MIRRORS 



157 



image of the object. If an open book is held toward a 

 mirror, the image has the printed matter backward. A 

 watch showing 9 A. M. forms an image in 

 which the hands are where we expect ' ^~ 

 them to be at 3 P. M. Let us see how 

 the regular reflection of light produces 



FIG. 148. 

 The image of 



FIG. 147. 



Suppose that MR Of Fig. 147 represents a The eye sees an object in 

 , . , . , ,. , . the direction from which 



vertical mirror, and that a point 01 some object the light of the object 

 is at 0. Rays of light from enters the eye ' 

 strike the surface of the mirror everywhere; but only 

 the ray that meets the mirror at F passes to the eye, 

 according to the rule of reflection ( 174). But the eye 

 sees only in the direction from which the light ray 

 comes as it enters the eye; so appears to be in the 

 imaginary position 0' (read this: prime). 0' is just as 

 far back of the mirror as is in front of it. Now suppose 

 that the object is not one point, but many points. An 

 arrow is a convenient form of object (Fig. 148). The 

 image of the arrow is of the same shape as the arrow 

 itself, but reversed sidewise. 



A piece of polished plate glass (Fig. 149), if 

 looked at at the right angle, will be a mirror, 

 and yet be a transparent body at the 

 same time. If a bottle of water is 

 placed behind the glass, and a burning 

 candle in front of it, we see both objects 

 in the direction from which their light 

 comes to the eye. Hence the candle 

 and the bottle appear to be in the 

 same place, behind the plate glass, LfaJEJ^**** 

 and the candle seems to be burning in tr 8 an\m!ft e e c r t0 o r f fight ; a the 



candle seems to be burn- 

 ing in the water. 



mirror is right 

 side up, but 

 reversed in a 

 right and left 

 direction. 



