52 THE PRINCIPLES OF AGRICULTURE. 



Hilly and mountainous regions, which the winds reach 

 first in their usual course, are generally well supplied, 

 while more level regions farther on have a drier climate. 



QUESTIONS. 



Of what is the atmosphere composed ? What are the two elements of 

 air ? Which of them is the more important V Of what use is nitro- 

 gen in the air ? How much water vapor does the air contain ? Where 

 does the air get it ? What becomes of it when there is more than the 

 air can hold ? In what three ways is the carbonic acid gas of the 

 atmosphere formed ? Name some of the impurities found in the 

 atmosphere. What finally becomes of these? 



How much does the atmosphere weigh ? Why is its pressure greater 

 in a valley than on a mountain? Is the atmosphere heavier or 

 lighter in stormy weather ? 



What is a barometer ? Why does the barometer fall before a storm ? 

 In which direction does the atmosphere press ? How many pounds 

 of air rest upon your outstretched hand ? How are you able to lift 

 so great a weight ? 



What is a thermometer ? What causes the mercury to rise and fall 

 in a thermometer ? 



What is the wind? What causes the wind to blow? Describe the 

 direction of the currents of air in a room with a hot stove at one 

 side. What causes a sea breeze in a hot day on the coast ? Why 

 is a thunder-shower usually accompanied by wind ? 



What is rain ? In what three ways is rain produced ? Why is the 

 air always warmer near the earth than away from it ? Why are 

 hills and mountains cooler than low places ? Why is there gener- 

 ally an abundance of rain on that side of a mountain range from 

 which the wind blows ? 



What is snow? Explain the formation of hailstones. Why does it 

 sometimes hail when the temperature is below the freezing point? 

 How can it snow when the temperature is above freezing? 



What are fogs, mists, and clouds ? What determines the height of 

 clouds? Why is it always cloudy before it rains ? 



Explain the cause of dew. How do clouds prevent the formation of 

 dew ? Why is there no dew upon a windy night ? What is the 



