136 Common Science 



196. The sun shines up into your face and sunburns you when you 



are on the water. 



197. People in the tropics dress largely in white. 



198. Menthol rubbed into your skin makes it feel very cold after- 



ward. 



199. We feel the heat of the sun almost as soon as the sun rises. 



200. You can shoot a stone far and hard with a sling shot. 



SECTION 23. The bending of light : Refraction. 



How do glasses help your eyes? 



On a hot day, how is it that you see " heat waves " rising 

 from the street ? 



What makes the stars twinkle ? 



Light usually travels in straight lines. If the light 

 from an object comes from straight in front of you, you 

 know that the object is straight in front of you. But 

 you can bend light so that it seems to come from a dif- 

 ferent place, thus making things seem to be where they 

 are not. 



Experiment 44. Hold a triangular glass prism vertically 

 (straight up and down) in front of one eye, closing the other 

 eye. Look through the prism, turning it or your head around 

 until you see a chair through it. Watch only the chair 

 through the prism. When you are sure you know just 

 where it is, try to sit down in it. 



Now look for a pencil or a piece of chalk through the 

 prism, in the same way. When you think you know where 

 it is, try to pick it up. 



The reason the chalk and chair seem to be where they 

 are not is that the prism bends the light that comes 

 from them and makes the light seem to come from some- 

 where else. 



As you already know, when you look at a chair you 

 see the light that reflects from it. You judge where 



