140 



Common Science 



bent. And when light is bent before reaching your eyes 

 it usually makes things seem to be where they are not. 



If light goes through 

 a perfectly smooth, flat 

 pane of glass, it is bent 

 one way when it goes 

 into the glass and back 

 the other way when it 

 comes out; so it seems 

 to be perfectly straight 

 and we see things 

 practically as they are 

 through a good window. 

 But if the window glass 

 has flaws in it, so that 

 some parts are a little 

 thicker than others, the 

 uneven parts act like 

 prisms and bend the 

 light to one side. This 



FIG. 68. The light is bent when it enters a 



window pane and is bent again in the op- makes anything W6 look 



at through a poor win- 



dow seem bent out of shape. Of course the things are 

 not bent any more than your pencil in the water was 

 bent, but they look misshapen because the light from 

 them is bent ; the reflected light is all we see of things 

 anyway. 



The air itself is uneven in a way. The parts of the 

 air that are warm, as you already know, are thinner 

 and more expanded than are the cold parts. So light 

 going from cold air into warm or from warm air into 



