THE EYE 347 



the two pictures are not exactly alike. When the views are blended 

 into one by the stereopticon; the image seems to stand out like a real 

 statue. Explain that in this way the two eyes gain a knowledge of 

 position and solidity. 



146. Illustrate double vision by pressing one eyeball aside while 

 looking at an object. 



147. Have a person gaze at your finger held at a distance from his 

 eye. Now bring the finger near the eye, and notice that the eyes each 

 turn towards the nose so as to keep directed toward the object. This is 

 the only manner in which we can move the eyes in opposite directions. 



148. Press hard upon the closed eyelids. Notice the ring of light 

 which appears. Explain that this is due to the irritation of the optic 

 nerve. 



149. Test the individual members of the class for color blindness 

 by showing them shades of red, green, and yellow, telling them to 

 match the shades and arrange them in order. Also test the power of 

 vision of the individual members of the class by placing before them 

 printing with letters of various sizes. Have each pupil read as far as 

 he can, all standing at the same distance. 



REVIEW TOPICS 



1. Describe light; color; focus; and the effects of light 



in a photographer's camera. 



2. Show that the eyeball is like a photographer's camera, 



describing its outer coverings ; its retina ; nerve ; 

 cornea ; iris, pupil, and lens. 



3. Describe the orbit ; eyelids ; the lachrymal gland ; 



tears, and the tear ducts. 



4. Show that a person can see more clearly directly in 



front of his eyes than upon either side. 



5. Show that the duration of a sight sensation changes 



the appearance of moving objects. 



6. Describe color blindness. 



7. Show that the retina may become unable to act from 



overwork, as by gazing at bright objects; at colored 



