Collisions of very small cloud drops

It is generally accepted that the growth of very small cloud droplets (radius less than 30 μ) by collision and coalescense is a process of fundamental importance in the formation of precipitation. Hocking's [1959] paper is a widely known treatment of the problem. This note will be in part a commentary on his work. Hocking's most significant conclusion was that drops with radii less than 19 μ never collide with smaller droplets when settling in still air (in the absence of electrical effects).