THE PATH OF LIGHT 109 



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 whitewashed fence injures the 

 eyes because of the glare which comes from the reflected 

 light. Neither of these could be called mirrors, however, be- 

 cause although they reflect light, they reflect it so irregularly 

 that not even a suggestion of an image can be obtained. 



Most of us are sufficiently familiar with mirrors to know 

 that the image is a duplicate of ourselves with regard to size, 

 shape, color, and expression, but that it appears to be back of 

 the mirror, while we are actually in front of the mirror. The 

 image appears not only behind the mirror, but it is also ex- 

 actly as far back of the mirror as we are in front of it ; if we 

 approach the mirror, the image also draws nearer ; if we with- 

 draw, it likewise recedes. 



104. The Path of Light. If a mirror or any other polished 

 surface is held in the path of a sunbeam, some of the light is 

 reflected, and by rotating the mirror the reflected sunbeam 

 may be made to take any path. School children amuse 

 themselves by reflecting sunbeams from a mirror into their 

 companions' faces. If the companion moves his head in order 

 to avoid the reflected beam, his tormentor moves or inclines 

 the mirror and flashes the beam back to his victim's face. 



If a mirror is held so that a ray of light strikes it in a 

 perpendicular direction, the light is reflected backward along 

 the path by which it came. If, however, the light makes an 

 angle with the mirror, its direction is changed, and it leaves 

 the mirror along a new path. By observation we learn that 

 when a beam strikes the mirror and makes an angle of 30 

 with the perpendicular, the beam is reflected in such a way 

 that its new path also makes an angle of 30 with the per- 

 pendicular. If the sunbeam strikes the mirror at an angle of 



