GOOD AND BAD MIRRORS 243 



the center of which is a bright spot. The light, the hole, and 



the bright spot are all in the same straight line. These simple 



observations lead us 



to think that light 



travels in a straight 



line. FIG. 112. The candle cannot be seen unless the 



We can always tell """ pinholes are in a straight Iine ' 



the direction from which light comes, either by the shadow 

 cast or by the bright spot formed when an opening occurs in 

 the opaque object casting the shadow. If the shadow of a 

 tree falls towards the west, we know the sun must be in the 

 east ; if a bright spot is on the floor, we can easily locate the 

 light whose rays stream through an opening and form the 

 bright spot. We know that light travels in a straight line, 

 and following the path of the beam which comes to our eyes, 

 we are sure to locate the light. 



Good and bad mirrors. As we walk along the street, we 

 frequently see ourselves reflected in the shop windows, in 

 polished metal signboards, in the metal trimmings of wagons 

 and automobiles; but in mirrors we get the best image of 

 ourselves. We resent the image given by a piece of tin, be- 

 cause the reflection is distorted and does not picture us as we 

 really are ; a rough surface does not give a fair representation 

 of us; if we want a true image of ourselves, we must use a 

 smooth surface like a mirror as a reflector. If the water in a 

 pond is absolutely still, we get a clear, true image of the trees, 

 but if there are ripples on the surface, the reflection is blurred 

 and distorted. A metal roof reflects so much light that the 

 eyes are dazzled by it, and a v/hitewashed fence injures the 

 eyes because of the glare which comes from the reflected light. 

 ; Neither of these could be called mirrors, however, because al- 

 though they reflect light, they reflect it so irregularly that not 

 even a suggestion of an image can be obtained. 



CLARK INTRO. TO SC. l6 



