252 



THE EYE. 



But if you make the experiment in the evening, and with 

 only one lamp in the room, or, when there are more than 

 one, if they are placed near together, and thi'ow the image 

 on the wall, or on a sheet of paper held near the wall, an 

 inverted picture of the flame or flames, of beautiful dis- 

 tinctness, will be formed. 



Images of any other objects, as well as of bright flames, 

 can be produced in this way, if only all extraneous light 

 can be excluded. This is exactly what is done in the eye. 

 The eye is simply a space inclosed, with an opening in the 

 front part of it, where a double lens is placed to receive 

 the light, all other light, except the rays that come through 

 the lens, being excluded. An image, then, of any outward 

 object toward which the eye is directed, is formed upon a 

 peculiar membrane at the back of it called the retina, 

 which serves as a screen. Of course the image is invert- 



EOTION OF TIIK EYE. 



