290 WIND. 



is heated in a similar way, till all is 

 warmed by " convective currents." 



Q. What is meant by " CONVECTIVE CURRENTS 

 of air?" 



A. Streams of air heated by the 

 earth, which rise upwards and carry heal 

 with them, are called " convective cur- 

 rents" of hot air. 



Q. Is the air in a ROOM in perpetual motion, 

 as the air ABROAD is ? 



A. Yes; there are always two currents 

 of air in the room we occupy, one of hot 

 air flowing out of the room, and another 

 of colder air flowing into the room. 



Q. How do you KNOW, that there are these 

 TWO currents of air in every occupied ROOM ? 



A. If I hold a lighted candle near 

 the crevice at the top of the door, the 

 flame will be blown outward (towards the 

 hall) ; but if I hold the candle at the 

 bottom of the door, the flame will be 

 blown inwards (into the room). 



Q. Why would the flame be blown OUTWARDS 

 (towards the HALL), if the candle were held at the 

 TOP of the door ? 



A. Because as the air of the room is 



