Show Action of the Air When large masses of air are warmed and forced upward they un un- undergo undergo un- un undergo dergo considerable expansion upon reaching the lower pressures of the upper air This expansion is ac accompanied a ac- ac accompanied companied by a surprising amount of cooling Dry air rising to an alti alti- altitude altitude altitude tude of a mile may be cooled by as much as twenty-five twenty degrees This I much cooling produces a drastic I reduction in the airs air's capacity for holding water and if the air should be only moderately humid to be be- begin begin begin gin with it finds itself with more water than it can carry This surplus water is then condensed first to clouds and md then to rain snow or hail |