the vapor pressure by a small amount. The increased pressure results in those droplets evaporating and the resulting water vapor condensing on the larger droplets. Due to the extremely small size of the evaporating water droplets, this process becomes largely meaningless after the larger droplets have grown to around 20 to 30 micrometres, and the second stage takes over. In the accretion phase, the raindrop begins to fall, and other droplets collide and combine with it to increase the size of the raindrop. Langmuir was able to develop a formula which predicted that the droplet radius would grow unboundedly within a discrete time period. Description The liquid water density within a cumulus cloud has been found to change with height above the cloud base rather than being approximately constant throughout the cloud. In one particular study, the concentration was found to be zero at cloud base. As altitude increased, the concentration rapidly increased to the maximum concentration near the middle of the cloud. The maximum concentration was found to be anything up to 1.25 grams of water per kilogram of air. The concentration slowly dropped off as altitude increased to the height of the top of the cloud, where it immediately dropped to zero again. Cumulus clouds can form in lines stretching over long called cloud streets. These cloud streets cover vast areas and may be broken or continuous. They form when wind shear causes horizontal circulation in the atmosphere, producing the long, tubular cloud streets. They generally form during high-pressure systems, such as after a cold front. The height at which the cloud forms depends on the amount of moisture in the thermal that forms the cloud. Humid air will generally result in a lower cloud base. In temperate areas, the base of the cumulus clouds is usually below above ground level, but it can range up to in altitude. In arid and mountainous areas, the cloud base can be in excess of . Cumulus clouds can be composed of ice crystals, water droplets, supercooled water droplets, or a mixture of them. The water droplets form when water vapor condenses on the nuclei, and they may then coalesce into larger and larger droplets. One study found that in temperate regions, the cloud bases studied ranged from above ground level. These clouds were normally above , and the concentration of droplets ranged from . This data was taken from growing