SPHERICAL REFLECTORS. 
Since, in all the cases of reflection from plane mirrors, the rays 
diverge as if they had issued from points behind the mirror, the 
images are always virtual or imaginary. 
9. IMAGES PRODUCED BY SPHERICAL REFLECTORS. 
Curved reflecting surfaces may have various forms, but 
those which are most important are spherical; that is, such 
as consist of a part of the surface of a globe of greater or 
less diameter. A concave spherical reflector is a part pf the 
surface of a globe seen from the inside, and a convex, seen from 
the outside. 
10. Let A c (fig. 6) be the section of a concave reflector, whose 
centre is o. The line o b through the middle of the reflector 
• Aarv- '/.? ■' ' ;; r ; t 
Fig. 6. 
and the centre, o, is called its axis. Let F be the middle point of 
the radius ob, 
If an object be placed before the reflector at any place, such as 
L M, beyond its centre o, an image of this object m /, will be 
found at a certain point between F and o. The pencils of rays 
which radiate from each point of the object, after encountering 
the surface of the reflector, will be reflected, converging to the 
corresponding points of the image. Thus the rays which proceed 
from l will be reflected, converging to /, and those which proceed 
from M will be reflected, converging to m. 
The image m l will therefore be inverted with relation to the 
object, the top of the one corresponding to the bottom of the other, 
the right to the left, and vice versa . 
It is evident also, that the linear dimensions of the image will 
bear to those of the object the exact proportion of their respective 
distances m o and m o from the centre of the reflector. 
11. The production of such an image can be easily verified 
experimentally. Let the object l m be a candle, and let a small 
piece of card be held between o and f at right angles to o b. An 
image of the candle will be seen upon the side of the card pre¬ 
sented to the reflector. The image will at first be nebulous and 
indistinct, but by moving the card alternately to and from the 
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