WATER CONDENSING HIGH IN THE AIR 35 



tain range, and rushes upward into a colder atmosphere, losing heat 

 as it does so. The air can no longer hold the moisture, and torrents 

 of rain result. 



A gallon of rain weighs 8.3 pounds and will cover an area of 

 2 square feet to the depth of 1 inch. One inch of rainfall gives 

 113 tons of water to the acre, or 72,600 tons to the square mile. 

 In Khase Hill in Bengal, India, the rainfall is the greatest in the 

 world, exceeding 600 inches yearly. 



Often clouds appear over the desert of Sahara and rain really 

 starts to fall, but the air is so dry that before it reaches the earth, 

 the moisture evaporates. 



The rivers come from the clouds, for clouds pour down rain, rain 

 fills the rivers, and the rivers supply the sea. The sea surface goes 

 into the air as vapor, and the vapor becomes clouds; so, whether 

 we start with mountain rivulet or clouds, the circle is complete, 

 for we always return to our starting point. 



Every school should have a rain-gauge placed in an exposed position, but 

 well protected from winds. 



Hail. When raindrops become frozen in their passage through 

 the air, they fall as hail. Fre- 

 quently a strong wind blows the 

 raindrops back, and other drops 

 of rain unite with them. This 

 process continues until the hail 

 becomes so large that the cold 

 current of air which is freezing 

 the rain is not strong enough 

 to force the hailstones back, FIG. 24. Structure of a Hailstone, 

 and they fall to the earth. 



The size of the hailstones will depend on how strong the current 

 of air is which is blowing them back. When moisture condenses 

 at a temperature below freezing point, minute crystals are formed. 

 When moisture condenses near the earth, below freezing, frost is 

 produced. Sometimes we see branches of trees, the telephone 

 wires, the clothes lines, etc., covered with beautiful ice crystals, often 

 called hoar frost. This is really produced by the direct deposit 



