162 SCIENCE OF COMMON THINGS. 



Utility of blackening stoves. Bright metal retains heat. Dew. 



Because the tree or wall radiates heat into the snow 

 beneath, which melts it. 



1053 Why sliould the flues (connected with stoves, etc.) be always black- 

 ened with black lead f 



In order that the heat of the flue may be more readi- 

 ly diffused throughout the room. Black lead radiates 

 heat more freely than any other known substance. 



1054 Would a metal pot serve to keep water hot if it were dull and 

 dirty f 



'No ; it is the bright polish of the metal which makes 

 it a bad radiator ; it it were dull, scratched, or dirty, 

 the heat would escape very rapidly. 



"Water in hot weather is also kept cookr in bright metal than in dull or 

 earthen vessels. 



1055 Why are dinner-covers made of bright tin or silver? 



Because li^ht-colored and highly-polished metal is a 

 very bad radiator of heat / and therefore bright tin or 

 silver will not allow the heat of the cooked food to es- 

 cape through the cover by radiation. 



CHAPTER Y. 



THE PHENOMENA OF DEW. 

 1O5B What is Dew f 



Dew is the moisture of the air condensed by coming 

 in contact with bodies colder than itself. 



1O57* Why is the ground sometimes covered with dew ? 



Because the surface of the earth (at sunset) is made 

 so very cold by radiation, that the warm vapor of the 

 air is chilled by contact, and condensed into dew. 



1O58 Why is the earth made colder than the air after the sun has set f 



Because the earth radiates heat very freely, but the 



