52 THE ruiNCii'LEs of aoiuculture. 



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 atmosj^here comijosed ? What are the two elements of 

 air? AVhich of them is the more important V Of wliat use is nitro- 

 gen in the air ? IIow mueli water vapor does tlie air contain ? Where 

 does tlie air get it ? AV hat 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 

 atmospliere. AMiat finally becomes of these? 



How much does tlie atmosphere weigh ? 'NMiy is its pressure greater 

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

 lighter in stormy weather ? 



What is a barometer ? A\'hy does the barometer fall before a storm ? 

 In which direction does the atmosphere press? IIow many pounds 

 of air rest upon your outsti'etched hand? IIow are you able to lift 

 so great a Aveight ? 



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 ? Mhy 

 is a thunder-shower usually accompanied by wind ? 



What is rain ? In what three wa}S is rain produced ? Why is the 

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

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

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

 which the wind blows ? 



What is snow? Exjtlain the formation of hailstones, ^^'hy does it 

 sometimes hall when the tempei'ature is below the freezing point? 

 IIow can it snow when tlie tem]ierature is above freezing? 



What are fogs, mists, and clouds? A\'hat determines the height of 

 clouds? Why is it always cloudy before it rains ? 



Explain the cause of dew. IIow do clouds jirevent the foi-iuation of 

 dew? Why is there no ilew upon a windy night? AN'liat is the 



