THE SENSES. 729 



ray of the cone of light issuing from B; the image of A is formed at , 

 the image of B at #, in the inverted position: therefore what in the ob- 

 ject was above is in the image below, and vice versa, the right-hand 

 part of the object is in the image to the left, the left-hand to the right. 

 If an opening be made in an eye at its superior surface, so that the 

 retina can be seen through the vitreous humor, this image of any bright 

 object, such as the windows of the room, maybe perceived inverted upon 

 the retina. Or still better, if the eye of any albino animal, such as a 

 white rabbit, in which the coats, from the absence of pigment, are trans- 

 parent, is dissected clean, and held with the cornea toward the window, 

 a very distinct image of the window completely inverted is seen depicted 

 on the posterior translucent wall of the eye. Volkmann has also shown 



Fig 432. Diagram of the formation of the image on the retina. 



that a similar experiment may be successfully performed in a living per- 

 son possessed of large prominent eyes, and an unusually transparent 

 sclerotic. 



An image formed at any point on the retina is referred to a point 

 outside the eye, lying on a straight line drawn from the point on the 

 retina outward through the centre of the pupil. Thus an image on the 

 left side of the retina is referred by the mind to an object on the right 

 side of the eye, and vice versa. Thus all images on the retina are men- 

 tally, as it were, projected in front of the eye, and the objects are seen 

 erect though the image on the retina is inverted. Much needless con- 

 fusion and difficulty have been raised on this subject for want of re- 

 membering that when we are said to see an object, the mini is merely 

 conscious of the picture on the retina, and when it refers it to the ex- 

 ternal object, or " projects" it outside the eye, it necessarily reverses it 

 and sees the object as erect, though the retinal image is inverted. 

 This is further corroborated by the sense of touch. Thus an object 

 whose picture falls on the left half of the retina is reached by the right 

 hand, and hence is said to lie to the right. Or, again, an object whose 

 image is formed on the upper part of the retina is readily touched by 

 the feet, and is therefore said to be in the lower part of the field, and 

 so on. 



Hence it is also, that no discordance arises between the sensations of 

 inverted vision and those of touch, which perceives everything in its 



