. Elementary physical geography . , the uprising of air, and the con-tact of warm moist air with cold land surfaces. Thegreater part ofthe rain of theworld fallseither (1) fromcumulus clouds,or (2) from cy-clonic storms,or (3) wheremoist windsblow from thewater upon theland. Away from places where these conditions occur, therainfall is usually light. Sometimes, though rarely, rain-drops fall from a clear sky. Snow. — This is the crystallized form assumed when watervapor condenses at temperatures below the freezing-point;and the forms thus produced are often very beautiful andfantastic (Fig. 58
. Elementary physical geography . , the uprising of air, and the con-tact of warm moist air with cold land surfaces. Thegreater part ofthe rain of theworld fallseither (1) fromcumulus clouds,or (2) from cy-clonic storms,or (3) wheremoist windsblow from thewater upon theland. Away from places where these conditions occur, therainfall is usually light. Sometimes, though rarely, rain-drops fall from a clear sky. Snow. — This is the crystallized form assumed when watervapor condenses at temperatures below the freezing-point;and the forms thus produced are often very beautiful andfantastic (Fig. 58). There is an intimate relation betweensnow and rain, and the same storm may produce snow on thehighlands and rain on the lowlands. Many of our winterrainstorms are due to the fact that the snow crystals havebeen melted in their downward passage; and the dampsnows are a partial step in this direction (Fig. 59). Thedifference of a few degrees thus produces a very markedchange. In the one case rain falls and speedily flows away,. Fig. of actual snowrlakes. 116 PHYSICAL GEOGRAPHY. while in the other case a cold covering of solid snow is laidupon the land, perhaps to stay for months. The clouds ofthe upper air are mostly made of ice or snow, and mountainpeaks that extend into these upper layers, rarely receive anyother form of precipitation. Hail. — At times, particularly in summer, balls of iceknown as hailstones fall from the clouds, especially from *-•# Q »*
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