Chap-. 5 .] Refleftor Half the Size of the Otjeff. 2 T 9 



to A B produced. Then the ray S B will be refiect- 

 ed in the direction B 0. Now join O q cutting A B 

 in D, and join QJ). The ray QJ) will be refleded 

 in tire direction D O, and the part of the object vifible 

 by reflexion will be feen in part of the reflecting fur- 

 face only D B. All the reft being fuperfluons as to 

 this objecl. Thus we can always find by what rays, 

 and by what part of a reflecting furface, an object is 

 feen. The limits of the fpace in which an objecl: 

 muft be placed to appear vifible by reflexion are, on 

 thefe principles, eafily determined. Join O B, O A, 

 and make the angles I B K, L A E equal to OBI, 

 O A L, then every objecl: placed within the lines B K, 

 A E indefinitely produced, will be vifible at O by re- 

 flexion. 



Thus, when we are placed before a looking-glafc 

 in a room, part of the room only is vifible -, as we 

 walk backwards and forwards other parts appear and 

 dif;ippear in fucceflion, and fome parts of the room are 

 never feen in the glais. 



When a perfon (lands before a looking-glafs of the 

 fame dimenfions with himfelf, hi r . image appears to 

 occupy the half of it, or, in other words, a looking- 

 glafs of half his dimenfions is capable of mewing him 

 the whole of his figure. Let A B (fig. 3.) be an ob- 

 ject placed before the reflecting furface gb i of the 

 plane mirror C D -, and let the eye be at o. Let A b 

 be a ray of light flowing from the top A of the objecl:, 

 and falling upon the mirror at h : and b m be a. per-* 

 pendicular to the furface of the mirror at b, the ray 

 A b will be reflected from the mirror to the -eye at o, 

 making . an angle mho equal to the angle A km: 

 then will the top 'of the image E appear to the eye in 

 the direction of the reflected ray o b produced to E, 

 where the right line ACE, from the top of the ob- 



