340 GENERAL SCIENCE 



lines can be drawn outward in all directions from the point 

 of origin as a center. There will be as many of them as 

 there are radii (ra'-di-i) from the center of any sphere an 

 innumerable number. Wherever any one of these lines 

 comes to the surface of the mirror, at that point there is a 

 change of direction. The incident line of light then becomes 

 a line of reflected light. These reflected rays, then, are as 

 many as there are points in the reflecting surface. 



An explanation of this location of images in plane mirrors 

 may be given by diagrams. Let any two radial lines repre- 

 senting rays of light be drawn from the same point of an 

 object (such as one of its extremities) to points on a line 

 representing a mirror surface 1 . These rays or directions 

 after the reflection will still be diverging lines. If they both 

 enter the eyes of any one observer, the apparent source 

 whence they both seem to come will be back along both lines 

 of reflection, and at the point of the apparent intersection 

 of these lines. All observers getting reflected light from this 

 same point of origin will locate in like manner all images of 

 it at the same image point. An image of the opposite ex- 

 tremity of the same object as a source of light is fixed in the 

 same way. So are all intermediate points. Any observer 

 getting at least two rays of light from every point on the 

 side of the body toward the mirror will locate in the same 

 way the image of every one of these points. These im- 

 age points will have the same order of arrangement with re- 

 ference to one another as was true for the points whence 

 the light originated. For diagrams in the class room the im- 

 ages of the two extremities of an object only are located, 

 and the parts between are filled in without construction work. 



With polished surfaces it is believed that the effect of the 

 mirror is simply to change the direction of 'the lines or rays 

 of light at the mirror surface, their directions relative to one 



1 Preferable these points should be close together. 



