244 



THE WEATHER 



9. When you blow your breath into a cold glass bottle or lamp 

 chimney, you form a deposit of dew on the inside. Why? How cold 

 must the condensing object be? 



10. Under what conditions can you "see your breath"? Why does 

 the condensed moisture disappear? 



11. Find out how large a hailstone may become. 



12. If a dish containing a mixture of salt and ice is left outside on a 

 cold day, it gathers little if any frost; but when it is brought into a 

 warm room, it condenses a great deal. Why? 



13. Clouds are often formed on the headland shown in Fig. 107, 

 132, which travel with the wind (horizontally) a short distance, and 

 then disappear. Why are the clouds formed? Why do they disappear? 



14. There is a steep ascent, in the form of hills or mountains, 

 practically the entire distance around the coast of Australia. Would 

 you expect the interior to be dry or moist? What are the facts regard- 

 ing Australia? 



274. The Winds. The cause of winds is the inequal- 

 ities of atmospheric pressure. The air, being gaseous, 

 has great freedom of motion; so that, if the pressure be- 

 comes low at any given place, the surrounding, heavier 

 air crowds in from all sides, and buoys the lighter air 

 upward. These horizontal currents are the winds. 



A fire, burning in the open air on a still day (Fig. 222), illustrates 



^ admirably the origin 



of winds. The warm 

 air and smoke are 

 carried upward to a 

 certain level, and then 

 spread out horizon- 

 tally. At some dis- 

 tance they return to 

 the earth, and move 

 toward the fire as 

 strong drafts. The 



Fig. 222. 

 The winds are fomed like the currents about an open fire. 



