DEVICES FOR SEEING 289 



The knack of judging distances is one that we acquire very 

 early as we correlate repeatedly the play of these muscles that 

 move the eyeball with our experience in reaching for objects or 

 in walking to them. Other factors enter into our judgment of 

 distance, such as the operation of the muscles that control the 

 focus of the lens of the eye, the haziness of the image when 

 objects are very distant; but they may be neglected in this 

 discussion of the apparent position of the mirror image. 



You may have been amused and possibly confused by going 

 into a mirror maze a room whose walls are set with mirrors 

 projecting at various angles. You see yourself in many places 

 simultaneously, and when you try to find the door to go out it is 

 difficult to tell which of the many doors you see is the real one. 

 The production of such multiple images may be illustrated with 

 a simple experiment. Stand two long mirrors on edge, one end 

 of each near the margin of a table, so that they are parallel 

 and face each other a foot or so apart. Between their ends 

 that are distant from the edge of the table, set some object, 

 say a spool. With your eye between the other ends of the 

 mirrors see how many images of the spool you see. Change 

 the position of the mirrors so they stand at an angle to each 

 other instead of lying parallel. How does this affect the number 

 of images visible? One of the most fascinating illustrations 

 of multiple images is found in the child's toy the kaleidoscope. 

 Directions for making this are found on page 83 of the Field and 

 Laboratory Guide in Physical Nature-Study. 



Suppose ab (Fig. 136) represents the surface of a cylindrical 

 mirror whose center of curvature is shown at c. The eye of 

 an observer is shown at/. The points d and e are the tips of an 

 arrow, the image of which is seen in the mirror by the observer. 

 If ab were a plane mirror, the image would appear as large 

 as the object and would be seen as far behind the mirror as the 

 arrow is in front of it. But since the light is now reflected 

 from a convex surface, the rays from d to the eye will be rendered 

 more divergent than they would be if reflected from a plane 



