investigation is to estimate quantitatively the effect on the values of the theoretical vapour concentration produced by the introduction of a lateral component of turbulence. It is shown that the theoretical evaporation is not appreciably affected by the modification introduced but that the concentration of vapour, and the rate of decay of concentration with height, are much nearer the experimental values, which, however, are very scanty. The investigation deals with a saturated area of parabolic shape. Extensions of the theory are contemplated.