WATER CONDENSING NEAR THE EARTH 



23 



water, runs down hill into the valley. The cold air that does not 

 reach the slope remains on the hill top. The warm air moves up 

 the hill from the valley as the cold air takes its place. The warm 

 air mixing with the cold air on the slope prevents the temperature 

 from falling below 32 F. 



Farmers often try to prevent frost by building fires in the field. 

 Clouds of smoke prevent radiation, and the air is set in motion, 

 making the cold air and warm air mix. In some parts of the country 

 where cranberries are raised, the ground is flooded with water dur- 

 ing the night. The water is too warm to freeze and prevents frost 

 from forming. 



Black frost is not frost in reality but frozen sap of plants. When 

 the sun comes out, the sap thaws and the plants turn black. 



Ice Storm. A sudden jar - 

 turns to a solid a liquid which is 

 cooled considerably below freez- 

 ing. This happens in cold 

 weather when raindrops or fog 

 products turn to ice on coming 

 in contact with terrestrial objects 

 such as trees, telegraph wires, 

 etc. The smooth coating of ice 

 which results from rain in cold 



weather, to which the name 

 glazed frost is applied, often 

 forms heavy deposits on branches 

 and wires, producing the familiar 

 " ice storm." 



Hoarfrost or Rime. Hoar- 

 frost or rime is produced by de- 

 posits of rough ice or of feathery 

 crystals which are formed by 

 fog when the temperature is 

 below freezing. This is unlike 

 the familiar ice storm since the coating of ice is not smooth. 



Fog. The air is full of solid particles known as dust. Dust 

 gets into the air from chimneys, forest fires, pollen of flowers, dry, 



F IG . 



