Lesson XI. 







153 



wards each other at an angle A c B. and 

 .- an object op placed between them. 



! images will be 



i in the circumference of a circle. 

 .::n h- mi'! : by drawing 



'ace behind each mirror, 

 with the image formed in turn by each 

 object. Thus we observe that the image, 

 mirror, AC, is po t while its 

 '//, and tl re f->re the 

 on of po in b c will be *"/>," while 

 the image of '// in AC will 1 

 Therefore it appears that p" o" is th< 

 image of both p"o' in the mirror 

 of o' // in the mirror a c, one of the images 

 :ig the other, if the angle B c A be 

 flO^, as in the diagram ; that is to 



part of a circle. If the nnjiV be 

 r or less, the image p" o" will be 

 Id. 



T. Does the angle formed by the 

 mirrors materially affect the number of 

 the images? 



/'. Yes: if the mirrors had inclined 

 at an angle of 45, or 36, or one-eighth 

 or one-tenth of the whole circumference, 

 we should have, inclusive of th 

 itself, eight or ten images. The number 

 i<es as the ancle dimi- 

 nishes, their number b. -coining infinitely 

 great if the angle of the mirrors be null; 

 that is, if the mirrors be parallel to each 



7*. We have hitherto been con- 



ction of objects from 



irfaces; but suppose that the mirror 



in which ti -1 was 



it would be the .:' 

 /'. I . image would be 

 present a miniature picture of th> 

 placed opposite it. The image must 

 always be small'-r than "-cause 



the rays which form them 



i^aqe to the ey- 

 spectator. Anoti 

 served in the image reflected in a convex 



mirror is its T.tline ; and this is 



ry Of virtual focus 



r difl'erent parts of 



- i tliat the central part 



alone 



li:.. r. Do concave mirrors exhibit 

 any remarkable phenomena? 



/'. 1 es ; ami sons.- of them are very 

 curious and interesting, depending upon 

 the -ituation of the object with respect to 

 the mirror and the observer. 



T. Is there not something very 

 remarkable in the image of an object 

 reflected in a concave in: 



P. Yes ; the image is inverted, or 

 turned upside down. Some curious optical 

 deceptions are produced by means of con- 

 cave mirrors, which almost appear super- 

 natural ; and a singular netural pheno- 

 menon, known as th<- * Sji.-etre of the 

 Brocken," is < r!ie reflection from 



a concave surface. This is observed at a 

 distance from the highest peak of the 

 Hanz Mountains, in Hanover. 



noxs ON LESSO 



1. Explain the meaning of the 

 pencil, and beam of light t, con- 



vergent, reflected, refracted, and parallel 

 rays; focus, principal focus, and focal 

 distai 



i. What is that part of optics, which 

 treats of reflected light, named? 



ace when a ray of light 

 falls (ijMin a plain mirror? 



: of a mirror in- 

 the reflection of an object? 

 < \m the image of an object be re- 

 :roin aiioth. and what is 



; the principle upon which 

 the k.i eil. 



: convex and 

 concave -I explain th reasons 



ence. 



\I. 



I In ;' i- red the laws relating to the reflection of light, but we 



have now to investigate the phenomena ,.f the refraction of light, or the sci. 

 'lioptricc.* Bj refraction we mean the dcvi. 



\ ray of light in patting from one medium to another, and before proceeding further. 

 >m the Gn*k dtoptomai t .- > % to we through. 



