NATURE-STUDY LESSONS. 173 



12. (a) Test the drafts made by letting down the 

 upper window sash a little and raising the 

 lower sash to the same extent, during a 

 cold day and while the air in the room is 

 warm. 



(J?) Describe the direction of these currents. 



(c) Compare the temperatures of the in-coming 

 and out-going currents. 



{d) Which current goes through the upper sash ? 



(e) Account for the hot air taking the course that 

 it does. 



L.-EVAPORATION. 



1. (a) Place a small quantity of water in a saucer and 



leave it exposed and observe what takes 



place. 

 (F) What has become of the water? 

 {c) Where is it now ? 

 {d) What caused it to disappear ? 



2. {a) Observe the wooden roofs of buildings when the 



sun shines strongly on them after a shower. 



{b) What do you notice ? 



The moisture in the air is called vapor and the process by which the water 

 is slowly changed into vapor is called evaporation. 



3. Where else have you noticed evaporation taking 

 place ? 



4. {a) Why are wet clothes hung on a line ? 

 {b) What becomes of the water ? 



5. Why are wet clothes sometimes placed near the 

 stove ? 



6. How does increase in temperature affect the rate of 

 evaporation ? 



