SCIENCE OF COMMON THINGS. 171 



Reflection of heat. What are rays of heat f 



CHAPTER YI 



REFLECTION, ABSORPTION, AND TRANSMISSION OF HEAT. 



1117 What is meant by the reflection of heat f 



Heat is said to be reflected when it is caused to re- 

 "bound or be thrown back from the surface of a reflect- 

 ing body. 



1118 What are the best reflectors of heat f 



All bright surfaces and light colors. 



1119 Are good absorbers of heat good reflectors also ? 



No ; those things which absorb heat best reflect heat 

 worst and those which reflect heat worst absorb it best. 



1130 Why are those things which absorb heat unable to reflect it f 



Because if anything sucks in heat, as a sponge does 

 water, it cannot throw it off from its surface ; and if 

 anything throws off heat from its surface, it cannot 

 drink it in. 



1131 Why are reflectors always made of light-colored and highly- 

 polished metal f 



Because light-colored and highly-polished metal makes 

 the best of all reflectors. 



If metal be such an excellent conductor of heat, how can it reflect 

 heat, or throw it off? 



Polished metal is a conductor of heat only when that 

 heat is communicated by actual contact; but when- 

 ever heat falls upon bright metal in rays* it is reflected 

 back again, and the metal remains cool,. 



1133 What is meant " by heat falling upon metal in rays" and not 

 " by contact ?" 



If a piece of metal were thrust into a fire, it would 

 be in actual contact with the fire ; but if it were held 

 before a flre^ the heat of the fire would fall upon it in 

 rays. 



1134 Why will a kettle be slower in boiling if the bottom and sides are 

 clean and bright f 



