450 CONVEX MIRRORS. 



A greatly magnified image may be obtained by throwing the 

 image of a candle upon the wall of the room. A very small 

 image may be produced by placing the mirror as far as possible 

 from the window, and projecting in daylight the image of the 

 window upon a small screen of thick white paper ; if the screen is 

 serai-transparent there is too much direct light from the window 

 for a clear definition of the reflected image, whether it be viewed 

 from one side or the other. 



The erect, magnified, virtual image which is produced behind 

 the mirror may be observed by holding the mirror like a common 

 looking-glass at a short distance in front of the eyes. 



In order to observe the real images, without screen, as indicated 

 in fig. 249, mirror and candle are set up in their proper places, and 

 by moving the head to and fro the most suitable position of the eye 

 may be found. The diminished image is more easily found than 

 the magnified one. This mode of viewing the images leads easily to 

 an optical deception, for the observer is apt to judge the images to 

 be situated behind the mirror, although they are in reality in front 

 of it, as may be proved by receiving them upon a screen. This 

 deception is more easily produced by small concave mirrors than by 

 large ones ; but even with small mirrors like those used in our experi- 

 ments the probability of illusions may be avoided, and the judg- 

 ment assisted by receiving the image first upon a translucent screen, 

 looking at the side of the screen which is turned away from the 

 mirror, and finally removing the screen. 



The images produced by convex mirrors present less 

 variety. The image is in all cases behind the mirror, 

 for convex reflecting surfaces do not bring rays of light 

 to convergence, but cause the incident rays to diverge 

 after reflection, and thus to appear as if proceeding from 

 points situated on the other side of the mirror. Fig. 

 254 exhibits the mode in which. a number of rays pro- 

 ceeding from the point A, are reflected. The per- 

 pendiculars at the points of incidence, that is the radii of 

 curvature drawn from the centre to these points and pro- 

 duced, are indicated by lines formed of alternate dots and 

 dashes, while the dotted lines represent the reflected rays 



