A vertical wind tunnel in which drop interaction could be observed both visually and photographically was designed and constructed. When considering the effects of stability and terminal velocity of a drop on coalescence efficiency it was indicated that the coalescence efficiency for large drops can, by no means, be assumed to be 100% but rather must be considered to be of the order of 50%. It was found that various modes of breakup play an important role in the resultant raindrop size distribution. The growth rate of a raindrop is mainly the sum of growth by direct capture and growth by wake capture. The ‘balance level’ is shown to be a region in a convective cloud where the growth rate of raindrops of diameters greater than 4.5 mm is maximum.