there is more at some times than at other times. We have also 

 seen how it has come into the air and that cold will cause it to 

 condense to liquid water on cold window panes and water-glasses. 

 There are other ways in which the vapor may be changed to 

 liquid. 



After a summer day, even when there has been no rain, soon 

 after the sun sinks behind the western horizon the grass becomes 

 so damp that one's feet are wet in walking through it. The dew 

 is "falling." During the daytime the grass is warmed by the 

 sun ; but when the sun is gone it grows colder, much as a stove 

 becomes cool when the fire is out. This cool grass chills the air 



L 



2. — A wreath of fog se tiled in a valley with the hilltops rising above it. 



near it and changes some of the vapor to liquid, which collects 

 in drops on the grass, just as the vapor collects on the outside of 

 a glass of ice-water. 



In the opposite season of the year, on a cold winter's day, 

 when you step out of a warm house into the chilly air, a thin 

 cloud, or fog, forms as you expel the air from your lungs, and you 

 say that you can **see your breath." What you really see is the 

 little drops of water formed as the vapor-laden breath is chilled on 

 passing from the warm body to the cold air The vapor is con- 

 densed to form a tiny mist. 



Doubtless you have seen a wreath of fog settling in a valley at 

 night time ; or in the morning you may have looked out upon a 

 fog that has settled there during the night (Fig. 2). If your 

 home happens to be upon a hillside you have perhaps been able 

 to look down upon the fog nestled there like a cloud on the land, 



