`Some Activities For Teaching the Mechanics of VisionCharles T. Buzek                John Spry School                                                          2400 S. Sacramento                                                          Chicago Il 60653                                                       (312)534-1700Objectives:   Students are to learn the relationship of light to vision, how light moves, how that affects what we see and some structural aspects of the eye.Materials Needed:   Small bowl, coin, and water   3 by 5 cards   soup cans with ends removed, aluminum foil, wax paperStrategy:   The following three activities will provide a good introduction to theprocess of sight:   Take the small bowl and place the coin in its bottom.  Place it in front ofa student at a distance that first renders the coin invisible to the student.Pour water into the bowl and the student will be able to see the coin that wasinvisible before.   Each student should have a 3 by 5 card held lengthways and inscribed on one end with an X in the left corner and a dot in the right corner.  Students are to hold the card at arm's length, closing the left eye and staring at the X with the right eye.  Instructed to draw the card closer to their face the students will notice something interesting about the image on the right.  Change eyes and the phenomenon occurs on the left.    Each student should have two soup cans as described.  One can to have one end covered with aluminum foil held in place with a rubber band.  The other can to have one end covered with wax paper.  Using a pencil point make a small hole in the center of the aluminum foil then, holding the aluminum foil can outermost with the wax paper can directly behind it (wax paper facing into the other can),place the cans in front of your eye and you will see an image appear on the wax paper. Performance Assessment:   In the first activity explain that light travels in a straight line unlessinterrupted by a material with a different molecular structure.  Given this,can the students explain why the coin seems to mysteriously appear?   The students must be able to describe the phenomenon and then come up with a theory to explain it based on their knowledge of ocular anatomy.  A little discussion beforehand wouldn't hurt.   For the third activity the students must be able to describe the phenomenonaccurately and draw a diagram to explain it.Conclusions:   It should be stressed to the students that none of these experiments in any way changed the physical world.  The phenomena that we observed occurred only within our brains.  The coin did not move, images didn't really disappear or appear nor did an object invert itself.  We perceived these things to happen because of the nature of our eyes and the way we interpret the information that comes to us from them. `