7 



COMMON THINGS THE LOOKING-GLASS. 



is placed. From c draw the perpendicular c o, and continue it 

 from o to c', so that o c' shall be equal to o c. In like manner, 

 Fig. 2i draw the perpendicular D r, and 



continue it so that P D' shall be 

 equal to P D. Then the image of c 

 will be at c', and the image of D at 

 D', and the image of all the inter- 

 vening points between c and D will 

 be at points intermediate between c' 

 and D', so that c' D' shall be inclined 

 to the reflector at the same angle as 

 c D is inclined to it, and the object 

 and the image will be inclined to 

 ach other at twice the angle at which either is inclined to the 

 reflector. 



Hence, if an object in a horizontal position be reflected by a 

 reflector forming an angle of 45 with the horizon, its image will 

 be in a vertical position; and if the object being in a vertical 

 position be reflected by such a mirror, its image will be in a 

 horizontal position. 



If a reflector be placed at an angle of 45 with a wall, the image 

 of the wall will be at right angles with the wall itself. 



If a reflector be horizontal the image of any vertical object 

 seen in it will be inverted. Examples of this are rendered 

 familiar by the effect of the calm surface of water. The country 

 on the bank of a calm river or lake is seen inverted on its surface. 

 5. If an object be placed between two parallel plane reflectors, a 

 series of images will be produced lying on the straight line drawn 

 through the object perpendicular to the reflector. This effect is 

 seen in rooms where mirrors are placed on opposite and parallel 

 walls, with a lustre or other object suspended between them. An 

 interminable range of lustres is seen in each mirror, which lose 

 themselves in the distance and by reason of their faintness. This 

 increased faintness by multiplied reflection arises from the loss of 

 light caused in each successive reflection, and also from the 

 increased apparent distance of the image. 



Let A B and c D, fig. 3, be two parallel reflectors ; let o be an 

 object placed midway between them. An image of o will be 

 formed at o' as far behind c D as o is before it, and another image 

 will be formed at o' as far behind A B as o is before it. The image 

 >o' becoming an object to the mirror A B, will form in it another 

 image o" as far behind A B as o' is before it, and in like manner 

 the image o' becoming an object to the mirror c D will form an 

 image o" as far behind c D as o' is before it. The images o" and 

 <o" will again become objects to the mirrors A B and c D respec- 

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