232 CONVECTION. 



kettle, carries heat to the water through 

 which it passes, (see p. 246). 



Q. Are LIQUIDS good CONDUCTORS of heat ? 



A. No; liquids are bad conductors ; 

 and are, therefore, made hot by con- 

 vection. 



Q. Why are LIQUIDS BAD CONDUCTORS of 

 heat ? 



A. Because heat converts a liquid 

 into steam, and flies off with the vapour, 

 instead of being conducted through the 

 liquid. 



Q. Explain how WATER is made HOT ? 



A. The water nearest the fire is first 

 heated,Ja.r\d (being heated) rises to the 

 top; other cold water succeeds, is also 

 heated, and rises in turn ; and this 

 interchange keeps going on, till all the 

 water boils. 



Q. Why is WATER in such continual FER- 

 MENT, when it is BOILING? 



A. This commotion is mainly pro- 

 duced by the ascending and descending 

 currents of hot and cold water. 



The escape of air from the water contributes also to 

 increase this agitation. 



