464 THE SENSORIAL FUNCTIONS. 



the true perceptions. It is not the eye which sees ; 

 it is the mind. The analogy which the optical 

 part of tlie eye bears to a camera obscura has per- 

 haps contributed to the fallacy in question ; for, in 

 using that instrument, we really contemplate the 

 image which is received on the paper, and reflected 

 from it to our eyes. But in our own vision nothing 

 of this kind takes place. Far from there being 

 any contemplation by the mind of the image on 

 the retina, we are utterly unconscious that such an 

 image exists ; and still less can we be sensible of 

 the position of the image with respect to the object. 

 All that we can distinguish as to the locality of 

 the visual appearance which an object produces, 

 is that this appearance occupies a certain place 

 iji the field of vision ; and we are taught, by the 

 experience of our other senses, that this is a sign 

 of the existence of the external object in a parti- 

 cular direction with reference to our own body. 

 It is not until long after this association has been 

 established that we learn, by deduction from scien- 

 tific principles, that the part of the retina, on which 

 the impression causing this appearance is made, 

 is on the side opposite to that of the object itself; 

 and also that the image of a straight object is 

 curved, as well as inverted. But this subsequent 

 information can never interfere with our habitual, 

 and perhaps instinctive reference of the appear- 

 ance, resulting from an impression made upon the 

 Tipper part of the retina, to an object situated below 

 us ; and vice versa. Hence we at once refer im- 

 pressions made on any particular part of the retina 

 to a cause proceeding from the opposite side. Thus 

 if we press the eye-ball with the finger applied at 



