VISION ASSISTED BY THE OTHER SENSES. 163 



squinting. Why should not those who squint, behold 

 two objects at once ? It is certain that the image cannot 

 be formed in both eyes, on corresponding points of the 

 retina, and you observed that this was necessary in or- 

 der that the mind should behold but one object. 



Dr. B. Undoubtedly, when people first begin to 

 squint, objects do appear double, but the mistake being 

 constantly corrected, the mind at last becomes conscious 

 of beholding but one object. 



Emily. I think I have heard that the sight of itself 

 alone, gives us no information in respect to the distance 

 of objects, but that this is the result of habit and judge- 

 ment. This may be very true, but I confess, I do not 

 clearly understand it. 



Dr. B. Have you never seen a young babe stretch 

 out its hands to grasp the moon, or any other distant 

 object ? To people also, who have been born blind, but 

 received their sight at an after period of life, objects at 

 a mile's distance, appear to be within their reach. It is 

 by the long habit of comparing together objects at dif- 

 ferent distances, that we judge of their absolute distance, 

 and not by any original power of the eye. When we 

 look at an object remote from others with which we 

 might compare it, it always appears much nearer to us 

 than it really is. Thus, a light in the dark, will always 

 appear nearer than it actually is, from our being unable 

 to compare it with intervening objects. It is the same 

 in regard to the size of objects in such situations. A 

 man, for instance, when seen from the top of a high 

 steeple, will seem much smaller than when beheld on 

 the same level with ourselves at a much greater distance. 



Emily. I have noticed this fact, but it never occur- 

 red to me that it was owing to my not being accustomed 

 to look at objects in a vertical direction. 



Dr. B. So too, the eye alone, unassisted by the 

 other senses, gives us no knowledge of \heforms of 

 bodies. Unaided by the sense of touch, all objects 

 would present the appearance of a flat, uneven surface. 



