172 CONDUCTION. 



Q. Why is WATER a BETTER CONDUCTOR of 

 heat than AIR ? 



A. Because it is less subtile ; and the 

 conducting power of any substance 

 depends upon its solidity, or the closeness 

 of its particles. 



Q. How do you know that WATER is NOT a 

 GOOD CONDUCTOR of heat ? 



A. Because water may be made to 

 boil at its surface, without imparting 

 sufficient heat to melt ice a quarter of an 

 inch below the boiling surface. 



Q. Why are NOT LIQUIDS GOOD CONDUCTORS 

 of heat ? 



A. Because the heat (which should 

 be transmitted) produces evaporation, 

 andjfties off in the vapour. 



Q. WJiy does a POKER (resting on the fender) 

 feel so much COLDER than the HEARTH-RUG, which 

 is further off the fire ? 



A. The poker (being an excellent 

 conductor) draws heat from the hand 

 much more quickly than the rug, which 

 is a bad conductor: and, therefore, 

 (though both are equally warm) the 

 poker seems to be much colder. 



