The growth of raindrops in cloud

A method is described by which the rate of growth of raindrops in cloud is deduced from the results of a balloon‐borne radio transmitter. The transmitter, during its passage up through the cloud, gives a continuous record of the drop‐size distribution of the rain. The values of the rates of growth of raindrops obtained in this manner differ considerably from those computed from accepted values of cloud‐drop distributions and raindrop‐collection efficiencies. The experimental values rise more rapidly than the computed values by a factor of from 3 to 4 in the 0.5 mm to 1.0 mm raindrop‐diameter range. It is concluded that the effect is real but, as yet, knowledge of the physical conditions within a cloud is insufficient to suggest a mechanism to account for it.