172 NATURE-STUDY LESSONS. 



{d) Describe the currents of water as indicated by 



the motion of the particles. 

 (^r) In what directions do they move? 



5. (a) Place a cork under the surface of water and 



release it. What becomes of it? 

 (d) Why does it rise ? 

 (c) From this infer why the heated water rises in 



the test-tube and beaker. 



In these cases the mass of water is said to be heated by convection, and 

 the currents you observed are called convection currents. 



6. Describe how a mass of water is heated from below. 



7. Observe the direction of the sparks and smoke from 

 a bonfire on a calm evening. 



8. {a) Let loose a small piece of paper a few feet from 



the bottom of the bonfire or near the open 



draft of a stove. 

 {b) What becomes of it ? In what direction did it 



move? 

 {c) What caused it to move in this direction ? 



9. (a) Compare the temperature of your back with 



that of your front while standing near and 



facing the bonfire. 

 (i5) Why is this the case ? 

 (c) Infer the direction of the currents of air and 



their comparative temperatures. 



These currents in air are also called convection currents. 



10. In which part of a closed, heated room will the air 

 be at the highest temperature ? Why ? 



1 1. {a) Let loose a small piece of paper at the mouth 



of a grate in which there is a bright fire. 

 (b) What becomes of the paper ? Why ? 

 if) Explain why there is a draft up the chimney 



while the fire burns. 



