Atmospheric Optical Illusions 83 
bounces back upon hitting a wall. In the air, droplets of water 
or crystals of ice may act as little mirrors. 
Refraction is observed when light travels from one medium 
into another. A ray of light changes its course when it goes 
from the air into water or into a denser mass of air. Nonuni- 
formity in the distribution of air, or the presence of water 
droplets or ice crystals suspended in the air may give rise: to 
refractive phenomena. 
WHITE LIGHT 
COLORS SEPARATED 
DISPERSION 
Dispersion occurs because different wave lengths, or 
colors, of light are refracted different amounts by the same 
refracting substance. White light, as almost everyone knows, 
is made up of many different colors. Dispersion tends to 
break white light up into its component parts, to form a 
_ spectrum or “rainbow.” Violet light is bent most, red light 
least. 
Diffraction is an interference phenomenon which causes 
light to bend slightly around corners, so that no shadows ever 
have a completely sharp edge. As in the case of dispersion, 
diffraction also results in a separation of the colors but in this 
