SCIENCE OF COMMON THINGS. 



How a cold body is heated. Good and bad conductors of heat. 



930 In what manner does a cold body become heated ? 



First, by heat passing into its surface either by con- 

 tact or radiation, or by both conjointly j and, secondly ^ 

 by tbe heat at its surface passing from particle to par- 

 ticle through its interior portions by conduction. 



931 Does heat pass through all bodies with tlie same velocity ? 



No ; some substances oppose very little impediment 

 to its passage, while through others it is transmitted 

 slowly. 



933 Into what two classes are bodies divided in respect to their conduc- 

 tion of heat ? 



Into conductors and non-conductors / the former are 

 such as allow heat to pass freely through them ; the 

 latter comprise those which do not give an easy pas- 

 sage to it. 



933 What are the best conductors of heat f 



Dense, solid bodies, such as metals, glass, some varie- 

 ties of stone, etc. 



934 What are the worst conductors of heat ? 



All light and porous bodies ; such as hair, fur, wool, 

 charcoal, and so on. 



935 Why do some things feel colder than otliers f 



Principally because they are better conductors, and 

 draw off heat from our body much faster. 



936 Why does a piece of wood blazing at one end not feel hot at the 

 other f 



Because wood is so bad a conductor that heat does 

 not traverse freely through it ; hence, though one end 

 of a stick be blazing, the other end may be quite cold. 



937 Why does hot metal feel more intensely warm than hot wool ? 



Because metal gives out a much greater quantity of 

 heat in the same space of time and the influx of heat 

 is, consequently, more perceptible. 



933 Why does a poJcer, resting on a fender, feel colder than the hearth- 

 rug, which is farther off from the fire ? 



Because the poker is an excellent conductor, and 

 draws heat from the hand much more rapidly than the 

 woollen hearth rug, which is a very bad conductor : 



