168 SCIENCE OF COMMON THINGS. 



Mist and dew vanish at sunrise. No dew in cities. 



for which reason the mist is not condensed into dew^ but 

 remains floating above the earth as a thick cloud. 



1097* This mitt seems to rise higher and higher, and yet remains quite 

 as dense below as at first : explain the cause of this. 



The air resting on the earth is first chilled, and chills 

 the air resting on it ; the air which touches this new 

 layer of mist being also condensed, layer is added to 

 layer ; and thus the mist seems to be rising, when (in 

 fact) it is only deepening. 



1O08 Why do mist and dew vanish as the sun rises f 



Because the air becomes warmer at sunrise, and ab- 

 sorbs the vapor. 



1OS9 Can the dew properly be said to "fall?" 



Kow ; dew is a\w&ys formed upon the surface of the 

 material upon which it is found, and does not fall from 

 the atmosphere. 



1100 Does the color of an object influence the deposition of dew f 



It does to a considerable extent. 



1101 How can this be sliown f 



If we take pieces of red, black, green, and yellow 

 glass, and expose them when the dew is condensing, we 

 shall find that moisture will show itself first on the 

 yellow and then on the green glass, but that none will 

 appear on the red or black glass. The same thing will 

 take place if we expose colored fluids in white glass 

 bottles. 



11O3 Why is the deposition of dew rarely observed in the close and 

 sheltered streets of cities f 



Because there the objects are necessarily exposed to 

 each other's radiation, and an interchange of heat takes 

 place, which maintains them at a temperature uniform 

 with the air. 



1103 When is dew converted into frost f \ 



If the temperature of the earth, or of the vessel, sink 

 to the freezing point or below, the moisture will be de- 

 posited as before ; but by freezing, it assumes the solid 

 Ibrm, and is called frost. 



1104 Why is a deiv-drop round f 



