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Our Surroundings 



the lens, and the retina. The iris regulates the amount of light 

 striking the lens. The lens focuses the rays of light on the retina. 

 The retina receives impressions of objects, called images, and 

 transmits them to the brain through the optic nerve. 



Comparison of the Eye with a Camera. There is a resem- 

 blance and a difference between the eye and the photographic 

 camera. Both are lightproof except where the light coming from 

 the object enters through the lens. The pupil of the eye corre- 

 sponds to the diaphragm, or adjustable opening, of the camera; 

 the lens and cornea to the lens of the camera; and the retina 

 to the sensitive film, or plate. The differences are in the 

 methods of focusing and in the nature of the sensitive plate 



and retina. 



In the eye, adjustment for 

 distances from the object is by 

 means of a change in the 

 curvature of the surfaces of 

 the lens, 'but in the camera 

 this is done by changing the 

 distance between the lens and 

 the plate. In the camera the 

 sensitive plate should receive 

 but one impression, and then 

 In the eye, the picture on the 

 retina passes quickly and the retina is always ready for a new 

 impression, though each impression received may be stored away 

 in the brain. 



To show that images are inverted in the camera, point a camera 

 at a lighted object, look on the ground glass finder and notice how 

 the object appears. Using a model or chart of the eye, explain its 

 structure and how it acts like a camera. 



Accommodation. The adjustment of the lens of the eye to 

 suit different distances from objects is called accommodation. 

 Eyes unable to see distant objects clearly are called nearsighted. 

 Eyes that perceive objects at a distance more clearly than objects 

 near-by are called far sighted. Convex glasses correct farsighted- 

 ness, and concave glasses correct nearsightedness. 



A CROSS SECTION OF THE EYE 



the picture must be developed. 



