OF OPTICS. 



271 



ject at B to the mirror at t; and n i a perpendicular LECT. 

 to the mirror from the point i, where the ray B i falls ^^s^ 

 upon it : this ray will be reflected in the line i o, mak- 

 ing an angle n i o, equal to the angle B i n, with that 

 perpendicular, and entering the eye at o: then will the 

 foot F of the image appear in the direction of the re- 

 flected ray o i, produced to F, where the right line 

 -B F cuts the reflected ray produced to F. All the 

 other rays that flow from the intermediate points of the 

 object A B, and fall upon the mirror between h and i, 

 will be reflected to the eye at o; and all the interme- 

 diate points of the image .Fwill appear to the eye in 

 the direction-line of these reflected rays produced. But 

 all the rays that flow from the object, and fall upon the 

 mirror above h, will be reflected back above the eye at 

 o ; and all the rays that flow from the object, and fall 

 upon the mirror below i, will be reflected back below 

 the eye at o : so that none of the rays that fall above h, 

 or below i, can be reflected to the eye at o ; and the 

 distance between h and i is equal to half the length of 

 the object A B. 



Hence it appears, that if a man sees his whole image A man will 

 in a plane looking-glass, the part of the glass that re- f^age in a 



fleets his image must be iust half as long and half asP lane 



loolcia^- 

 broad as himself, let him stand at any distance from it glass, "that 



whatever; and that his image must appear just as far 

 behind the glass as he is before it. Thus, the man A B 



viewing himself in the plain mirror C D, which is just 



