i the Perception of Relief . 



It is no answer to this to say that ^ . _^ 



conditions upon which the perception of relief depends. This 

 has been splendidly done by Wheatstone, Dove, and others, 

 and is beautifully illustrated by the stereoscope ; but this has 

 no necessary connection with the question before us. When 

 I say— we hear intuitively — it is nothing, in the way of refuta- 

 tion, to explain to me the acoustic conditions upon which hear- 

 ing depends, or to assert that Mozart had no intuitive perception 

 of melody or harmony because the laws are fixed by which a 

 melody ought to proceed, and harmony, to be such, must be ac- 

 cording to the formula of Thorough Base, whereas the child 

 Mozart could not know all this. So with the matter in question ; 

 all men see solidity who have the proper use of their eyes ; very 

 few indeed know how it is effected, or are able to distinguish 

 acutely between the perception of binocular relief and the per- 

 ception of mere perspective, or the appearance of distance with- 



The perception of reZiV/ depends upon the angle formed by the 

 rays which proceed from any object of sight to the right and 

 left eyes respectively ; the larger this angle the more relief is 

 apparent, provided the eyes can unite the dissimilar images; but 

 when by reason of distance this angle becomes nothing, practi- 

 cally, and the rays are parallel as they enter the eyes, relief 

 vanishes. 



The perception of the perspective depends upon very different 

 conditions, such as the direction of the lines that compose a view", 

 the light and shade, the apparent size, the tint, &c. 



When we consider the matter it is not surprising that these 

 two modes of perception should often be confounded. True 

 relief dmiinishes so gradually, and melts so gently away, leaving 

 perspective entirely master of the field, that the essential differ- 

 ence between them is likely to be lost sight of That this is the 

 case may be shown by the following examples:— 



It requires a series of very careful experiments to determine 

 how far, under ordinary conditions, we can perceive relief. Ex- 

 periments of my own lead me to believe that the distance is 

 under three hundred yards. The only reason a good painting, 

 whose foreground is represented as it appears at the distance ot 

 two or three hundred yards, is not a complete illusion when seen 

 under favorable conditions, is, that we can chan^^e our point of 

 view; and motion to one side or the other will impart the idea 

 of relief in nature, but as there is no relief, properly so-called, 



and the illusion i 



L one poin 



r\.^ 1 r "" •" "" "" ^i'^- Hence, paintings ougui' iv. 



observed by one eye, and from one point of view to obtain 1 



