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GENERAL SCIENCE 



15. Why does an image look different in a silver pitcher from 

 what it does in a mirror? 



THE EYE 



Results of eye trouble. Many people suffering from indigestion, 

 neuralgia, headaches, or mental exhaustion often find that such 

 troubles are due to the eyes. Children who are wayward, incor- 

 rigible, backward, stupid, or defective, may be the victims of eyes 

 which see things out of focus. The real remedy may be found 

 in properly adjusted glasses. 



The constant physical effort of trying to see things clearly with 

 defective eyes uses up a tremendous amount of physical energy and 

 vital nerve force. 



Lens of the Eye. The eye contains a lens which bends the light 

 rays and brings them together at a point on the retina. We have 



FIG. 222. Myopia, short sightedness. Emmetropia, normal sight. Hyper- 

 metropia, far sightedness. 



learned that a thick convex lens causes the light rays to meet at 

 a point nearer the lens than does a thin convex lens. Sometimes 

 the eyeball is too flat or too elongated to bring the rays of light 

 to a point on the retina. If this is the case, the muscles of the eye 

 must cause the crystalline lens, which is like firm gelatin, to become 

 thicker than usual, and assume a more convex surface. Sometimes 

 the eyeball is elongated, and the rays of the light do not meet on 

 the retina but at a point in front of it. If this is the case the crystal- 

 line lens becomes more flattened. 



The crystalline lens is held in position by an elastic capsule 

 attached to the sides of the eyeball. Joining the surface of the eye- 



