REFRACTION. 



565 



of the landscape. If we place a piece of transparent paper 

 behind the lens, we can throw a representation of the picture on 

 it, which, however, will be seen to be inverted. This power of 

 convex lenses is employed in the instrument used for taking 

 photographic pictures, called a camera, which consists of a box 

 or chamber into which the light is allowed to pass through a 



FIG. 221. 



Diagram showing the course of parallel rays of light from A, in their passage through 

 a biconvex lens, L, in which they are so refracted as to bend toward and come to a focus 

 at a point, F. 



convex lens, so that an inverted image of the objects before it is 

 thrown upon a screen of ground glass within the box. When 

 the sensitive plate replaces the screen, the light coming through 

 the lens makes the photographic picture. 



Just in the same way an inverted image of the things we look 

 at is thrown on the retina of the eye by the refracting media. 



FIG. 222. 





Diagram showing the course of diverging rays, which are bent to a point further from 

 the lens than the parallel rays in last Figure. 



This may be seen in a dark room, if a candle be placed at a suit- 

 able distance in front of the cornea of a fresh eye taken from a 

 recently-killed white rabbit. When cleared of fat and other 

 opaque tissues, the sclerotic is transparent enough to act as a 

 screen upon which the inverted candle flame can be recognized. 

 Though our organ of vision is commonly compared to a camera 



