112 LIGHT 



own way, and as a result the beam is scattered in every 

 direction. The innumerable reflecting surfaces of which the 

 paper is composed (Fig. 63) cause irregular diffuse reflections 



of the beams, and hence the re- 

 flected rays leave the paper in 

 every conceivable direction. It 

 is hard for us to realize that a 

 smooth sheet of paper is by no 

 means so smooth as it looks. It 

 is rough compared with a pol- 

 ished mirror. The law of reflec- 



FIG. 63. -The surface of the paper, al- tion alwa Y S h lds > however, no 



though smooth in appearance, is in matter what the reflecting sur- 



reality rough, and scatters the light in f , r n 



every direction. face is, the angle of reflection 



always equals the angle of inci- 

 dence. In a smooth body the reflecting surfaces are all par- 

 allel and reflect in the same direction ; in the case of a rough 

 body, the tiny reflecting surfaces are inclined to each other in 

 all sorts of ways, and no two beams are reflected in exactly 

 the same way. 



Hot coals, red-hot stoves, gas flames, and candles shine by 

 their own light, and are self-luminous, while other bodies, like 

 chairs, tables, carpets, have no light within themselves and are 

 visible only when they receive light from a luminous source 

 and reflect that light. These objects are not self-luminous 

 because at night they are visible only when a lamp or gas is 

 burning. When light from any luminous object falls upon 

 books, desks, or dishes, it meets rough surfaces, and hence 

 undergoes diffuse reflection, and is scattered irregularly in all 

 directions. No matter where the eye is, some reflected rays 

 enter it, and the various objects are clearly seen. 



