INVERSION OF THE IMAGE. 565 



So also more bending of the rays occurs between the aqueous 

 humor and the anterior surface of the lens than between the 

 posterior surface of the lens and the vitreous humor. 



The lens is not of the same density throughout, but denser in 

 the centre, and being made up of layers, the central part refracts 

 more than the outer layers. 



The manner in which the inversion of the image is produced 

 by a convex lens is shown in the accompanying figure, in which 

 the lines correspond to the rays passing from two points through 

 the lens. If the arrow a a' be taken for the object, from either 



FIG. 223. 



Showing the course of the rays of light from two luminous points to the 

 retina. The rays from the point a, on passing through the cornea, lens, 

 etc., are collected on the retina at 6. Those from a' meet at 6 7 , and thus 

 the lower point becomes the upper. 



extremity of it rays pass through, and are more or less bent by 

 the lens. It will be sufficient to follow the course of three rays 

 from the head of the arrow. One of these passes through the 

 centre of the lens, and leaves it in the same direction which it 

 entered, because the two surfaces at the points where it entered 

 and left may be regarded as parallel, and so cause no refraction. 

 The rays which do not pass through the centre are bent on en- 

 tering and on leaving the lens, so that they all meet at the same 

 point and there produce an image of the head of the arrow at b'. 

 In exactly the same way the feather end of the arrow is produced 

 at b ; the position of the image of the object is thus reversed by 

 the light rays passing through the lens. 



