THE PHENOMENA OF LIGHT 



341 



another remaining the same. But when light falls upon 

 unpolished surfaces, the reflection is of such a character that 

 the reflected rays no longer maintain the same relative direc- 

 tions to one another. They are so scattered in their relative 

 directions as to make image formation as discussed above 

 impossible. Reflection of this sort is called diffusion. It 

 is to diffused light that we owe the freedom from images in all 

 smooth surfaces by which we are surrounded, and the even- 

 ness in distribution of light within our rooms and out of 

 doors. 



FIG. 1 14. Diffusion of light is scattered irregular reflection owing to rough- 

 ness of the reflecting surface. (Tower, Smith & Turton.) 



SUMMARY 



In reflection of light the ether waves are thrown back from the re- 

 flecting surface into the same medium whence they came. But a change 

 in their direction due to their passage obliquely from one medium into 

 another of different density is known as refraction. 



An image is an apparent reproduction of an object. This appearance 

 is due to the fact that the light which originally comes from the object 

 itself enters the eye in a direction such that it seems to originate in the 

 image position. 



The image of any point of an object is at the place of intersection 

 of two or more lines of light from that point after they have been re- 

 flected or refracted. This intersection is often apparent rather than 

 real as in case of images in plane mirrors. All these image points have 

 the same relative position to one another as do the corresponding points 

 in the object, thus reproducing the object so far as form and general 

 appearance goes. 



Where light is reflected from surfaces not sufficiently smooth, the 

 relative directions of the light rays is not the same after reflection as 



