A theoretical expression for the evaporation of small spherical water drops in still air is developed from the general evaporation equation of Jeffreys. Experimental data for the evaporation of drops ranging from 25 to 2600 microns in diameter are obtained at several temperatures and relative humidities. After making approximate corrections for the cooling of the drops it is found that the results are in general agreement with the theoretical evapooration equation. Residual variations which are functions of the drop size and the difference between the water vapor density at the surface of the drop and at a distance from the drop are probably due to inaccuracies in the method used for computing the drop temperatures. The results of the paper furnish a means for computing the total time required for the complete evaporation of a drop of liquid water into a still atmosphere at any given temperature and relative humidity.
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